Calcification of the human heart valves: a mineralogical approach

Normal physiologic processes result in development of mineralized tissue. Bones and tooth enamel are the main example of biominerals. Pathologic processes lead to calcification of the atherosclerotic plaques, kidney and salivary stones and other pathologic deposits. Most of these seem to be constituted from a mixture of calcium phosphate phases but their formation mechanisms are not completely known. In cardiac pathology, calcification of heart valves can be advanced by a congenital malformation or an infectious process or related to the senile degeneration. Pathological mineral deposits occurring in human cardiac valves were studied using Polarizing Microscopy, Scanning Electron Microscopy (SEM-EDS), Electron Microprobe (EMPA), X-Ray Powders Diffraction (XRPD), Infrared Spectroscopy (FTIR). Samples were obtained as surgical waste from thirty patients undergoing valvular replacement in case of severe aortic and mitral stenoses. The experimental results showed that the mineral phase grown in human cardiac valves is a calcium phosphate with poor crystallinity. It develops as nodules in the organic matrix. The FT-IR spectra may be used to infer the presence of carbonate group. The carbonate bands in the infrared spectra have a saw-tooth profile similar to sample PC18, a synthetic type A-B CAp but in samples of aortic valves a-parameter is smaller and the c-parameter is greater than those of PC18 [i.e. TV12 a=9.4165(8) Å, c= 6.8951(7) Å; PC18 a=9.4803(3) Å, c=6.8853(3) Å] probably due to substitutional carbonate groups in phosphate positions which cause a shrinkage in the a-parameter. Pathological phase investigated can be considered a bioapatite as the inorganic component of bone and tooth enamel, even if it possesses unusual morphologies for a calcium phosphate and a Ca/P ratio unlike that of normal mineralized tissue.