The role of the sewing ring in tissue healing: a pathologic study of explanted mechanical heart valves

Serious complications may occur after heart valve replacement, and many such patients will require reoperation. The study aim was to identify the pattern of tissue response around the sewing ring of those valves that have been explanted as a result of various valve-associated complications.

A total of 51 mechanical heart valves (MHVs) was explanted from 45 patients who had undergone reoperation for valve-related complications. The examination of the valves included an analysis of the operative findings, macroscopic findings, histopathology, and dissection of the sewing ring.

The extent of tissue hyperplasia was variable around the sewing rings of valves explanted for various pathologies. In pannus, the hyperplastic tissue extended into the valve orifice and produced an obstruction to flow, whereas in thrombosed valves the thrombus was attached to the tissue at the annulus. In non-infective pathologies, the histology revealed cellular infiltration that was limited to the peripheral fabric layers of the sewing ring, though the extent of infiltration was not increased with the duration of implantation. In prosthetic valve endocarditis (PVE), the surrounding hyperplastic tissue was granulomatous, but cellular infiltration into the sewing ring was absent. The dissection of various models of explanted valves revealed that different types of filler and fixing mechanisms had increased the bulk of the sewing ring.

Tissue hyperplasia of varying extent occurs around the sewing ring after MHV implantation. The cellular elements grow into the peripheral layers, but not the deeper layers, of the sewing ring. In PVE, there was an absence of cellular infiltration into the sewing ring.