Developments in cardiovascular valve technology - Biomaterials and Devices for the Circulatory System - page 87

a fresh aortic homograft. The donor valve was explanted from a young man
killed in an automobile accident, and implanted into a patient dying from
heart failure secondary to severe aortic insuffi ciency. Murray et al. reported
that the valve functioned without complications for about 8 years. 18
On May 6, 1953, John Gibbon at the Jefferson University Hospital in
Philadelphia, succeeded in performing the fi rst open-heart surgery. He
closed a secundum atrial septal defect in an 18-year-old woman utilizing a
pump-oxygenator for 26 minutes. Gibbon's 23 years of research culminating
in the fi rst successful application of cardiopulmonary bypass in a patient
ushered in the modern age of cardiac valve replacement. 19 The years fol-
lowing the introduction of open heart techniques were an intense period of
development of new valvular prosthetic devices to treat a variety of con-
genital and acquired valvular conditions.
On September 21, 1960, Albert Starr and M. Lowell Edwards at the Uni-
versity of Oregon performed the fi rst implantation of a caged-ball valve in
the mitral position in a 52-year-old man with mitral stenosis. 20 At about the
same time Dwight Harken in Boston implanted a ball-valve with a double
cage design in the aortic position. 21 The successful implantation of these
prosthetic cardiac devices stimulated many investigators to develop a mul-
titude of different devices. Two distinct categories of implantable valves
emerged, the mechanical prosthesis and the biologic tissue prosthesis.

4.3 Mechanical prosthetic cardiac valves

4.3.1 Caged-ball valves

The introduction of the Starr-Edwards caged-ball prosthesis marked
a watershed in the history of mechanical valves. This pioneering valve
design set the standard against which subsequent valves are judged. The
fi rst Starr-Edwards caged-ball valve consisted of a Lucite cage with a
Te fl on sewing ring and a silastic rubber ball (Fig. 4.2). The major drawback
of the original Starr-Edwards valve was the high profi le of its cage. The
Starr-Edwards valve underwent many design modifi cations to improve its
durability and hemodynamic characteristics, lower its cage profi le and
reduce its thrombogenicity (Fig. 4.3). However, in 1963 reports of throm-
boembolic events began to appear. Investigations revealed the 'ball vari-
ance' phenomenon, i.e. critical changes in ball diameter due to wear caused
by chronic exposure to phasic pressures within the heart. This phenomenon
was more pronounced after aortic valve replacement and occasionally led
to catastrophic cases of acute escape of ball, causing sudden death. Patho-
logical examination and chemical analyses of the silastic rubber coated balls
at surgical explantation or autopsy revealed gross abnormalities with cracks,
fractures, loss of substance, distortion of spherical shape, and discoloration

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