TnECHO Echocardiography Protocol and Approach to Evaluation

Targeted Neonatal Echocardiography protocol

1) Parasternal Long Axis View – Full sweep Anterior-Posterior (2D and then Colour)

a. 2D-grayscale and 2D-color at Aorta-Mitral valve level

b. 2D-grayscale and 2D-colour of zoom of Aortic Valve (to measure LVOT)

c. M-Mode at Left Atrium / Aorta junction for: LA/Ao ratio

d. M-Mode at tip of mitral valve for Shortening fraction, LV measurements, and LV-Mass

e. 2D-grayscale of tricuspid valve (scan posteriorly) +  2D-color of tricuspid valve

                                               i. CW Doppler of tricuspid valve to obtain Tricuspid regurgitant jet if present (and Systolic-Diastolic time ratio)

                                              ii. PW Doppler of RV inflow

f.  2D--grayscale and 2D-Color of Pulmonary valve (scan anteriorly). 2D will be used for measurement of RVOT and 2D-Color to evaluate flow and presence of pulmonary insufficiency.

                                               i. PW-Doppler at level of RVOT

                                              ii. PW-Doppler at tip of Pulmonary Valve (will be used for PAAT/RVET and for velocity time integral [VTI])

                                             iii. CW-Doppler for pulmonary insufficiency.

g. If VSD detected (to be done in every view): 2D and Colour zoom

                                               i. Obtain PW if low velocity

                                              ii. Obtain CW-Doppler

2) Parasternal short axis (PSAX) view: Full sweep from Aortic Valve to LV Apex (2D and then Colour)

a. 2D-grayscale and 2D-Colour at Pulmonary valve and Aortic valve level

                                               i. PW-Doppler at Tip of Pulmonary Valve

                                              ii. CW-Doppler of pulmonary valve if pulmonary insufficiency

b. M-Mode at LA-Ao junction and M-Mode at Tip of mitral valve in PSAX

c. 2D-grayscale view (3 beats) at mitral valve level

d. 2D-grayscale view (3 beats) at mid-papillary muscle level

e. 2D-grayscale view (3 beats) at LV apex level

f.  Scan with 2D-Color septum from Base to Apex to rule out septal defect – if septal defect detected, CW-Doppler of the flow.

g. If tricuspid regurgitant jet present in PSAX: CW-Doppler

3) Apical View – Full sweep from Anterior to Posterior (2D and then Colour)

a. 2D-grayscale Apical 4 chamber view in 2D – LV focused

                                               i. 2D-color box (low velocity) over the pulmonary veins in the left atrium

                                              ii. PW of the pulmonary veins in A4C from the left atrium

b. 2D-grayscale Apical 4 chamber view in 2D – RV focused

c. 2D-color for Tricuspid and Mitral valve.

                                               i. PW below the tricuspid valve for E/A velocities

                                              ii. PW below the mitral valve for E/A velocities

                                             iii. CW of Mitral valve for dp-dt if present.

                                             iv. CW-Doppler of tricuspid valve to obtain Tricuspid regurgitant jet – even if unavailable, please record so that we can do a systolic-diastolic time ratio. Dp-Dt of RV to be done if 2 m/s reached.

d. PW of each pulmonary veins

e. A4C: Zoom on LA for dimensions

f.  A4C: Zoom on RA for dimensions

g. M-Mode in A4C for the Lateral wall of the RV to get TAPSE (line of interrogation should cross the Apex).

h. Tissue Doppler Imaging (TDI)

                                               i. TDI on RV free wall below the tricuspid valve

                                              ii. TDI on LV free wall below the mitral valve

                                             iii. TDI of septum below the attachment of mitral valve

i.   Apical 3 Chamber view of LV in 2D-grayscale

                                               i. Apical 3 chamber view in 2D-Color to see flow through Aortic Valve

1. PW just above the tip of the aortic valve for the LV-VTI

2. PW inflow-outflow

j.   Apical 2 Chamber view of the LV in 2D: Colour and 2D grayscale

                                               i. PW at inflow of mitral valve

                                              ii. CW of Mitral valve for dp-dt if present.

                                             iii. Zoom on LA for dimensions (Biplane)

k. Slide from the Apical 2 Chamber view of the LV towards the sternum to obtain a RV Inflow to Outflow tract (RV “3 chamber view”).

                                               i. PW of RVOT

                                              ii. PW of inflow of RV

                                             iii. CW of tricuspid valve

                                             iv. Colour view recorded

                                              v. 2D gray scale recorded

l.   3D LV, 3D RV (Probe X7; use the High Volume Capture for each and at least 4Q capture for each).

                                               i. Only if 3D volumes available

4) Subcostal:

a. Subcostal long axis: (Full Sweep from IVC to RVOT: 2D and Colour)

                                               i. 2D-grayscale and 2D color over the inter-atrial septum (for inter-atrial shunt)

                                              ii. Doppler of subhepatic veins and IVC + Colour flow

                                             iii. PW and/or CW through the inter-atrial shunt (especially if concern of RV and/or LV diastolic dysfunction)

b. Subcostal short axis: (Full Sweep Anterior to Posterior).

                                               i. 2D-grayscale and 2D color over the inter-atrial septum (for inter-atrial shunt)

                                              ii. 2D-colour over the descending aorta

                                             iii. PW of the descending aorta.

                                             iv. Doppler of subhepatic veins and IVC + Colour flow

                                              v. RVOT PW-Doppler

                                             vi. PW and/or CW through the inter-atrial shunt (especially if concern of RV and/or LV diastolic dysfunction)

c. Sweep in 2D-grayscale to get anatomy in short and long-axis

5) Suprasternal view:

a. Long axis - Aortic Arch in 2D-grayscale and 2D-color

                                               i. PW in Ascending Aorta

                                              ii. PW in Descending Aorta pre ductal

                                             iii. PW in Descending Aorta post-ductal

                                             iv. Sweep to confirm bifurcation of brachiocephalic artery towards the right

b. Short axis

                                               i. Sweep to confirm bifurcation and arch sidedness (color and 2D)

                                              ii. SVC in 2D and Colour

1. PW of SVC (retrograde flow presence? Torrential flow presence?)

6) Patent Ductus Arteriosus View

a. 2D grayscale for measurement and 2D color for flow. Please record to confirm closure if no flow.

b. CW through the ductus arteriosus if present.

c. PW through the ductus arteriosus if unrestrictive and large.

d. 2D and Colour (simultaneous views).

7) Branch Pulmonary artery (Moustache view)

a. 2D-grayscale and 2D-Color

                                               i. PW in MPA, LPA and in RPA

b. Crab view for pulmonary veins – 2D-color with low velocity (Nyquist). Obtain PW in each pulmonary vein (if possible) at osteum.

8) Head ultrasound (Cebrovasculature)

a. Transcranial view (temporal bone) for MCA Doppler

b. Sagittal view with 2D-color over the anterior cerebral artery (ACA)

                                               i. PW- Doppler of ACA

c. Coronal view with 2D-Color over the circle of Willis

                                               i. PW-Doppler of ACA and MCA

Example of playlists we used during the TNE as a strategy to reduce stress

TnECHO Report at the Montreal Children's Hospital developed by Dr. G. Altit

Approach to the neonatal hemodynamics evaluation and diagrams

Below are some schematics that I find particularly useful (inspired from Dr Rudolph) when discussing a patient’s hemodynamic condition. I encourage trainees/fellows to include detailed information in their assessments, such as: Pressures (systolic/diastolic/mean) and oxygen saturations in all vessels and cardiac chambers (measured, estimated, or inferred). Presence of shunts, their directionality, and volume of shunting, which are critical for understanding the trajectory of blood flow. I also recommend incorporating additional elements into these schematics: 

• Cardiac systolic function and outputs: Specify the impact on right and left ventricular function. 

• Pulmonary and systemic blood flow: Highlight any imbalances or alterations. 

• Pulmonary and systemic venous return, filling.

This approach provides a comprehensive visual representation of the patient’s hemodynamics, which can significantly aid in tailoring management strategies. By mapping out these details, it becomes easier to identify the optimal course of action for the patient. Additionally, I have provided guidelines for performing Neonatal Hemodynamics evaluations as part of a comprehensive assessment.

Views and Measurements in Targeted Neonatal Echocardiography

This review outlines standardized views and measurements recommended for targeted neonatal echocardiography (TNE). These recommendations align with updated guidelines from 2024, including those for TNE in the NICU and pediatric transthoracic echocardiography, aiming to standardize practice, facilitate communication, and support research efforts. Standardized measurements often reflect established practices based on existing literature and normative data. Echocardiography provides 2D images of the complex 3D heart, making consistent viewing angles crucial for accurate assessment.

General principles involve adapting probe positioning based on the patient's cardiac axis and any chest abnormalities like dextrocardia or congenital diaphragmatic hernia (CDH). Echocardiographic images provide important information such as scale (indicating size), frame rate, probe frequency (higher frequency for better resolution at shallower depths in neonates), ECG tracing (for timing cardiac cycle events like QRS marking end-diastole), depth, gain, and compression.

1. Parasternal Long Axis (PSLA) View

The PSLA view is a foundational view obtained by positioning the probe typically on the left chest, adapting for individual variations in heart position.

• Central Cut: Shows the Right Ventricular Outflow Tract (RVOT) anteriorly, the Left Ventricle (LV), Left Ventricular Outflow Tract (LVOT), Aortic Valve (AoV), ascending Aorta (Asc Ao), Mitral Valve (MV) (anterior and posterior leaflets with papillary muscles), and Left Atrium (LA) (posterior to the aorta). The Aortic valve is a tri-leaflet valve with right coronary, left coronary, and non-coronary cusps. The Aortic valve and Pulmonary valve are open during ventricular systole (ejection).

• Sweep Posteriorly: Reveals more of the Right Ventricle (RV), the Tricuspid Valve (TV) (anterior and posterior leaflets), Right Atrium (RA), Inferior Vena Cava (IVC), and sometimes the Eustachian valve. The Tricuspid valve has three leaflets.

• Sweep Anteriorly: Visualizes the RVOT, Pulmonary Valve (PV), and Pulmonary Artery (PA).

Key Measurements & Assessments in PSLA:

• M-Mode: A single line of interrogation showing tissue motion over time. Can be placed through the LV at the tip of the mitral valve leaflets. Displays RV wall, RV diameter, septum, LV diameter, and posterior wall motion. Used for assessing ventricular mass/hypertrophy (e.g., posterior wall thickness). It is angle-dependent and assesses only a narrow segment, making it discouraged by major guidelines for some measurements in favor of B-mode. Its advantage is very high temporal resolution.

  • Left Ventricular Fractional Shortening (LVFS): Calculated from M-Mode LV diameters at end-diastole (LVEDD) and end-systole (LVESD): (LVEDD - LVESD) / LVEDD * 100. Marker of LV systolic function.

• LVOT Diameter: Measured in 2D at the hinge points of the aortic valve leaflets during peak systole (when the valve is open). Crucial for estimating cardiac output.

• Ascending Aorta Diameter: Measured at the aortic root, sinotubular junction, and ascending aorta during systole.

• LA Diameter / LA:Ao Ratio: Measured in M-Mode or 2D. The LA diameter is typically measured posterior to the aorta. The ratio is LA diameter divided by Aortic diameter. It is a marker of LA dilation, but can be high due to a large LA or a small aorta (e.g., in coarctation or hypoplastic arch). Historically measured in M-Mode at the closure of the aortic valve (end-ventricular systole), when the LA is maximally filled.

• RVOT Diameter: Measured at the hinge points of the pulmonary valve. Typically larger than the LVOT diameter in neonates.

• RVOT/Pulmonary Valve Doppler: Color Doppler assesses flow direction and turbulence. Pulse Wave (PW) Doppler is obtained at the pulmonary valve.

  • Velocity Time Integral (VTI): The area under the PW Doppler curve, representing the distance blood travels with each beat (stroke distance). VTI multiplied by heart rate and the RVOT cross-sectional area estimates Right Ventricular Output.

  • Acceleration Time (AT) / Right Ventricular Ejection Time (RVET) Ratio: AT is time from flow onset to peak velocity, RVET is total ejection time. The ratio (AT/RVET) is a marker of RV afterload. A ratio < 0.25 (or 0.3 in some articles) is suggestive of pulmonary vascular disease (PHN).

  • Continuous Wave (CW) Doppler: Used for high velocity flows like pulmonary stenosis or insufficiency. Provides pressure gradients (4V²) across the valve. The Pulmonary Insufficiency (PI) jet can estimate pulmonary arterial pressures in diastole.

2. Parasternal Short Axis (PSSA) View

Obtained by rotating the probe approximately 90 degrees from the PSLA view. A sweep from the aortic valve level superiorly down to the LV apex inferiorly allows assessment of various structures.

• Aortic Valve Level: Shows the tri-leaflet AoV (visualized as a circular structure with three cusps), PV, LA, RA, RVOT, and part of the RV. Can see septal and anterior leaflets of the TV. Can also see the bifurcation of the main PA into the right and left pulmonary arteries.

• Mitral Valve Level: Visualizes the anterior and posterior MV leaflets as a "fish mouth", the two papillary muscles (posterior medial and anterior lateral), the LV, RV, interventricular septum, and LV posterior wall.

• Mid-Papillary Muscle Level: Key level for assessing LV wall motion and septal curvature. Ideally, only the RV and LV should be visible (no atria) in this view in neonates.

• Apex Level: Reaching the tip of the LV to assess apical wall motion and look for apical VSDs.

Key Measurements & Assessments in PSSA:

• Aortic Valve: Assess in motion to confirm three leaflets and rule out fusion, important for identifying bicuspid valves prone to stenosis.

• Pulmonary Artery Branching: Assess Main PA, RPA, and LPA morphology and measure diameters at branching. Check for flow acceleration (e.g., peripheral pulmonary stenosis).

• Coronary Arteries: Can often visualize the right and left coronary arteries branching from the aorta. Use low Nyquist color Doppler to see flow, typically during diastole.

• Interventricular Septal Curvature / Eccentricity Index: Assessed at the mid-papillary level. Eccentricity Index > 1.3 in systole suggests flattening or bowing of the septum towards the LV, indicating high RV pressure relative to LV pressure (e.g., PHN, RV pressure overload). Septal flattening in diastole can indicate RV volume overload (e.g., ASD, AV malformation). Assessment of septal motion should consider the relative pressures and volumes in both ventricles.

• Left Ventricular Fractional Area Change (LVFAC): Can be measured at the mid-papillary level in PSSA by tracing the endocardial border at end-diastole and end-systole. (Diastolic Area - Systolic Area) / Diastolic Area * 100. Provides a quick estimate of LV circumferential function. Angle dependent.

3. Apical Views

Obtained by placing the probe at the cardiac apex, typically angled upwards and towards the head.

• Apical 4-Chamber View: Standard view showing the four chambers: RA, RV, LA, LV. Visualizes the MV and TV (note the TV's slightly more caudal insertion). Assess chamber size, wall thickness, and valve morphology/motion. Can see pulmonary veins entering the LA. Can see the coronary sinus entering the RA, which may be dilated in high RA pressure or abnormal venous drainage (LSVC, TAPVR). Important for assessing the interatrial and interventricular septa for shunts. Sweep from posterior to anterior and check the apical septum for VSDs.

• Apical 2-Chamber View: Rotated 90 degrees from the 4-chamber view. Shows the LV in cross-section with the anterior and posterior walls. Can see the left atrial appendage. Used in conjunction with the 4-chamber view for calculating LV volume and ejection fraction.

• Apical 5-Chamber View: Adds the LVOT and Aortic Valve to the 4-chamber view. Good for aligning for LVOT Doppler.

Key Measurements & Assessments in Apical Views:

• Left Ventricular Volume and Ejection Fraction (EF): Primarily calculated using the Simpson's biplane method. Tracing the LV endocardial border in both the 4-chamber and 2-chamber views at end-diastole (MV closed, QRS) and end-systole (AoV closed). This method sums estimated volumes of multiple discs along the LV length, assuming a bullet shape. Do not include papillary muscles in the tracing. EF = (LVEDV - LVESV) / LVEDV. Normal values vary (e.g., >55% in pediatrics). EF can be preserved despite regional wall motion abnormalities.

• Bullet 5/6 Method: An alternative method for LV volume estimation. Uses LV area from PSSA (mid-papillary) and LV length from Apical 4C: Area * Length * 5/6. May be more sensitive to septal distortion.

• Left Atrial Volume/Area (Planimetry): Calculated using Simpson's biplane method in 4C and 2C views. Measured at the peak of ventricular systole (MV closed) when the LA is largest. LA Area can be measured by tracing the LA border in the 4C view. Increased LA volume/area indicates LA dilation due to increased inflow (PDA, ASD) or obstructed outflow (MV issues, LV diastolic dysfunction).

• Atrioventricular Valve (MV/TV) Diameter: Measured at the hinge point when the valve is open during diastole (for inflow). Z-scores are based on open valve measurements.

• Atrioventricular Valve Inflow Doppler (MV/TV): PW Doppler placed at the valve tips. Records flow velocities during ventricular diastole. E-wave represents early passive ventricular filling, A-wave represents filling during atrial contraction.

  • E/A Ratio: Reflects ventricular filling patterns and compliance. In normal, compliant ventricles, E/A > 1. Premature and young term babies may have E/A < 1 due to ventricular stiffness, which normalizes later. A high E/A ratio can indicate increased left atrial pressure/volume (e.g., significant PDA shunt).

  • Variability with Breathing: Significant beat-to-beat variation in E/A velocities with spontaneous breathing (TV E/A variation >40%, MV E/A variation >25%) can indicate diastolic restriction, as seen in cardiac tamponade.

• Tricuspid Annular Plane Systolic Excursion (TAPSE): M-Mode along the lateral TV annulus towards the RV apex. Measures the distance the TV annulus moves towards the apex during systole. A distance measurement (mm) reflecting RV longitudinal systolic function. It is an easy, quantifiable metric, often used in POCUS. Normative Z-scores are available.

• Mitral Annular Plane Systolic Excursion (MAPSE): Same concept as TAPSE but for the MV annulus towards the LV apex. Measures LV longitudinal function. Less commonly used as LV function is primarily circumferential.

• Right Ventricular Fractional Area Change (RVFAC): Measured in the Apical 4-Chamber view by tracing the RV endocardial border at end-diastole and end-systole, typically using a straight line between the tricuspid annulus points. RVFAC = (Diastolic Area - Systolic Area) / Diastolic Area * 100. A value below 30% is concerning for RV systolic dysfunction. Correlates well with RV ejection fraction by MRI. Can also be measured in the RV 3-chamber view (RV inflow/outflow).

• Tricuspid (TR) and Mitral (MR) Regurgitation Doppler: CW Doppler is used to capture high-velocity regurgitant jets. The peak velocity of the jet can be used with the Bernoulli equation (4V²) to estimate the pressure gradient across the valve during systole.

  • RV Systolic Pressure Estimation: TR jet gradient (4V²) + estimated RA pressure (commonly 5mmHg) = estimated RV systolic pressure. This estimates systolic pulmonary arterial pressure in the absence of RVOT obstruction.

  • LV/RV dP/dt: A measure of the rate of pressure generation during systole. Calculated from the slope of the acceleration phase of the MR (for LV) or TR (for RV) CW jet. Requires measuring the time taken to go from 1 m/s to 3 m/s (for LV) or 1 m/s to 2 m/s (for RV). Normal LV dP/dt > 1200 mmHg/s, normal RV dP/dt > 400 mmHg/s. Reflects ventricular contractility.

  • Systolic-to-Diastolic Time Ratio (S/D Ratio): Can be measured from the duration of systole and diastole on the TR or MR CW Doppler envelope. An increased ratio can indicate ventricular dysfunction. Used in monitoring patients with BPD/PHN and HLHS.

• Pulmonary Vein Doppler: PW Doppler obtained at the pulmonary vein ostia entering the LA. Assess flow pattern (S, D, Ar waves) and velocities. Loss of phasicity or increased velocity can indicate pulmonary vein stenosis (mean gradient >4 mmHg concerning) or increased flow (e.g., PDA over-circulation). Rule out TAPVR if pulmonary veins are not seen draining normally into the LA.

• Tissue Doppler Imaging (TDI): PW Doppler applied to myocardial tissue motion, typically at the valve annulus. Provides myocardial velocities (S' systolic, E' early diastolic, A' late diastolic) and time intervals (IVCT, IVRT, ET).

  • E/E' Ratio: Ratio of the MV inflow E-wave velocity to the myocardial E'-wave velocity. Relates passive filling speed to myocardial relaxation speed, a marker of ventricular stiffness/diastolic dysfunction. A higher ratio suggests a stiffer ventricle.

  • Myocardial Performance Index (MPI) or Tei Index: Calculated from TDI time intervals: (IVCT + IVRT) / ET. A global marker combining systolic and diastolic function. Normative values are available for neonates. Extremes in values may indicate dysfunction. TDI is preferred over blood flow Doppler for MPI due to better temporal resolution.

• LV Mass: Can be estimated using M-Mode (less preferred), or more accurately using 2D methods like Area-Length or Truncated Ellipsoid, requiring tracing the endocardium and epicardium in PSSA and length in Apical 4C. Useful for assessing hypertrophy (e.g., in IDM or steroid exposure).

4. Subcostal Views

Obtained by placing the probe below the costal margin, angled superiorly towards the heart. The liver provides an excellent acoustic window. These views are particularly useful when thoracic views are poor (e.g., BPD, post-sternotomy).

• Situs Assessment: Essential view to confirm abdominal situs (IVC on the right, Aorta on the left relative to the spine). Sweep to visualize the IVC draining into the RA. Rule out interrupted IVC/azygous continuation.

• Views: Can obtain both short axis (cross-sectional) and long axis views. Provides views of the RV inflow, body, and outflow tract (tripartite RV). Can see LV inflow and outflow. Excellent for visualizing the pericardium and assessing for effusion. Useful for checking central line (IVC, SVC) positions.

• Septal Geometry: Can be the best view to assess interventricular septal curvature when thoracic windows are limited.

• Key Measurements & Assessments in Subcostal:

  • Interatrial Septum / Patent Foramen Ovale (PFO): Excellent view to visualize the interatrial septum and the PFO flap. Color Doppler demonstrates shunting direction. Measure the PFO diameter in 2D. A large right-to-left shunt across the PFO (especially strict R-L) requires prompt rule-out of Total Anomalous Pulmonary Venous Return (TAPVR). Other causes of R-L shunt include severe PHN/RV failure, pulmonary or tricuspid atresia, or high venous return states (vein of Galen, hepatic AVM). Rule out Sinus Venosus ASD (pulmonary vein unroofing into SVC) in this view.

  • Interventricular Septum / VSDs: Can visualize muscular VSDs with color Doppler. Doppler the VSD jet (CW or PW) to estimate the LV-RV pressure gradient, providing a quick assessment for the presence and severity of pulmonary hypertension.

  • IVC/SVC Diameter and Doppler: Measure diameters. Doppler flow (typically PW for low velocity venous flow). Assess flow pattern. Significant retrograde flow (>50% of cardiac cycle) in the SVC or subhepatic veins suggests increased RA pressure/RV diastolic failure. IVC diameter alone is a less reliable indicator of volume status in mechanically ventilated or PHN infants.

5. Suprasternal Views

Obtained by placing the probe in the suprasternal notch and angulating inferiorly.

• Views: Excellent for visualizing the Aortic Arch (ascending, transverse, isthmus, descending) in long axis (candy cane) and short axis (crab view showing vessel branching). Also shows the Pulmonary Artery (RPA in crab view) and Left Atrium. Can see the thymus anteriorly. Good for assessing the relationship between the aorta and PA (e.g., Transposition of the Great Arteries where they are parallel).

• Key Measurements & Assessments in Suprasternal:

  • Aortic Arch Anatomy: Assess arch sidedness (typically left), branching pattern of head and neck vessels (brachiocephalic, left carotid, left subclavian), and arch dimensions (compare to Z-scores for hypoplasia). Identify the isthmus (preductal segment). Rule out vascular rings.

  • Coarctation of the Aorta: Look for narrowing of the arch (especially the isthmus) and a posterior shelf. Use CW Doppler through the narrowed segment to measure the pressure gradient (>15-20 mmHg concerning) and assess flow turbulence. Assessment may be more accurate after PDA closure.

  • Patent Ductus Arteriosus (PDA): Can visualize the PDA connecting the PA to the descending aorta. This view allows assessment of the PDA's relationship to the arch.

  • Aortic Doppler: PW Doppler in the ascending, transverse, or descending aorta assesses flow pattern. Retrograde diastolic flow in the descending aorta indicates a steal phenomenon, often caused by a large Left-to-Right PDA shunt. Other causes include Truncus Arteriosus, AP window, BT shunts, vein of Galen malformations, severe Aortic Insufficiency, or MAPCAs.

  • Pulmonary Vein Assessment: The short axis (crab) view is excellent for visualizing the four pulmonary veins draining into the LA. PW Doppler at the ostia assesses flow pattern (normally biphasic/triphasic) and velocity. Loss of phasicity or high velocity suggests pulmonary vein stenosis (mean gradient >4 mmHg concerning) or high pulmonary blood flow (e.g., PDA). This view is key for ruling out TAPVR (pulmonary veins not draining to LA).

6. Specific Assessments & Doppler

• Patent Ductus Arteriosus (PDA): Assessment includes visualizing and measuring the diameter (narrowest point at the pulmonary end), often normalized to LPA diameter or body weight. Doppler (PW or CW) assesses flow direction and pattern.

  • Left-to-Right PDA: Flow from aorta to PA. Doppler pattern indicates pressure gradient and flow resistance.

    • Unrestrictive/Large: Velocities drop to baseline in diastole (pulsatile flow). Pressures equalize across the duct. Indicates low PVR relative to SVR. Leads to increased pulmonary blood flow and potential over-circulation. May cause descending aortic steal (retrograde diastolic flow).

    • Restrictive/Small: High velocities throughout the cardiac cycle (sawtooth pattern). Significant pressure gradient between aorta and PA. Indicates a narrower duct offering resistance to flow.

  • Right-to-Left PDA: Flow from PA to aorta. Doppler pattern shows flow away from the probe. Indicates high PVR relative to SVR or low systemic pressure. Seen in severe PHN/RV failure, pulmonary atresia, tricuspid atresia, or critical coarctation with a closing duct. Can offload the RV but causes postductal desaturation.

  • Bidirectional PDA: Mixed flow pattern. Seen with similar PA and Aortic pressures. Context is key (e.g., early preterm with high PVR, critical coarctation, severe RV dysfunction).

• End-Organ Perfusion: Doppler assessment of systemic arteries can indicate the impact of shunts/cardiac function on systemic blood flow.

  • Cerebral Arteries (e.g., Middle Cerebral Artery MCA, Anterior Cerebral Artery ACA): Doppler (PW) can assess flow patterns. Retrograde diastolic flow indicates cerebral steal, often due to a large PDA.

  • Mesenteric Arteries (Celiac, Superior Mesenteric Artery SMA): Doppler can assess flow. Reduced or absent diastolic flow can indicate mesenteric steal.

  • Resistive Index (RI) and Pulsatility Index (PI): Metrics calculated from arterial Doppler waveforms to quantify downstream resistance and pulsatility. RI = (Peak Systolic Velocity - End Diastolic Velocity) / Peak Systolic Velocity. PI = (PSV - EDV) / Mean Velocity. Higher RI/PI (especially RI > 1 indicating retrograde flow) suggests increased downstream resistance or steal.

7. Physiological Concepts

Understanding basic cardiovascular physiology is critical for interpreting echocardiographic findings.

• Pressures: Pressures vary throughout the cardiac cycle in different chambers and vessels. Relative pressures drive shunt directions (e.g., higher pressure pushes flow to lower pressure). Knowledge of normal neonatal pressures (e.g., RA low, RV systolic ~PA systolic, LA low, LV systolic ~Ao systolic, diastolic pressures low) and how they change (e.g., PVR drop after birth) is essential. Wedge pressure measured in the cath lab estimates left-sided filling pressures.

• Volume: Ventricular volumes change throughout the cycle (end-diastolic volume is maximum fill, end-systolic volume is residual after contraction). Atrial volumes change based on venous return and AV valve function. Volume overload in one chamber affects others (e.g., RV volume overload from ASD affects RV shape and filling).

• Cardiac Output: The volume of blood pumped per minute. Calculated as Stroke Volume (volume per beat) * Heart Rate. Stroke volume is derived from VTI and outflow tract area. Often indexed to patient weight (mL/kg/min), with a normal range around 150-400. High output can be seen with significant shunts (PDA), low output with ventricular dysfunction. The Fick principle is a method used in the cath lab to calculate output.

• Resistance and Flow: Flow between two points is driven by the pressure difference and opposed by resistance. Resistance is influenced by vessel length, viscosity, and radius (Poiseuille's Law). Shunt flow (like PDA) is determined by the pressure gradient between the connected systems and the resistance of the shunt itself, as well as the peripheral resistances (PVR vs. SVR).