Continuous right-to-left ductal flow in a newborn

Abstract

We describe a 7-day-old newborn who presented with arterial desaturation and respiratory distress. The evaluation showed a duct with a continuous right-to-left shunt and an anomalous origin of the right pulmonary artery from the aorta. We discuss the hemodynamics leading to continuous right-to-left ductal flow and the subsequent intraoperative evaluation that resulted in a successful single-stage surgical repair of this interesting case.

INTRODUCTION

Anomalous origin of the right pulmonary artery (PA) from ascending aorta (AORPAA) is a rare anomaly, with patients presenting within the first 6 months with respiratory distress and heart failure.[1,2] This results in the right lung being exposed to systemic pressure and the left lung to the entire systemic venous return. Patients with AORPAA presenting late often have differential PA pressures with differential pulmonary vascular resistance (PVR) elevation. We present a neonate with AORPAA, where a patent ductus arteriosus (PDA) demonstrated a continuous right-to-left shunt, further exaggerated by pulmonary vasodilators, creating a diagnostic enigma.

CASE REPORT

A 7-day-old newborn was referred for respiratory distress and arterial desaturation. The baby was born through cesarean section at 36 weeks’ gestation with a birth weight of 1.7 kg. The child cried immediately after birth but had respiratory distress, requiring oxygen support. There was no history of meconium-stained liquor, gestational diabetes, or maternal chorioamnionitis. The prenatal ultrasonogram did not reveal oligohydramnios or structural lung abnormalities. After 96 h, distress improved, but desaturation was persistent. Therefore, the child was referred to us. At presentation, vitals were: heart rate 170/min, good peripheral pulses, respiratory rate 48/min, no significant retractions/nasal flaring, blood pressure (BP) 70/36 mmHg, and oxygen saturation (SpO₂) 88%–90% in all four limbs (oxygen-2 L/min). On systemic examination, the chest was clear, with a loud second heart sound, no murmur, and the liver was palpable 1 cm below the costal margin.

Complete blood count, hepatic and renal function tests were normal. The chest radiograph revealed mild cardiomegaly with oligemic lung fields and no loss of lung parenchymal volume [Figure 1a]. Echocardiography showed a left-sided heart, usual atrial arrangement, concordant atrioventricular and ventriculo-arterial connections, and normally related arterial trunks. The branch PAs were nonconfluent. The main PA (MPA) continued as left PA, and there was AORPAA [Figures 2 and 3]. There was a nonrestrictive PDA with continuous PA to aorta flow throughout the entire cardiac cycle with associated holodiastolic flow reversal in the ascending aorta [Figures 4 and 5]. In addition, there was a left-sided aortic arch with a circumflex arch, midline descending thoracic aorta, and aberrant right subclavian artery (ARSA). The pulse wave Doppler of the pulmonary veins was intriguing. The velocity-time integral of the left lower pulmonary vein was less than that of the right-sided pulmonary vein, suggesting a higher PVR in the left lung [Figure 6]. Computed tomographic angiography was performed for anatomical delineation, which revealed the same findings [Figure 7]. In addition, there was tracheal compression due to an incomplete vascular ring formed by the midline descending aorta, the circumflex course of the arch, and the PDA.

Figure 1.

Chest radiograph (a) Baseline, (b) 48 h after starting sildenafil

Figure 2.

Echocardiography in high parasternal short-axis view, (a) Patent ductus arteriosus present between main pulmonary artery (MPA) and descending thoracic aorta, (b) Right pulmonary artery arising from the ascending aorta and MPA continuing as left pulmonary artery. AO: Aorta, DTA: Descending thoracic aorta, LPA: Left pulmonary artery, MPA: Main pulmonary artery, PDA: Patent ductus arteriosus, RPA: Right pulmonary artery

Figure 3.

Echocardiography with color Doppler. High parasternal short-axis view showing right (red arrow) and left pulmonary artery (white arrow)

Figure 4.

Color Doppler in high parasternal short-axis view, (a) Systole showing right-to-left flow in patent ductus arteriosus (PDA), forward flow through the arch, (b) Diastole showing right-to-left flow in PDA, reversal in arch. Asc Ao: Ascending aorta, DTA: Descending thoracic aorta, MPA: Main pulmonary artery, PDA: Patent ductus arteriosus

Figure 5.

Echocardiography in suprasternal long-axis view, (a) Systole showing forward flow through the arch, (b) Diastolic phase showing reversal of flow in arch

Figure 6.

Echocardiography in high parasternal view. Pulse-wave Doppler sample of (a) Right lower pulmonary vein, (b) Left lower pulmonary vein

Figure 7.

Computed tomography angiogram. Volume-rendered image showing the aortic arch and anomalous origin of right pulmonary artery from aorta from behind. AORPAA: Anomalous origin of the right pulmonary artery from the aorta, ARSA: Aberrant right subclavian artery, Asc Ao: Ascending aorta, MPA: Main pulmonary artery, PDA: Patent ductus arteriosus

Presuming persistent pulmonary hypertension of the newborn (PPHN) as the reason for right-to-left ductal flow, oral sildenafil at 0.5 mg/kg/dose thrice a day was started. Over the ensuing 48 h, there was no change in the directionality of ductal flow; however, clinical worsening was observed, necessitating the escalation of respiratory support to noninvasive ventilation. Chest radiograph showed bilateral plethoric lung fields [Figure 1b]. This prompted the replacement of sildenafil with decongestive therapy.

It is intuitive not to operate on a patient having a continuously right-to-left shunting PDA. This created an operability enigma necessitating clarification through a detailed intradepartmental discussion. It was decided to proceed with single-stage repair, with a backup plan of staged repair by right PA (RPA) banding. For a better understanding of hemodynamics, we preplanned intraoperative measurements of MPA pressure, right femoral artery (RFA) pressure, and left upper limb (LUL) SpO₂ at baseline, as well as during maneuvers: temporary PDA occlusion, simultaneous PDA and RPA occlusion, and RPA occlusion alone.

After informed consent, general anesthesia was administered, targeting a low fraction of inspired oxygen and permissive hypercarbia to prevent pulmonary steal. SpO₂, end-tidal carbon dioxide, and cerebral near-infrared spectroscopy were observed along with standard anesthetic monitoring. After mid-sternotomy and pericardial marsupialization, MPA pressure, RFA pressure, and LUL SpO₂ were recorded at baseline and with maneuvers [Table 1]. Both systolic and diastolic RFA pressures reduced after occluding PDA, as RPA continued to steal systemic blood while ductal flow into the aorta ceased. Simultaneous occlusion of PDA and RPA resulted in an increase in RFA pressure as the steal stopped. The PA pressure also increased but remained subsystemic despite blood flow solely into the left lung. Upon occluding the RPA alone, epicardial echocardiography demonstrated a change in ductal flow from right to left to a bidirectional pattern.

Table 1.

Intraoperative hemodynamic information at baseline and with maneuvers

Maneuver	ABP (mmHg)	PAP (mmHg)	HR (/min)	SpO2 in LUL (FiO2=0.21) (%)	PDA flow
Baseline	53/16	45/15	135	93	Right to left
PDA occluded	45/17	44/13	134	92	-
RPA and PDA occluded	68/27	55/22	132	92	-
RPA occluded with PDA patent	65/21	50/20	132	93	Bidirectional

ABP: Arterial blood pressure, PAP: Pulmonary artery pressure, HR: Heart rate, LUL: Left upper limb, PDA: Patent ductus arteriosus, SpO₂: Oxygen saturation, RPA: Right pulmonary artery

After the institution of cardiopulmonary bypass, PDA was divided. AORPAA was detached from the ascending aorta, and the aortic end was primarily closed using a 6-0 polypropylene suture. RPA was unifocalized to MPA utilizing a posteriorly based MPA flap with anterior augmentation using untreated autologous pericardium. ARSA was divided, and a posterior aortopexy was added in view of tracheal compression. Cardiopulmonary bypass time was 144 min. Postoperative PA: RFA pressure ratio was 0.6. The child was weaned from ventilation after 72 h and discharged on postoperative day 10. Echocardiography at discharge revealed mild tricuspid regurgitation with no pulmonary hypertension (right ventricular systolic pressure = right atrial pressure + 25 mm Hg, noninvasive BP 94/63 mm Hg), normal biventricular function, and mild mid-RPA flow turbulence (peak systolic gradient 11 mm Hg). The child was discharged on sildenafil, which was stopped at 1-month follow-up.

DISCUSSION

AORPAA is well known to result in lungs being exposed to differential pressures, leading to differential PVR elevation.[1,2] Pressure in the left PA is known to be elevated, although rarely, above systemic pressure. The proposed mechanisms for this include increased pulmonary blood flow, left ventricular failure, a high amount of circulating vasoconstrictors, and neurogenic crossover from the unprotected lung.[3]

Our patient had a similar clinical scenario of differential PVR elevation. Flow reversal in the ascending aorta and arch indicated a low PVR in the right lung. Nevertheless, the absence of any left-to-right shunt through PDA also implied that PVR in the left lung was high or at least higher than in the right lung. PVR elevation in our case was likely due to failure of normal circulation transition after birth. PPHN coupled with AORPAA leads to differential PVR elevation, necessitating further hemodynamic clarification. A catheterization study was not planned, as differential blood flow and vascular resistance in both lungs in patients with AORPAA make the hemodynamic assessment difficult to interpret.[4] The calculation of the PVR of each lung with balloon occlusion of PDA and RPA has been described, but it is cumbersome. Recently, catheterization data combined with phase-contrast magnetic resonance imaging to determine operability in an older patient with AORPAA have been reported.[4]

Although the data to guide decisions in a patient with AORPAA are limited, existing literature states that when PVR in one lung is high, and low in the other lung, expected PVR following their surgical connection is usually in the operable range and lesser than the lower resistance (1/R = 1/R₁ + 1/R₂) due to establishment of a parallel circulation.[5]

Matsuda et al. described two neonates undergoing staged repair in whom preoperative cardiac catheterization revealed suprasystemic PA pressures. Poor reaction to oxygen was cited as a reason for deferring primary repair, although oxygen responsiveness has low predictive value in quantifying pulmonary blood flow where there is a marginal difference in oxygen levels between the pulmonary veins and the artery.[6]

We used intraoperative hemodynamic assessment with various maneuvers to determine the need for staged repair, thereby avoiding cumbersome tests. Simultaneous occlusion of the RPA and PDA resulted in an increase in systemic BP and subsystemic PA pressure. These findings confirmed that right-to-left ductal shunting was due to a difference in PVR between the two PA branches, with the left lung having a higher PVR. This difference in PVR leads to the stealing of blood by RPA from the LPA throughout systole and diastole, resulting in a continuous right-to-left shunt through the ductus.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the legal guardian has given his consent for images and other clinical information to be reported in the journal. The guardian understands that names and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.