Revista de citología e histología

Ultrafine Structure of Human Aortic Valve Calcific Deposits

Abstract

Felix Grases, Otakar Sohnel and Marketa Zelenkova

Objective: To elucidate the mechanism of formation of calcific deposits inside the human natural heart valve based on their ultra-fine structure on nanometer scale observed by atomic force microscope.
Methods: Cross-sections of an aortic valve calcification were observed by scanning electron microscope. Thin slices several micrometeres thick from the same deposit were observed by atomic force microscopy in the Peak Force Imagining mode providing topographic, adhesion and quantitative nanoscale elastic modulus maps of the surface.
Results: Most of the aortic valve calcification was composed of large blocks of mostly compact matter, porous on the microscopic scale. The mineral blocks consisted mainly of closely arranged elongated needle- and plate-like crystals, 30 to 70 nm in diameter, and irregularly disseminated areas of soft organic material.
Conclusions: Crystals forming mineral blocks of mostly compact matter are nucleated on organic substrates, with their growth controlled by the diffusion of building units through the virtually stagnant layer of interstitial fluid wetting the deposit surface. Preferentially formed precursors of hydroxyapatite, dicalcium, octacalcium and/or amorphous calcium phosphate, are in later stages of deposit development transformed into biological hydroxyapatite.