Effect of abnormal pulmonary flow distribution on ventilatory efficiency and exercise capacity after arterial switch operation for transposition of great arteries.

Patients with anatomic repair of transposition of the great arteries (TGA) can present with branch pulmonary artery (PA) stenosis; however, its relation to an abnormal cardiopulmonary response to exercise is unknown. We investigated the relation between the PA anatomy and pulmonary blood flow (PBF) distribution and the cardiopulmonary response to exercise in patients with anatomic repair of TGA. We used cardiopulmonary exercise testing and magnetic resonance imaging to study 55 consecutive patients (62% male; age 14.4 ± 2.3 years) who had undergone neonatal anatomic repair of TGA. The peak oxygen uptake and slope of carbon dioxide elimination/minute ventilation was 79 ± 15% of predicted and 29.8 ± 3.8, respectively. Abnormal peak oxygen uptake (R = 0.363, p = 0.0082) and slope of carbon dioxide elimination/minute ventilation (R = 0.612, p <0.0001) values were associated with an abnormal right/left PBF distribution. However, although an increased ventilatory response to exercise appeared to be primarily related to an abnormal right/left PBF distribution, exercise capacity appeared to be related to the extent of the proximal PA branches and main PA stenosis (R = 0.476, p = 0.0004), suggesting that mechanical obstruction to PBF during exercise could be the main mechanism causing an abnormal exercise capacity. In conclusion, an abnormal PBF distribution related to branch PA stenosis or hypoplasia was associated with a reduced exercise capacity and increased ventilatory drive during exercise in patients with anatomic repair of TGA. Cardiopulmonary exercise test data can complement the anatomic and magnetic resonance imaging data in selecting those lesions that are functionally important.