Structural changes in porcine bioprosthetic valves of a left ventricular assist system in human patients

Background and aim of the study: Porcine, specially manufactured bioprosthe tic valves regulate blood flow from the left ventricle to pump sac (inflow valve) and from the pump to the aorta (outflow valve) in a wearable, electr ically powered left ventricular support system (LVAS, Novacor). The increas ed need for long-term circulatory assistance requires information on the ev olution of these valves when exposed to specific hemodynamic conditions and inflammatory reactions in the device. The study aim was to examine structu ral changes in valves from explanted LVASs. Methods: Thirteen patients (11 males, two females; mean age 42 years (range : 17-64 years) were supported for a mean of 285 days (range: 37-1,293 days) with LVAS. Histologic sections from explanted inflow and outflow valves we re studied immunohistochemically using peroxidase-labeled antibodies and av idin-biotinylated peroxidase complex for detection. Results: In the macroscopically normal inflow valves (11/13), the outflow s urface (facing the pump) was covered with a discontinuous deposit of fibrin , macrophages and granulocyte elastase. Fibrinogen, IgG, complement protein s C1q and C3 had infiltrated the extracellular matrix (ECM) between 37 and 1,293 days. The crevices were enlarged during circulatory support, and fibr inogen/fibrin insudations were detected in the spongiosa. The collagen laye rs in the fibrosa were disrupted after 293 days, and eroded on the inflow s urface in the ventricularis after 1,293 days. In a deteriorated valve from a patient with endocarditis, Gram-positive bacteria and metalloproteinases were concentrated in the ECM. In the macroscopically normal (11/13) outflow valves, fibrin and complement proteins had penetrated the ECM from the inf low side (facing the pump), while macrophages and granulocytes were localiz ed mainly on the outflow surface. IgG and complement proteins were detected on and beneath the cusp surface up to 200 days and covered the disrupted E CM as implant time progressed. Conclusions: Structural changes appear to progress more rapidly in the infl ow than in the outflow of bioprosthetic valves. This difference indicates t hat the effects of biological factors are modulated by mechanical stress.