Calcification of porcine bioprosthesis implanted into human heart: high resolution scanning electron microscopic and scanning tunneling microscopic investigation.

High-resolution scanning electron microscopy (HR-SEM) combined with scanning tunneling microscopy (STM) was used to investigate the calcification mechanism occurring in the porcine bioprostheses implanted into the human heart. Eleven explanted porcine heart valves obtained during open heat surgery were prepared for HR-SEM and STM observations. HR-SEM examinations of all explanted valves with secondary and backscattered electron imaging revealed abnormal accumulation of calcium in various shapes and sizes on the defective valve surface and in the underlying basement membrane. Calcific deposits were consistently observed within the pinhole defects on the valve surface and in the subsurface structures of the valve tissues along the surface defects. In addition, calcium-containing crystals were often present just underneath the disrupted valve surface. STM examinations also showed that calcific deposits were frequently accumulated in or around the pinhole defects on the valve surface. Thus, STM findings were compatible with HR-SEM observations. In view of the occurrence of calcific deposits in the vicinity of the surface defects on the valve tissue and frequent observation of calcific spots and crystals in the subsurface structures just beneath the defective valve surface, our results prove the hypothesis that alteration of the valve surface is an important factor for calcification occurring in the implanted bioprosthetic heart valves.