Download Initial Clinical Experience with the HeartMate® II Axial

Clinical
Investigation
Initial Clinical Experience
with the HeartMate® II
Axial-Flow Left Ventricular
Assist Device
O.H. Frazier, MD
Courtney Gemmato, BS
Timothy J. Myers, BS
Igor D. Gregoric, MD
Brano Radovancevic, MD
Pranav Loyalka, MD
Biswajit Kar, MD
The redesigned HeartMate® II, an axial-flow left ventricular assist device, is simpler, smaller,
and easier to operate than are pulsatile pumps. These design characteristics should make
the HeartMate II more reliable and durable and broaden the eligible population base.
We implanted the HeartMate II in 43 patients (average age, 42 yr). The indication for
use was bridge-to-heart transplantation in 26 patients and destination therapy in 17.
The average duration of device support was 258 days (range, 1–761 days), and cumulative duration, more than 31 patient-years. Hemodynamic function improved in all patients
during support. By 48 hours after implantation, the mean cardiac index had increased from
1.9 ± 0.27 L/(min⋅m 2) (baseline) to 3.5 ± 0.8 L/(min⋅m2), and the pulmonary capillary wedge
pressure had decreased from 24.8 ± 11 mmHg to 18.5 ± 5.3 mmHg. Of the 43 patients,
35 were discharged from the hospital. Support is ongoing in 27 patients (longest duration,
>700 days). Nine patients died during support. Four patients had sufficient heart recovery
to undergo pump explantation. Three patients underwent transplantation. One patient underwent device replacement after the pump driveline was fractured in a skateboarding
accident; the device was removed in another patient because of a pump-pocket infection
after 749 days of support. Of the 10 patients in whom the HeartMate II replaced a failed
HeartMate I, 8 were discharged from the hospital.
We have seen excellent results with use of the HeartMate II. Functional status and
quality of life have greatly improved in patients who survived the perioperative period. (Tex
Heart Inst J 2007;34:275-81)
A
Key words: Axial flow
pump; cardiomyopathies;
equipment design; heartassist devices; HeartMate
II; hemodynamic processes
From: Department of Cardiac Transplantation and
Heart Failure, Texas Heart
Institute at St. Luke’s Episcopal Hospital, Houston,
Texas 77030
Address for reprints:
O.H. Frazier, MD,
Texas Heart Institute,
MC 3-114, P.O. Box 20345,
Houston, TX 77225-0345
E-mail: lschwenke@heart.
thi.tmc.edu
© 2007 by the Texas Heart ®
Institute, Houston
Texas Heart Institute Journal
xial-flow left ventricular assist devices (LVADs) have been under development for the past decade and are now being tested in clinical trials. These
devices are smaller and simpler than pulsatile pumps.1-4 Having only 1 moving component, no valves, and no vent or compliance chamber greatly reduces the
complexity of these pumps and should lead to better reliability than that shown by
the widely used implantable pulsatile pumps. Because of their small size, axial-flow
LVADs can be used in smaller patients, including children. Furthermore, the procedure for implantation is less invasive, which reduces operative complications such as
bleeding, infection, and thromboembolism.
The 1st design of the HeartMate® II (Thoratec Corp.; Pleasanton, Calif ) was used
in a European study beginning in February 2001. The study was halted early, in
2002, when it became evident that thrombosis related to the texturing of the internal blood-contacting surfaces was resulting in poor outcomes. Extensive experience
with the HeartMate I (IP and VE LVAS [left ventricular assist system]) had shown
that textured surfaces promote the development of a biocompatible tissue lining, thus
eliminating the blood–biomaterial interface.5 The proliferation of tissue on this surface within an axial-flow pump, however, narrows the blood-flow path already compromised by the design of the pump. This narrowing, combined with the low pressure
generated by the failing heart, may have contributed to primary pump thrombosis
in the European study. The textured surface in the HeartMate II pump housing was
eliminated, and clinical studies resumed in 2003 with the new design.
In November 2003, we were the first to implant the newly designed HeartMate II
pump.4 Since then, we have implanted the device in 42 additional patients. We have
completed the feasibility phase of the clinical trial and are enrolling patients in the
phase II pivotal trial. In this report, we describe our experience from both the pilot
Initial Clinical HeartMate II Experience
275
and pivotal trials with the first 43 patients supported by
the HeartMate II at the Texas Heart Institute (THI).
Methods
The HeartMate II is an axial-flow pump that is implanted through a median sternotomy with cardiopulmonary bypass (CPB) support. The surgical approach
is similar to that of the HeartMate I, except that the
subdiaphragmatic abdominal space required for pump
placement is considerably smaller than that for the
HeartMate I. Detailed descriptions of the HeartMate
II system and the implantation procedures have been
published.2-4 Once implanted, the pump sits just below
the left hemidiaphragm; the inflow cannula is within
the left ventricle and the outflow graft is anastomosed
to the ascending aorta (Fig. 1). The pump is powered by
a pair of lead-acid batteries or by a bedside power base
unit. The microprocessor-based system controller, worn
on a belt, maintains pump speed, monitors device function, and provides audible and visual alerts if system
problems occur. Because of the wearable design of this
system, patients are mobile and can live outside the hospital and resume their normal, daily activities.
We enrolled 43 patients with severe heart failure in
the study. There were 32 men and 11 women with a
mean age of 42 years (range, 14–73 yr), and a mean
body surface area (BSA) of 1.94 m2 (range, 1.50–2.47
m2). The indication for use was bridge-to-heart transplantation in 26 patients and destination therapy in 17.
The diagnosis was idiopathic cardiomyopathy in 30
patients and ischemic cardiomyopathy in 13. All patients gave informed written consent to participate in
the study. At the time of preoperative evaluation, all 43
patients were classified in New York Heart Association
(NYHA) functional class IV and were receiving optimal medical management in the hospital. Fourteen patients were being supported by an intra-aortic balloon
pump, and 6 patients had been supported by a TandemHeart percutaneous ventricular assist device (pVAD)
(CardiacAssist, Inc.; Pittsburgh, Pa) before receiving the
HeartMate II. The HeartMate II was placed in 10 patients after their HeartMate I devices failed (Table I).
Patients received routine, postimplantation medical
support after their operations; however, a more aggressive anticoagulation protocol was recommended after the
experience with pump thrombosis in the initial HeartMate II implants. A combination of heparin, warfarin,
aspirin, and dipyridamole is used for anticoagulation
and suppression of platelet function during HeartMate
II support (Table II). Once patients are stabilized and
become ambulatory, proper nutrition, rehabilitation,
and education become a focus of care. After discharge
from the hospital, patients return to our heart failure
clinic for routine follow-up at a decreasing frequency, depending on their needs. Serial echocardiographic studies are performed at regular intervals for inpatients and
outpatients to evaluate the adequacy of ventricular unloading.
Results
Fig. 1 The HeartMate II® consists of an implanted blood pump,
a microprocessor-based system controller, and a 12-volt power
supply. The pump lies below the left hemidiaphragm. The inflow conduit is placed within the left ventricle, and the outflow
graft is anastomosed to the ascending aorta. The electrical lead
(driveline) is tunneled subcutaneously and exits the right lateral
abdominal wall.
276
Initial Clinical HeartMate II Experience
Patient Support. The average duration of support
was 258 days (range, 1–761 days). Excluding perioperative and intraoperative deaths, the average duration
of support was longer than 300 days. The total duration of support was more than 31 patient-years. Of the
43 implanted patients, 35 (81%) survived the operation without significant complications and were discharged from the hospital in NYHA functional class
I. Protocol restrictions prevented our 1st patient from
being discharged until 167 days after pump implantation. All other HeartMate II recipients were discharged
a mean of 36 days (range, 14–106 days) after implantation. Three patients underwent heart transplantation after 175, 641, and 187 days of support. After 749
days of support, our 1st patient, whose device was implanted in November 2003, had the device explanted emergently because of a pump-pocket infection; he
underwent heart transplantation 4 months later. Support is ongoing in 27 patients (longest duration, >700
days).
Volume 34, Number 3, 2007
TABLE I. Patients’ Characteristics and Outcomes
LVEDD
(cm)
LV
Ejection
Fraction
Idiopathic
6.6
<0.15
IABP
1.69
749
Recovered
Idiopathic
6.8
0.20
—
2.12
641
Transplant
Pt.
No.
Age/Sex
Type CMP
Diagnosed
1
19/M
2
50/F
Previous
Type of
Support
Cardiac
Index
(L/[min⋅m2])
Duration of
Support
(days)
Outcome
3
49/M
Ischemic
6.7
<0.20
IABP
1.50
175
Transplant
4
14/M
Idiopathic
N/A
NA
IABP
1.40
761
Recovered
5
21/M
Idiopathic
6.1
<0.20
—
N/A
704
Ongoing
6
61/F
Idiopathic
6.6
<0.20
—
1.80
102
Died
Ongoing
7
29/M
Idiopathic
N/A
N/A
8
30/F
Idiopathic
5.3
0.25–0.29
IABP
2.20
592
HM XVE
N/A
568
9
41/M
Idiopathic
7.6
0.20
Ongoing
1.90
556
Ongoing
10
56/M
Ischemic
6.5
<0.20
IABP
N/A
128
Died
11
32/M
Idiopathic
8.6
<0.15
HM XVE
1.60
529
Ongoing
—
12
56/M
Ischemic
4.3
N/A
HM XVE
1.90
507
Ongoing
13
37/M
Idiopathic
5.3
0.25–0.29
IABP
1.54
347
Recovered
14
17/M
Idiopathic
6.3
<0.20
IABP
1.80
456
Recovered
15
60/M
Ischemic
6.2
N/A
HM XVE
N/A
444
Died
16
58/F
Ischemic
N/A
N/A
2.30
400
Ongoing
—
17
40/M
Idiopathic
6.4
N/A
HM XVE
N/A
1
18
50/M
Ischemic
8.1
<0.20
IABP
1.80
26
Died
19
70/M
Ischemic
6.8
<0.20
IABP
1.70
378
Ongoing
20
48/M
Ischemic
N/A
N/A
HM XVE
2.00
364
Ongoing
Died
21
47/M
Ischemic
6.6
<0.15
HM XVE
1.70
187
Transplant
22
48/M
Idiopathic
7.2
<0.20
IABP
1.80
309
Ongoing
23
37/M
Idiopathic
7.0
<0.20
HM XVE
N/A
1
Died
24
42/M
Idiopathic
7.6
<0.20
IABP
1.90
226
Ongoing
25
37/M
Idiopathic
8.1
<0.20
—
1.70
207
Ongoing
26
17/M
Idiopathic
N/A
N/A
IABP
1.31
177
Ongoing
27
49/F
Ischemic
6.5
0.20–0.24
—
1.92
171
Ongoing
28
34/M
Idiopathic
6.1
<0.20
—
1.80
169
Ongoing
29
44/M
Idiopathic
N/A
N/A
—
N/A
168
Ongoing
30
65/F
Ischemic
6.2
0.20–0.24
1.46
165
Ongoing
31
26/F
Idiopathic
8.3
<0.20
32
52/M
Ischemic
2.8
N/A
33
17/M
Idiopathic
5.2
0.20–0.29
34
58/M
Ischemic
6.4
0.20
TH
1.20
159
Ongoing
HM XVE
—
2.40
134
Ongoing
TH
1.27
120
Ongoing
IABP
2.28
113
Ongoing
35
73/M
Ischemic
5.8
0.20
—
1.67
4
36
50/M
Idiopathic
9.0
<0.15
IABP
1.80
101
Died
37
55/M
Ischemic
5.9
0.25–0.29
—
2.27
95
Died
38
29/F
Idiopathic
6.6
<0.20
—
2.87
94
Ongoing
39
15/M
Idiopathic
7.2
<0.15
—
N/A
93
Ongoing
40
34/M
Idiopathic
4.6
N/A
—
N/A
80
Ongoing
Ongoing
Ongoing
41
61/F
Idiopathic
5.8
<0.20
HM XVE
2.10
66
42
59/F
Idiopathic
7.4
<0.20
IABP
2.89
21
Died
43
30/M
Idiopathic
6.3
0.20
—
2.70
16
Ongoing
CMP = cardiomyopathy; HM XVE = HeartMate vented-electric left ventricular assist system; IABP = intra-aortic balloon pump;
LV = left ventricular; LVEDD = left ventricular end-diastolic diameter; N/A = not available; TH = TandemHeart
All patients were initially in New York Heart Association (NYHA) functional class IV.
Texas Heart Institute Journal
Initial Clinical HeartMate II Experience
277
Nine patients died while receiving device support.
Five patients died during the early postoperative period because of a combination of right-sided heart failure,
multisystem organ failure, and bleeding complications.
In a 6th patient, bleeding associated with small-bowel
arteriovenous malformations necessitated the discontinuation of all anticoagulation and antiplatelet therapy.
Although the pump flow was adequate for circulatory
support, the patient’s left ventricular dimensions were
not reduced by the pump. Poor myocardial contractility
resulted in a lack of aortic valve opening and thrombus
generation in the non-coronary sinus (Fig. 2). The patient developed ventricular arrhythmias and, eventually,
ventricular fibrillation. The thrombus embolized during
cardiac massage for resuscitation and caused neurologic
death. The 7th patient who died had severe, generalized
atherosclerotic vascular disease, coronary artery occlusive disease, and diabetes. She had been discharged but
was readmitted 125 days after implantation because of
a transient ischemic attack with minimal neurologic residual effects. To avoid further arterial blockage, systemic anticoagulation with heparin was administered.
The next day, she became obtunded, with progressive
neurologic deterioration, and studies showed a massive
hemorrhagic stroke. Support was discontinued. Two patients experienced sudden death at home at 326 and 81
days. Although autopsies were performed, no obvious
cause of death was determined in either patient. Both
pumps appeared to be functioning normally at the time
of death.
The postimplant course has been uncomplicated in
the 34 remaining patients, all of whom are in NYHA
TABLE II. Anticoagulation Guidelines
Before leaving the operating room, completely reverse
anticoagulation.
• Optional: Postimplantation, as early as possible, administer
10% low-molecular-weight dextran (25 mL/hr)
Begin intravenous heparin after 12–24 hours or when chest
tube drainage is <50 mL/hr:
• Initially titrate to a partial thromboplastin time (PTT) of
45–50 sec for 24 hours (1.2–1.4 times control)
• Then increase heparin to a target PTT of 50–60 sec
(1.4–1.7 times control)
• After another 24 hours, increase heparin to a target PTT of
55–65 sec (1.5–1.8 times control)
Postoperative days 2 to 3:
• Initiate aspirin (81–100 mg, once/day) and dipyridamole
(75 mg, 3 times/day).
Postoperative days 3 to 5, once there is no evidence of
bleeding and the chest tubes are removed:
• Initiate warfarin administration (concurrent with heparin)
• Discontinue heparin administration after obtaining an
acceptable, stable international normalized ratio (INR)
• Maintain INR in the range of 2.0–3.0
Keep patients on aspirin, dipyridamole, and warfarin
throughout the duration of support.
278
Initial Clinical HeartMate II Experience
Thrombus in Aorta
Fig. 2 Echocardiogram shows thrombus in the non-coronary
sinus of a patient with persistent gastrointestinal bleeding, in
whom all anticoagulant therapy was discontinued. This patient
never developed aortic valve opening and is the only patient to
have experienced thrombotic complications in this series.
Real-time
motion
are available
at texasheart.org/journal
Click here
forimages
real-time
motion
image: Fig. 2.
functional class I. In 1 patient, the HeartMate II device
was exchanged on an emergency basis after the pump
driveline was fractured in a skateboarding accident 6 ;
the patient was discharged 1 week later. Eight of the 10
HeartMate I to II pump-exchange patients have been
discharged and are doing well. The other 2 pumpexchange patients died during the perioperative period,
one of bleeding and the other of diffuse intravascular
clotting that was thought to be secondary to factor VII
administration. Our current method of pump exchange
is via subcostal incision alone; with this approach, patients have experienced rapid postoperative recovery and
none have died. Superficial driveline infections occurred
in 3 patients; 2 of these were treated successfully with
local wound care. However, the superficial infection in
our 1st implant patient from 2003 was never satisfactorily controlled and worsened with the patient’s weight
gain (>13 kg). Eventually a pump-pocket infection developed, and the device had to be removed more than 2
years after the initial implantation.
Hemodynamic and Echocardiographic Evaluation. Hemodynamic function improved from preoperative levels
in all patients during support with the HeartMate II. By
48 hours after device implantation, the average cardiac
index had increased significantly, from 1.9 ± 0.27 to 3.5
± 0.8 L/(min⋅m2), and the pulmonary capillary wedge
pressure had decreased significantly, from 24.8 ± 11 to
18.5 ± 5.3 mmHg. Inotropic support was reduced after
implantation, and all patients were weaned within the
1st week. Serial echocardiographic studies showed improvement in left ventricular dimensions. The average
left ventricular diastolic dimension decreased by 16%
(from 6.7 cm to 5.6 cm) 1 month after implantation.
Hematology. All 43 patients received a combination of
heparin, warfarin, aspirin, and dipyridamole as anticoagulant therapy to achieve an international normalized
Volume 34, Number 3, 2007
ratio between 2.5 and 3.5 during support. Anticoagulation was temporarily discontinued in 1 patient because
of gastrointestinal bleeding from arteriovenous malformations. Eighteen devices were explanted: 3 after successful bridging to transplantation, 4 after recovery of
native heart function sufficient to warrant pump explantation, 1 after damage in a skateboarding accident,
1 for pump-pocket infection, and 9 post mortem. None
of the removed devices showed evidence of thrombus.
No bearing wear was detected in any of the explanted
pumps. Two pumps had been operational longer than
2 years. In the 35 patients who were discharged, hemoglobin, hematocrit, and end-organ function had reached
normal levels by the time of discharge and remain normal in all current outpatients. Hemolysis was seen in
the patient who had gastrointestinal bleeding and aortic thrombosis but has not been observed in the other
surviving patients.
HeartMate II System Operation. The technical performance of the HeartMate II has been excellent, and
patients have been extremely satisfied with the small,
quiet pump. An overall Kaplan-Meier survival rate of
80% has been gratifying in this very ill patient cohort
(Fig. 3).
Before discharge, all patients were trained in the care
and use of their equipment and batteries. The patients
participated in a physical rehabilitation program that
comprised graduated ambulation within the hospital
and treadmill exercise under observation. The speed
setting of the treadmill was predetermined by use of
echocardiographic studies to determine the degree of
unloading and exercise tolerance. Life-threatening arrhythmias, possibly generated by contact of the intraventricular cannula with the endocardium, developed
in 3 patients.
No device malfunction or system problem has been
seen in the outpatient setting. In our 1st patient, the device was removed after 749 days of use, and physical examination of the pump showed no wear of the bearing.
Moreover, measurements of function showed no difference in technical operation of the pump before implantation and after explantation (Fig. 4).
A
B
Fig. 4 Photographs of the inlet bearing’s ball (A) and cup (B) of
a HeartMate II removed 749 days after implantation in the 1st
patient of our series. Radial score marks are visible on the ruby
ball but are considered normal for all pumps after initial bearing
wear-in. No physical wear of the bearing was detected. Test
measurements of operation for this pump were identical before
implantation and after explantation.
Discussion
Fig. 3 Kaplan-Meier survival curve for the HeartMate II patients
at 1 year (n=43).
Texas Heart Institute Journal
Our initial experience with the redesigned HeartMate
II at THI has been favorable and has shown this model
to be safe, durable, and effective. This implantable axialflow pump evolved from a prototype, originally developed by the Nimbus Corporation in the early 1990s.
Richard Wampler, then an employee of Nimbus, demonstrated that effective, short-term circulatory support
was possible with a small axial-flow pump operating at
25,000 rpm (the Hemopump). The Hemopump was
first used clinically at THI in 1988.3 Enlargement and
modification of the original Hemopump, combined
with the addition of blood-lubricated bearings, culmiInitial Clinical HeartMate II Experience
279
nated in the development of the long-term, implantable
pump described in this report—the HeartMate II.
After modifications to the initial clinical pump, the
current HeartMate II design was finalized and pump
implantations began at our institution in 2003.4 The
technical function of this design has been excellent.
We have seen no pump failures or operational problems with this technology to date. In our experience, the
Jarvik 2000, another axial-flow pump, has shown reliability and durability for more than 6 years, and studies are ongoing. The HeartMate II has a similar pump
design and the potential for comparable long-term efficiency.
In this series, 35 of 43 patients were discharged from
the hospital, and problems with the HeartMate II system have been minimal. Arrhythmias have been noted,
particularly if the patient becomes volume depleted
or if the pump’s unloading of the ventricle is excessive
(Fig. 5). Lowering the rpm and ensuring adequate volume status, especially during the postoperative period,
can resolve this issue. Our patient group differs slightly from the typical bridge-to-transplant population, because our patients were younger (mean age, 42 years vs
50–62 years in other studies) and were small (with a
mean BSA, 1.94 m2; range, 1.42–2.57 m2).7-9 The small
size and reduced weight of this technology have enabled
us to implant this device in more women who have terminal heart failure. Women, because of their comparatively small size, have heretofore received limited benefit
from the larger pulsatile pumps. Younger, smaller patients can also benefit. Our 3 youngest patients to receive the HeartMate II were 14, 15, and 17 years old at
pump implantation.
The introduction of continuous-flow left ventricular assist devices has created a new physiology of cardiac support. This technology has definitively shown
that ambulatory, effective circulatory support can be
achieved long-term in patients with advanced heart failure who require cardiac support, even when they do not
have a detectable pulse. However, by changing the internal physiology, this therapy introduces physiologic
Fig. 5 Increasing pump speed associated with ventricular
arrhythmias may be caused by contact of the cannula with
the endocardium.
280
Initial Clinical HeartMate II Experience
phenomena and accompanying clinical problems, such
as arteriovenous malformations leading to gastrointestinal bleeding, septal shift with resultant right-sided
heart failure, thrombosis of the aortic valve noncoronary sinus, aortic valve fusion, and aortic valve insufficiency. These problems are medically manageable, but
physicians must be aware of them when applying this
life-saving technology.
We pay particular attention to the proper level of anticoagulation and to the measurement and control of
blood pressure in patients without a detectable pulse.
To date, experience with these pumps in a limited patient population has suggested an increased incidence
of hemorrhagic stroke. This may be related to the difficulty of properly monitoring blood pressure due to the
absent or dampened pulse imparted by this technology.
If hypertension is present but not easily measurable, inadequate pharmacologic control of blood pressure may
result, in turn subjecting these patients to an increased
risk of hypertensive hemorrhagic stroke. An additional
concern is that the altered stress on the aortic valve may
result in valve leaflet fusion and aortic insufficiency and
stenosis. This has been reported in patients with pulsatile assist pumps, but we have also seen this problem in
patients with continuous-flow pumps.10
Our initial experience with the 43 patients described
here has been favorable. We are encouraged by our results with the use of the redesigned HeartMate II in the
treatment of patients with advanced heart failure. We
believe that this small, axial-flow blood pump is durable and safe and will offer an extended, improved quality of life for critically ill heart failure patients of varying
sizes and clinical statuses.
References
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Croitoru M, et al. Initial clinical experience with the Jarvik
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2. Burke DJ, Burke E, Parsaie F, Poirier V, Butler K, Thomas
D, et al. The Heartmate II: design and development of a fully
sealed axial flow left ventricular assist system. Artif Organs
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J, et al. Replacement of a malfunctioning HeartMate II left
Volume 34, Number 3, 2007
ventricular assist device in a 14-year-old after a sudden fall. J
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7. Salzberg S, Lachat M, Zund G, Oechslin E, Schmid ER, DeBakey M, Turina M. Left ventricular assist device as bridge
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8. McCarthy PM, James KB, Savage RM, Vargo R, Kendall K,
Harasaki H, et al. Implantable left ventricular assist device. Approaching an alternative for end-stage heart failure. Implantable
LVAD Study Group. Circulation 1994;90(5 Pt 2):II83-6.
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9. Jaski BE, Kim JC, Naftel DC, Jarcho J, Costanzo MR, Eisen
HJ, et al. Cardiac transplant outcome of patients supported on
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Heart Lung Transplant 2001;20:449-56.
10. Connelly JH, Abrams J, Klima T, Vaughn WK, Frazier OH.
Acquired commissural fusion of aortic valves in patients with
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