Catheter Hemodynamics

Introduction to Cardiac Catheterization & Historical Context

Cardiac catheterization, particularly in its modern interventional form, is a well-established technique that predates the development of cardiac echocardiography. The concept of catheterization was first introduced in 1667 by Lower, and the earliest cardiac risk assessment was performed by Hales in 1711. In 1844, Claude Bernard described the first measurements of intracardiac pressure and temperature. Subsequently, in 1861, Chauveau and Marey introduced a double-lumen catheter into the jugular vein of a horse to record intracardiac pressures. In 1870, Adolf Fick introduced the principle of cardiac output calculation based on oxygen consumption and oximetry—a concept that remains foundational in congenital cardiology today. The invention of X-rays by Roentgen in 1895 paved the way for the first angiographic procedure performed by Haschek in 1896. The first human cardiac catheterization was performed by Werner Forssman in 1929. In 1936, André Cournand and Dickinson Richards (building on Forssman's work) refined the techniques for right and left heart catheterization, including pressure measurements, oximetry, and cardiac output—work for which they later received the Nobel Prize. By 1945, catheterization was applied to congenital heart diseases such as atrial septal defects (ASD) and ventricular septal defects (VSD). In 1953, Sven-Ivar Seldinger described his eponymous technique, which revolutionized vascular access and remains in use today for central line and vascular catheter insertion. Accidental selective coronary angiography was first documented in 1958, and in 1966, the Rashkind balloon atrial septostomy—performed with an unmodified balloon—was described, a procedure still performed in neonatal cardiology. Interventional advances continued with the first percutaneous transluminal angioplasty performed by Charles Dotter in 1964, a pioneering technique that led to the awarding of the Nobel Prize in 1978. Further technical innovations included the development of multipurpose catheters such as the LPA catheter by Shoonmaker in 1968 and the introduction of the Swan-Ganz catheter for pulmonary artery pressure monitoring in 1978. Modern history recap:

• 1929: Werner Forssmann performed the first self-catheterization by inserting a probe into his own vein and advancing it into his heart, identifying his position by a pressure curve. He later received the Nobel Prize for this.

• 1953: Early attempts at valve dilation were made. Rubio-Alvarez

• 1965-1966: The Rashkind (atrial septostomy) was developed. This technique, particularly crucial for transpositions of the great arteries, dramatically improved survival rates from 5% to 95% for children aged one year with this condition, even though it did not fully correct the malformation.

• 1967: Portsmann, a German physician working in Berlin, created the first device for closing an atrial septal defect (ASD).

• 1974: American doctors King and Mills developed the first occluder for ASD closure.

• 1980s: Ductus arteriosus closure became possible with other devices.

• 1986: Professor Puel in Toulouse first used a coronary stent. Stents were also used in congenital heart diseases, especially for coarctations and pulmonary artery stenoses, by the 1990s.

• 1990s-2000s: Advances in digital imaging (flat panel detectors in 2002) significantly improved the procedure.

• 2000: Bonhoeffer, a German physician, performed the first percutaneous pulmonary valve implantation at Necker Hospital, marking the origin of the Melody valve.

• 2010s: Echo Navigator developed, and evolution of transcatheter valve replacement, including the Melody and Edward SAPIEN valves.

Definition and Purpose of Cardiac Catheterization

• • Cardiac catheterization involves introducing a radiopaque probe into heart cavities and vessels under X-rays.

  • Historically, it has been used to distinguish between right heart catheterization (entering right heart chambers) and left heart catheterization (entering left heart chambers, often via the femoral artery), though this distinction can be somewhat artificial.

  • Indications for performing a cardiac catheterization include:

• Gathering information that echocardiography (echo) might not provide, such as precise gradients or discordance in calculations.

• Accurate shunt calculations.

• Identifying associated lesions.

• Performing corrective procedures or assessing the feasibility of a gesture, particularly in complex malformations. 

• • Catheterization allows for measuring pressures in different heart cavities and vessels.

  • It also enables measuring cardiac output, taking blood samples, and performing blood gas analyses for oximetry.

  • Finally, angiography (injection of radiopaque contrast media) is performed to study morphology, kinetics, and the state of pulmonary parenchyma or distal circulation.

  • The purpose of cardiac catheterization is to determine anatomy (though CT scans can be good, catheterization adds hemodynamics).

  • It helps evaluate cardiac function via oximetry and cardiac output measurements.

  • It assesses pulmonary arterial hypertension for diagnosis, follow-up, treatment response, and evolution.

  • In complex heart diseases, catheterization is crucial for evaluating patient operability and guiding surgeons.

  • Navigation during Catheterization: Requires strong knowledge of normal and patient-specific anatomy, and how cardiac structures project on fluoroscopy.

Personnel and Environment for Pediatric Cardiac Catheterization

• A dedicated team is required in the catheterization lab, including trained radio manipulators for scopy arcs and X-rays, and nurses trained in catheterization techniques and equipment.

• All personnel are trained in radiation protection.

• For pediatric catheterization, an anesthesia team (anesthesiologists, respiratory therapist and nurses) handles analgesia, sedation, and general anesthesia. In our center, it is a pediatric cardiac anesthetist. 

• Pediatric cardiac catheterization, especially interventional, requires significant training, starting with diagnostic catheterization, which is often complex due to fragile or very ill patients (e.g., those with pulmonary arterial hypertension).

• A strong basic knowledge of normal and abnormal physiology, as well as congenital cardiology, is essential.

• A specific environment is needed to prevent complications, including expertise in pediatric cardiology to understand children's specific physiology and heart defects.

• Pediatric cardiac anesthesiologists are crucial, as anesthetizing a child with a single ventricle differs greatly from general anesthesia.

• Ideally, a pediatric intensive care unit should be nearby to manage complications.

• On-call staff are needed for emergencies, which often occur at night.

• Cardiac catheterization complements other imaging modalities like MRI, CT, and echocardiography to optimize patient care.

• Successful catheterization relies on meticulous planning and foresight:

  • Understand Anatomy and Objectives: Always clearly define the goals of the procedure (e.g., pressure measurement, shunt calculation, intervention).

  • Equipment Availability: Ensure all necessary equipment and materials are available, especially for complex procedures or specific device sizes (e.g., occluders).

  • Personnel Communication: Effective communication with the entire catheterization lab team is crucial for seamless procedure flow.

  • Anticipate Difficulties: Plan for potential challenges, such as difficult vascular access (e.g., thrombosed veins from previous procedures). Use imaging (echo, CT, MRI) to anticipate these issues.

  • Complication Preparedness: For interventional procedures, always anticipate specific complications and have a backup plan.

    1. Aortic Angioplasty/Stenting: Have a covered stent readily available for vascular dissection or rupture.

    2. Pulmonary Artery Stenting: Have a covered stent available for perforation.

    3. Aortic Valvuloplasty (in neonates): Prepare a defibrillator, as ventricular fibrillation can occur.

    4. High-Risk Procedures: Involve surgical backup if the procedure is particularly risky.

• Post-Procedure Follow-up: Implement a clear protocol for monitoring the patient post-catheterization, including vital signs, saturation, and puncture site checks. For device closures, an echocardiogram follow-up and chest radiography should be done after the procedure.

• Open Communication with Patients/Parents: Always provide honest information about results and potential complications. While reassurance is important, a truthful discourse is always better than hiding issues. Catheterization is acknowledged as a dangerous procedure, and anticipating problems helps to limit them.

Indications, Contraindications, Risks, and Complications

• • Understanding the indications and contraindications of cardiac catheterization is essential.Kno wing the risks and complications helps avoid them and manage them if they occur.

  • Patient and family consent is vital; children (when in age of) and families are informed of risks and benefits. Patients undergo pre-catheterization assessments; catheterization is avoided in infected or very unstable children due to increased complication risk.It is medico-legally mandatory to obtain authorization from both parents or the legal guardian. The procedure, its purpose (e.g., correcting shunts, measuring pressures), and how it will be performed (e.g., anesthesia, puncture site) must be explained clearly, often with diagrams.

  • Standard blood tests are performed, including renal function, coagulation, hemoglobin levels, gaz. Renal biomarkers (creatinine, urea) to monitor for potential issues with contrast medium. Allergy Assessment: Inquire about allergies to iodine, although iodine allergy is not a contraindication to catheterization; patients can be prepared if contrast is needed.

  • Review of Medical History:

    • Surgical History: Review previous surgeries for any particularities, especially concerning re-interventions.

    • Prior Catheterizations: For complex heart diseases, patients often have multiple previous catheterizations. This is crucial because repeated access can lead to thrombosed vessels (unilateral or bilateral), vascular stenosis, or new allergies (e.g., cutaneous rash to iodine appearing after several procedures). These issues can make future access challenging, sometimes requiring alternative routes like jugular or basilic veins, or even eco-guided vascular puncture. Pre-procedure vascular ultrasound can provide valuable information on vessel patency.

  • Recent echocardiography is important for functional evaluation and assessment of obstructive lesions by Doppler.

  • Anticoagulation is stopped before the procedure.

  • For cyanotic children with very high hemoglobin or hematocrit (above 65%), a exchange transfusion may be performed at the start of catheterization as polycythemia can complicate the procedure.

  • Diagnostic catheterization is often performed before interventional procedures (e.g., before valve implantation).

  • In pulmonary hypertension (PH), catheterization evaluates operability in congenital heart disease (measuring resistances and pulmonary/systemic flows).

  • For PH not associated with congenital heart disease, it is used for diagnosis, severity assessment, and follow-up.

Cardiac catheterization involves several key measurements and interventions:

• Pressure Measurements: Pressures are typically recorded in the right atrium, right ventricle, pulmonary artery, and pulmonary capillary wedge pressure (PCWP), which approximates left atrial pressure (if no obstruction between the pulmonary capillaries and the left atrium - and when the pulmonary veins are draining into the left atrium and not somewhere else like the right atrium, SVC, IVC, coronary sinus or ambiguous atrium). For left heart catheterization, pressures are taken in the aorta, pulmonary capillary wedge, and left ventricular end-diastolic pressure (LVEDP). The LVEDP assesses dysfunction and filling status.

• Coronary evaluations (such as in Kawasaki, fistulas, post-arterial switch, concern for stenosis or infarction, etc. )

• Oxygen Saturation (Oximetry): Stage-by-stage oximetry is performed to detect shunts, looking for oxygen enrichment in specific chambers.

• Cardiac Output Measurement: This is typically done using a thermodilution catheter or the Fick principle. However, thermodilution is inaccurate in the presence of shunts.

• Vascular Resistance Measurement: Pulmonary vascular resistance (PVR) is measured.

• Angiography: Contrast medium is injected to visualize the cardiac chambers and vessels, creating a "negative" image.

• Biopsies: Tissue samples can be taken (i.e. Post-transplant).

• Interventional Procedures:

  • Dilation: Coarctations can be dilated.

  • Closure: Patent ductus arteriosus (PDA) acan be closed percutaneously. Atrial septal defects (ASDs) can also be closed.

  • Valve Replacement: Aortic valve replacement (TAVI) is increasingly used in adults and is anticipated for younger patients with valvular aortic pathology in the future - although still under investigation.

• Occlusion Tests: Temporarily occluding a defect (e.g., fenestration in a Fontan circuit, PDA, inter-atrial shunt) to assess the patient's tolerance before definitive closure.

• Intracardiac Echocardiography (ICE): Using an ultrasound probe on the catheter to visualize cardiac structures from within the heart (sometimes coronaries).

Risks and Complications:

Complications may arise from both the technical procedure and from sedation/anesthesia. Preparation should address both aspects.

• Pre-Procedural Stability: Ensuring physiological stability (e.g., pH, pCO₂, hemoglobin) is essential for accurate hemodynamic assessment.

  1. Example, evaluation of a patient for pulmonary vasculature but acidosis such as low pH or high pCO2 - hemodynamics data will be difficult to interpret. 

  2. Viscosity with severe anemia can also impact hemodynamics data. Important to initate evaluation upon adequate condition to answer carefully the questions asked. 

  3. Unsure that the catheter-based evaluation is not expected to significantly decompensate the patient. 

• Radiation Exposure: Minimized through careful planning and preference for single-plane imaging, especially important in growing children.

• Anesthesia Risks: High in medically fragile or complex patients (e.g., single ventricle physiology). Appropriate anesthetic protocols and agent selection are critical to avoid decompensation.

• Hypothermia: Children, especially infants, are prone to rapid heat loss. Use of warmed contrast agents and flushes, along with active thermal management, is necessary to prevent cooling.

• Hypoxia and Cyanosis: Patients with cyanotic congenital heart disease (e.g., Tetralogy of Fallot) are vulnerable to deterioration due to fasting, anesthesia-induced hypotension, or hypovolemia. Angiography may exacerbate cyanosis or trigger pulmonary vasospasm.

• Blood Loss and Anemia: Even minimal blood loss (e.g., from sheath placement or sampling) can lead to significant anemia in small children. Hemostasis must be carefully managed.

• Renal Insufficiency: Although rare in children due to generally robust renal function, adequate hydration remains important to prevent contrast-induced nephropathy.

• Intramyocardial Injection: Accidental myocardial contrast injection can damage a fragile ventricle. Careful technique and low injection pressures reduce this risk.

• Post-Procedural Risks: Include hematomas at the puncture site and stroke, particularly in cyanotic children with intracardiac shunts, where thromboembolism or air embolism can bypass the lungs.

• Fallot Spells: Patients with Tetralogy of Fallot are particularly vulnerable to peri-procedural "spells" triggered by fasting, anesthesia, hypovolemia, or contrast injection. Preventive measures should be in place.

• Key Principles:

  1. Never Force: Forcing a catheter can cause vascular or cardiac perforation, leading to hematomas (retroperitoneal, potentially fatal) or cardiac tamponade.

  2. Prevent Air Embolism: Ensure no air bubbles in the circuit when injecting contrast or flushing. Air embolism in the right heart usually resolves in the lungs, but in the left heart (e.g., via a shunt), it can cause coronary or cerebral embolisms, leading to bradycardia, hypotension, or stroke.

  3. Careful Catheter Manipulation: Use gentle rotation and push-pull movements.

  4. Guidewires: Used to advance catheters, including standard and hydrophilic guides (very flexible, plastic-sheathed).

  5. Balloon Catheter Retrieval: Always deflate the balloon before withdrawing a balloon-tipped catheter to avoid damaging valves (e.g., pulmonary, tricuspid).

• Contrast-Related Complications:

  1. Allergic Reactions (Anaphylaxis): Ranging from cutaneous rash (managed with corticosteroids) to severe anaphylactic shock (managed with adrenaline). If an allergy occurs, it must be documented for future procedures.

  2. Nephropathy: Renal injury due to iodinated contrast, more common in small infants or with high doses. Use low-osmolarity contrast and ensure patient hydration. Dialysis patients can undergo catheterization if scheduled for dialysis post-procedure.

• Catheter Manipulation-Related Complications:

  1. Arrhythmias: Extrasystoles are common, but more serious arrhythmias like ventricular fibrillation can occur, requiring defibrillation. Catheter contact with the endocardium can provoke transient arrhythmias, which typically resolve once stimulation ceases. However, aggressive or prolonged manipulation can lead to sustained rhythm disturbances.

  2. Embolism:

     1. Air Embolism: Due to air bubbles in the circuit, potentially causing stroke or angina. Avoidance of air bubbles in contrast and flushes is essential, particularly in young children where even small emboli can have significant effects.

     2. Paradoxical Embolism: Particularly in patients with right-to-left shunts, the risk is mitigated by strict air elimination and appropriate anticoagulation.

     3. Thrombus/Plaque Embolism: Due to dislodged clots or atherosclerotic plaques, more common in older patients.

  3. Vascular Dissection/Perforation: Catheter causing injury to the vessel wall, leading to contrast extravasation, hematoma, or even cardiac tamponade if the heart is perforated. Covered stents may be needed to repair vascular breaches. Risk of vessel or chamber perforation requires meticulous catheter technique and vigilance. Risks include hematoma formation and nerve injury. Ultrasound-guided access is strongly recommended to minimize failed or repeated punctures.

  4. Bleeding: From vascular injury or excessive anticoagulation (heparin), which can be neutralized by protamine.

• Access Site Complications:

  1. Hematoma: Common, usually superficial.

  2. Pseudoaneurysm: A contained rupture of the vessel wall.

  3. Arteriovenous Fistula: An abnormal connection between an artery and a vein, often managed with compression or surgical ligation.

  4. Thrombosis/Ischemia: Occlusion of the vessel, especially in the femoral artery in infants, potentially leading to limb ischemia (though rarely amputation). Anticoagulation (heparin) is often used.

  5. Infection: Less common, but possible at the puncture site.

Access Routes for Catheterization

• • The choice of access route depends on patient age (umbilical access for newborns), vessel size (usually max 4 French arterial introducer in newborns to prevent arterial damage), and the type of procedure.

  • It also depends on the child's heart defect (complex anatomies) and vascular access permeability (previous surgeries/catheterizations can block femoral access).

  • The chosen route must allow for quick and accurate answers to clinical questions with minimal risk. Time efficiency is key for sick children under anesthesia.

  • Venous Access (Right Heart):

    • Femoral vein: The most common and preferred elective route.

    • Umbilical vein: Used in newborns, for procedures like Rashkind atrial septostomy.

    • Basilic or Cephalic vein (arm veins): Used in older children, particularly if single ventricle anatomy (e.g., Fontan circulation) or bilateral femoral vein thrombosis exists. Usually used when more than 10 kg. When post-Fontan: need to go by jugular vein or basilic vein to access the pulmonary artery. 

    • Jugular or Subclavian vein: Can be used, often with ultrasound guidance for jugular access.

    • Hepatic vein: In cases where other veins are occluded, a hepatic vein can be punctured under ultrasound guidance, allowing access to the right heart via the inferior vena cava.

  • Arterial Access (Left Heart):

    • Femoral artery: The most common arterial route.

    • Carotid artery: Accessed with surgical exposure for repair after the procedure.

    • Subclavian or Axillary artery: Used in older children or adults if femoral arteries are stenosed or thrombosed.

    • Umbilical artery: Used in newborns.

  • Unusual/Hybrid Approaches:

    • Direct Cardiac Puncture: The heart can be directly punctured during a mini-thoracotomy (hybrid procedure). Examples include puncturing the pulmonary infundibulum in hypoplastic left heart syndrome (HLHS) to stent the ductus arteriosus.

    • Transatrial/Transseptal Puncture: Accessing the left atrium from the right atrium across the interatrial septum.

  • Review of common access routes:

    • Femoral (artery and vein): Most frequently used.

      1. Femoral Approach and Introducers

         1. Proper patient positioning is crucial.

         2. The puncture site is disinfected, and local anesthesia is given if the child is not under general anesthesia.

         3. The femoral pulse is located, and puncture is performed about 1 cm below the inguinal ligament.

         4. Heparin is almost systematically administered in all diagnostic or interventional catheterizations to protect vessels and prevent thrombus formation.

         5. Ultrasound-guided puncture is increasingly important.

         6. The rule is to use the smallest possible introducer (e.g., 4 French for newborns), only increasing size if needed for specific procedures or larger catheters (e.g., 7 French for a Swan-Ganz catheter for cardiac output measurement).

         7. The choice also depends on whether arterial, venous, or both accesses are needed.

    • Humeral (artery and vein): Rarely used, sometimes for coarctation of the aorta (superior approach).

    • Jugular: Used when both femoral veins are blocked or at certain stages of single ventricle palliation (e.g., partial cavopulmonary derivation), as the superior vena cava connects to pulmonary arteries. Jugular puncture is always done under general anesthesia in children as it is anxiety prone for the pediatric patient.

    • Umbilical: Used in newborns.

    • Transhepatic: Used when no other access is available and femoral/jugular routes are blocked.

Types of Catheters and Guides

• • Catheters are mainly derived from adult coronarography.

  • Examples of catheters:

    • Rashkind cathether - 6 fr. Used for septostomies in dTGA, HLHS restrictive septum, Tricuspid Atresia restrictrive septum, Taussig Bing anomaly, etc. 

    • Right coronary catheter: Used for right heart exams (right atrium, right ventricle, pulmonary artery, ascending/descending aorta).

    • NIH (multi-hole lateral but not distal) catheter: Used for angiography.

    • Balloon catheter (Swan-Ganz): Used for cardiac output measurement and measuring wedge pressure.

    • Pigtail catheter: Used for angiography, identifiable by its coiled tip.

    • Left coronary catheter: Curve for left coronary. Used for PDA for stenting. 

    • Multi-track catheter: A catheter specifically developed by congenital cardiologists, with lateral holes, able to slide over a guide wire. It allows pressure measurement and angiography while keeping the guide in place, useful for tight stenoses (i.e. critical pulmonary valvular stenosis).

  • Guides: Available in various sizes, lengths, and rigidities, each with specific uses.

    • Hydrophilic guides (e.g., Terumo): Used frequently in pediatric cardiac catheterization; require wetting to move.

    • Rigid guides: Used for valve implantation but can perforate pulmonary arteries; avoided if not implanting a valve.

    • Exchange guides.

    • Coronary guides (very small): Used to pass tight neonatal pulmonary valvular stenoses.

  • Knowing the appropriate guide is key to reaching the desired location.

Describing the Catheterization Path/Trajectory

• • It is crucial to describe the catheter's trajectory during catheterization, especially in complex congenital heart diseases, as it helps understand the physiology and how cavities were accessed.

  • Examples:

    • PDA closure (arterial approach) - smaller PDA: Catheter inserted via the artery, advanced into the aorta, then through the PDA into the pulmonary artery to deploy a coil. Trajectory: Aorta -> PDA -> Pulmonary Artery: coil liberation.

    • PDA closure with a very large PDA - there is significant opacification of the PA via the aortic injection (venous/arterial approach). Aortic access for opacification and visuzalition. Then, catheter inserted via the vein, through right atrium, right ventricle, pulmonary artery, then across the PDA into the aorta to deploy a plug. Trajectory: Vein -> Right Heart -> Pulmonary Artery -> PDA with guide -> Aorta. Plug from the Aorta towards the PA. This demonstrates that the access route can vary significantly for the same procedure depending on the material used.

  • The choice of device (coil vs. plug) depends on the size of the PDA. A larger PDA requires a larger plug to ensure containment against high pressure.

• Pressure Values: Normal pressures vary by age but generally, left-sided pressures are higher than right-sided pressures.

  • PA systolic/diastolic: ~25-30/5 mmHg.

  • PCWP: ~12 mmHg.

  • LV systolic: ~80-90 mmHg (in infants).

• Pressure Curves: Distinct waveforms reflect different cardiac events (e.g., atrial contraction, valve closure, ventricular ejection, relaxation, filling).

Atrial Pressure:

• • • Right atrial 

      1. A pressure: 2-8 mmHg

      2. V pressure: 2 to 7.5 mmHg

      3. Mean pressure: 1-5 mmHg. RA mean: ~5 mmHg.

    • Left atrial 

      1. A pressure: 3 to 12 mmhg

      2. V pressure: 5 to 13 mmHg

      3. Mean pressure: 2-10 mmHg.

    • Right atrial pressure is measurable via venous access.

    • Left atrial pressure can be measured directly if an interatrial shunt (PFO, ASD) exists. Otherwise, it is estimated using pulmonary capillary wedge pressure (PCWP), which reflects left atrial pressure if there's no pulmonary vein disease/stenosis. A Swan-Ganz catheter with a balloon can be used to obtain PCWP.

Mitral insufficiency 

Mitral regurgitation/insufficiency significantly alters left atrial (LA) dynamics and pressure profiles, both acutely and chronically. Mitral insufficiency is characterized by retrograde flow of blood from the left ventricle (LV) to the left atrium (LA) during systole. 

Acute mitral regurgitation leads to sudden volume overload of the LA during systole. The LA is non-compliant (has not had time to adapt), leading to markedly elevated LA pressures (especially v wave), pulmonary venous congestion → acute pulmonary edema, no significant LA dilation yet. 

• LA Pressure Waveform: 

  • a wave: May be blunted or masked 

  • v wave: Tall and early-peaking, due to regurgitant volume entering LA during systole (This “giant v wave” is a hallmark of acute severe MR) 

  • Giant v waves in the wedge pressure tracing (if using a PA catheter) suggest significant mitral regurgitation. 

Chronic Mitral Regurgitation: The LA gradually undergoes volume adaptation and dilation, becoming more compliant. Despite continued regurgitant flow, mean LA pressure may remain near-normal or only modestly elevated. Pulmonary venous congestion may be mild or absent at rest. But LA dilation predisposes to atrial arrhythmias (e.g., atrial fibrillation).

• LA Pressure Waveform: 

  • a wave: Often reduced or absent (especially if in atrial fibrillation) 

  • v wave: Still elevated but less dramatic than in acute MR due to increased compliance 

  • Chronic MR may present with preserved LV function but progressive LA and LV dilation, atrial arrhythmias, and symptoms of congestive heart failure. Pulmonary hypertension may develop secondarily if LA pressure chronically transmits backward into pulmonary veins.

Mitral Stenosis

Mitral stenosis is a narrowing of the mitral valve orifice that impairs blood flow from the LA to the LV during diastole. During diastole, the left atrium must generate higher pressure to push blood across the stenotic mitral valve into the left ventricle. This leads to chronic elevation in LA pressure and progressive LA dilation over time. MS causes a pressure gradient between the pulmonary capillary (or left atrium) and the left ventricle during diastole. This gradient is visible as a difference between the PCWP/LA pressure curve and the LV diastolic pressure curve. Both a maximum gradient and mean gradient are measured.

Left Atrial Pressure Waveform in MS 

• a wave: May be prominent (especially in sinus rhythm), as the atrium contracts against a stiff valve. 

• v wave: Often blunted, because LA emptying is impaired. 

• Mean LA pressure: Elevated, particularly during diastole, creating a diastolic pressure gradient between LA and LV. This gradient is the hallmark of MS (e.g., LA mean pressure 25 mmHg vs LVEDP 10 mmHg). 

If acute (e.g., after mitral valve repair gone wrong), leads to: Abrupt ↑ LA pressure, pulmonary edema, marked decrease in LV preload and cardiac output. If chronic: Left atrial remodeling and dilation, progressive pulmonary venous hypertension, leading to: pulmonary congestion, pulmonary hypertension (passive initially, reactive over time), risk of atrial fibrillation (due to atrial stretch), which worsens symptoms by eliminating atrial contraction contribution to preload of the LV.  Risk of thrombus formation in the dilated LA → embolic stroke. Diastolic murmur best heard at the apex (low-pitched, rumbling, with opening snap).

Aortic insufficiency (AI) — also called aortic regurgitation 

AI/AR profoundly affects left ventricular (LV) dynamics, loading conditions, and pressures, both acutely and chronically. In aortic insufficiency, the aortic valve fails to close completely during diastole, allowing retrograde flow of blood from the aorta into the LV. 

Immediate (Acute) Effects on LV:

• Volume Overload During Diastole: The LV receives blood from both the left atrium and the aorta, dramatically increasing end-diastolic volume. This acutely increases LV end-diastolic pressure (LVEDP). The non-compliant LV cannot accommodate this sudden increase → steep rise in diastolic pressure, leading to: elevated left atrial pressure → Pulmonary venous congestion → pulmonary edema. 

• Low forward stroke volume and hypotension: Widened pulse pressure (↓ diastolic BP due to the steal effect, ↑ systolic BP due to increased stroke volume) 

• Pressure Tracings (LV and Aorta): LV diastolic pressure rises abnormally high. Aortic diastolic pressure falls due to regurgitation. Widened pulse pressure: hallmark of AI. Aortic pressure waveform may show a steep downstroke in diastole ("water-hammer" pulse) 

Chronic AI:

• Eccentric Hypertrophy and Remodeling: Chronic volume overload leads to LV dilation (eccentric hypertrophy) to maintain stroke volume via Frank-Starling mechanism. LV becomes more compliant, so LVEDP may remain normal for years despite volume overload. 

• LVEDV (end-diastolic volume) is incrased

• LVEDP: Normal or mildly elevated early, rises over time 

• Stroke volume: Increased (due to augmented preload), but forward stroke volume is reduced due to regurgitation 

• Ejection fraction: May be preserved early but declines with LV systolic dysfunction in late stages 

• Aortic diastolic pressure remains low (runoff into LV). LV pressure curve shows a gradual rise during diastole, no isovolumic relaxation phase (since aortic valve is incompetent). Bounding peripheral pulses (Corrigan’s pulse), head bobbing (de Musset’s sign), capillary pulsations (Quincke’s sign). Chronic AI can lead to progressive LV dilation, Heart failure symptoms (dyspnea, fatigue), Subendocardial ischemia from reduced coronary perfusion (↓ diastolic aortic pressure) and increased LVEDP.

Angiography can provide a qualitative assessment of valve regurgitation:

• Contrast injected into the aorta will show reflux into the left ventricle.

  • Grade 1 (Minimal): Barely visible opacification of the left ventricle.

  • Grade 2 (Mild): Opacification of the left ventricle, but less dense than the aorta.

  • Grade 3 (Moderate): Equivalent opacification of the left ventricle and aorta.

  • Grade 4 (Severe/Massive): Greater opacification of the left ventricle than the aorta. This angiographic grading system (1-4) is historical and similar to echocardiographic quantification, though echo is often preferred today.

Aortic stenosis (AS) 

AS imposes a fixed obstruction to left ventricular (LV) outflow during systole. This creates a pressure overload state, leading to distinct changes in LV dynamics, loading conditions, and intracardiac pressures. Aortic stenosis causes resistance to LV ejection, requiring the ventricle to generate higher systolic pressure to overcome the narrowed outflow tract (sub-aortic, aortic or supra-valvalar obstruction). Causes a systolic pressure gradient between the left ventricle and the aorta. Catheterization can measure both peak-to-peak and instantaneous maximal gradients, which differ from echocardiography's instantaneous maximal gradient. Catheterization is often used when echo overestimates the gradient.

Left Ventricular Hemodynamic Changes

• Pressure Overload: The LV must contract against a high afterload, often reaching systolic pressures >200 mmHg in severe AS. This leads to: concentric hypertrophy (wall thickening without dilation), increased myocardial oxygen demand, reduced compliance (diastolic dysfunction). 

• Systolic LV pressure is markedly elevated, especially compared to the aortic pressure. Example: LV systolic pressure 180 mmHg, aortic systolic 100 mmHg → gradient of 80 mmHg. 

• Diastolic LV pressure may be mildly elevated if hypertrophy leads to stiffening 

• LV-Aortic Gradient The peak-to-peak gradient (difference between peak LV and peak aortic pressure) is a key measure of AS severity. Severe AS: in adult, mean gradient ≥40 mmHg, valve area <1.0 cm²

• Gradients:

  • Peak-to-peak gradient – This is the difference between the peak LV pressure and the peak aortic pressure, regardless of when each occurs. It is easy to measure, but not physiologically exact, because the LV and Ao peaks do not occur at the same time. The aortic pressure rise is slow, and its peak is delayed.

  • Maximum instantaneous gradient. This is the maximum difference at any one time point between the LV and Ao curves during systole. It is the most accurate representation of true systolic obstruction. It corresponds to what Doppler echocardiography measures using the modified Bernoulli equation (ΔP = 4v²). 

  • Mean gradient. This is the average pressure gradient over the entire systolic phase. It gives a reliable measure of overall hemodynamic burden on the LV. Often used in quantifying severity of aortic stenosis.

Ventricular and Aortic Pressures

• • Ventricular Pressure: Systolic and diastolic pressures.

    • The end ("tele")-diastolic pressure usually reflects the left atrial pressure and indicates ventricular compliance. An exception is when there's a mitral valve anomaly or cor-triatriatum sinister.

  • Aortic Pressure: Includes systolic, diastolic, and mean pressures.

    • Diastolic pressure is crucial because it's when the coronary arteries are perfused (except in a disease like HLHS or critical aortic stenosis where it is perfused retrograde in systole via the duct).

    • Very low diastolic pressures (e.g., in large PDA, aortic valvular insufficiency, large aortopulmonary collaterals, Anomalous origin of the pulmonary artery from the aorta, aorto-pulmonary window, aorto-ventricular tunnel, larve AV malformation, or large BTT shunt) can lead to myocardial ischemia.

    • The mean aortic pressure provides a good overall assessment of the child's vascularization and general condition.

Pulmonary Pressures and Wedge Pressure

• • Pulmonary Artery Pressure (PAP):

    • Normal systolic: 15-30 mmHg.

    • Normal diastolic: 2-12 mmHg.

    • Normal mean: 7-18 mmHg.

    • Systolic PAP is compared to aortic systolic pressure to determine if pulmonary hypertension (PH) is infra-, iso-, or supra-systemic.

    • Mean PAP defines PH (mean PAP ≥ 20 mmHg).

  • Pulmonary Capillary Wedge Pressure (PCWP): 

    • Obtained by inflating a balloon at the distal tip of a catheter in the pulmonary artery, blocking forward flow.

    • It reflects left atrial pressure, provided there are no pulmonary vein stenoses.

    • It can also be estimated by gently advancing a catheter (like a right coronary catheter) until it wedges in a small vessel, showing a flattened, respiratory-varying pressure curve.

    • The Swan-Ganz catheter is typically used for this, allowing measurement of right atrial, right ventricular, pulmonary artery, and wedge pressures sequentially.

Pulmonary Hypertension

• Pulmonary Hypertension (PH): According to the recent WSPH (Nice, 2018), PH is defined as a mean Pulmonary Artery Pressure (mPAP) > 20 mm Hg in children older than 3 months of age at sea level. It is important to note that even mildly elevated mPAP values (20–24 mm Hg, with a prognostic threshold of 17 mm Hg) are considered independent predictors of poor survival in adults with PH.

• Pre-capillary PH: 

  • mPAP > 20 mm Hg

  • Pulmonary Artery/Capillary Wedge Pressure (PAWP) or Left Ventricular End-Diastolic Pressure (LVEDP) ≤ 15 mm Hg

  • Pulmonary Vascular Resistance (PVR) index ≥ 3 Wood Units (WU) × m2 (or PVR ≥ 3 WU in adults)

  • A Diastolic TPG (DPG) ≥ 7 mm Hg is considered an adjunct criterion.

• Isolated post-capillary PH (Ipc-PH): In adults, this type, exemplified by predominantly diastolic Left Ventricular (LV) dysfunction (Heart Failure with preserved Ejection Fraction, HFpEF), is defined by:

  • mPAP > 20 mm Hg

  • PAWP or LVEDP > 15 mm Hg

  • PVR index < 3 WU × m2 (or PVR <3 WU in adults)

  • A Diastolic TPG (DPG) < 7 mm Hg is an adjunct criterion. It is often useful to measure PAWP simultaneously with LVEDP in these instances.

• Combination of pre-capillary and post-capillary PH (Cpc-PH): In adults, this condition is defined by:

  • mPAP > 20 mm Hg

  • PAWP or LVEDP > 15 mm Hg

  • PVR ≥3 WU (or PVR index ≥ 3 WU × m2 in children).

• Pulmonary Arterial Hypertension (PAH):

  • mPAP > 20 mm Hg

  • PAWP or LVEDP ≤ 15 mm Hg

  • PVR index ≥ 3 WU × m2

  • Additionally, it must meet the criteria for group 1 PH.

• Idiopathic PAH (IPAH): This refers to PAH where there is no underlying disease known to be associated with PAH.

• Heritable PAH (HPAH): This is PAH where there is no known underlying disease, but the index patient has a positive family history or positive genetic testing.

• Eisenmenger syndrome (ES): This describes a patient with longstanding pulmonary hypertension, suprasystemic PVR and PAP (Pulmonary Artery Pressure), and consequently, right-to-left cardiovascular shunting with systemic hypoxemia. Examples include unrepaired Ventricular Septal Defect (VSD) or Patent Ductus Arteriosus (PDA).

• Pulmonary Hypertensive Vascular Disease (PHVD):

  • For biventricular circulations, PHVD is defined as mPAP > 20 mm Hg and PVR index ≥ 3 WU × m2.

  • For circulations with cavopulmonary anastomosis (e.g., Fontan physiology), it is defined by a Mean TPG > 6 mm Hg (calculated as mPAP minus mean Left Atrial Pressure (mLAP) or PAWP) or PVR index > 3 WU × m2. It should be noted that the PVRI-Panama classification of pediatric PHVD from 2011 used mPAP ≥ 25mm Hg to define PH. Also, in adults, PVR is usually not indexed to Body Surface Area (BSA).

Cardiac Output Measurement (Thermodilution and Fick Principle)

• • Thermodilution 

    • Used to measure cardiac output when there are no intracardiac shunts (RV output = LV output).

    • Stewart-Hamilton principle

    • Involves injecting a known volume of cold liquid into the right atrium and measuring temperature changes distally in the pulmonary artery using a Swan-Ganz catheter.

    • Three successive injections are performed for an average measurement.

    • Normal cardiac output in adults: 4-8 L/min; indexed cardiac output: 2.5-4 L/min/m².

    • Pulmonary vascular resistance (PVR) is calculated using mean PAP, PCWP, and cardiac output: PVR = (Mean PAP - PCWP) / Cardiac Output.

    • For children, indexed PVR (PVRI) is used, dividing by indexed cardiac output.

• • Fick Principle

    • Used to estimate Qp:Qs (pulmonary flow to systemic flow ratio) in children with congenital heart disease and shunts.

    • It calculates flow based on a substance secreted/absorbed by an organ, its entry/exit concentrations, and its consumption/secretion rate per unit time.

    • Oxygen consumption (VO2) is key: VO2 = Cardiac Output x (Arterial O2 Content - Venous O2 Content).

    • VO2 can be measured directly (complex and constraining for children) or estimated from nomograms based on age, sex, and heart rate.

    • Cardiac Output = VO2 / (Arterial O2 Content - Venous O2 Content).

    • Oxygen content calculation: Saturation x Hemoglobin x 1.34 + 0.0031 x PaO2 (PaO2 term often simplified).

    • Normal VO2: ~10 mL/kg/min.

    • Qp:Qs Ratio: Calculated from saturation data (aorta, vena cava, pulmonary veins, pulmonary artery).

    • Qp:Qs = (SaO2 - SmvO2) / (SpvO2 - SpaO2), where SaO2 is aortic, SmvO2 is mixed venous (SVC/IVC average), SpvO2 is pulmonary venous, and SpaO2 is pulmonary artery oxygen saturation.

    • If pulmonary venous saturation cannot be measured (no atrial shunt), it's estimated at 100% assuming good lung function in an infant.

    • For right-to-left shunts, pulmonary artery saturation is the same as vena cava saturation.

    • In cases like pulmonary atresia with a BTT shunt, Qp:Qs can often be estimated without full catheterization if the child is stable and good lung function is presumed, as pulmonary artery saturation would equal aortic saturation (PA only perfused by the BTT shunt). 

Qp:Qs

Qp:Qs represents the ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs). In a normal heart without shunting, Qp/Qs is equal to 1, meaning pulmonary blood flow equals systemic blood flow. The most common formula for calculating Qp:Qs from oxygen saturations is: Qp:Qs = (Ao sat - MV sat) / (PV sat - PA sat)

Where:

• Ao sat = Aortic saturation (systemic arterial oxygen saturation).

• MV sat = Mixed venous saturation.

• PV sat = Pulmonary venous saturation.

• PA sat = Pulmonary arterial saturation.

How to Obtain Saturation Values in the Cath Lab

Blood samples are taken from specific locations within the heart and great vessels to determine these saturations.

• Aortic Saturation (Ao sat): This is typically obtained from a sample taken from any systemic artery, such as the aorta, femoral artery, or radial artery.

• Mixed Venous Saturation (MV sat):

  • Ideally, a mixed venous oxygen saturation should be obtained from the most distal right heart chamber or a site where there is no left-to-right shunt.

  • In the absence of an intracardiac shunt, the pulmonary artery sample provides the best mixed venous sample.

  • If intracardiac shunting is present, the superior vena cava (SVC) saturation is often used as the mixed venous saturation for hemodynamic calculations. SVC saturation can be unusually high due to reflux from other sources. In infants, an equal upper and lower body venous return is sometimes assumed for calculating mixed venous saturation from SVC and IVC (inferior vena cava) values. However, IVC saturations can be inconsistent due to high renal venous and low hepatic venous oxygen content.

• Pulmonary Venous Saturation (PV sat):

  • Ideally, a sample would be obtained directly from the pulmonary vein or left atrium.

  • If direct sampling is not possible, it is often assumed to be 95% or 98% in the absence of lung disease and if the patient is breathing room air. For patients on 100% oxygen, PV sat may reach 100%.

• Pulmonary Arterial Saturation (PA sat): This is obtained from the pulmonary artery. In patients with patent ductus arteriosus (PDA), oxygen saturations in the main and branch pulmonary arteries may differ. In cases like Hypoplastic Left Heart Syndrome (HLHS) with shunt physiology, the pulmonary artery saturation is often considered equal to the aortic saturation because the only source of pulmonary blood flow is the shunt.

Example: large VSD that is shunting left to right: oxygenated blood entering the PA. Aortic Saturation at 100, Pulmonary venous saturation at 100, Mixed venous saturation at 70 (30-point extraction of oxygen in the body). The mixed venous saturation will reach the PA and mix with oxygenated blood. Let's say it is 85%. This gives (100-70) / (100 - 85) = 30/15 = Qp/Qs of 2.

Interpretation of Qp:Qs Values

• Qp:Qs between 1 and <1.5 is generally considered a small left-to-right shunt and of relatively minor clinical consequence.

• Qp:Qs >1.8:1 indicates a large left-to-right shunt.

• Qp:Qs <1 indicates a net right-to-left shunt.

• Patients with a flow ratio greater than 2:1 are usually considered surgical candidates.

• In specific conditions like Tetralogy of Fallot (TOF), where the ventricular septal defect (VSD) equalizes pressures in both ventricles, Qp:Qs is related to the ratio of resistance offered by the right ventricular outflow obstruction and the systemic vascular resistance (SVR).

• Definition of Significant Shunt: A left-to-right shunt is generally considered significant if the pulmonary-to-systemic flow ratio (Qp/Qs) is greater than 1.5. H

• Detection of a shunt could be suspected by catheter trajectory (e.g., catheter passing from RA to LA via ASD) or by step-up in oxygen saturation (oximetry) in chambers distal to the shunt. For example, a significant oxygen enrichment in the pulmonary artery compared to the right ventricle or in the right atrium compared to the superior vena cava suggests a shunt.

• Oxygen Content Calculation: The amount of oxygen in blood depends on hemoglobin concentration and oxygen saturation, with a minor contribution from dissolved oxygen.

  • Formula: Oxygen Content = (Hemoglobin concentration (g/dL) * 1.36 mL O2/g Hb * Saturation %) + (0.003 mL O2/dL/mmHg * PO2).

  • Oxygen Content "CaO₂"=(Hb×1.36×SaO₂)+(0.003×PaO₂); Where: 

    1. Hb = Hemoglobin concentration (g/dL); 

    2. 1.36 mL O₂/g Hb = Oxygen-carrying capacity of hemoglobin (Some texts use 1.34; both are physiologically acceptable depending on source) 

    3. SaO₂ = Oxygen saturation (%) as a fraction (e.g., 97% = 0.97) 

    4. PaO₂ = Partial pressure of oxygen in arterial blood (mmHg) 0.003 = Solubility coefficient of oxygen in plasma (mL O₂/dL/mmHg). Often considered as "0". > 98% of oxygen is carried by hemoglobin, not dissolved in plasma. The dissolved oxygen term (0.003 × PaO₂) contributes minimally under normal conditions, but becomes more relevant under hyperbaric oxygen therapy or in extracorporeal support settings.

  • Traps: Be mindful of units (e.g., hemoglobin in g/dL, oxygen content in mL O2/dL). Venous oxygen saturation is often assumed to be 70% if not measured.

• Cardiac Output (Fick Principle): A common method for cardiac output and shunt calculation in the presence of shunts.

  • Formula: Cardiac Output = Oxygen Consumption (VO2) / (Arterial O2 Content - Venous O2 Content).

  • VO2 Measurement: Measured directly by a metabolic mask worn by the patient, which measures oxygen consumption and CO2 production. If direct VO2 measurement is not available, estimated values based on age, sex, and heart rate can be used.

    1. Wilkinson JL. Haemodynamic calculations in the catheter laboratory. Heart. 2001 Jan;85(1):113-20. doi: 10.1136/heart.85.1.113. PMID: 11119478; PMCID: PMC1729580.

    2. LaFarge CG, Miettinen OS. The estimation of oxygen consumption. Cardiovasc Res. 1970 Jan;4(1):23-30. doi: 10.1093/cvr/4.1.23. PMID: 5416840.

    3. Oxygen consumption (assumed values): Infant <3 months is ~130 ml/min/m2 . 2–5 years ~150–200 ml/min/m2 . Adolescents ~120–180 ml/min/m2 . Adult females ~100 ml/min/m2 . Adult males ~110–120 ml/min/m2 . 1–2 years ~200 ml/min/m2 . According to: Butera, Gianfranco, et al. Cardiac catheterization for congenital heart disease. Springer International Publishing, 2021.

• Qp/Qs Ratio:

  • Full Fick Formula: Qp/Qs = (Aortic O2 Content - Mixed Venous O2 Content) / (Pulmonary Venous O2 Content - Pulmonary Artery O2 Content). VO2 cancels out in this ratio. Mixed venous oxygen content is often taken from the SVC if the IVC is not available, or an average of both. Pulmonary venous oxygen content is usually assumed to be 100% (or arterial O2 content if pulmonary circulation is normal).

  • Simplified Fick Formula: 

    1. Qp/Qs = (Aortic O2 Saturation - Mixed Venous O2 Saturation) / (Pulmonary Venous O2 Saturation - Pulmonary Artery O2 Saturation). 

    2. This simplified formula is commonly used by catheterizers as it does not require VO2 measurement.

    3. Example - ASD left to right.

       1. Aortic Saturation 100%

       2. Mixed Venous Saturation 70%

       3. Pulmonary Venous Saturation 100%

       4. PA saturation 85% (increased oxygen saturation compared to Mixed venous because of the left to right ASD bringing higher oxygen content into the RV and PA).

       5. (100-70)/(100-85) = 30/15 = 2 Qp/Qs

• Localization of Shunts (Oximetry Step-up Criteria): 

  • An oxygen step-up of 1.9 volume % (nearly 2%) between SVC and RA - differential diagnosis: 

    1. ASD shunting left to right 

    2. An abnormal pulmonary venous return to RA. 

    3. It could also be secondary to a shunt from the LV to the RA (Gerbode defect). 

    4. It could also be secondary to a shunt from the left-sided ventricular chamber to the right-sided atrial chamber in a AV septal defect. 

    5. VSD (left to right) with Tricuspid Insufficiency

    6. Rupture of the sinus of Valsalva of the Aortic Valve into the right atrium (RA) creating an aorto–atrial fistula, allowing oxygenated blood from the high-pressure aorta to shunt directly into the low-pressure right atrium.

    7. Coronary fistula towards right atrium

  • A step-up of 0.9 volume % (nearly 1%) between RA and RV differential diagnosis: 

    1. Most commonly a VSD 

    2. A ruptured sinus of Valsalva of the aortic valve into the right ventricle. 

    3. Coronary to RV fistula

    4. PDA that is left to right with a pulmonary valvular insufficiency

    5. An aorto-ventricular tunnel towards the RV

  • A step-up of 0.5 volume % between RV and PA suggests:

    1. A left to right PDA;

    2. An aortopulmonary collateral.

    3. An aortopulmonary window

Limitations and Potential Sources of Error

Several factors can interfere with the accuracy of Qp:Qs calculations based on the Fick method:

• Steady State The method assumes the patient is in a steady state with stable hemodynamics.

• Sample Contamination Blood samples must be representative of the chamber or vessel and not contaminated by air bubbles or blood from a distal chamber (e.g., atrioventricular valve regurgitation).

• Dissolved Oxygen When a patient is breathing enriched oxygen (FiO2 >30% or >21%), the amount of dissolved oxygen becomes significant and must be accounted for in the oxygen content calculation; otherwise, the flow calculation will be in error and could lead to a significant overestimate of pulmonary blood flow.

• Detection Sensitivity Small shunts may be poorly detected, and in high-flow situations, the mixed venous sample's oxygen saturation may be high, reducing detection sensitivity.

• Anatomical vs. Physiological Shunts These calculations provide estimates of physiological shunting, not necessarily the exact anatomical volumes of blood shunted, especially in complex cases with bidirectional shunting at multiple levels.

• Variability of Samples Oxygen saturation can be variable in different parts of a chamber due to inadequate mixing of venous streams (e.g., SVC, IVC, coronary sinus in the right atrium).

• Hemoglobin Levels Oximeters may not be accurate for saturation measurements if hemoglobin is very high (>200 g/L).

• Cardiac Output Assumptions If cardiac output is reduced, venous oxygen saturation is lowered due to increased oxygen extraction.

Vascular Resistances

• Ohm's Law Analogy: Resistance = Pressure Gradient / Flow; (R = ΔP / Q).

• Systemic Vascular Resistance (SVR): (Mean Aortic Pressure - Mean Right Atrial Pressure) / Systemic Flow.

• Pulmonary Vascular Resistance (PVR): (Mean Pulmonary Artery Pressure - Mean Pulmonary Capillary Wedge Pressure or Left Atrial Pressure) / Pulmonary Flow.

• Often we express the PVR/SVR ratio. 

• Units: PVR is expressed in Wood Units (WU) or Dynes·s·cm⁻⁵ (Dynes). 1 Wood Unit = 80 Dynes·s·cm⁻⁵. For calculation in Wood Units, pressures are in mmHg and cardiac output in L/min.

• Clinical Significance: Elevated PVR can contraindicate surgery. Classically, PVR > 3 WU is a contraindication for heart transplant, and PVR > 5 WU is often a contraindication for closing a shunt lesion due to risk of post-operative pulmonary hypertension and mortality.

Angiography: Principles and Parameters

• • Angiography requires defining a clinical question and choosing the correct incidence to visualize structures accurately (e.g., to not miss a coarctation or PDA).

  • The appropriate catheter must be selected, avoiding distal-end hole catheters for high-flow injections to prevent vessel injury for example.

  • Contrast volume: Sufficient but not excessive; too little will not show the structure adequately, too much can obscure it or be harmful.

  • Injection duration: Important to visualize entire circulation (e.g., pulmonary arteries, parenchyma, and venous drainage).

  • Parameters are not standard; they depend on the child's age, weight, and injection site (e.g., manual injection for small vessels/children, pump-injectors for large structures).

  • Angiography involves higher radiation than fluoroscopy due to higher image cadence. Radiation exposure is minimized by performing only necessary angiographies, optimizing incidence, and using biplane imaging (one injection, two views).

    • Fluoroscopy: A real-time X-ray imaging technique that allows continuous visualization of internal structures, often used to guide procedures such as catheter placement. 

    • Angiography: An imaging technique that uses fluoroscopy along with contrast dye injected into blood vessels to visualize arteries, veins, or heart chambers.

  • Low-osmolarity non-ionic contrast media are used; renal toxicity is rare in children if they are well-hydrated.

  • Manual injections are used for selective injections into small arteries/veins or sequestrations, while pump injections are used for large structures like the main pulmonary artery or aorta.

  • Incidences vary based on the structure to be injected.

    • Single ventricle montage: Face and profile views.

    • Pulmonary infundibulum/main pulmonary artery/pulmonary valve: Profile view.

    • Right pulmonary artery: RAO (Right Anterior Oblique) view.

    • Left pulmonary artery: LAO (Left Anterior Oblique) view.

    • Aortic arch: Profile view (good for PDA or aortic arch visualization). RAO for PDA, LAO for aortic arch.

    • More on projections / incidences

Hemodynamic Case Examples (Stenosis, Coarctation, Mitral Stenosis, Pulmonary Venous Stenosis)

• • Aortic Stenosis/Coarctation: There will be a pressure gradient between the left ventricle (high systolic pressures) and the aorta (lower systolic pressure due to obstacle). It is important to evaluate the pressures along the course of the aorta to detect for example a gradient between ascending and descending aorta indicating a coarctation.

  • Wedge pressure (capillary pressure) should be about the same as the diastolic LV pressure, since the LA equalizes pressure with the LV during ventricular diastole when the mitral valve is open, since the LA and LV are in contuinty. If there is a higher wedge than LV diastolic pressures, there is an obstacle along the course of Capillary-Pulmonary veins-LA continuum. A high wedge pressure combined with a normal or low left ventricular end-diastolic pressure indicates an obstruction between the pulmonary capillaries and the left ventricle. As such, it is important to rule out: 

    • Pumonary veins osteal stenosis

      1. High pulmonary capillary pressure (wedge) with a normal left atrial or left ventricular tele-diastolic pressure suggests pulmonary vein stenosis. This can be congenital or post-surgical.

    • Pulmonary venous occlusive disease

    • Mitral stenosis (high left atrial pressure)

    • Severe mitral regurgitation increasing left atrial pressure

    • Cor triatriatum sinister 

    • A supramitral ring is a rare, congenital heart defect where a ridge of tissue, usually fibrous, forms above the mitral valve (the valve between the left atrium and left ventricle). This ring can obstruct the flow of blood from the left atrium into the left ventricle, leading to mitral stenosis. It's distinct from cor triatriatum, another condition causing left-sided heart obstruction. The exact embryologic mechanism underlying supramitral ring (SMR) remains uncertain, though it is thought to arise from an incomplete separation of the endocardial cushion tissue. In contrast, cor triatriatum is believed to develop due to partial failure in the incorporation of the common pulmonary vein into the left atrium during the fifth week of gestation. A key anatomical distinction is that in cor triatriatum, the membrane separating the proximal and distal chambers typically contains a single, restrictive opening located above the mitral valve and anterior to the left atrial appendage. On histologic examination, the SMR consists of a dense, fibrous band of tissue resembling valve-like material but lacking the defined trilaminar architecture of normal valvular tissue. Meanwhile, the membrane seen in cor triatriatum usually displays a bilayered muscular composition. It is important to distinguish SMR from other causes of left ventricular inflow obstruction, such as a dilated coronary sinus or a rare condition called supramitral ridge, which is characterized by an invagination of the left atrial free wall just above the mitral annulus. Reference: https://www.sciencedirect.com/science/article/pii/S1522294204000509 

  • Global Pulmonary Artery Hypoplasia: Very small central and lobar pulmonary arteries, leading to high right ventricular pressure but low distal pulmonary artery pressures; poor surgical/interventional outcomes.

  • Pulmonary Arteriovenous Fistulas: Abnormal connections where arterial blood directly shunts into pulmonary veins, causing desaturation (e.g., in hepatopulmonary syndrome).

  • Blalock-Thomas-Taussig (BTT) Shunt: Angiography can show the surgical shunt (Gore-Tex tube) connecting the aorta to the pulmonary arteries, assessing its patency and any induced stenoses. It also allows pressure measurement distal to the shunt.

  • Fontan Circulation: Catheterization is crucial between palliation stages for single ventricle patients to assess operability, pulmonary pressures, artery size, and rule out collaterals or veno-venous fistulas.

    • Fenestration: A small hole created between the Fontan circuit and the left atrium to reduce Fontan pressure and effusions, leading to some desaturation.

    • Angiography will demonstrate the cavopulmonary connections and the Gore-Tex tube, along with fenestrations.

  • Pulmonary Sequestration: A portion of lung tissue with anomalous arterial supply (usually from abdominal aorta) and no gas exchange function. Can cause hyperperfusion, heart failure, or hemoptysis. Can be diagnosed and treated by endovascular embolization.

New Strategies and Technologies in Catheterization Lab

• • 3D Echocardiography: Provides detailed imaging of cardiac structures like ASDs (atrial septal defects), showing their varied morphology.

  • Fusion Imaging: Superimposes CT or MRI images onto fluoroscopy, aiding in precise catheter positioning within the heart.

  • Rotational Angiography: The C-arm rotates around the patient during contrast injection to acquire a 3D volume, allowing detailed 3D reconstruction of vascular trees (e.g., pulmonary arteries) and visualization of stent positioning.

  • Intra-Operative 3D Imaging: Allows visualization of coronary arteries relative to the pulmonary artery, crucial for procedures like pulmonary artery stenting.

  • MRI-guided Catheterization: Future direction, already in research, to avoid X-ray exposure and provide excellent tissue imaging. Requires non-metallic catheters and guides.

  • Echo-guidance during catheterism

Acute vasoreactivity testing from PHA (Click here)

Acute vasoreactivity testing, typically performed in the cardiac catheterization laboratory, is a crucial diagnostic procedure used to assess the responsiveness of the pulmonary vasculature to vasodilator agents. Its primary purpose is to identify patients who are likely to respond to medical treatment for pulmonary hypertension (PH) and to help determine the operability of patients with congenital heart disease. It may also be used in an evaluation pre-cardiac transplant, especially if heart-lung may need to be considered.

"Interpretation/Positive test: The 2009 ACC/AHA and 2015 ESC/ERS guidelines define a positive study based on a reduction in the mean pulmonary artery pressure of at least 10 mmHg to an absolute mean PA pressure of less than 40 mm Hg with a stable or improved cardiac output. Patients should have normal oxygen saturation prior to starting inhaled nitric oxide so that one can assess the true response on pulmonary vascular tone and not response to improved oxygenation."

"Acute vasoreactivity testing in children is undertaken to assess the response of the pulmonary vascular bed to pulmonary specific vasodilators. Similarly, the current practice in children with IPAH or familial PAH (isolated PVHD) is to use AVT to define the likelihood of response to long-term treatment with CCB therapy and for prognosis. There are 2 definitions of responders to AVT in IPAH or isolated PHVD, including 1) a decrease in mPAP of at least 10 mmHg to below 40 mmHg with a normal or increased increase in cardiac output; and 2) a decrease in mean PAP = 20% and increase or no change in CI and decrease or no change in PVR:SVR. AVT in children with PH associated with congenital heart disease (CHD) is undertaken to assess if the PVR will decrease sufficiently for surgical repair to be undertaken in borderline cases. In general, positive AVT for borderline cases with post tricuspid shunts is defined as decreases in PVRI to < 6-8 WUm2 or PVR:SVR <0.3. However, AVT is only one measure used to define operability and the whole clinical picture, the age of the patient and the type of lesion need to be taken into consideration. AVT may be studied with iNO (20–80 ppm), 100% oxygen, inhaled or intravenous PgI2 analogues, intravenous adenosine or sildenafil."

Apitz C, Hansmann G, Schranz D. Hemodynamic assessment and acute pulmonary vasoreactivity testing in the evaluation of children with pulmonary vascular disease. Expert consensus statement on the diagnosis and treatment of paediatric pulmonary hypertension. The European Paediatric Pulmonary Vascular Disease Network, endorsed by ISHLT and DGPK. Heart. 2016 May;102 Suppl 2:ii23-9. doi: 10.1136/heartjnl-2014-307340. PMID: 27053694. 

From this important resource here: https://heart.bmj.com/content/102/Suppl_2/ii23 :

• "Barst criteria, 1986: decrease in mPAP of ≥20%, unchanged or increased cardiac index, and decreased or unchanged PVR to SVR ratio (PVR/SVR); 

• Rich criteria, 1992: decrease in mPAP and PVR of ≥20%; 

• Sitbon criteria, 2005: decrease in mPAP of ≥10 mm Hg reaching an mPAP value of ≤40 mm Hg, and an increased or unchanged cardiac output."

How Acute Vasoreactivity Testing is Performed

The process involves measuring hemodynamic parameters before and after the administration of specific vasodilator agents (or the wean of them). Typically, pulmonary vasodilators with a short half-life would be used to be able to challenge with a wean (example: iNO, Oxygen, epoprostenol, adenosine). 

The steps generally include:

• Baseline Hemodynamic Assessment: Initial measurements of blood flows (including Qp:Qs, when relevant) and PVR are obtained. This also includes measuring pulmonary artery pressures, capillary pressures, and resistances.

• Administration of Agents (or weaning of the agents): Patients are exposed to (or weaned from) pulmonary vasodilator agents to test their vascular reactivity. Common agents and protocols include:

  • Oxygen: Administering 100% oxygen for a minimum of 10 minutes, followed by repeat measurements of saturations and pressures. The effect of oxygen in reducing PVR is significant, especially when pulmonary venous Po2 is reduced or in cases with mild pulmonary edema and hypoxia.

  • Inhaled Nitric Oxide (NO): This is currently the preferred agent due to its strong pulmonary vasodilator effect and minimal impact on systemic circulation. It is typically administered at concentrations of 20–80 ppm, often starting at 80 ppm.

  • Intravenous Agents: Other vasodilators that have been used include:

    • Prostacyclin (Epoprostenol): Administered intravenously, typically at 5 to 15 ng/kg/min.

    • Adenosine: Can also be used.

    • Tolazoline hydrochloride (Priscoline): One of the first agents used, injected slowly at 1 mg/kg into the main pulmonary artery.

    • Sildenafil: A phosphodiesterase V inhibitor, it is also an effective pulmonary vasodilator.

  • Repeat Measurements: After each agent, all relevant hemodynamic parameters are remeasured, and PVR is recalculated. When using enriched oxygen (FiO2 >30%), the dissolved oxygen becomes significant and must be accounted for in the oxygen content calculation.

• Addressing Acidosis: It is important to correct any respiratory or metabolic acidosis, as its presence can lead to an overestimation of PVR.

Interpretation of Results

The interpretation of acute vasoreactivity testing aims to distinguish between reversible (vasoconstrictive) and irreversible (organic) changes in the pulmonary vascular bed.

• Positive Vasoreactivity Response:

  • A positive test is typically defined by a decrease in mean pulmonary arterial pressure (mPAP) by at least 10 mmHg, leading to a resultant mPAP drop to less than 40 mmHg, without a fall in cardiac output.

  • A clear drop in pulmonary vascular resistances is expected.

  • If pulmonary vascular resistance falls more significantly than systemic vascular resistance, there will be a relative increase in pulmonary blood flow, and consequently, a rise in systemic arterial oxygen saturation. A marked change in oxygen saturation indicates a very responsive pulmonary circulation.

  • A positive response suggests that the elevated PVR is primarily due to vasoconstriction related to medial hypertrophy of smooth muscle, which implies a good prognosis for improvement with medical therapies.

• Negative or Blunted Response:

  • If the decrease in PVR is small or insignificant, or if oxygen saturation does not change or falls slightly, it suggests that the elevated PVR is due to more fixed, organic changes (e.g., hyalinization, fibrosis, intimal proliferation).

  • This indicates a lower likelihood that surgical correction of a congenital heart defect will result in a major fall in vascular resistance.

The assessment of PVR is particularly important for:

• Single-ventricle patients prior to cavopulmonary anastomoses (Glenn/Fontan procedures), as the risk of postoperative complications increases with PVR > 3 Wood Units (WU).

• Risk stratification for patients awaiting heart transplant, where a PVR > 6 WU (even with oxygen or NO) is associated with a higher risk of postoperative right heart failure.

• Predicting the responsiveness to medical therapies for patients with pulmonary hypertension related to increased PVR.

It is important to measure mixed venous oxygen saturation to ensure it does not change significantly after drug administration, as this can affect the reliability of the study.

Cases Examples

Case 1 - Pulmonary Arterial Hypertension with Vasoreactivity

• At baseline, the patient is evaluated in room air with iNO at 10 ppm. 

  • RA pressure is 5 mmHg with a RA saturation of 69% (SVC saturation 72%, IVC satuation 67%). The saturation at the LPA is also 69% outlining there is no left to right shunt in the post-tricuspid area (VSD or PDA that would bring oxygenated blood in the PA). Mixed venous saturation is the same as PA saturation.

  • The RV pressures are 44/4 compared to LV pressures of 82/8. The RV pressure is half systemic. 

  • The MPA pressure is 45/17 (mean of 30). The mean PA ressure corresponds to pulmonary hypertension (≥20 mmHg). The RV systolic pressure (44) and MPA systolic pressure (45) are the same. There is no RVOT obstruction

  • The RPA and LPA pressure are similar (46/19; mean 30 for the RPA; 48/19; mean 30 for LPA). There is no obstruction at the level of the pulmonary arterial branches.

  • The wedge pressure on both side is similar (9 and 10 mmHg). This indicates that there is acceptable drainage pressure - no sign of post-capillary restriction. The LV end-diastolic pressure is similar at 8 mmHg. As such, no signs of PV stenosis, pulmonary venous occlusive disease (PVOD), mitral valvular disease or LV diastolic impairment (HFpEF). 

  • The Aortic pressures are 82/52 and the LV pressures are 82/8. There is no LVOT obstruction. The aortic saturation is 95%, assumed to be the same as the LV saturation, LA saturations. There is a small right to left inter-atrial shunt, decreasing slightly the LA saturation. The pulmonary saturation can be assumed to be higher than 95%, unless there is some lung disease.

• With iNO 20 ppm and 100% oxygen there is a acute vasoreactivity testing. In this context, the PA pressure is 46/22 (mean 33). There is no marked response since these pressures are similar to baseline. However, when the patient is placed off iNO and in room air, removing all potential pulmonary vasodilators, there is suddenly a sharp increase in the PA pressures at 84/47 (mean 62). As this point, the systolic pulmonary arterial pressure and diastolic pulmonary arterial pressure doubles. In this context, the patient has supra-systemic PA pressure since the Aortic pressure is then 53/38. The drop in aortic pressure is explained by a drop in left atrial and left ventricular preload due to diminished pulmonary blood flow, as well as a compressive effect of the RV into the left ventricle (pancaking of the LV due to the acute dilation of the RV). 

  • mPAP and mean Wedge Pressure are in mmHg; 

  • Cardiac Index is in L/min/m². 

  • The factor 80 converts mmHg·min/L to dyn·s·cm⁻⁵·m², which is a legacy unit (you can also express PVRI in Wood units·m² without multiplying by 80). 

  • The transpulmonary gradient reflects the pressure difference between the pulmonary artery and the left atrium (or pulmonary capillary wedge pressure) and is used to assess pulmonary vascular disease. TPG in our case = 33 mmHg − 9 mmHg = 24mmHg. CI=3.8L/min/m². PVRI = 24/3.8 ≈ 6.3 Wood units·m² = 504 dyn·s/cm⁵·m² .

• A high PVRI (e.g., >3–6 WU·m² in children) suggests elevated pulmonary vascular resistance, concerning for pulmonary vascular disease. Responsiveness to iNO and/or 100% O₂ indicates reactive pulmonary vasculature, potentially amenable to vasodilator therapy.

• Units of PVRI 

  • Standard: Wood units·m² (WU·m²) 

  • SI equivalent: dyn·s·cm⁻⁵·m² (multiply WU·m² by 80).

Conclusion: Severe pulmonary arterial hypertension with vasoreactivity. The LVEDP was normal and there was no evidence of pulmonary veins or mitral valve stenosis, indicating pre-capillary pulmonary hypertension. The mean pulmonary artery pressure increased to 62 mmHg when weaned to room air with no iNO and the systemic blood pressure dropped to 53/38. The mean pulmonary artery pressure returned to 33 mmHg with iNO and the systemic blood pressure normalized. These findings indicate severe, pre-capillary pulmonary hypertension that is responsive to and dependent on iNO therapy, with no evidence of post-capillary contribution to this diagnosis. Oximetry: Ratio Qp:Qs: 1.00. 

The patient meets the criteria for PAH: 

• Elevated pulmonary pressures (mPAP > 20 mmHg) 

• No post-capillary pulmonary hypertension / Normal left heart filling pressure (PAWP ≤ 15 mmHg)

• Increased pulmonary vascular resistance (PVR ≥ 3 WU)

Case 2 - Pre-capillary pulmonary hypertension with a bidirectional PDA

4-month-old ex-preterm infant with chronic lung disease, an atrial septal defect (ASD) and patent ductus arteriosus (PDA), referred for diagnostic cardiac catheterization to evaluate severe pulmonary hypertension (PH). The patient is on multiple therapies: iNO, Sildenafil, Bosentan, and Treprostinil.

At baseline (on 60% oxygen and 20 ppm of inhaled nitric oxide), the mean right atrial pressure is 9 mmHg and the mean left atrial pressure is 10 mmHg, indicating nearly equal atrial pressures. The SVC saturation is low at 47%, and there is evidence of a right-to-left interatrial shunt, resulting in desaturated left atrial blood (86%). The right ventricular pressure is markedly elevated at 95/10 mmHg, and the pulmonary artery pressure is 86/51 mmHg (mean 66 mmHg), which fulfills the criteria for pulmonary hypertension (mean PAP ≥ 20 mmHg). The systolic pulmonary artery pressure (sPAP) of 86 mmHg is nearly systemic compared to the systolic aortic pressure of 95 mmHg, indicating a near-systemic pulmonary circulation. The diastolic PA pressure is iso-systemic. A patent ductus arteriosus (PDA) is present, which likely allows bidirectional pressure transmission, contributing to the equalization of pressures between the pulmonary and systemic circuits. When the dose of iNO is reduced to 10 ppm, the systolic PA pressure increases further to 90 mmHg, becoming fully systemic.

With inhaled nitric oxide (iNO) at 40 ppm, the systolic pulmonary artery pressure (sPAP) is 83 mmHg, nearly equal to the systolic systemic arterial pressure of 86 mmHg, confirming systemic-level pulmonary hypertension. The pulmonary capillary wedge pressure (PCWP) is measured at 11 mmHg, which is within the normal range and excludes significant post-capillary (left-sided) contribution to pulmonary hypertension (i.e., no evidence of pulmonary venous hypertension or left heart disease, as PCWP < 15 mmHg). Oximetry reveals important regional differences in pulmonary venous return: 

• The left pulmonary veins show saturations of 97–99%, indicating that the left lung is well ventilated and oxygenated. 

• In contrast, the right pulmonary vein saturation is markedly reduced at 71%, suggesting significant ventilation-perfusion (V/Q) mismatch in the right lung—likely due to advanced pulmonary vascular disease, parenchymal abnormalities, or abnormal perfusion. This regional hypoxemia in the right pulmonary veins may contribute to the low right atrial saturation, as desaturated blood returning from the right lung enters the systemic venous pool. Additionally, the presence of an occasional right-to-left interatrial shunt may allow this hypoxemic blood to bypass the lungs entirely and enter the left atrium, contributing to systemic desaturation. The inter-atrial shunt becomes bidirectional at times considering the near-equal LA and RA pre

The mixed venous saturation in the main pulmonary artery (MPA) is 64%, and the lower body (post-ductal) saturation is 89%, suggesting limited ductal shunting but persistent systemic desaturation. The pulmonary vascular resistance index (PVRI) is elevated at 13.7 Wood units·m², indicating severe pulmonary vascular disease. The Qp:Qs ratio is calculated at 1.2, indicating mild net left-to-right shunting, likely through the PDA and ASD, but not enough to cause volume overload.

With inhaled nitric oxide (iNO) at 40 ppm and 95% oxygen, the systolic pulmonary artery pressure (sPAP) is 83 mmHg, nearly equal to the systolic systemic arterial pressure of 86 mmHg, confirming systemic-level pulmonary hypertension. The pulmonary capillary wedge pressure (PCWP) is measured at 11 mmHg, which is within the normal range and excludes significant post-capillary (left-sided) contribution to pulmonary hypertension (i.e., no evidence of pulmonary venous hypertension or left heart disease, as PCWP < 15 mmHg). Oximetry reveals important regional differences in pulmonary venous return: 

• The left pulmonary veins show saturations of 97–99%, indicating that the left lung is well ventilated and oxygenated. 

• In contrast, the right pulmonary vein saturation is markedly reduced at 71%, suggesting significant ventilation-perfusion (V/Q) mismatch in the right lung—likely due to advanced pulmonary vascular disease, parenchymal abnormalities, or abnormal perfusion. This regional hypoxemia in the right pulmonary veins may contribute to the low right atrial saturation, as desaturated blood returning from the right lung enters the systemic venous pool. Additionally, the presence of an occasional right-to-left interatrial shunt may allow this hypoxemic blood to bypass the lungs entirely and enter the left atrium, contributing to systemic desaturation. The inter-atrial shunt becomes bidirectional at times considering the near-equal LA and RA pressures. 

The mixed venous saturation in the main pulmonary artery (MPA) is 64%, and the lower body (post-ductal) saturation is 89%, suggesting limited ductal shunting but persistent systemic desaturation. The pulmonary vascular resistance index (PVRI) is elevated at 13.7 Wood units·m², indicating severe pulmonary vascular disease. The Qp:Qs ratio is calculated at 1.2, indicating mild net left-to-right shunting, likely through the PDA and ASD, but not enough to cause volume overload.

With a PDA occlusion test performed under the same conditions (95% oxygen and 40 ppm of iNO), the aortic pressure is measured at 80/46 mmHg (mean 61 mmHg) and the main pulmonary artery (MPA) pressure is 77/40 mmHg (mean 58 mmHg). This indicates that the pulmonary artery pressure remains near-systemic, even in the absence of ductal flow. The minimal change in pressures with PDA occlusion suggests that the ductus is not a major contributor to the elevated pulmonary pressures, and that the pulmonary hypertension is intrinsic and pre-capillary in nature. The persistent elevation in MPA pressure despite test occlusion supports the presence of fixed pulmonary vascular disease, and confirms that the PDA is not the driving mechanism of the pulmonary hypertension. One may chose to keep the PDA open in this context, acting as a natural Pott shunt (i.e.: pop-off of the right ventricle), until the pulmonary vasculature is treated and remodeled. 

Finally, when inhaled nitric oxide (iNO) was adjusted to 20 ppm with 95% oxygen, the pulmonary artery pressure measured 88/47 mmHg (mean 67). Under a different condition—35 ppm iNO with 60% oxygen—the pulmonary artery pressure was 85/47 mmHg (mean 62). For comparison, under the prior setting of 40 ppm iNO with 95% oxygen, the pressure was 88/51 mmHg (mean 65). These findings indicate that increasing the concentration of iNO alone (from 20 ppm to 35 ppm) without increasing inspired oxygen does not significantly reduce pulmonary pressures. Similarly, maintaining a high FiO₂ (95%) while decreasing iNO from 40 to 20 ppm does not improve hemodynamics, as pressures remain systemic. The modest variation in mean PA pressures across all three conditions (67, 65, and 62 mmHg) demonstrates that the pulmonary vasculature in this patient is relatively unresponsive to incremental changes in iNO dose or FiO₂—a hallmark of advanced pulmonary vascular disease. This further supports the interpretation of fixed pulmonary vascular resistance, with limited potential for acute vasodilator-mediated reversal. Of note, these are done under treprostinil / sildenafil / bosentan, which may have saturated the mechanisms of pulmonary vasodilation. However, a trial of weaning the iNO to 10 ppm resulted in rapid decrease in the oxygen saturation and more right to left shunt across the PDA, indicating that between 10 and 20 ppm, there was vasoreactivity.

Conclusion: The hemodynamics showed severe pre-capillary pulmonary hypertension at different conditions. The mean pulmonary artery pressure is iso-systemic with mean pulmonary capillary wedge pressure of 11 mmHg and transpulmonary gradient of 54 mmHg. The oxygen saturation discrepancy between the right and the left pulmonary veins is suggestive for significant right lung disease. The ASD and the PDA are shunting bidirectionally. There is no evidence of obstructive left heart disease. There is no evidence that shows contribution of the ductus arteriosus to the pulmonary hypertension and its test occlusion doesn’t change the hemodynamics.

1. Severe pre-capillary pulmonary hypertension with advanced pulmonary vascular disease. 

2. Despite high ventilatory support, the oxygen tension remained low in all blood gas samples from different sites except from the left lower pulmonary vein sample. Indicating significant V/Q mismatch. 

3. There is no obstructive left heart disease. 

4. The PDA is large shunting right to left during systole and left to right during diastole. Under the current conditions, it does not contribute significantly to the degree of pulmonary hypertension as the test occlusion of the PDA did not change the hemodynamics. 

5. A trial of weaning the iNO to 10 ppm resulted in rapid decrease in the oxygen saturation and more right to left shunt across the PDA.

Case 3 - Pulmonary Vein Stenosis with a component of PVR reactivity 

Angiogram in the Left Pulmonary Artery

Angiogram in the Main Pulmonary Artery

Angiogram in a lower branch of the Left Pulmonary Artery

Angiogram in a lower right pulmonary vein

Conclusions: Moderate pulmonary hypertension reactive to pulmonary vasodilation with oxygen and nitric oxide. Severe obstruction to drainage through the right upper and left upper pulmonary veins with redistribution of flow to the lower veins in the respective lungs. The left upper and right upper pulmonary veins could not be accessed from the left atrium despite multiple attempts, suggesting severe obstruction. Tiny patent ductus arteriosus shunting left to right. Mild desaturation in room air suggesting presence of V/Q mismatch and intrapulmonary right-to-left shunting.

Case 4 - "PH" with a left to right PDA

Case 5 - Pulmonary Veins Stenosis with High Wedge Pressure

Case 6 - Left to Right VSD with high PVR

• Ventricular Septal Defect (VSD) with Pulmonary Hypertension:

  • A patient with a VSD, demonstrating oxygen saturation step-up (SVC 70%, PA 85%) and elevated mean PA pressure (55 mmHg). Hemoglobin is 14 g/dL, VO2 is measured at 150 mL/min by mask-test.

SVC saturation = 70%; MPA saturation: 85%

MPA pressure: 85/40 (mean 55)

RV pressure: 85/0

RA pressure: 6

Aortic pressure: 85/50 (mean 60); Aortic saturation of 95%

LV pressure: 85/0

LA mean pressure: 8

VO2 = 150 mL/min; Hb = 14 g/dL

Oxygen Solubility and Content Calculations

• O₂ Solubility Coefficient (Hüfner constant) = 1.36 mL O₂/g Hb
  
  

O₂ Content Calculations (C = 1.36 × Hb × SatO₂)

• Cₐₒ O₂ (Aortic) = 1.36 × 14 × 0.95 = 18.0 mL/dL

• Cₛᵥₘ O₂ (Mixed Venous, i.e., SVC) = 1.36 × 14 × 0.70 = 13.3 mL/dL

• Cₐₚ O₂ (Pulmonary Artery) = 1.36 × 14 × 0.85 = 16.1 mL/dL

• Cᵥₚ O₂ (Pulmonary Venous) = 1.36 × 14 × 1.00 = 19.0 mL/dL
  
  

Arterial-Venous Differences

• Systemic Arterial-Venous Difference (DAVₛ)
  DAVₛ = Cₐₒ O₂ − Cₛᵥₘ O₂ = 18.0 − 13.3 = 4.7 mL/dL

• Pulmonary Arterial-Venous Difference (DAVₚ)
  DAVₚ = Cᵥₚ O₂ − Cₐₚ O₂ = 19.0 − 16.1 = 2.9 mL/dL

Qp/Qs calculation

• Pulmonary Flow (Qp): VO2 / DAVₚ = 150 (mL/min) / 2.9 (mL/dL) = 51.7 dL/min = 5.17 L/min (after unit conversion).

• Systemic Flow (Qs): VO2 / DAVₛ = 150 (mL/min) / 4.7 (mL/dL) = 31.9 dL/min = 3.19 L/min (after unit conversion).

• Qp/Qs Ratio: 5.17 / 3.19 = 1.62. This is a significant left-to-right shunt. 

• The simplified Fick formula gives a similar Qp/Qs of 1.67: Fick calculation: Qp:Qs = (SaO2 - SmvO2) / (SpvO2 - SpaO2) = (95 - 70) / (100 - 85) = 20/15 = 1.67. Here the pulmonary venous saturation is assumed 100%.  

• PVR Calculation: (PA mean - Left Atrial Pressure/PCWP) / Qp = (55 - 8) / 5.17 = 9.0 Wood Units.

• SVR Calculation: (mean Aortic pressure - mean RA pressure)/Qs = (60 - 6) / 3.19 = 16.93 Wood Units

• Clinical Significance: A PVR of 9.0 WU is extremely high, making the patient likely inoperable. A dobutamine challenge could be performed to assess if drop of resistance with increased output, if resistances remain high, heart-lung transplantation might be considered in the future. Alternative solutions might include pulmonary artery banding in children to reduce pulmonary flow, or partial VSD closure with a restrictive patch to allow some off-loading.