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390 Anticoagulation Therapy
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16
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Chapter
PROSTHETIC HEART VALVES
Douglas C. Anderson
INTRODUCTION
Patients with mechanical valve prosthesis (MVP) are at high risk for thromboembolic complications (e.g., cerebrovascular accident [CVA]), and all MVPs require
antithrombotic prophylaxis. Bioprosthetic valves are less thrombogenic but not as
durable as MVP and are, thus, more prone to failure requiring replacement. An ideal
valve, which would be infinitely durable and non-thrombogenic, does not exist.
•
Prosthetic valves are made of a broad range of materials that differ in their thrombogenicity.
•
Valve prosthetics alter cardiac hemodynamics causing turbulence and other flow
anomalies.
1
Newer materials reduce the thrombogenicity, and future materials such
as polymerics may reduce thrombogenicity even more.
3
MVPs in particular create high sheer stresses, which destroy blood
elements leading to activation of platelets, endothelial cells, and some
coagulation proteins, thus resulting in a very high level of thrombogenicity.
2
•
Thromboembolic events include valve thrombosis, which may necessitate treatment
with fibrinolytics or valve replacement, systemic embolism, and stroke.
• Since valve position, type, and materials affect
thrombogenicity, it is important to determine exactly
which valve has been repaired and which prosthesis
was used to avoid mistakes in anticoagulation.
• There are a finite number of times a valve can be
replaced. After two replacements, careful oversight
of anticoagulation is critical to avoid any future
replacements.
393
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RISK FACTORS FOR THROMBOSIS
•
Annual risk for thromboembolism for MVP ranges 4−23% without prophylaxis.
•
With prophylaxis, the relative risk of thromboembolic events (TEs) in patients
with MVP is reduced to 0.21, or 1–2 per 100 patient years.
•
Risk of TE is highest in the early post-surgical period (approximately 3 months)
until the valve is fully endothelialized.
7
5,6
• Transesophageal echocardiography (TEE) is
the gold standard for imaging heart valves for
thrombosis, and preferred over transthoracic
echocardiograms (TTEs) because of higher
sensitivity of TEE in detecting thrombi.
8
TYPES OF VALVES
Mechanical Prostheses
•
Three basic types of mechanical valves: caged ball/disk, tilting disk, and bileaflet
(Table 16-1).
•
Older caged ball and tilting disk valves are more thrombogenic than bileaflet
valves.
•
Annual TE event rate in patients who are anticoagulated to an international
normalized ratio (INR) 2.5−4.9.
Bileaflet 0.5% per year.
Tilting disk 0.7% per year.
Caged ball 2.5% per year.
9
4,5
TABLE 16-1: Types and Models of Mechanical Valves
Type Models Example
Caged-ball Starr-Edwards Starr-Edwards ball mitral heart
Tilting disc Björk-Shiley
Bileaflet St. Jude
Monostrut
Medtronic Hall
Omniscience
Omnicarbon
Ultracor
Carbomedics
Baxter TEKNA
Duromedics
Sorin Bicarbon Baxter TEKNA
Duromedics
Sorin Bicarbon
valve (see Figure 16-1)
Medtronic-Hall valve
(see Figure 16-2)
On-X -ConformX-Aortic valve
(see Figure 16-3]
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FIGURE 16-1. Starr-Edwards Ball Mitral Heart Valve
Source: Photo used with permission of Edwards Lifesciences LLC, Irvine, CA. Edwards,
Edwards Lifesciences, and Starr-Edwards are trademarks of Edwards Lifesciences
Corporation.
FIGURE 16-2. Medtronic-Hall Tilting Disc Valve
Source: Used with permission. Copyright © 2016 Medtronic, Inc.
Bioprostheses
•
Bioprosthetic valves (Table 16-2) use a ring of material attached to valves from
an animal source (e.g. porcine, bovine).
•
Bioprosthetics are less thrombogenic than MVPs.
Fewer disturbances in hemodynamics.
Less damage to cellular components of blood.
•
Bioprosthetics are less durable than MVPs and are more likely to require replacement for valve failure.
•
Homografts involve replacing aortic or pulmonary valves with donated human
valves.
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FIGURE 16-3. On-X ConformX Bileaflet Aortic Valve
Source: Photo reproduced with permission from Austin, TX: On-X Life Technologies.
TABLE 16-2: Types and Models of Bioprosthetic Valves
Type Models Example
Porcine Hancock I
Transcatheter aortic valve
replacement (TAVI, TAVR)
Hancock II
Intact
Carpentier-Edwards
Freestyle
Bicor
SAPIEN 3 Transcatheter Heart
Valve with Novaflex+ Delivery
System
CoreValve Evolut R TAVI
System
Hancock II valve
(see Figure 16-4)
SAPIEN 3 valve
(see Figure 16-5)
FIGURE 16-4. Hancock II Porcine Bioprosthetic Valve
Source: Used with permission. Copyright © 2016 Medtronic, Inc.
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FIGURE 16-5. SAPIEN 3 Transcatheter Heart Valve with
Novaflex+ Delivery System
Source: Used with permission from Edwards Lifesciences LLC, Irvine, CA. Edwards,
Edwards Lifesciences. Edwards SAPIEN, SAPIEN, SAPIEN XT, and SAPIEN 3 are
trademarks of Edwards Lifesciences Corporation.
•
Transcatheter aortic valve replacement (TAVR) utilizes a bioprosthetic tissue
valve compressed onto an expandable balloon that is inserted into the aortic
valve via catheter.
It may be preferable to open-heart procedures for patients who
are poor surgical risks.
It has been described as “valve-in-valve” because the TAVR is
inserted into the diseased valve, which is left in place.
It may be used to “replace” a diseased native valve, or
it may also be used for patients with a failed biopros
thetic valve.
Proprietary delivery systems are used to put the valve in place.
VALVE POSITION
•
Valve position influences thrombogenicity.
MVPs in mitral position appear to be more thrombogenic than
MVPs in the aortic position.
Annual TE rate with St. Jude Medical bileaflet valves
without antithrombotic prophylaxis
Aortic position: 12%
Mitral position: 22%
5-year TE event rate with Starr-Edwards valves
Aortic 35%
Mitral 70%
10
:
-
11
:
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Tricuspid valves are rarely replaced; however, they are the highest
risk valves when they are replaced.
•
Other factors such as multiple valve replacement and co-morbidities also influence thrombogenicity (Table 16-3).
TABLE 16-3: Other Risk Factors for Thrombosis and/or Total
Morbidity/Mortality
Co-Morbid
Condition
Aortic + mitral
valve replacement
Atrial fibrillation TE rate 1.6 x higher than patients with AVR in sinus rhythm, and long-term
Poor LV function/
heart failure
Left atrial
enlargement
Age >70 years 1.9 x higher incidence of stroke compared to patients <70 years.
History of prior TE Patients with history of pre-operative TE had 3.2 x risk for TE and 5.4 x risk
AVR: aortic valve replacement, LV: left ventricle, MVP: mechanical valve prosthesis, MVR: mitral
valve replacement, NYHA: New York Heart Association, TE: thromboembolic event
Effect(s) on Morbidity/Mortality
TE rate 2.4 x higher than AVR alone and 1.33 x higher than MVR alone.
9,12
Early mortality rate 3 x higher than AVR alone and 1.4 x higher than MVR
alone.
mortality rate 2.2 x higher.
Patients with NYHA IV heart failure were 10.7 x more likely to die within
5 years of aortic valve replacement with MVP compared with NYHA I-II.
13
13
3 x higher incidence of systemic embolism in patients with left atrial
dimension ≥4 cm compared with patients with left atrial dimension
14
<4 cm.
Higher risk of perioperative mortality.
17,18
Higher incidence of valve-related reoperation.
for repeated TE after AVR.
13
19
15-17
ANTITHROMBOTIC PROPHYLAXIS
Mechanical Valve Prostheses
•
Bridging for initiation of anticoagulation post-mechanical valve replacement:
American College of Cardiology (ACC)/American Heart Associa-
American College of Chest Physicians (ACCP): prophylactic dose
•
Choice of anticoagulant influenced by position, number of valves, and type of
valves:
Vitamin K antagonist (VKA) currently recommended (Table 16-4)
Target INR influenced by position(s) and number of valve replace-
Two studies (Table 16-5) suggest that certain specific valves or valve
tion (AHA): unfractionated heparin (UFH) or low molecular weight
heparin (LMWH)
UFH, or prophylactic or therapeutic dose LMWH
18,19
6
over antiplatelet agents alone or DOACs.
ments.
types may be treated with a lower INR than current guidelines.
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TABLE 16-4: Summary of ACC/AHA and ACCP
Recommendations
Condition ACC/AHA
AVR
Agent(s)
18,19
ACCP
6
VKA Preferred over antiplatelet
agents alone
Target INR 2.5 (range 2–3) for bileaflet
or current-generation single
tilting disc and no risk factors
3 (range 2–3) if additional risk
factors* or older generation
valves (e.g., caged-ball)
Aspirin Added to VKA Added to VKA, if low risk of
Aspirin Dose 75–100 mg/day 50–100 mg/day
MVR
Agent(s)
VKA Preferred over no VKA or
antiplatelet agents alone
Target INR 3 (range 2.5–3.5) 3 (range 2.5–3.5)
Aspirin Added to VKA Added to VKA, if low risk of
Aspirin Dose 75–100 mg/day 50–100 mg/day
AVR and MVR
Agent(s)
Preferred over no VKA or
antiplatelet agents alone
2.5 (range 2–3) for all valves
bleeding**
Preferred over no VKA or
antiplatelet agents
bleeding**
VKA Preferred over no VKA or
Target INR 3 (range 2.5–3.5) 3 (range 2.5–3.5)
Aspirin Added to VKA Added to VKA, if low risk of
Aspirin Dose 75–100 mg/day 50–100 mg/day
*See Table 16-3. Patients should be considered high risk if they have one or more risk factors.
**ACCP: “Caution should be used in patients at increased bleeding risk, such as history of GI
bleeding.”
ACC: American College of Cardiology, ACCP: American College of Chest Physicians, AHA:
American Heart Association, AVR: aortic valve replacement, INR: international normalized ratio,
MVR: mitral valve replacement, VKA: Vitamin K antagonist
antiplatelet agents
Preferred over no VKA or
antiplatelet agents
bleeding**
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