In vitro calcification of pericardial bioprostheses

The lifetime of bioprosthetic heart valves is limited by calcification. To investigate the calcification behavior of bioprostheses and gain insight into the etiology of valve calcification, a test protocol for accelerated valve calcification was developed. This protocol includes a pulsatile valve tester, a synthetic calcification fluid, and non-destructive radiographic assessment of calcification sites. About 40 porcine bioprostheses from different manufacturers have been investigated previously using this test protocol and showed that valves exhibited different calcification patterns and even different degrees of calcification within their leaflets. A positive correlation of calcification versus tissue anomalies/stress concentrations (r = 0.72; n = 29 valves) and lipid deposits (r = 0.81) was found. In the present study, bovine pericardial valves were investigated in comparison with porcine valves.

Four bovine pericardial and two porcine mitral valves (Baxter) with a tissue annulus diameter (TAD) of 29 mm (one 27 mm) were investigated in parallel under identical test conditions. The valves were cyclically loaded at 300 per min with a delta p of 110 mmHg at 37 degrees C for up to 19 x 10(6) cycles. The synthetic calcification fluid was changed weekly. Sites of calcification were assessed by microradiography. Radiographs were analyzed by PC images processing with respect to the degree of calcification, defined as calcified surface area in relation to total leaflet surface area.

This analysis showed that, for bovine pericardial valves, the mean degree of calcification increased by 14% and 20% after 12 and 19 x 10(6) cycles, respectively. Under identical conditions, the mean degree of calcification of porcine valves increased by 28% and 37%.

Pericardial valves appear less prone to calcification than porcine valves. Further studies must be performed in order to prove this finding since, as recognized previously in porcine valves, other factors such as tissue or manufacturing anomalies may be as important as the tissue source itself.