Developments in cardiovascular valve technology - Biomaterials and Devices for the Circulatory System - page 90

4.4 Example of a lenticular valve prosthesis. Dacron-velour covered
Beall Surgitool prosthesis with a compressed Tefl on disc and
turtleneck sewing cuff.

design changes; the most important of these was the introduction of a pyro-
lytic poppet disc, which improved durability. Although thromboemboli were
less frequent than with the Starr-Edwards prosthesis, there still was a con-
siderable transvalvular diastolic pressure gradient. The valve also had an
unacceptably high re-operation rate as a result of severe hemolytic anemia
due to valve malfunction caused by total separation of the cloth cover
around the infl ow orifi ce. 33-37 Other caged-disc contemporaries of the Beall-
Surgitool valve included the Cross-Jones, Kay-Shiley, and Cooley-Cutter
devices. These valves had a lenticular (Fig. 4.4) or conical occluder. All of
these devices were discontinued in the 1970s due to the limitations listed
above. 38-41

4.3.3 Tilting-disc valves

By the 1970s there was a variety of prosthetic valves available, but surgeons
were dissatisfi ed with the high profi le cage-ball valves and the poorly func-
tioning caged-disc valves. A new type of valve, the tilting-disc prosthesis,
was introduced in the early 1970s, with a novel design that promised excel-
lent hemodynamics, with low valvular pressure gradients. Specifi c models
of the tilting-disc prosthesis included the Lillehei-Kaster, Björk-Shiley, and
Medtronic-Hall devices. These valves were designed for placement in the
mitral, tricuspid or aortic positions.
The Björk-Shiley prosthesis was designed by Dr V.O. Björk of Sweden
and D. Shiley, an engineer and founder of the Shiley laboratories. Intro-
duced in 1969, this valve consisted of a Stellite cage with a Tefl on sewing
ring and a disc made of Delrin, a more durable material than the com-
pressed Tefl on of the Beall valve. The disc, which opened to a 60° angle, was
secured in position by infl ow and outfl ow struts. In 1971 the disc was
changed to pyrolytic carbon, an extremely durable and easily manufactured
material which was immediately adopted by the mechanical valve industry.

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