Prosthetic heart valve replacement

In vitro evaluation of prosthetic heart valves: anomalies and limitations

The in vitro evaluation of fifteen commercially available prosthetic heart valves is described. The group comprised both mechanical and bioprosthetic valves. The experimental studies were carried out in a steady flow circuit which included a flexible valve test section, the geometry of which was modelled on the aortic anatomy. The fluidic performance of the valves was examined over a range of flows and in particular, the phenomenon of "pressure recovery" distal to the valve was studied in depth. A number of theoretical parameters which might be used to define valve performance were evaluated but none was found to be ideal. The conclusions of the study emphasise the limitations of such in vitro testing and the danger of extrapolating such experimental data to the possible valve performance in vivo.

Oxidized orlon as a blood interface

Polyacrylonitrile fabric (Orlon) may by oxidized by heating in air, when it becomes black and carbonized. During the heat treatment, the fibers shrink; this shrinkage allows components such as diaphrams to be shaped around molds. Oxidation reduces the tensile strength by about 25% and also reduces the stiffness of the material. The oxidized Orlons was screened in tissue culture for possible cytotoxic effects. Finding none, patches of the material were sutured into the right atrium of dogs and examined after 48 hr. Because of encouraging results, 10 atrial patches, consisting of Dacron velour and oxidized Orlon side-by-side, were implanted into the right atrium of dogs. Five patches were backed with Silastic to render them impervious, and five with segmented polyurethane. The atrial patches were examined after 48 hr, and in all instances the oxidized Orlon part of the patch was coated with a thinner and smoother fibrin layer than was the Dacron velour half. a left ventricular bypass pump was fabricated from oxidized Orlon and spray-coated on the nonblood surface with segmented polyurethane. After 48 hr implantation in the chest cavity of a calf, pumping without systemic anticoagulation, the pump was found covered by a thin, smooth, firmly attached layer of fibrin.

Aortic valve replacement with frame-supported autologous fascia lata grafts. II. Clinical and laboratory findings

Thirty-five patients with a frame-supported autologous fascia lata graft implanted in the aortic annulus were investigated 11 to 36 months after operation. The group comprised 7 patients with pure aortic stenosis, 11 with combined stenosis and incompetence and 17 with pure aortic incompetence. Seven patients had concommitant mitral valve disease. The follow-up investigation included ECG, a work test on a bicycle ergometer, dynamic spirometry, roentgenological heart volume determination and haematological "screening tests" for intravascular haemolysis. Concomitant with a marked subjective improvement of the patients, there was a considerable objective improvement, as judged by physical working capacity, ECG signs of left ventricular hypertrophy and heart volume. The serum haptoglobin values were somewhat lower postoperatively (mean value 44 mg%), but no ahaptoglobinaemia occurred. Thus, no definite signs of intravascular haemolysis were noted. No thrombo-embolism occurred within this observation period, despite the fact that none of the patients with isolated aortic valve replacement were treated with anticoagulants. This investigation shows that a frame-supported autologous fascia lata valvular graft in the aorta can function well during a period of up to 3 years.

Total prosthetic replacement of atrioventricular valves in the dog. 3. local tissue reactions in the heart caused by tricuspid valve prostheses

The metal parts of cardiac valve prostheses cause reactions in the surrounding tissues of the heart. In some dogs rather abnormal reactions were found, and were attributed to corrosion of the stainless steel in the cage of the valve with subsequent local metallosis of the heart and microscopic symptoms of corrosion disease.

Early clinical experience with cloth-covered valvular prostheses

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