Impaired cardiac output during exercise in adults operated for ventricular septal defect in childhood: a hitherto unrecognised pathophysiological response

Background: Recent studies have demonstrated that surgical ventricular septal defect closure in childhood is associated with reduced functional capacity and disruption of the right ventricular force-frequency relationship during exercise. To further describe long-term cardiac function, we performed a non-invasive assessment of cardiac index during exercise in adults having undergone surgery for ventricular septal defect in early childhood. Methods: A total of 20 patients (surgical age 2.1 +/- 1.4 years, age at examination 22.1 +/- 2.2 years) and 20 healthy, matched controls (23.4 +/- 2.1 years at examination) underwent continuous supine bicycle ergometry during MRI. Their blood flow was recorded in the ascending aorta and the pulmonary trunk at increasing exercise levels. Cardiac index, retrograde flow, and vessel diameters were determined by blinded, post hoc analyses. Results: The patient group had normal cardiac index at rest (2.9 +/- 0.7 L/minute/m(2)), which was comparable with that of the controls (3.0 +/- 0.6 L/minute/m(2)); however, they had a lower increase in cardiac index during exercise (reaching 7.3 +/- 1.3 L/minute/m(2) at submaximal exercise) compared with controls (8.2 +/- 1.2 L/minute/m(2)), p< 0.05. Patients had a significantly higher ascending aorta retrograde flow than controls at rest and throughout exercise. In the pulmonary artery, the retrograde flow was minimal at rest in both groups, but increased significantly in patients during exercise compared with controls. Conclusions: Young adults with a surgically closed ventricular septal defect have a reduced cardiac index during exercise compared with healthy, young adults. The impaired cardiac index appears to be related to an increasing retrograde flow in the pulmonary artery with progressive exertion.