Transapikaler Mitralklappenersatz : Histologische Charakterisierung verschiendener Stenttypen in Bezug auf entzündliche und gewebliche Veränderungen im Langzeitversuch am Hausschwein
Objective The aim of this study was the histological evaluation of mitral valved stents in an experi-mental in vivo porcine model four to 12 weeks after implantation with a focus on inflamma-tory reactions. Methods The self-expanding mitral valved stents were implanted in healthy porcine models via trans-apical approach in the beating heart. In this study, a histological evaluation of five animals is presented. The stents were implanted in vivo for a period of four weeks or longer. Posthu-mously, samples of the native mitral annulus and the atrial stent’s bed were taken and histo-logically analyzed (H&E, Masson's trichrome, Elastica van Gieson, Movat’s Pentachrome and von Kossa). Furthermore, leukocytes, B-cells, T-cells and macrophages were detected by specific immunohistochemically staining (CD45, CD3, CD20, CD68). Results The tissue’s architecture showed largely physiological regular structure, but also presented local areas in which the integrity of the tissue was damaged to different extents. In all ani-mals the formation of fibrin was detected to different extends. In all but one animal partly mild (n=2) or no (n=2) accumulations of calcium carbonate were shown. Some inflammation in the surrounding tissue was detectable. In three of five animals a strong, in one animal a locally restricted and in one animal only a sporadic presence of CD45+ leucocytes were found. A moderate (n=4) or strong (n=1) distribution of CD68+ mac-rophages was detectable. Only low numbers of CD3+ T cells and CD20+ B cells were found in all animals but one. These results indicate an innate immune response but only low adaptive immune response after up to 12 weeks post-implantation. No differences between annulus and the atrial stent’s bed were visible. Discussion The histological evaluation of five mitral valved stents showed widely a good integration into the native heart`s tissue. The stent surrounding tissue was classified and characterized for the first time. However, signs for inflammation and slight presence of calcification show po-tential risks. This has to be evaluated in more detail in a future study including a larger number of cases.