Gabriel Altit (McGill University) - Online May 1st, 2026

Clinical context

This infant was born extremely preterm at 28 weeks’ gestation and was assessed at 38 weeks corrected age, with a weight of approximately 2.5 kg. The neonatal course was significant for DiGeorge syndrome, evolving chronic lung disease, and a large hemodynamically significant patent ductus arteriosus. Prior to closure, the infant had persistent echocardiographic evidence of pulmonary overcirculation and systemic steal on targeted neonatal echocardiography (TNE), with difficulty weaning from non-invasive respiratory support and progressive left heart volume loading. The pre-ligation TNE phenotype was consistent with a large, unrestrictive PDA with predominant left-to-right shunting. The ductal shunt resulted in excessive pulmonary blood flow, increased pulmonary venous return, left atrial and left ventricular dilation, increased left ventricular output, and systemic diastolic steal. In this context, the left ventricle had been operating for a prolonged period under a very specific loading condition: high preload from pulmonary venous return, high total output, but relatively low effective systemic afterload because part of the systemic circulation was continuously decompressed into the low-resistance pulmonary vascular bed through the PDA. Due to the excessive pulmonary venous return, there was acceleration at the mitral inflow, a hallmark often called "function" mitral valve stenosis due to the excessive total flow attempting to enter the left ventricle. There had also been concern for a narrow aortic arch and possible coarctation. This was clinically important because device closure of the PDA was felt to be unsafe. Given the large PDA, the narrow arch, and the risk of encroachment from a transcatheter device on either the aortic isthmus or adjacent vascular structures, the infant was judged not to be an appropriate candidate for catheter-based closure. Surgical ligation was therefore pursued, as the infant had reached term-corrected age and had an underlying genetic condition, making spontaneous ductal closure increasingly unlikely at this stage. Direct intraoperative assessment confirmed that there was no coarctation of the aorta.

On postoperative day 1, the infant remained intubated, sedated, and mechanically ventilated with low oxygen requirement. The ventilator mean airway pressure was approximately 11 cmH₂O and the FiO₂ is 21% (prior to the intervention the infant was on CPAP +5, with FiO2 21-25%). Despite reassuring gas exchange and a low lactate, the infant was noted to be significantly hypertensive, with a blood pressure of 124/84 mmHg and a mean arterial pressure of approximately 99 mmHg. Targeted neonatal echocardiography was requested and demonstrated moderate left ventricular systolic dysfunction and mild-to-moderate aortic valvular insufficiency (see TNE below). This constellation of findings raises an important physiologic question: why would a baby develop systemic hypertension and left ventricular dysfunction after successful PDA ligation?

Pre-ligation physiology: a chronically low-resistance systemic circuit

A large PDA is not simply an additional vessel; it fundamentally changes the circulatory architecture. In this infant, the PDA created a persistent connection between the systemic arterial circulation and the pulmonary vascular bed. Because pulmonary vascular resistance is relatively low by this postnatal age, the ductus functioned as a low-resistance runoff from the aorta into the pulmonary arteries. This has several consequences.

• First, pulmonary blood flow increases. More blood returns through the pulmonary veins to the left atrium and left ventricle. This explains the preoperative findings of left atrial dilation, left ventricular dilation, acceleration at the mitral inflow in diastole, increased LV output, and pulmonary venous Doppler changes consistent with pulmonary overcirculation.

• Second, systemic diastolic perfusion is altered. During diastole, blood preferentially runs off into the pulmonary circulation rather than being maintained in the descending aorta and systemic organs due to the low pulmonary vascular resistance relative to the systemic vascular resistance. This can produce reduced, absent, or reversed diastolic flow in systemic arteries, including the descending aorta, mesenteric vessels, renal arteries, and cerebral vessels depending on severity and timing. 

• Third, the left ventricle adapts to an abnormal loading state. The LV becomes accustomed to high preload (by progressive underlying hypertrophy and remodelling) and high output, but it is not ejecting into a normal closed systemic circuit. Because the systemic circulation is connected to the pulmonary vascular bed through the PDA, the effective total peripheral resistance faced by the LV is lower than expected. The LV therefore becomes conditioned to eject into a circuit with a substantial low-resistance “escape route.” In simple terms, before ligation, the LV is volume-loaded but partially afterload-protected.

Neurohormonal adaptation before surgery

The systemic circulation also adapts to the chronic ductal runoff. When there is persistent systemic steal, particularly renal diastolic steal, the body may activate compensatory mechanisms to preserve organ perfusion. These include sympathetic nervous system activation, endogenous catecholamine release, and stimulation of the renin–angiotensin–aldosterone system. These mechanisms are initially adaptive. They increase vascular tone, support blood pressure, preserve renal perfusion pressure, and help maintain systemic blood flow in the face of runoff. However, they may become maladaptive immediately after ductal closure, which leads to rapid and brutal changes in the systemic vascular compartment. The important concept is that the neurohormonal system does not switch off instantly when the surgeon ligates the PDA. Therefore, immediately after ligation, the infant may have persistent high systemic vascular tone, persistent catecholamine effect, and persistent RAAS activation, but the low-resistance ductal runoff has suddenly disappeared. The same compensatory tone that was helping systemic perfusion before ligation can now contribute to systemic hypertension after ligation. This is particularly relevant in an infant with preoperative systemic steal and pulmonary overcirculation. The kidney may have spent days or weeks exposed to abnormal diastolic perfusion. Once the PDA is closed and renal perfusion pressure improves, there may be a transient mismatch between vascular tone, intravascular volume, renal sodium/water handling, and systemic afterload.

Why the blood pressure is high in this infant

Several mechanisms likely contribute to the marked postoperative hypertension. 

1. The first is mechanical and immediate: removal of the ductal runoff. Before ligation, the aorta was connected to a low-resistance pulmonary circuit. After ligation, that pathway is gone. Effective systemic vascular resistance rises (due to disconnection of the pulmonary circuit that is low resistance), and diastolic pressure may increase substantially due to the increase filling within the aorta in diastole. 

2. The second is neurohormonal: persistent preoperative catecholamine and RAAS activation. The infant had chronic systemic steal physiology, including probable renal underperfusion during diastole. The body may have responded with increased vasoconstrictor tone and sodium/water-regulating systems. Once the PDA is closed, these mechanisms may continue transiently, now producing an exaggerated hypertensive response. 

3. The third is renal: renal perfusion changes abruptly. With closure of the PDA, renal diastolic perfusion may improve rapidly. However, renal vascular tone, intrarenal autoregulation, and RAAS activity may lag behind the new circulatory state.

4. The fourth is postoperative: pain, agitation, endotracheal tube stimulation, sedation/analgesia weaning, steroids if used, and surgical stress can all increase blood pressure. These factors should always be assessed and treated. However, in this case, the simultaneous finding of LV dysfunction strongly suggests that the hypertension is not only a pain response; it is part of the post-ligation hemodynamic transition.

5. The fifth is vascular anatomy and aortic loading. There was preoperative concern about a narrow arch. Even though coarctation was excluded intraoperatively, a relatively small arch or altered aortic compliance may still amplify the rise in proximal systolic pressure after ductal closure. This is especially relevant in a patient with mild-to-moderate aortic insufficiency, where high diastolic and systolic pressure may worsen regurgitant load.

Why the LV becomes dysfunctional

The moderate LV dysfunction is best understood as acute afterload mismatch superimposed on a deconditioned ventricle. Before ligation, the LV was exposed to chronic volume loading and high output, but it was also ejecting into a low-resistance effective circuit. The PDA allowed part of the LV output to pass into the pulmonary circulation instead of being delivered entirely to the systemic vascular bed. The LV therefore did not need to generate the same pressure-volume work that it must generate after ligation. After closure, the LV suddenly faces a higher resistance circuit. The end-systolic wall stress increases. Stroke volume may fall. Ejection fraction or qualitative systolic function may worsen. Mitral inflow and pulmonary venous flow patterns change because pulmonary venous return decreases. The LV end-diastolic dimension may rapidly decrease compared with the preoperative volume-loaded state, while systolic function appears depressed because the ventricle cannot adapt quickly to the increased afterload. This is why the post-ligation echo should not be interpreted in isolation as “new cardiomyopathy.” It is more accurate to describe this as acute post-ligation LV systolic dysfunction in the context of abrupt loading change. The presence of mild-to-moderate aortic insufficiency adds another layer. Aortic insufficiency causes diastolic regurgitant flow back into the LV. When systemic pressure is high, the regurgitant gradient may increase, potentially worsening LV volume load and reducing effective forward systemic output. Even if the aortic insufficiency is not the primary cause of dysfunction, it can become more hemodynamically relevant in the setting of hypertension and LV systolic impairment.

Targeted neonatal echocardiography assessment post-ligation

The post-ligation TNE should be structured around the clinical question: is this infant tolerating the new circulation? Key elements include LV systolic function, LV size, mitral inflow, pulmonary venous return, LV output, aortic valve function, arch patency, systemic blood flow patterns, RV function, pulmonary pressure estimates, left and right pulmonary arterial caliber and flow (as accidental ligation of a branch pulmonary artery or the aorta, although rare, remains a critical complication to exclude) and end-organ perfusion surrogates. For the LV, the assessment should include qualitative systolic function, shortening fraction or ejection fraction where feasible, LV dimensions, LV output, tissue Doppler or strain if available, and assessment of whether the LV is underfilled, hypertensive/afterload stressed, hypertrophied, dilated or still volume loaded. For the aortic valve, the degree of aortic insufficiency should be documented carefully. The width, duration, and hemodynamic impact of regurgitation should be followed over time, particularly as systemic pressure normalizes. For the arch, it remains important to confirm there is no residual obstruction after ductal closure. This includes evaluation of the transverse arch and isthmus, Doppler pattern in the descending aorta, upper and lower limb blood pressures, femoral pulses, and abdominal aortic Doppler. For systemic perfusion, the TNE should look for abdominal aortic diastolic flow recovery, mesenteric and renal Doppler patterns if clinically needed, LV output, and signs of low output despite hypertension. A low lactate is reassuring, but lactate is not a perfect marker of early cardiovascular stress. For the RV and pulmonary circulation, the TNE should assess RV size and function, septal position, TR jet if present, PAAT/RVET, and inter-atrial shunting. Pulmonary vascular disease remains relevant in this ex-preterm infant with evolving chronic lung disease.

Management approach

The immediate management priority is to recognize that this is a cardiovascular transition state. The infant is hypertensive, but also has moderate LV dysfunction. Treating the blood pressure without understanding the LV physiology could be harmful. Conversely, ignoring the hypertension because perfusion appears acceptable could perpetuate afterload stress and delay LV recovery.

1. Confirm the clinical phenotype: The first step is to integrate bedside and echocardiographic data. The infant has high blood pressure, low oxygen requirement, reassuring ventilation, low lactate, and warm perfusion. This suggests that there is no overt systemic shock at the time of assessment. However, the TNE demonstrates moderate LV dysfunction, meaning the cardiovascular system is under stress. The team should trend blood pressures, pulses, urine output, lactate, acid-base status, perfusion, and heart rate. A single blood pressure value is less informative than the trajectory over time and the relationship between blood pressure, LV function, and perfusion.

2. Optimize pain and sedation: Postoperative hypertension can be worsened by pain, agitation, endotracheal tube stimulation, inadequate analgesia, or withdrawal. The infant should have adequate postoperative analgesia and sedation, especially after thoracotomy. Pain control is not just comfort care; it is cardiovascular care. Uncontrolled pain increases catecholamines, systemic vascular resistance, oxygen consumption, and afterload. Pain medication as needed and non-pharmacological interventions should be prioritized and optimized. Excessive sedation may delay extubation and may alter vascular tone. The goal is balanced comfort, not deep unnecessary sedation.

3. Reduce LV afterload while supporting contractility: Milrinone seems as physiologically well suited to this phenotype (although ongoing RCT on the subject). It provides inotropy, lusitropy, and systemic vasodilation. In a baby with post-ligation hypertension and LV systolic dysfunction, milrinone can improve ventricular performance while reducing afterload. In this case, milrinone was increased up to 0.5 mcg/kg/min. The subsequent normalization of blood pressure and progressive improvement in LV systolic function on follow-up TNE supports the interpretation that the LV dysfunction was at least partly load-dependent and reversible. If hypertension had persisted despite optimized analgesia and milrinone, additional antihypertensive therapy could be considered according to local neonatal practice, renal function, and arterial access. However, the threshold and agent selection should be individualized. 

4. Avoid unnecessary volume loading: The post-ligation LV may appear smaller because pulmonary venous return has fallen. This does not automatically mean the baby needs fluid boluses. In fact, indiscriminate volume administration can worsen pulmonary edema, increase LA pressure, and impair respiratory recovery, especially in an infant with chronic lung disease and residual LV dysfunction. Volume should be guided by clinical perfusion, urine output, lactate, echocardiographic filling, and respiratory status. If the LV appears underfilled and systemic output is low, cautious volume may be considered. But in a hypertensive infant with pulmonary overcirculation history and postoperative LV dysfunction, routine boluses should be avoided.

5. Reassess diuretics: LV dysfunction and aortic insufficiency can increase left-sided filling pressures and contribute to pulmonary edema. Therefore, the diuretic plan should be dynamic. The team should avoid both extremes: continuing high-dose diuretics reflexively despite reduced preload, or stopping all diuretics despite postoperative LV dysfunction and chronic lung disease. Judicious ponctual dosages of diuretics can be considered in infants with excessive pulmonary edema on chest radiography or body fluid edema. Electrolytes are central here with electrolyte repletion being part of cardiovascular optimization (especially calcium). Calcium is important for myocardial contractility and vascular tone. In a baby with DiGeorge syndrome, calcium monitoring is particularly important. Hypocalcemia may contribute to myocardial dysfunction and should be corrected.

6. Correct modifiable contributors to myocardial dysfunction: the hemoglobin was slightly low at 74 g/L. In a stable preterm infant this may be tolerated, but in the context of postoperative LV dysfunction, chronic lung disease, and recent surgery, anemia may reduce oxygen delivery and increase cardiac workload. The decision to transfuse should follow local thresholds and clinical context, but anemia should not be ignored in the hemodynamic interpretation.

7. Respiratory management and extubation timing: From a respiratory standpoint, extubation may appear attractive. However, post-ligation LV dysfunction changes the risk-benefit analysis. Extubation increases the work of breathing and changes intrathoracic pressure dynamics. In a stable infant with improving LV function, extubation is desirable because it reduces ventilator-associated morbidity and supports recovery. But extubation during active afterload mismatch and moderate LV dysfunction may precipitate increased oxygen consumption, respiratory fatigue, pulmonary edema, or cardiovascular instability. It may also alter cardio-respiratory interactions that would worsen the LV function, as gentle mechanical ventilation can support the LV. The practical approach is to optimize cardiovascular status first, document improving blood pressure and LV function, ensure adequate analgesia, correct electrolytes/anemia as needed, and then proceed toward extubation when the infant demonstrates stability. Serial TNE can help identify the right timing.

8. Follow-up echocardiography: Serial assessments are essential. The first postoperative echo identifies the phenotype. Follow-up echo determines whether the physiology is improving, stable, or worsening. In this infant, follow-up TNE demonstrated progressive normalization of LV systolic function after milrinone and blood pressure control. The milrinone was weaned after normalization of BP and TNE at 24 hours of infusion. This trajectory is highly reassuring and supports a reversible post-ligation afterload mismatch rather than fixed cardiomyopathy. The aortic insufficiency should also be reassessed. If it improves as blood pressure normalizes, it may have been functionally exaggerated by the hypertensive state. If it persists or worsens, it may require cardiology follow-up and more detailed structural assessment.

Evolution in this case

The infant’s postoperative course is best described as transient post-ligation hypertension with associated LV afterload mismatch and moderate LV systolic dysfunction. The marked systemic hypertension likely reflected the abrupt removal of ductal runoff combined with persistent neurohormonal vasoconstrictor activation after weeks of systemic steal physiology. The LV dysfunction likely reflected acute exposure to increased afterload, reduced preload from decreased pulmonary venous return, and limited myocardial reserve after prolonged preoperative volume loading. Milrinone was escalated to 0.5 mcg/kg/min. With this strategy, blood pressure normalized and follow-up TNE showed progressive recovery of LV systolic function. This response confirms that the physiology was dynamic and treatable. It also reinforces the value of targeted neonatal echocardiography in distinguishing hypertension with preserved cardiac adaptation from hypertension causing myocardial stress. The expected trajectory is gradual cardiovascular stabilization over the following 24–72 hours, with improving LV systolic function, reduced need for afterload reduction, and improved respiratory mechanics as pulmonary overcirculation resolves. Diuretic requirements should be reassessed as the infant transitions away from the pre-ligation volume-loaded state. Extubation can be pursued once the infant has stable blood pressure, improving LV function, acceptable gas exchange, and adequate pain control (with appropriate respiratory drive).

Teaching points

Post-ligation physiology is one of the clearest examples of why neonatal hemodynamics cannot be reduced to blood pressure alone. A high blood pressure may appear reassuring because it suggests adequate systemic pressure, but in this case the blood pressure itself was part of the problem. The LV was suddenly exposed to a much higher afterload after weeks of ejecting into a low-resistance ductal circuit. The result was hypertension with LV systolic dysfunction, a phenotype that requires afterload reduction and myocardial support rather than simple observation. A large PDA chronically alters both sides of the circulation. It increases pulmonary blood flow and pulmonary venous return, causing left atrial and left ventricular dilation. At the same time, it lowers effective systemic vascular resistance through runoff into the pulmonary circulation. The pre-ligation LV is therefore not a normal LV. It is a ventricle adapted to high preload, high output, and relatively low effective afterload. When the PDA is closed, that adaptive state is abruptly removed.

Systemic hypertension after PDA ligation can reflect more than pain. Pain and agitation must be treated, but the physiology often includes removal of the low-resistance ductal runoff, persistent catecholamine activation, RAAS activation, and rapid restoration of systemic and renal perfusion pressure. In a baby with previous systemic steal, these mechanisms can produce a transient hypertensive overshoot after ligation. Post-ligation LV dysfunction is often an afterload mismatch phenomenon. The LV may not be intrinsically diseased; it may be unable to immediately adapt to the new pressure load. This is particularly likely when dysfunction improves after afterload reduction. In this case, the improvement in blood pressure and serial recovery of LV function after milrinone strongly supports a reversible load-dependent process.

The fall in preload after ligation is also important. Closure of the PDA reduces pulmonary overcirculation and therefore reduces pulmonary venous return to the left atrium. The LV can move rapidly from a volume-loaded state to a relatively lower-preload, higher-afterload state. This combination is especially unfavorable for stroke volume and myocardial performance. Milrinone is a logical therapy when post-ligation hypertension is accompanied by LV dysfunction. It supports contractility, improves relaxation, and reduces systemic vascular resistance. It treats the mechanism of afterload mismatch. However, it should be used with close monitoring of blood pressure, perfusion, renal function, rhythm, and serial echocardiographic response. Serial TNE/ECHO and clinical assessments are central to management. The first echo identifies the hemodynamic phenotype; the next echo determines whether the chosen treatment is working. In this case, serial imaging demonstrated progressive normalization of LV systolic function, allowing the team to move from stabilization toward respiratory weaning and recovery.

Finally, PDA closure is not the end of the disease process. It is the beginning of a new physiology. The infant must transition from a ductal, volume-loaded, low-resistance circulation to a closed systemic circulation with normal pulmonary venous return and higher effective systemic afterload. Understanding this transition allows the clinician to anticipate complications, individualize therapy, and avoid both undertreatment and overtreatment.

TNE pre-ligation

TNE at day 1 post-ligation

Follow-up Echo for LV function

Milrinone was continued for 24 hours and then discontinued once blood pressure normalized. This echocardiogram was obtained 24 hours after cessation of milrinone.