Developments in cardiovascular valve technology - Biomaterials and Devices for the Circulatory System - page 106

4.15 Braunwald cloth-covered aortic prosthesis showing wear and tear
of the polypropylene cloth, exposing two struts (arrows) and clinically
causing peripheral embolization and valve failure.

prosthesis. Initial results were promising and there appeared to be a reduc-
tion in thromboembolism. 82,83 Unfortunately with time the cloth covering
wore causing disruption and device failures (Fig. 4.15). 84,85 Fernandez et al.
reported analysis of 96 cloth covered prosthesis explanted over a 13-year
period. The Dacron-Velour covering typically showed dehiscence at the
inlet, 86 although thrombotic occlusion was a rare occurrence with this valve
(Fig. 4.16).
Current prostheses are primarily bileafl et or tilting pyrolytic disc or
poppet with improved hemodynamics. The orifi ce cross-sectional areas have
been expanded to minimize pressure gradients for both aortic and mitral
valves. These design changes contribute greatly to the maintenance of high
fl ow across the valve, therefore preventing stagnation of blood, and also
serve to limit turbulence. Biological tissue valves have the advantage of
resembling the anatomy and function of human valves, thereby reducing
thromboembolic and thrombolic complications. Unstented biological valves
exhibit lower embolic events and show superior hemodynamic performance
when compared to either mechanical or biological stented valves. Antico-
agulation is not mandatory, and these valves are the prosthesis of choice
for active young patients or patients with a small aortic root. 87

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4.5.3 Infection

With the improvements in design, materials and operative management
cardiac valve replacement is accomplished with a relatively low operative