Download Thirty-Five Years of Mechanical Circulatory Support at the Texas

Review
Thirty-Five Years of
Mechanical Circulatory
Support at the
Texas Heart Institute
An Updated Overview
Courtney J. Gemmato, BS
Matthew D. Forrester, BS
Timothy J. Myers, BS
O.H. Frazier, MD
Denton A. Cooley, MD
Since the 1960s, the Texas Heart Institute has been intimately involved in the development of mechanical circulatory support devices (for example, ventricular assist devices,
aortic counterpulsation pumps, and total artificial hearts) for both short- and long-term
use. Here, we review the varied clinical experience with these technologies at the Texas
Heart Institute over the last 35 years. (Tex Heart Inst J 2005;32:168-77)
The human heart, about the size of a man’s fist,
pumps enough blood in the course of a lifetime to fill
the Rose Bowl. The wonderful thing about the heart
is that it replenishes itself. To duplicate that mechanically is going to be a very difficult thing to do.
— Denton A. Cooley, MD*
R
Key words: Equipment
design; heart, artificial;
heart-assist devices; heart
failure, congestive; heart
transplantation; history of
medicine, 20th cent.;
mechanical circulatory
support
From: The Cardiovascular
Research Laboratories,
Texas Heart Institute at St.
Luke’s Episcopal Hospital,
Houston, Texas 77030
Address for reprints:
O.H. Frazier, MD, Texas
Heart Institute, MC 2-114A,
P.O. Box 20345, Houston,
TX 77225-0345
E-mail:
[email protected]
© 2005 by the Texas Heart ®
Institute, Houston
168
eplacing the failing human heart has had a turbulent history. The 1st
human-to-human heart transplantation, performed by Christiaan Barnard
in 1967,1 marked an exciting advance in cardiac surgery. It revealed to the
medical community at large and to the public that failing hearts could be replaced,
at least technically, with healthy ones. However, the initial excitement was quickly
overshadowed by the difficulty of managing the attendant immunosuppressive
complications. By the early 1970s, only 4 institutions in the world were still
performing cardiac transplantation.2 Heart transplantation was reintroduced to a
broader surgical population with the advent of the new immunosuppressive agent
cyclosporine in the early 1980s.3 This agent spared the nonspecific immune system and allowed the possibility of performing transplantation in patients who required support with mechanical circulatory support (MCS) devices. Before this,
3 patients supported with an MCS device as a bridge to transplant—two with an
artificial heart and one with a left ventricular assist device (LVAD)—had died of
overwhelming sepsis due to generalized immunosuppression while receiving azathioprine. In March 1984, Frazier performed cardiac transplantation in a young
woman who was septic with Staphylococcus aureus and Candida albicans at the time
of transplantation. In spite of overwhelming sepsis, she survived the transplantation and was ultimately discharged safely from the hospital.4 This experience,
which showed that successful cardiac transplantation was feasible with cyclosporine
use even in severely infected patients, stimulated research into the eventually successful use of MCS devices as a bridge to transplantation.
In 1966, DeBakey reported the 1st successful use of a ventricular assist device
(VAD) for postcardiotomy support in a patient who was supported by the device
for 10 days.5 In 1969, Cooley became the first to implant an artificial heart (which
was designed by Liotta) in a human being6 (Table I). Since the 1960s, the Texas
Heart Institute (THI) has been involved in the development of other MCS devices, including univentricular and biventricular devices, aortic counterpulsation
*Oral communication to M.D. Forrester; 26 June 2001.
Mechanical Circulatory Support at THI
Volume 32, Number 2, 2005
TABLE I. Summary of Mechanical Circulatory Support Systems Used at Texas Heart Institute
Year First
Used
Clinically
at THI
Device
Total No.
Patients
Supported
at THI
Original
Intended Use
FDA
Regulatory
Status
Liotta artificial heart
1969
1
Bridge to transplant
N/A
Akutsu model III artificial heart
1981
1
Bridge to transplant
N/A
TECO model VII ALVAD
1975
22
Postcardiotomy support
N/A
Jarvik-7 TAH
1986
2
Bridge to transplant
N/A
Hemopump
1988
43
Cardiogenic shock
N/A
HeartMate IP LVAS
1986
87
Bridge to transplant
PMA granted 1994
HeartMate VE/XVE LVAS
1991
141
Bridge to transplant;
destination therapy
PMA granted 1998
Thoratec® PVAD
1987
89
Bridge to transplant;
postcardiotomy support
PMA granted 1995
HeartMate® II LVAS
2003
8
Bridge to transplant
IDE approved 2003
Jarvik 2000 Heart LVAD
2000
54
Bridge to transplant
IDE approved 2000
AbioCor™ TAH
2001
5
Destination therapy
IDE approved 2000
ABIOMED BVS 5000 VAD
1988
63
Postcardiotomy support;
bridge to transplant
PMA granted 1993
ABIOMED AB5000™ VAD
2003
22
Postcardiotomy support;
bridge to transplant
PMA granted 2003
TandemHeart® pVAD™
2003
21
High-risk PTCA support;
cardiogenic shock
IDE approved 2002
Levitronix® CentriMag® VAD
2003
17
Postcardiotomy support
IDE approved 2003
®
®
®
ALVAD = abdominal left ventricular assist device; FDA = Food and Drug Administration; IDE = investigational device exemption;
LVAD = left ventricular assist device; LVAS = left ventricular assist system; PMA = premarket approval; PVAD = paracorporeal ventricular assist device; pVAD = percutaneous ventricular assist device; TAH = total artificial heart; VAD = ventricular assist device
pumps, and total artificial hearts (TAHs). Historically, these devices were used to provide short-term support for patients in cardiogenic or postcardiotomy
shock or as a bridge to transplantation. More recently,
they have come to be used to provide support during
high-risk interventional procedures, as a bridge to recovery, or as destination therapy. Here, we review the
varied clinical experience with these technologies at
THI over the last 35 years.
Historical Use of Mechanical Circulatory
Support at the Texas Heart Institute
Since 1969, VADs or TAHs have been implanted in
576 patients at THI. An abdominal left ventricular
assist device (ALVAD), the TECO Model VII (Thermo Electron Corp.; Waltham, Mass), was used to support 22 patients between 1975 and 1980.7 The Akutsu
model III artificial heart, developed at THI, was implanted in 1 patient in 1981.8 The Jarvik-7 TAH, designed at the University of Utah College of Medicine
and first implanted by DeVries at the University of
Texas Heart Institute Journal
Utah in 1982, was used at THI in 2 patients in 1986.9
In 1988, the Hemopump (Johnson & Johnson Interventional Systems; Rancho Cordova, Calif ) was first
used at THI by Frazier and colleagues10 and was ultimately implanted in 43 patients over the next 5 years.
Current Era of Mechanical Circulatory
Support at Texas Heart Institute
Long-Term Support Devices
Long-term MCS devices are used as a bridge to transplant, as a bridge to recovery, or as destination therapy.
Currently at THI, 6 systems are being used clinically
for long-term MCS. These include 5 VADs and a totally implantable artificial heart. Three of these systems
are commercially available and 3 are investigational.
HeartMate® IP. The HeartMate implantable pneumatic left ventricular assist system (HeartMate IP
LVAS, Thoratec Corp.; Pleasanton, Calif ) (Fig. 1) is a
pulsatile blood pump that provides left ventricular support. The HeartMate IP is used in patients as a bridge
Mechanical Circulatory Support at THI
169
Fig. 1 HeartMate® implantable pneumatic (IP) left ventricular assist system. (Courtesy of Texas Heart Institute)
to transplant or bridge to recovery. The system consists
of a pusher-plate blood pump, an interconnecting
drive line, and an external drive console.11,12 The pump
is positioned in the upper left abdominal quadrant, either intraperitoneally or preperitoneally. A percutaneous drive line attached to an external console delivers
pulses of air that cause the pusher-plate and diaphragm
to eject blood from the pump. A sensor, located in the
lower housing of the blood pump, monitors the position of the diaphragm in order to determine the stroke
volume. The pump can produce a stroke volume of 83
mL and flows of up to 11.5 L/min.
The Texas Heart Institute has been involved in research and development of the HeartMate LVAS
technology for more than 30 years. In 1978, the 1st
clinical trial of a predecessor of the HeartMate, the
Model 7 LVAD, was initiated in 20 postcardiotomy
patients at THI. The 1st clinical trial of the HeartMate IP LVAS began in 1986, also at THI. The initial trial was expanded to 17 centers in the late 1980s
and early 1990s. In 1994, the US Food and Drug Administration (FDA) granted marketing approval for
the HeartMate IP LVAS as a bridge to transplant. The
HeartMate IP LVAS has been implanted in 87 patients at THI. Since the development of an electrically driven version of the HeartMate (described below),
use of the pneumatic version at THI has decreased
considerably. Nevertheless, our experience has demonstrated that the HeartMate IP LVAS is highly reliable for extended periods.
HeartMate® VE and XVE. The HeartMate vented
electric LVAS (HeartMate VE LVAS; Thoratec Corp.)
170
Mechanical Circulatory Support at THI
and an improved version called the HeartMate extended vented electric LVAS (HeartMate XVE LVAS)
(Fig. 2) are very similar to the HeartMate IP LVAS.
The major difference between the IP device and the
VE devices is the method of actuation.12,13 The HeartMate XVE is driven by an internal motor that requires
12 V of direct-current power. The motor controls the
pusher-plate and diaphragm within the pump. This
system is used as a bridge to transplant, as a bridge to
recovery, and as destination therapy. A percutaneous
drive line attaches to a controller, which connects to a
power base unit. The drive line also has a percutaneous vent tube, the purpose of which is to equalize
the pressure in the motor chamber.12 The HeartMate
XVE can be powered for short periods (4–6 hours) by
portable batteries, thus providing a distinct advantage
over the pneumatic version and allowing more patient
mobility.
Clinical trials of the HeartMate VE as a bridge to
transplant began in 1991. This was the 1st device that
allowed untethered patients to be discharged in order
to return home and, in some cases, return to work,
while awaiting transplantation.14,15 The FDA approved
the HeartMate VE as a bridge to transplant in 1998
and approved the HeartMate XVE LVAS for the same
purpose in 2001. In light of the encouraging results of
the multicenter REMATCH trial,16 which compared
LVAD therapy and optimal medical management in
patients ineligible for cardiac transplantation, the FDA
approved another slightly modified version of the
pump, the HeartMate® SNAP-VE, as destination therapy. In 2003, the HeartMate XVE LVAS was also apVolume 32, Number 2, 2005
proved by the FDA as destination therapy. The HeartMate VE or XVE LVAS has been implanted in 141
patients at THI.
Thoratec® PVAD. The Thoratec paracorporeal ventricular assist device (PVAD) system (Thoratec Corp.)
(Fig. 3) is a pneumatically driven pump that can provide either univentricular or biventricular support.17
Fig. 2 HeartMate® extended vented electric (XVE) left
ventricular assist system. (Courtesy of Texas Heart Institute)
Indications for the Thoratec PVAD include acute
heart failure, postcardiotomy shock, and bridge to
transplant in cases of end-stage heart failure refractory
to maximal medical therapy. The system consists of a
blood pump, inflow and outflow cannulas, and a drive
console. The external pump and the cannulas rest on
the abdomen and connect to the drive console via
pneumatic and electric drive lines. The pneumatic console provides alternating negative and positive air pressure that cause the pump’s blood sac to fill and eject
blood.18 The pump can produce a stroke volume of 65
mL and flows of up to 7 L/min.
Clinical trials with the Thoratec PVAD began in
1976, and the FDA granted marketing approval in
1995. In 1997, THI began using the Thoratec PVAD
in patients requiring right-, left-, or both-sided support for either short or long periods of time. The Thoratec PVAD has been implanted in 89 patients at THI.
HeartMate® II. The HeartMate II left ventricular
assist system (Thoratec Corp.) (Fig. 4) is an implantable axial-flow blood pump that provides left ventricular support. It is used as a bridge to transplant. The
system consists of a blood pump, a system driver, a
power base unit, and portable batteries. The blood
pump contains a single moving rotor powered by an
electromagnetic motor. A drive line, tunneled through
the patient’s abdomen, connects to the system driver,
which controls the motor. This system uses the same
power base unit and portable batteries as does the
HeartMate XVE. The HeartMate II has an operating
range of 6,000–15,000 rpm and provides up to 10 L/
min of continuous cardiac output.18
Fig. 3 Thoratec ® paracorporeal ventricular assist device (PVAD) system. (Courtesy of Texas Heart Institute)
Texas Heart Institute Journal
Mechanical Circulatory Support at THI
171
The Nimbus Corporation began development of
the HeartMate II in 1991. The internal components
of the device were based on those of the Hemopump
—the implantable, catheter-mounted axial-flow pump
that was first applied clinically at THI in 1988 but is
no longer used. The bearings of the HeartMate II are
blood lubricated. The 1st clinical trials were initiated
in Europe in June 2000. The initial clinical experience
was unfavorable and led to several design changes. The
FDA allowed the clinical trial to start again in 2003.
The 1st clinical use of the redesigned HeartMate II was
at THI in November 2003 in an 18-year-old man who
had dilated cardiomyopathy. The patient was successfully rehabilitated and was discharged in April 2004
after the FDA granted permission for study patients to
be discharged home to await transplant. The HeartMate II has been implanted in 8 patients at THI and
in a total of 42 patients in the United States. Preliminary results indicate that the problems encountered in
the initial trial may have been resolved.
Jarvik 2000. The Jarvik 2000 Heart left ventricular
assist device (Jarvik Heart, Inc.; New York, NY) (Fig.
5) is an implantable axial-flow pump used for longterm support as a bridge to transplant. The system
consists of a blood pump, an external controller, and
portable batteries. The blood pump is approximately
the size of a C-cell battery and has a single moving impeller in the center of a titanium housing. A power
cable, tunneled through the abdomen of the patient,
connects to the external controller. Lead acid or lithium ion batteries provide power to the pump. The
pump’s operating range is 8,000–12,000 rpm, which
can be manually adjusted to provide up to 6 L/min of
continuous flow under optimal physiologic conditions.19 The Jarvik 2000 can be surgically implanted
Fig. 4 HeartMate® II left ventricular assist system. (Courtesy
of Thoratec Corp.)
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Mechanical Circulatory Support at THI
Fig. 5 Jarvik 2000 Heart left ventricular assist device. (Courtesy of Texas Heart Institute)
via a midline sternotomy, left thoracotomy, or subcostal (nonthoracic) approach. The various surgical
approaches and the small size of the device allow it to
be implanted in patients who may not be candidates
for support by other LVADs.
Jarvik Heart, Inc., and THI began development of
the Jarvik 2000 in 1988. Clinical trials of the Jarvik
2000 as a bridge to transplant began in April 2000. In
2003, the FDA granted permission for patients in that
study to be discharged home to await transplant. The
Jarvik 2000 has been implanted in 54 patients at
THI. Twelve of these patients have been discharged,
and one of them has been supported by the device for
more than 2 years.
AbioCor™ Total Artificial Heart. The AbioCor TAH
(ABIOMED, Inc.; Danvers, Mass) (Fig. 6) is a permanently implantable replacement heart system that provides total circulatory support. The AbioCor TAH is
currently implanted in patients who are ineligible for
heart transplant, have a 30-day predicted mortality of
greater than 70% despite maximal medical therapy,
and have no other suitable treatment options.
The AbioCor system consists of 4 internal components and 4 external components.20 The internal
components include the thoracic unit, a battery, a
controller, and a transcutaneous energy transfer (TET)
coil. The external components include a TET coil,
batteries, a TET module, and a bedside console. The
Volume 32, Number 2, 2005
Fig. 6 AbioCor™ total artificial heart. (From: Cohn LH, Edmunds
LH Jr. Cardiac Surgery in the Adult. 2nd ed. New York: McGrawHill; 2003. p. 1512. Published with permission of The McGrawHill Companies.)
thoracic unit consists of an energy converter and 2
pumping chambers that function as the left and right
ventricles. Power is provided to the thoracic unit, and
the device’s internal battery is recharged transcutaneously, by electromagnetic coupling of the internal and
external TET coils. The internal TET is positioned
under the skin in the upper left or right chest. The
external TET is attached with an adhesive to the skin
above the internal TET and then connected to the
bedside console. Alternatively, power can be supplied
to the AbioCor TAH by a pair of portable batteries
for up to 60 min. Thus, recipients of the AbioCor
TAH may be fully ambulatory. The pump’s motor operates at 3,000–10,000 rpm and can generate a flow
of up to 8 L/min.20 One disadvantage of the device is
its large size, which limits its use in smaller patients
such as women, small men, and children. A smaller
version is being developed.21
Researchers at THI participated in preclinical trials of the AbioCor TAH from 1993 to 2000. During
this period, the AbioCor went through several design
changes and was implanted experimentally in 43 calves.
In January 2001, the FDA granted permission to begin
a multicenter clinical trial of the AbioCor TAH with
15 patients. The Texas Heart Institute is one of 5 centers participating in this initial trial. Five patients at
THI and 14 patients overall have received the AbioCor
TAH. The longest surviving recipient at THI was supported by the device for 142 days. The longest surviving recipient overall was supported for 512 days.
Short-Term Support Devices
Short-term circulatory assistance is often used to support patients in cardiogenic shock or postcardiotomy
shock, to provide protection during high-risk procedures, or to serve as a bridge to definitive therapy.
Four short-term devices are currently in clinical use at
THI.
BVS 5000®. The BVS 5000 VAD (ABIOMED, Inc.)
(Fig. 7) is a pneumatically driven, pulsatile, extracorporeal, asynchronous pump that can be used for
short-term left ventricular, right ventricular, or biventricular support.22 The device is used primarily as a
bridge to recovery in patients who have exhausted all
other medical therapeutic options. The BVS 5000
Fig. 7 ABIOMED BVS 5000® circulatory support system. (Courtesy of Texas Heart Institute)
Texas Heart Institute Journal
Mechanical Circulatory Support at THI
173
system consists of a dual-chamber blood pump, cannulas, and a drive console. The device is positioned at
the patient’s bedside and fills passively by gravity. A
bladder within the ventricular chamber is collapsed
by pulsed air delivered through drive-line tubing connected to the external console. The BVS 5000 can
produce a stroke volume of 80 mL and flows of up to
6 L/min. Clinical trials of the BVS 5000 as treatment
for cardiogenic shock began at THI in 1988. The
FDA granted marketing approval of the BVS 5000 as
a postcardiotomy support device and as a bridge to
transplant in 1993. The BVS 5000 has been implanted in 63 patients at THI.
AB5000™. The AB5000 circulatory support system
(ABIOMED, Inc.) is similar to the BVS 5000 in that it
uses the same drive console and tubing, but different
in that its prosthetic ventricle consists of a membrane
and 2 trileaflet valves. The indications for its use are
the same as those for the BVS 5000. Like the BVS
5000, the AB5000 can produce a stroke volume of 80
mL and flows of up to 6 L/min. In 2003, the FDA
granted marketing approval for use of the AB5000
device as postcardiotomy support and as a bridge to
transplant. The Texas Heart Institute is one of 20 centers where the device is now being used clinically. The
AB5000 has been implanted in 22 patients at THI.
TandemHeart® pVAD™. The TandemHeart pVAD
(CardiacAssist, Inc.; Pittsburgh, Pa) (Fig. 8) is a percutaneous, continuous-flow, left ventricular assist device that provides short-term circulatory support. The
TandemHeart is used as support during cardiogenic
shock, as a bridge to long-term MCS, and for support
during high-risk percutaneous coronary interventions. The system consists of a small blood pump,
transseptal and arterial cannulas, and a power base
controller. The pump contains a magnetically driven
rotor supported by a fluid-lubricated hydrodynamic
bearing. The TandemHeart can be inserted percutaneously in the cardiac catheterization laboratory or
surgically in the operating room. The TandemHeart
pVAD typically operates at speeds of 3,000–7,500
rpm and can provide a continuous flow of up to 4.0
L/min.
Development of the TandemHeart began in 1991.
In 2002, THI was one of 17 study sites that began enrolling patients in a phase II randomized clinical trial.
In July 2003, the FDA granted a 510(k) exemption
approving off-study use of the TandemHeart for up
to 6 hours in patients who did not meet the study
entry criteria. Three patients were enrolled in the trial,
and 18 others have been supported by the device under the 510(k) exemption at THI.
Levitronix® CentriMag®. The Levitronix CentriMag
(Levitronix LLC; Waltham, Mass) (Fig. 9) is a continuous-flow left ventricular assist device with a magnetically levitated impeller. It can provide circulatory
174
Mechanical Circulatory Support at THI
Fig. 8 TandemHeart ® percutaneous ventricular assist device.
(Courtesy of CardiacAssist, Inc.)
Fig. 9 Levitronix ® CentriMag ® left ventricular assist device.
(Courtesy of Levitronix LLC)
Volume 32, Number 2, 2005
support for up to 14 days in patients in cardiogenic
shock. The system consists of a small blood pump,
cannulas, a magnetic motor, and a bedside controller.
An advantage of this device is that it can be attached
to cardiopulmonary bypass cannulas already in place.
The Levitronix CentriMag system is capable of delivering 9.9 L/min of flow at 5,500 rpm. The Texas
Heart Institute is one of 5 study sites that is now enrolling patients in a phase I clinical trial that began in
2003. Four patients at THI have been enrolled in the
trial, and 13 patients have received the device under a
510(k) exemption.
Discussion
The 1st implantation of an artificial heart by Cooley
at THI was a last resort to prolong the life of a dying
man. After an extensive surgery, the patient’s heart
could not be weaned from cardiopulmonary bypass.
The heart was excised and replaced with a cardiac
prosthesis, which supported the patient for 64 hours
before a suitable donor heart became available for
transplantation. Without the Liotta heart, the patient
would have died on the operating table, because a
suitable donor organ was not available at the time.5
These circumstances have been repeated numerous
times since 1969. Whether the cause is postcardiotomy failure, cardiogenic shock, or ischemic or idiopathic cardiomyopathy, there is an inevitable point at
which the human heart loses its ability to pump
blood despite maximal medical therapy.
The clinical indications for MCS continue to expand in step with improvements in technology and
patient management. With time, devices are becoming smaller, easier to implant, more reliable, and more
efficient. Implantation has been made faster and easier by improvements in design and surgical techniques.
In some instances, the smaller axial-flow VADs can
be implanted without cardiopulmonary bypass.23 Because artificial surfaces and valves that come into contact with blood pose an inherent risk of thrombosis
and associated complications, the application of most
MCS systems still requires concomitant systemic anticoagulation therapy. In some cases, however, the need
for anticoagulation and the risk of bleeding complications have been reduced by the use of biocompatible surfaces such as those in the HeartMate VE and
XVE.24 Improved engineering has increased the durability and reliability of MCS devices, although there
still remains room for improvement. The increasing
need for prolonged pump function is limited not only
by the finite mechanical lifetime of the devices, but
also by the current inability to provide an efficient,
inexhaustible, and portable power source. Most MCS
devices require externalization of either a pneumatic
or electrical drive line. Although totally implantable
Texas Heart Institute Journal
systems such as the AbioCor TAH are under development, the internal batteries are able to provide sufficient power only for about 30 minutes. Hence, the
transcutaneous transmission of energy from an external source is still required.
There has also been much discussion about the appropriate timing of VAD implantation and the selection of appropriate recipients. Initially, MCS was
considered only after all other options had been exhausted. Unfortunately, such a delay might allow
multiple organ failure to progress until function is irrecoverable and prognosis is poor. However, recent evidence indicates that MCS may in some cases improve
and restore end-organ function and thereby serve as a
bridge to recovery. As MCS becomes safer and more
effective, it may become possible to place patients on
MCS earlier, thus improving their chances of functional recovery. In cases of bridging to transplant, the
use of MCS to restore adequate blood flow to organs
before they become permanently damaged is critical
for improving the prognosis after transplantation.
Therefore, the use of MCS at earlier stages in the progression of heart failure will likely become increasingly accepted.
Although bridge to transplant remains one of the
principal uses for modern long-term MCS devices,
other uses are envisioned as well. Myocardial recovery
due to ventricular unloading and workload reduction
with a VAD has been noted,25 especially in patients
with acute cardiogenic shock. Reverse remodeling
after long-term MCS has been noted too. Nevertheless, explanting MCS devices from a chronically supported patient is still typically performed only under
extenuating circumstances such as infection or mechanical malfunction. Further understanding of the
phenomenon of reverse remodeling may lead to the
use of long-term MCS in selected cases as a bridge to
recovery instead of a bridge to transplant.
Increasing experience with MCS has also highlighted the potential use of MCS devices as destination
therapy. The AbioCor TAH is presently under investigation as destination therapy in patients who do not
qualify for heart transplantation and whose conditions are refractory to optimal medical management.
The HeartMate XVE LVAD, which has been in use
in some form since the early 1980s, was approved
for clinical use as destination therapy by the FDA in
2002. Even axial-flow LVADs such as the Jarvik 2000
and the HeartMate II, which are now being investigated at THI and in Europe as bridges to transplant,
show the potential to be used as permanent long-term
therapy. Thus far, the experience with the Jarvik 2000
suggests that it may provide reliable support for several years. One patient in Europe26 has now been supported with a Jarvik 2000 LVAD for over 4 years.
Here in the United States, 12 patients supported by
Mechanical Circulatory Support at THI
175
the Jarvik 2000 have been discharged from the hospital, and 1 patient has been supported with the device
for more than 2 years.
Several recently introduced VADs provide shortterm MCS. Two of them in particular, the TandemHeart pVAD and the Levitronix CentriMag, are now
being investigated at THI as part of multicenter clinical trials. The potential clinical indications for shortterm support with these devices include cardiogenic shock, high-risk percutaneous interventions, offpump coronary artery bypass grafting, and bridge to
definitive therapy. Both devices are small extracorporeal circuits that can temporarily assume the work of
the ventricle.
Our long, single-center experience with the development of MCS devices has imparted valuable information concerning the difficult problem of congestive
heart failure. It is clear, for example, that the function
of the device must match the needs of the patient and
must be applied appropriately. Our early experience
with the intra-aortic balloon pump, in which the device was used in 34 patients over a 3-year period before
a single patient left the hospital after its application,
dramatically illustrates the importance of the suitability and timing of support.27 Today, the mechanism
of the intra-aortic balloon pump remains essentially
unchanged, and a 70% to 80% survival rate can be
expected when this technology is applied to the appropriate patient. The first use of the ALVAD led to a
similar observation. The device worked well both experimentally and clinically, but none of the 22 patients
who were supported with it survived. This experience
aptly reinforces the importance of proper timing of device application and its relationship to patient survival.
Another important observation has been the difficulty of implanting a biventricular pulsatile pump
(that is, the TAH). This technology’s current apogee
of development is the AbioCor TAH. Its clinical efficiency has been exemplary to date. Nevertheless, the
AbioCor TAH remains large and will not comfortably
fit within the chest cavity of most candidate patients.
Therefore, its minimization with the use of continuous flow technology, used so successfully in LVADs,
may play an important role in future clinical applications of the TAH.
Technological improvements and the increasing
availability of both short- and long-term MCS devices
are broadening the use of MCS. The demand for
MCS is increasing as improved medical therapies keep
patients with heart failure alive for longer periods of
time and as nontransplant surgical techniques for
heart failure provide options for many patients who
would otherwise require transplantation. Despite medical or surgical management, sick hearts will eventually
fail to pump enough blood to meet circulatory needs.
Simply replacing failing hearts with healthy ones is
176
Mechanical Circulatory Support at THI
not the ultimate solution to heart failure that many
thought it would be. Given the widely acknowledged
limitations of heart transplantation, MCS may evolve
beyond a temporary therapeutic alternative into an accepted long-term, and perhaps even permanent, alternative. In the meantime, further research is warranted
to develop MCS devices that more closely duplicate
the healthy human heart in terms of reliable function
over long periods of time.
References
1. Barnard CN. The operation. A human cardiac transplant:
an interim report of a successful operation performed at
Groote Schuur Hospital, Cape Town. S Afr Med J 1967;41:
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2. Cooper DKC. Experimental development and early clinical
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editors. The transplantation and replacement of thoracic
organs: the present status of biological and mechanical replacement of the heart and lungs. 2nd ed. Dordrecht: Kluwer Academic Publishers; 1996. p. 153-60.
3. Borel JF, Feurer C, Gubler HU, Stahelin H. Biological effects of cyclosporin A: a new antilymphocytic agent. Agents
Actions 1976;6:468-75.
4. Frazier OH, Cooley DA, Okereke OU, Radovancevic B,
Chandler LB. Cardiac transplantation in a patient with septicemia after prolonged intraaortic balloon pump support:
implications for staged transplantation. Tex Heart Inst J
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