Calcification

Calcification of heart valve prosthesis Copyright: CVEAME Figure 1: In vitro calcification of a porcine heart valve prosthesis and a bovine pericardium prosthesis

Background

The major problem of any kind of biological heart valve prostheses is the pronounced addiction to calcification. Mostly the valve leaflets are affected and calcification appears in deposition of apatite on the leaflet surface and inclusion of apatite inside the leaflet tissue (figure 1 and 2). The valve leaflets stiffen and show constrained opening and closing movement, resulting in valve stenosis, insufficiency and finally in valve failure. In any case calcification sooner or later lead to prosthesis replacement or implantation of a catheter based prosthesis (TAVR, TMVR).

Method

At the department of Cardiovascular Engineering CVE a special in vitro method for the testing of the calcification behaviour of biological heart valve prostheses was developed. The in vitro calcification of the test prostheses is performed in the durability test system CVE-FT2 at accelerated normotensive pressure conditions. By default the testing frequency is approximately 350 BPM at a maximum differential pressure across the closed prosthesis of 100 mmHg. The tested prostheses are fixed in separate, individually adjustable test compartments. By means of a high speed video system the prostheses can be inspected and documented to detect beginning calcification and resulting damages already in an early stage.

The calcification test fluid developed in our labs and based on a fluid, which was first mentioned in a publication of Starcher and Urry (B.C. Starcher, D. W. Urry, Biochemical and Biophysical Research Communications 1973, 53 (1), 210-216). Against the human blood plasma the CVE calcification fluid has a modified electrolyte amount; particularly the amount Calcium and Phosphate is increased. The ph-value is buffered and in the range as for human blood plasma.

The generated calcification can be examined by means of light microscopy, van Kossa stain of tissue sections, x-ray and -CT.

Microscopic image of aheart valve prosthesis Copyright: CVEAME Figure 2: Microscopic image of the in vitro calcification of a porcine heart valve prosthesis