Processing factors as determinants of tissue valve calcification

The effect of different processing factors on tissue valve calcification were studied in the subdermal rat model. Factors evaluated, were the influence of tissue ischaemia (4 degrees and 25 degrees C), different blocking reagents (KH2PO4, T6, MgCl2 and AlCl3), fixation pressures (0, 10 and 20 mmHg) and the pH (3.72 and 7.40) of the fixative. Tensile strength tests performed, showed that all blocking reagents tend to weaken valve tissue. Histologically calcification originated mainly in the spongiosa of the valve leaflets. Tissue ischaemia at 4 degrees C significantly (p less than 0.05) decreased the calcification potential of the valve tissue. Ischaemia at 25 degrees C significantly (p less than 0.05) increased this process. Blocking reagents KH2PO4, T6 and MgCl2 significantly (p less than 0.05) reduced calcification of valve tissue. AlCl3 pretreatment virtually prevented it to such an extend that the calcification process was down to 92% of the control group. Different fixation pressures had no influence on the calcification potential of the tissue. AlCl3 was dependent on a low pH (3.72) to act as a blocking reagent on tissue calcification. It is concluded that certain processing factors do influence the calcification potential of valve tissue. These factors should be considered when constructing bioprostheses with glutaraldehyde-treated porcine valves.