Valved and nonvalved right ventricular--pulmonary arterial extracardiac conduits. An experimental comparison.

Extracardiac conduits are essential in operations for congenital discontinuity between the right ventricle and the pulmonary artery. The disturbing degree of obstruction reported in clinical series of extracardiac conduits containing porcine valves has been attributed in part to early valve deterioration and the development of a thick neonintimal lining within the Dacron graft. This study compares the hemodynamic differences and the thickness of the neointimal lining in right ventricular extracardiac conduits with and without a porcine valve. Woven Dacron conduits (16 mm) were implanted in 15 adult mongrel dogs, and then the proximal pulmonary artery was occluded with Dacron tape. In six dogs, the extracardiac conduit contained a porcine valve, whereas in the other nine it did not. Cardiac output, transconduit gradient, and resistance were measured at operation and 6 and 12 months postoperatively in both groups. No hemodynamic differences were noted. After 1 year, the thickness of the neointimal lining was threefold greater in valved conduits (1,370 +/- 313.1 mu versus 367 +/- 28.07 mu, p less than 0.005). The neointima along the Dacron graft was thickest proximal and distal to the porcine valve. The luminal peel in valved conduits contained fenestrations and intimal flaps, similar to those observed clinically. In our model, a porcine valve in a right ventricular extracardiac conduit is associated with intimal hyperplasia not seen in nonvalved conduits. If the pulmonary vascular resistance is normal, then the absence of a valve within the conduit does not significantly change hemodynamics and may warrant clinical application to prevent late conduit obstruction.