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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3655_Библиотеки_им_академика_М_И_Перельмана
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Pathology ofMechanical Prosthetic
Данная книга находится в списке для перевода на русский язык сайта https://meduniver.com/
Cardiac Valves
UbertoBortolotti, MilaDella Barbera, TomasoBottio,
andGaetanoThiene
7
With the advent of extracorporeal circulation in the early
1950s, surgical repair of many acquired and congenital cardiac diseases became possible. In those years, rheumatic disease was very common, with a frequent involvement of
cardiac valves. Until then, most surgical procedures were
conned to the treatment of mitral valve stenosis by means
of closed commissurotomy. Prosthetic valve replacement
became a reality when the rst mechanical devices were
available to be used in orthotopic position. The rst commercially manufactured models were constructed based on the
“ball-in-a- cage” concept where a spherical occluder (poppet)
was allowed to move freely into a metallic cage; the prostheses had a cloth-covered sewing ring to facilitate the implant
in the native annuli (Fig.7.1). Caged-ball prostheses were
followed by other models, aimed to improve the hemodynamic performance and reduce thrombogenicity, including
specic changes in design. These were represented by cageddisc, tilting-disc, and bileaet prostheses (Fig.7.2).
The rst models of mechanical prostheses showed an evident suboptimal hemodynamics characterized by the presence
of high transprosthetic gradients, especially when small-sized
devices were implanted. This was the consequence of the specic design of caged-ball and caged-disc valves producing
lateral ows due to the central presence of the occluder.
Switching later to the tiling-disc concept and then to the bileaflet design improved signicantly the hemodynamic performance providing a central, physiological blood ow.
Availability of mechanical prostheses had a great impact
in the management of patients with valvular heart disease.
Nevertheless, soon some important complications related to
their use, pertaining to all of them and some being typical of
specic models, started to be observed.
U. Bortolotti
Section of Cardiac Surgery, Cardio-thoracic and Vascular
Department, University Hospital of Pisa, Pisa, Italy
e-mail: uberto.bortolotti@med.unipi.it
M. Della Barbera (*) · G. Thiene
Department of Cardiac, Thoracic, Vascular Sciences and Public
Health, University of Padua Medical School, and Cardiovascular
Pathology Unit, University Hospital of Padua, Padua, Italy
e-mail: mila.dellabarbera@unipd.it; gaetano.thiene@unipd.it
T. Bottio
Division of Cardiac Surgery, Emergency and Transplant
Department, University Hospital of Bari, Bari, Italy
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
G. Thiene et al. (eds.), Pathology of Cardiac Valve Disease, https://doi.org/10.1007/978-3-031-35498-4_7
105
106
U. Bortolotti et al.
ab
Fig. 7.1 The Starr-Edwards caged-ball prosthesis. (a) The original
model used for the rst mitral valve replacement (left) was made of a
lucite cage, a silicone rubber (Silastic) ball, and a Teon sewing ring.
(b) The last model of the same prosthesis consisted in a metallic cage
made of stellite, a cobalt-chromium-molybdenum-nickel alloy and a
Silastic ball with a silicone rubber and sponge in the sewing ring
ab
cd
7 Pathology ofMechanical Prosthetic Cardiac Valves
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107
Fig. 7.2 Different blood ow patterns through the various models of mechanical prostheses. (a) Caged-ball; (b) caged-disc with lateral transpros-
thetic ow; (c) tilting-disc; and (d) bileaet models with both central and lateral ows
Thrombosis andThromboembolism
mechanical prostheses, both in mitral and aortic positions,
requires lifelong administration of oral anticoagulants.
The major drawback of mechanical prostheses, regardless
of their specic model, is represented by the occurrence
of thrombus deposition on the surface of the fabric and
metallic components. Thrombosis is extremely dangerous
since it may extend to interfere with the movement of the
occluders, causing sudden, acute malfunction (Fig.7.3).
Moreover, systemic embolization may also occur with
ischemic complications and severely debilitating or even
lethal consequences (Figs. 7.4 and 7.5). Implant of
Anticoagulation management is sometimes difcult due
to absence of patient compliance, associated diseases, or
drug interference. Most cases of prosthetic thrombosis are
related to inadequate anticoagulant treatment or its arbitrary suspension; conversely, an excessive anticoagulation
may cause hemorrhagic complications with possible fatal
sequelae. Pyrolytic carbon (Carbolm) was introduced to
prevent thrombus formation by coating the poppet, the
struts and even the sponge of the sewing ring.
108
U. Bortolotti et al.
abc
Fig. 7.3 Thrombosis of three different mechanical prosthetic models. (a) caged-disc, (b) tilting-disc, and (c) bileaet. In all cases thrombus depo-
sition interfered with the occluder movements, causing blockage and dysfunction
a
b
c
Fig. 7.4 (a) Cerebral ischemia in a patient with a mechanical prosthesis, who died of a thromboembolic stroke. (b) Embolic occlusion of a coro-
nary artery. (c) Myocardial infarction at the histology. Haematoxylin-eosin disclosing infarction
7 Pathology ofMechanical Prosthetic Cardiac Valves
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109
Fig. 7.5 Gross aspect of the
kidney in a patient who died
of mechanical prosthesisrelated thromboembolism.
Acute infarction shown on the
kidney surface (a) and in the
parenchyma (b)
ab
Fibrous Tissue Overgrowth
Excessive reaction by the host tissue may occur at the prosthetic sewing ring and native valvular annulus as expression
of a healing process. This is represented by formation of
brous tissue which can cover the fabric ring, protruding on
the valve orice with reduction of the prosthetic effective
orice area (Fig.7.6). This process starts with progressive
deposition of platelets brin and formation of a thrombotic
lining which subsequently becomes organized in brous tissue overgrowth (Fig.7.7).
110
U. Bortolotti et al.
Fig. 7.6 Fibrous tissue
overgrowth in a patient
reoperated because of severe
stenosis of a Starr-Edwards
caged-ball prosthesis
implanted in aortic position.
Fibrous tissue is present on
the ventricular view (a),
covering entirely the sewing
ring and signicantly
reducing the effective
prosthetic of the orice. On
the aortic view (b), the brous
pannus climbs the lower part
of the cage struts, interfering
with ball excursion
Fig. 7.7 (a, b) Two explanted
tilting-disc mechanical valve
prostheses with evidence of
thrombotic deposition close to
the sewing ring and brous
tissue overgrowth. Thrombus
and brous tissue apposition
clearly interfere with the disc
movements. The organization
of continuous thrombus
formation may explain the
growth of the brous pannus
ab
a
b
7 Pathology ofMechanical Prosthetic Cardiac Valves
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111
Structural Deterioration
The rst models of caged-ball prostheses contained a silicone poppet which was noted to undergo with time to
swelling due to absorption of plasma proteins and lipids
from the blood stream. This caused a variation in the structure, size, and shape of the occluder, a phenomenon known
as ball variance which interfered with the ball movements
(Fig.7.8).
Despite being constructed with apparently strong and
fatigue-resistant materials, some of the mechanical prostheses implanted clinically showed failures due to wear or rupture of part of their structural elements.
Fig. 7.8 (a, b) Caged-ball
prostheses with ball variance;
in both cases the ball becomes
swollen and larger than the
initial size, so that cage may
be unable to contain it. (c) In
another caged-ball valve, the
occluder shows an evident
fracture indicating an
impending risk of
embolization
a
Rupture of components of a mechanical prosthesis, such
as the metallic struts of the cage, have been observed in the
past. As a consequence, cases of fatal valve dysfunction with
systemic ball embolization have occurred (Fig.7.9).
Occasionally, wear of the disc has been observed in some
models with erosion sites due to contact with the cage with
eventual disc embolization (Fig.7.10).
In some tilting-disc and bileaet prostheses, rupture of
some components has occurred with frequent fatal consequences due to sudden and acute device failure (Fig.7.11).
Such failures have been attributed to faulty prosthetic
designs which have required recall of such devices from the
market.
b
c
112
U. Bortolotti et al.
a
b
Fig. 7.9 (a) Fracture of the cage struts of an aortic prosthesis; (b) a
pyrolytic carbon ball escaped from the ruptured cage and was found at
necropsy in the aortic carrefour
abc
Fig. 7.10 (a, b) Wear (arrows) of the disc of caged-disc prostheses occurred by contact with the stent. (c) Escape of the disc
ab
7 Pathology ofMechanical Prosthetic Cardiac Valves
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113
a
b
Fig. 7.11 (a, b) Fracture of one of the retaining struts from the ring of
Bjork-Shiley tilting-disc prosthesis. Rupture occurred at the welding
points (arrowheads) with fatal disc embolization. Subsequent models
eliminated this complication since the struts were not fused to the ring but
obtained from a single piece of metal as integral part of the ring itself
TRI-Tech Bileaet Prostheses andLeaet
Escape
The TRI-Tech valve was a low-prole mechanical bileaet
cardiac valve prosthesis with pyrolytic carbon (Fig.7.12).
The two leaets were designed to reduce both turbulence and
the transvalvular gradient. The leaets were housed in the
orice ring by two tabs inserted into orice hinges, while a
metal band reinforced the housing system. The polyestermade swing ring was covered by a small ledge of pyrolytic
carbon, on both the inow and outow surfaces.
The catastrophic structural deterioration of this mechanical valve model was tab fracture, due to tab height asymmetry (Figs.7.13 and 7.14), with sudden leaet escape. For this
reason, the implantation program was interrupted with even
prophylactic prosthetic replacement. The valve was withdrawn from the market.
Among a total of almost 5550 TRI-Tech prostheses
implanted worldwide, leaet escape has been reported in 9
cases. In Padua, this complication occurred in three patients,
two aortic and one mitral, 10days, 40days, and 22months
after surgery, respectively.
A 52-year-old male underwent uneventful implantation of
a 25mm TRI-Tech aortic valve with ascending aorta replacement and died suddenly at home, 10 days postoperatively.
The predischarge echocardiogram had shown a normal prosthetic valve function (mean gradient 12mmHg). At autopsy,
an escaped leaet was found in the descending thoracic
aorta.
Fig. 7.12 The unimplanted bileaet mechanical TRI-Tech valve prosthesis, in both closed (a) and open (b) positions
114
ab
Fig. 7.13 (a) The escaped leaet found in the thoracic aorta. Note the fracture of a pivot system with 0.55mm asymmetry of the tabs height
(0.75mm of fractured tab versus 1.30mm of nonfractured tab). (b) Close-up, which highlights the fractured pivot
U. Bortolotti et al.
a b
Fig. 7.14 (a) The successfully replaced mitral TRI-Tech prosthetic valve with one missing leaet. (b) The missing leaet, found in the left com-
mon iliac artery, with tab asymmetry of 0.33mm
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