Performance of the Tilt-Disc Valve in the Inferior Vena Cava: An Animal Study

Abstract

The authors' laboratory recently reported long-term patency of valvular xenografts in the canine inferior vena cava. Valve fibrosis, however, followed early nonocclusive perileaflet thrombosis. A potential design flaw in the tricus pid prototype with open leaflets juxtaposed to the vascular wall possibly caused flow stagnation in valve cusps and initiated thrombus formation. The authors evaluated this hypothesis by design modification to a tilt-disc mechanical proto type with no valve cusps and continuous washing of the open midlumenal disc. The study included 12 metal alloy, tilt-disc valves placed in the canine infe rior vena cava. Daily aspirin (80 mg) and dipyridamole (50 mg) were begun on the day before implantation, with a single bolus of intravenous heparin (100 units/kg) administered prior to vascular occlusion. Angiography followed by complete autopsy was performed at two weeks in 6 animals, and at four weeks in 4 animals. Two animals underwent valve explantation fifteen minutes after reflow with examination of the vena cava at the site of valve placement by scan ning electron microscopy. Five valves were patent at two weeks. Four valves were patent at four weeks. Thrombus formed on the surface of the disc and supporting structure in all 9 patent valves, however, and underwent progressive organization with eventual valve fibrosis. A small, asymptomatic pulmonary embolus was discovered upon autopsy at four weeks in 1 animal. Scanning electron microscopy showed leuko cyte adherence to the lumenal surface within fifteen minutes after reflow. This study, as well as previous work, shows feasibility for maintenance of prosthetic valve patency in the vena cava. Correction of a potential design flaw in the tricuspid tissue valve by elimination of the sinus with continuous leaflet washing in a tilt-disc mechanical prototype failed, however, to prevent peri leaflet thrombosis.