Microvessels Observed in Bioprosthetic Leaflets

Yu Sato and his colleagues at CVPath Institute have observed new findings that suggest a causal link between implanted heart valve degeneration and foreign microvessels from bovine and porcine pericardial tissue found present before valve manufacturing.

The procedure known as TAVR (transcatheter aortic valve replacement) treats aortic stenosis, a condition in which the diseased leaflets of an aortic valve do not open and close properly and prevent blood from flowing efficiently from the heart to the body. This condition can weaken the heart muscle and may initially cause fatigue, dizziness, shortness of breath, and swelling. During a TAVR procedure, a transcatheter heart valve (THV) is inserted with a catheter into the stenotic valve and expanded with a balloon once positioned. After it is implanted, the THV replaces the function of the organic leaflets by acting as an artificial “door” that allows blood to flow from the heart again normally.

In the study report, Sato et al. provide a histopathological evaluation of one THV that had been explanted two months after a TAVR procedure. The THV was severely deteriorated and showed microvessels originating from the animal pericardial tissue used for the bioprosthetic leaflets (see figure below.) The new growth of blood vessels, known as neovascularization, indicated a possible reason for the valve’s dysfunction. However, Sato et al. caution against making conclusions about the histopathological evidence too soon, as they expect to conduct more studies on cases from CVPath’s registry of over 200 THVs, some of which (including both deteriorated and early explants) also exhibited microvessels.

In a recent interview with Dr. Sato, he said, “A paper from Sellers et al. demonstrated that microvessels were observed in a transcatheter aortic valve that was explanted due to degeneration. They suggested that microvessels are one of the key players in bioprosthetic valve degeneration. However, from our experiences of pathological examinations of bioprosthetic aortic valves, microvessels are seen not only in degenerative valves, but also in the valves that are explanted just after the implantation procedure. This suggests that microvessels are present at the time of manufacturing (i.e., microvessels are observed in the bovine/porcine pericardium). It is clear that microvessels exist in porcine/bovine pericardium. Therefore, we need to show a causal relationship between the presence of microvessels and bioprosthetic valve degeneration. Mechanisms of bioprosthetic valve dysfunction remain poorly understood. At CVPath Institute, we are trying to understand it and solve these important questions to improve clinical outcomes and patients’ quality of life in the future.”

JACC: Cardiovascular Interventions accepted Sato et al.’s paper on August 1st, 2023. It is available to read through the following link: https://pubmed.ncbi.nlm.nih.gov/37737800/

Written by Gina Miller

Sources:

Sato, Y., Kawai, K., Torii, S., Tanaka, T., Finn, A. V., & Virmani, R. (2023). Microvessels Are Normally Observed in All Pericardial Bioprosthetic Leaflets. JACC. Cardiovascular Interventions, 16(20), 2572–2573. https://doi.org/10.1016/j.jcin.2023.08.004

Yoon J, Jelisejevas J, Meier D, et al. (2023). Neovascularization in Structural Bioprosthetic Valve Dysfunction. J Am Coll Cardiol Intv. 16 (5) 606–608.
https://doi.org/10.1016/j.jcin.2023.01.007