Are stentless aortic heterografts suitable for right ventricular outflow tract reconstruction? An experimental study in juvenile sheep.

Allograft valved conduits are used routinely for reconstruction of the right ventricular outflow tract in children with congenital heart disease; however, allografts are scarce. The purpose of this study was to evaluate two stentless aortic valves that might be suitable alternatives for right ventricular outflow tract reconstruction. Twelve juvenile sheep underwent implantation of stentless aortic heterografts as an interposition in the pulmonary artery: six porcine aortic valves (Freestyle) and six fully pericardial valves (Pericarbon stentless). In each series, three valves were explanted after 3 months, the other three after 6 months. Valves were analyzed by gross inspection, radiography, and light microscopy. The porcine aortic stentless valve (Freestyle) showed extensive calcification of its aortic wall portion, with perfectly functioning, pliable cusps without calcification or fibrous overgrowth up to 6 months. The pericardial valves (Pericarbon stentless) showed extensive fibrous sheathing, causing progressive retraction of the leaflets and severe regurgitation. After 3 months, minimal calcification was seen in the pericardial wall. Calcification was more pronounced after 6 months, sometimes causing complete calcification of pericardial wall and leaflets, leading to a significant stenosis. We conclude that the pericardial stentless valve becomes rapidly dysfunctional after right-sided implantation as a result of fibrous sheathing and severe calcification. The porcine aortic stentless valve remains functional, but severe calcification of the aortic wall portion is problematic.