Abstract 16098: Mechanism of Branch Pulmonary Artery Stenosis After the Arterial Switch Operation

Abstract

Background: Branch pulmonary artery (PA) stenosis, most commonly on the left, is a recognized postoperative complication of the arterial switch operation (ASO) for transposition of the great arteries. We hypothesized that greater rightward rotation of the neopulmonary root and dilation of the ascending aorta are associated with stenosis of the left PA (LPA). Methods: This study represents a retrospective analysis of cardiac magnetic resonance imaging (CMR) studies performed in patients after ASO. Neo-pulmonary root position in relation to the aorta was expressed as an angle, with a negative angle implying a rightward neo-pulmonary root. For the purpose of this study, perfusion imbalance was defined as <40% of pulmonary blood flow to the affected lung. The offset between the LPA and right PA (RPA) as a result of cranial displacement of the LPA by asymmetric aortic root dilation was measured in the coronal plane. Results: 74 patients / studies were included for analysis. 73% had no branch PA stenosis, 24% had LPA stenosis and 3% had RPA stenosis. LPA area indexed to BSA was smaller than RPA area (287 ± 185mm2 vs 151 ± 114mm2, p=0.001). Smaller LPA area correlated with reduced LPA flow (r=0.213, p=0.0001) and a greater rightward positioning of the neopulmonary to aortic root (r=0.361, p=0.002). There was no correlation between LPA size or flow and offset of the LPA take-off due to an enlarged aortic root. Patients with reduced relative LPA flow were more likely to have required pulmonary arterioplasty with the primary repair (17% vs 2%, p=0.04), had a smaller LPA area [102±102mm2 vs 160±108mm2, p=0.04) and a smaller anterior-posterior thoracic diameter (101±53mm vs 131±55mm, p=0.04). There was no significant difference in patient demographics, cardiac diagnosis, age at operation, aortic root dimension, ventricular volumetrics or ventricular function between patients with normal LPA flow vs. reduced LPA flow. Patients with reduced LPA flow did not have greater peak gradients on echo. Conclusions: Greater rightward rotation of the neopulmonary root is associated with reduced LPA size and likely contributes to the development of LPA stenosis after ASO.