Aortopulmonary Window with Crisscross Pulmonary Arteries: Anatomically Type 1, Physiologically Type 2.

Aortopulmonary window (APW) is a rare congenital anomaly. We report an association of APW with crisscross pulmonary arteries (hitherto unreported) in a 6-month-old child. There was differential flow to the right pulmonary artery was evident by the chest X-ray. We discuss the pathophysiology of the differential pulmonary blood flow in a case of APW.

INTRODUCTION

Aortopulmonary window (APW) is a rare congenital malformation resulting from abnormal septation of the truncus arteriosus into the aorta and the pulmonary artery.[1] APW constitutes 0.1% of all congenital heart diseases. These lesions present with increased pulmonary blood flow. We herein present a case with differential blood flow to the lungs and discuss the causes of the same.

CASE REPORT

A 6-month-old child with birth weight of 3 kg was diagnosed to have APW at 2 months of age and was subsequently lost to follow-up. At present, he was failure to thrive with weight of 3.5 kg. He was tachypoenic with respiratory rates of 55/min with no respiratory distress, heart rate of 140/min and liver was 2 cm below coastal margin. Chest was bilaterally clear. On auscultation S1 was normal, S2 was narrow split with loud p2 component, and mid diastolic murmur was present at the apex. Chest X-ray [Figure 1] showed mild cardiomegaly with differential blood flow to the right lung. Transthoracic echocardiography showed a large AP window proximal type with predominant left to right shunt, dilated left atrium and left ventricle (Z score +2.5). There was crisscross pulmonary artery with the APW proximal to the right pulmonary artery [Figures 2 and 3]. There was normal ventricular function.

Figure 1

Chest X-ray aortopulmonary view in the case of aortopulmonary window showing differential lung flow (marked by arrow)

Figure 2

Transthoracic echocardiography with colour compare in parasternal short axis view showing with nonrestricted aortopulmonary window, with selective blood flow to the right pulmonary artery. MPA: Main pulmonary artery, RPA: Right pulmonary artery, LPA: Left pulmonary artery, AA: Ascending aorta, APW: Aortopulmonary window

Figure 3

Transthoracic echocardiography with colour compare in parasternal short axis view showing the blood flow from the main pulmonary artery getting selective shunted to left lung. The right pulmonary artery and the aortopulmonary window cannot be demonstrated in this view because of the crisscross pulmonary arteries. MPA: Main pulmonary artery, RPA: Right pulmonary artery, LPA: Left pulmonary artery, AA: Ascending aorta

DISCUSSION

APW can result from incomplete fusion (Type I), poor alignment (Type II), or total absence (Type III) of the right and left conotruncal cushions, which normally complete conotruncal septation between weeks 5 and 8 of intrauterine life. APW may occur as an isolated lesion and/or associated with minor and simple repair anomalies (patent ductus arteriosus, atrial septal defect, patent foramen ovale) or as part of a larger complex of lesions such as tetralogy of Fallot (TOF), pulmonary atresia, aortic arch interruption, aortic arch hypoplasia with or without coarctation, and anomalous origin of coronary arteries. Fifty percent of patients usually have no other heart defects.[23]

APW may be classified into 3 types: Type I (proximal) defects occur in theproximal part of aortopulmonary septum; Type II (distal) defects occur in the distal part of the aortopulmonary septum adjacent to the right pulmonary artery; the Type III defect is a combination of Types I and II.[3]

The hemodynamic abnormalities of APW are similar to those seen with a large, unrestrictive ventricular septal defect or patent ductus arteriosus. APW is characterized by a large left-to-right shunt that becomes progressively worse as pulmonary vascular resistance falls during the new born period. Volume overload and pulmonary over circulation lead to progressive left ventricular dysfunction and congestive heart failure as was present in our case. In fact, it is important to look for AP window whenever one finds a lesion with decreased pulmonary blood flow such as TOF physiology or pulmonary stenosis situation with clinical presentation of congestive heart failure or increased pulmonary blood flow.[4] In our case, since the communication is proximal, it is anatomically Type I but physiologically because the shunted flow is mainly directed toward the right pulmonary artery and the left pulmonary artery is receiving only the flow coming from main pulmonary artery it is Type 2. There was no stenosis in any of the branch pulmonary arteries and hence this deferential flow was resulting from the presence of crisscross pulmonary arteries branching with selective increased pulmonary blood flow to the right lung in view of the proximal APW to the right pulmonary artery. The other rare cause of differential blood flow includes the absence of a single pulmonary artery.[5] This combination of APW and crisscross pulmonary arteries, and hence, the hemodynamic implication with selective increased pulmonary blood flow to the right lung has not yet been reported.

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Conflicts of interest

There are no conflicts of interest.