P0384 - Diastolic right-to-left shunting PDA in neonatal coarctation is a sign of severe pulmonary hypertension

In severe neonatal coarctation, patients require a patent ductus arteriosus (PDA) for systemic perfusion. What may go unrecognized is the importance of differentiating ductal flow in systole versus diastole. Right-to-left ductal flow in systole would be a normal finding in severe coarctation as this is essential for distal systemic perfusion. Right-to-left ductal flow during diastole is abnormal and represents severely elevated pulmonary vascular resistance. This differentiation during diastole and systole is not well described in the literature, as pure right-to-left shunting is rare. We describe two neonates with critical coarctation of the aorta with pure right-to-left ductal flow with evidence of pulmonary hypertensive crisis after repair.

Case 1: 34-week premature male with prenatal concern for coarctation. The postnatal echocardiogram demonstrated critical coarctation, right-to-left shunting patent foramen ovale (PFO), continuous right-to-left shunting across a large PDA and diastolic retrograde flow in the aortic arch requiring prostaglandin (PGE) infusion. While awaiting surgical repair, the patient developed progressive pre/post ductal saturation gradients with preductal saturations of 90s and postductal saturation of low 90s to low 60s. There was also an increase in the near-infrared spectroscopy (NIRs) gradient with somatic NIRs down trending from 90s to 30s. There was no four-extremity blood pressure gradient noted. The patient underwent an uneventful coarctation repair. On arrival to the ICU, he developed evidence of pulmonary hypertensive crises with echocardiogram demonstrating severely depressed right ventricular function and tricuspid regurgitation jet velocity of 4.8 m/s for an estimated right ventricular systolic pressure of 92 mmHg above right atrial pressure. The patient eventually passed away despite triple pulmonary vasodilator therapy. Postmortem examination revealed a diagnosis of alveolar capillary dysplasia.

Case 2: 1-day old term male who presented in cardiogenic shock with echocardiogram demonstrating critical coarctation, ventricular septal defect (VSD) and depressed left ventricular systolic function. The patient was intubated and initiated on PGE, epinephrine and nitric oxide with hemodynamic improvement. Repeat echocardiogram demonstrated improved systolic function and continuous right-to-left shunting across the PDA. While awaiting surgical repair, preductal saturations were stable in the high 90s while postductal saturations would intermittently downtrend from 90s to 70s. The patient underwent aortic arch advancement, PDA ligation, VSD and PFO closure. Intraoperatively, there was concern for impaired cardiac output and pulmonary hypertension. Direct needle measurement of pulmonary artery pressures revealed 80% systemic pressures. He returned to the ICU on epinephrine, calcium, vasopressin, and nitric oxide. Over the next 3-4 days, vasoactive and pulmonary vasodilator therapy were able to be weaned off and survived long-term.

In critical coarctation, right-to-left ductal flow is crucial to maintain adequate systemic perfusion. Diastolic right-to-left shunting at the PDA is abnormal and signifies the presence of pulmonary vascular disease, and may signal an increased risk for morbidity and mortality.