Discussion

APA from the aorta remains an investigational field in paediatric cardiac surgery due to the low incidence of this congenital malformation. ^{Reference Kutsche and Van Mierop1,Reference Patel, Zakir and Sethi2} The largest reported series includes 52 patients who underwent surgery for this anomaly over a 19-year period. ^{Reference Dong, Yan, Xu, Duan and Liu3} In our study, the most commonly associated anomaly was patent ductus arteriosus, as consistent with a previous report. ^{Reference Kajihara, Imoto and Sakamoto4} Though APA is different from aortopulmonary window, a combination of APA, aortopulmonary window, coarctation of aorta, and interrupted aortic arch is referred as Berry syndrome. ^{Reference Johnson, Watson, Strauss and Spray5}

It has been reported that histological features of pulmonary vascular disease can be seen as early as the first month of life with this condition. ^{Reference Peng, Shanmugam, Macarthur and Pollock14} One-year survival of children with APA is around 30% without surgical treatment. ^{Reference Benatar, Kinsley, Milner, Dansky, Hummel and Levin6} To avoid developing irreversible pulmonary vascular disease and improve the outcome, APA must be repaired in early infancy. All our surviving patients were operated during infancy. ^{Reference Benatar, Kinsley, Milner, Dansky, Hummel and Levin6}

The first successful surgical correction of APA was reported by Armer in 1961 ^{Reference Armer, Shumacker and Klatte9} in which he used a dacron graft to anastomose the APA. Various surgical techniques have been described later that include implantation using an autologous pericardial patch, homograft, and direct implantation of the anomalous branch to main pulmonary artery. ^{Reference Fucci, di Carlo, Di Donato, Marino, Calcaterra and Marcelletti10–Reference Salaymeh, Kimball and Manning12} Direct re-implantation of right pulmonary artery was first described by Kirkpatrick et al, ^{Reference Kirkpatrick, Girod, Caplan and King13} the advantage of which is the growth potential of the native pulmonary artery and less chances of anastomotic obstruction, provided the anastomosis is achieved without tension. ^{Reference Nakamura, Yasui, Kado, Yonenaga, Shiokawa and Tokunaga11,Reference Fong, Anderson, Siewers, Trento and Park15} The disadvantage of other techniques is that it almost always requires a second surgery.

Direct re-implantation after excision of the anomalous pulmonary artery as a button akin to coronary button in an arterial switch operation is our technique of choice now. Mobilisation of main pulmonary artery and both branches upto the hilum helps to reduce the tension in the anastomosis. Reconstruction of ascending aorta after the re-implantation (in case of right pulmonary artery) provides excellent exposure to avoid any inadvertent twists. Reconstruction of harvest site with a pericardial patch reduces the tension in the aortic suture line, thus preventing any posterior displacement leading to compression of translocated right pulmonary artery.

Patients with APA who underwent surgical treatment early in infancy have excellent short- and long-term outcomes. ^{Reference Liu, Cheng and Qian16} However, the most common late complication after surgical treatment is the anastomotic site stenosis. Significant stenosis requiring further intervention is considered as an important cause of morbidity. ^{Reference Fong, Anderson, Siewers, Trento and Park15,Reference Liu, Cheng and Qian16} There was no anastomotic site stenosis seen in any of our patients.

The calculation of pulmonary vascular resistance could be fallacious in APA. The source of pulmonary blood flow to both lungs are separate, and the pulmonary vascular resistance in each lung could also be different. Hence, the net Qp (pulmonary blood flow) in this situation would be difficult to estimate and saturation alone cannot be relied for pulmonary vascular resistance estimation. The ideal scenario, in this situation, would be to do a functional MRI to calculate the pulmonary venous return of individual left and right pulmonary veins to calculate the true Qp (pulmonary blood flow). This would help in calculating the true PVRI in each lung. Hence, in this situation, if the PVRI is calculated by assuming the Qp, this may result in fallaciously high value. ^{Reference Dimopoulos, Diller and Opotowsky17} In this series, presence of sub-systemic pulmonary artery pressures in the APA with clinical X-ray and echocardiographic evidence of operability has been considered for surgical repair. The cut-off for operability based on calculated PVRI is still unknown.