Nature and properties of cardiovascular deposits.

Mineral deposits from human aortas and bioprosthetic devices implanted in experimental animals show close similarities in chemical composition, solubility and structural characteristics. Chemical analyses show compositions corresponding to a Na, Mg, CO3 substituted apatitic calcium phosphate. Synergistic XRD, FT-IR and Raman microprobe spectroscopic data provided coherent indication of Type-B CO3(2-) incorporation. Microscopic and electron microprobe microanalyses, however, indicate substantial morphological and spatial heterogeneity in the deposits. Solubility and kinetic dissolution data of the mineral fraction of deposits can be compared with the corresponding data of octacalcium phosphate (OCP). This may indicate that OCP is a possible precursor phase which initiates formation of the mineral deposit. Our data indicate that the deposits can be represented by a series of carbonate-substituted products, arising from OCP that has hydrolyzed to varying degrees. Dissolution of deposits can be described kinetically as a surface controlled rate process. The similarities in the two types of deposits suggest that they form by a common mechanism (e.g., OCP could be the precursor for both deposits).