A ventricular assist device is an electromechanical circulatory device
that is used to partially or completely replace the function of a failing heart.
The function of VADs differs from that of artificial cardiac pacemakers. Some
VADs are intended for short term use, typically for patients recovering from
heart attacks or heart surgery, while others are intended for long-term use,
typically for patients suffering from advanced congestive heart failure.
VADs are distinct from artificial hearts, which are designed to completely
take over cardiac function and generally require the removal of the patient's
heart. VADs are designed to assist either the right or left ventricle, or
both at once. The type that is used depends primarily on the underlying
heart disease and the pulmonary arterial resistance that determines the load on
the right ventricle. LVADs are most commonly used, but when
pulmonary arterial resistance is high, right ventricular assistance may become
necessary. Long term VADs are normally used to keep patients alive with a good
quality of life while they wait for a heart transplantation. However, LVADs
are sometimes used as destination therapy, meaning they will never undergo
heart transplant, and sometimes as a bridge to recovery.
In the last few years, VADs have improved significantly in terms of
providing survival and quality of life among recipients.
Design = Pumps=
The pumps used in VADs can be divided into two main categories – pulsatile
pumps, that mimic the natural pulsing action of the heart, and continuous flow
pumps. Pulsatile VADs use positive displacement pumps. In some of these
pumps, the volume occupied by blood varies during the pumping cycle, and if
the pump is contained inside the body then a vent tube to the outside air is
required. Continuous flow VADs are smaller and
have proven to be more durable than pulsatile VADs. They normally use either
a centrifugal pump or an axial flow pump. Both types have a central rotor
containing permanent magnets. Controlled electric currents running through coils
contained in the pump housing apply forces to the magnets, which in turn
cause the rotors to spin. In the centrifugal pumps, the rotors are shaped
to accelerate the blood circumferentially and thereby cause it
to move toward the outer rim of the pump, whereas in the axial flow pumps
the rotors are more or less cylindrical with blades that are helical, causing
the blood to be accelerated in the direction of the rotor's axis.
An important issue with continuous flow pumps is the method used to suspend the
rotor. Early versions used solid bearings; however, newer pumps, some of
which are approved for use in the EU, use either electromagnetic suspension or
hydrodynamic suspension. These pumps contain only one moving part.
History The first successful implantation of a
left ventricular assist device was completed in 1966 by Dr. Michael E.
DeBakey to a 37-year-old woman. A paracorporeal circuit was able to
provide mechanical support for 10 days after the surgery. The first successful
long-term implantation of an artificial LVAD was conducted in 1988 by Dr.
William F. Bernhard of Boston Children's Hospital Medical Center and Thermedics,
Inc of Woburn, MA under a National Institutes of Health research contract
which developed Heart-mate, an electronically controlled assist device.
This was funded by a three year $6.2 million contract to Thermedics and
Children's Hospital, Boston MA from the National Heart and Lung and Blood
Institute, a program of NIH. The early VADs emulated the heart by using a
"pulsatile" action where blood is alternately sucked into the pump from
the left ventricle then forced out into the aorta. Devices of this kind include
the HeartMate IP LVAS, which was approved for use in the US by the Food
and Drug Administration in October 1994. These devices are commonly referred to
as first generation VADs. More recent work has concentrated on
continuous flow pumps, which can be roughly categorized as either
centrifugal pumps or axial flow impeller driven pumps. These pumps have the
advantage of greater simplicity resulting in smaller size and greater
reliability. These devices are referred to as second generation VADs. A side
effect is that the user will not have a pulse, or that the pulse intensity will
be seriously reduced. Third generation VADs suspend the
impeller in the pump using either hydrodynamic or electromagnetic
suspension, thus removing the need for bearings and reducing the number of
moving parts to one. Another technology undergoing clinical
trials is the use of trans cutaneous induction to power and control the
device rather than using percutaneous cables. Apart from the obvious cosmetic
advantage this reduces the risk of infection and the consequent need to
take preventative action. A pulsatile pump using this technology has CE Mark
approval and is in clinical trials for US FDA approval.
A very different approach in the early stages of development is the use of an
inflatable cuff around the aorta. Inflating the cuff contracts the aorta
and deflating the cuff allows the aorta to expand – in effect the aorta becomes
a second left ventricle. A proposed refinement is to use the patient's
skeletal muscle, driven by a pacemaker, to power this device which would make it
truly self-contained. However a similar operation was tried in the 1990s with
disappointing results. In any case, it has substantial potential advantages in
avoiding the need to operate on the heart itself and in avoiding any contact
between blood and the device. This approach involves a return to a
pulsatile flow. Peter Houghton was the longest surviving
recipient of a VAD for permanent use. He received an experimental Jarvik 2000
LVAD in June 2000. Since then, he completed a 91-mile charity walk,
published two books, lectured widely, hiked in the Swiss Alps and the American
West, flew in an ultra-light aircraft, and traveled extensively around the
world. He died of acute renal failure in 2007 at the age of 69.
Studies and outcomes = Recent developments=
In July 2009 in England, surgeons removed a donor heart that had been
implanted in a toddler next to her native heart, after her native heart had
recovered. This technique suggests mechanical assist device, such as an
LVAD, can take some or all the work away from the native heart and allow it time
to heal. In July 2009, 18-month follow-up results
from the HeartMate II Clinical Trial concluded that continuous-flow LVAD
provides effective hemodynamic support for at least 18 months in patients
awaiting transplantation, with improved functional status and quality of life..
Heidelberg University Hospital reported in July 2009 that the first
HeartAssist5, known as the modern version of the DeBakey VAD, was
implanted there. The HeartAssist5 weighs 92 grams, is made of titanium and
plastic, and serves to pump blood from the left ventricle into the aorta.
A phase 1 clinical trial is underway, consisting of patients with coronary
artery bypass grafting and patients in end-stage heart failure who have a left
ventricular assist device. The trial involves testing a patch, called
Anginera(TM) that contains cells that secrete hormone-like growth factors that
stimulate other cells to grow. The patches are seeded with heart muscle
cells and then implanted onto the heart with the goal of getting the muscle
cells to start communicating with native tissues in a way that allows for regular
contractions. In September 2009, a New Zealand news
outlet, Stuff, reported that in another 18 months to two years, a new wireless
device will be ready for clinical trial that will power VADs without direct
contact. If successful, this may reduce the chance of infection as a result of
the power cable through the skin. The National Institutes of Health
awarded a $2.8 million grant to develop a "pulse-less" total artificial heart
using two VADS by Micromed, initially created by Michael DeBakey and George
Noon. The grant was renewed for a second year of research in August 2009. The
Total Artificial Heart was created using two HeartAssist5 VADs, whereby one VAD
pumps blood throughout the body and the other circulates blood to and from the
lungs. HeartWare International announced in
August 2009 that it had surpassed 50 implants of their HeartWare Ventricular
Assist System in their ADVANCE Clinical Trial, an FDA-approved IDE study. The
study is to assess the system as bridge-to-transplantation system for
patients with end-stage heart failure. The study, Evaluation of the HeartWare
LVAD System for the Treatment of Advance Heart Failure, is a multi-center study
that started in May 2009. On June 27, 2014 Hannover Medical School
in Hannover, Germany performed the first human implant of HeartMate III under the
direction of Professor Axel Haverich M.D., chief of the Cardiothoracic,
Transplantation and Vascular Surgery Department and surgeon Jan Schmitto,
M.D., Ph.D. On January 21, 2015 a study was
published in Journal of American College of Cardiology suggesting that long-term
use of LVAD may induce heart regeneration. This may explain the
bridge to recovery phenomenon first described by the Yacoub group in NEJM in
2009. The majority of VADs on the market today
are somewhat bulky. The smallest device approved by the FDA, the HeartMate II,
weighs about 1 pound and measures 3 inches. This has proven particularly
important for women and children, for whom alternatives would have been too
large. One device gained CE Mark approval for
use in the EU and began clinical trials in the US. As of June 2007 these pumps
had been implanted in over 100 patients. In 2009, Ventracor was placed into the
hands of Administrators due to financial problems and was later that year
liquidated. No other companies purchased the technology, so as a result the
VentrAssist device was essentially defunct. Around 30–50 patients worldwide
remain supported on VentrAssist devices as of January 2010.
The Heartware HVAD works similarly to the VentrAssist – albeit much smaller
and not requiring an abdominal pocket to be implanted into. The device has
obtained CE Mark in Europe, and FDA approval in the U.S. Recently, it was
shown that the Heartware HVAD can be implanted through limited access without
sternotomy. In a small number of cases left
ventricular assist devices, combined with drug therapy, have enabled the
heart to recover sufficiently for the device to be able to be removed.
= HeartMate II LVAD pivotal study= A series of studies involving the use of
the of HeartMate II LVAD have proven useful in establishing the viability and
risks of using LVADs for bridge-to-transplantation and
destination therapy. The pilot trial for the HeartMate II
LVAS began in November 2003 and consisted of 46 study patients at 15
centers. Results included 11 patients supported for more than one year and
three patients supported for more than two years.
The HeartMate II pivotal trial began in 2005 and included the evaluation of
HeartMate II for two indications: Bridge to transplantation and destination
therapy, or long-term, permanent support. Thoratec Corp. announced that
this was the first time the FDA had approved a clinical trial to include
both indications in one protocol. A multicenter study in the United States
from 2005 to 2007 with 113 patients showed that significant improvements in
function were prevalent after three months, and a survival rate of 68% after
twelve months. Based on one-year follow up data from
the first 194 patients enrolled in the trial, the FDA approved HeartMate II for
bridge-to-transplantation. The trial provided clinical evidence of improved
survival rates and quality of life for a broad range of patients.
Eighteen-month follow up data on 281 patients who had either reached the
study end-point or completed 18 months of post-operative follow-up showed
improved survival, less frequent adverse events and greater reliability with
continuous flow LVADS compared to pulsatile flow devices. Of the 281
patients, 157 patients had undergone transplant, 58 patients were continuing
with LVADs in their body and seven patients had the LVAD removed because
their heart recovered; the remaining 56 had died. The results showed that the
NYHA Class of heart failure the patients had been designated had significantly
improved after six months of LVAD support compared to the pre-LVAD
baseline. Although this trial involved bridge-to-transplant indication, the
results provide early evidence that continuous flow LVADs have advantages in
terms of durability and reliability for patients receiving mechanical support
for destination therapy. Following the FDA approval of HeartMate
II LVAD for bridge-to-transplantation purposes, a post-approval study was
undertaken to assess the efficacy of the device in a commercial setting. The
study found that the device improved outcomes, both compared to other LVAD
treatments and baseline patients. Specifically, HeartMate II patients
showed lower creatinine levels, 30-day survival rates were considerably higher
at 96%, and 93% reached successful outcomes.
= HARPS= The Harefield Recovery Protocol Study is
a clinical trial to evaluate whether advanced heart failure patients
requiring VAD support can recover sufficient myocardial function to allow
device removal. HARPS combines an LVAD with conventional oral heart failure
medications, followed by the novel β2 agonist clenbuterol. This opens the
possibility that some advanced heart failure patients may forgo heart
transplantation. To date, 73% of patients who underwent
the combination therapy regimen demonstrated sufficient recovery to
allow explantation and avoid heart transplantation; freedom from recurrent
heart failure in surviving patients was 100% and 89% at one and four years after
explantation, respectively; average ejection fraction was 64% at 59 months
after explantation – all patients were NYHA Class I; and no significant adverse
effects were reported with clenbuterol therapy.
= REMATCH= The REMATCH clinical trial began in May
1998 and ran through July 2001 in 20 cardiac transplant centers around the
USA. The trial was designed to compare long-term implantation of left
ventricular assist devices with optimal medical management for patients with
end-stage heart failure who require, but do not qualify to receive cardiac
transplantation. As a result of the clinical outcomes, the device received
FDA approval for both indications, in 2001 and 2003, respectively.
The trial demonstrated an 81% improvement in two-year survival among
patients receiving HeartMate XVE compared to optimal medical management.
In addition, a destination therapy study following the REMATCH trial demonstrated
an additional 17% improvement in one-year survival of patients that were
implanted with a VAD, with an implication for the appropriate
selection of candidates and timing of VAD implantation.
A test carried out in 2001 by Dr. Eric A. Rose and REMATCH study group with
patients with congestive heart failure that were ineligible for a transplant
showed a survival at two years of 23% for those implanted with an LVAD
compared with 8% for those who were treated with drugs. The two major
complications of VAD implantation were infection and mechanical failure.
According to a retrospective cohort study comparing patients treated with a
left ventricular assist device versus inotrope therapy while awaiting heart
transplantation, the group treated with LVAD had improved clinical and metabolic
function at the time of transplant with better blood pressure, sodium, blood
urea nitrogen, and creatinine. After transplant, 57.7% of the inotrope group
had renal failure versus 16.6% in the LVAD group; 31.6% of the inotrope group
had right heart failure versus 5.6% in the LVAD group; and event-free survival
was 15.8% in the inotrope group versus 55.6% in the LVAD group.
Complications and side effects Bleeding is the most common
postoperative early complication after implantation or explantation of LVADs,
necessitating reoperation in up to 60% of recipients. The implications of
massive blood transfusions are great and include infection, pulmonary
insufficiency, increased costs, right heart failure, allosensitization, and
viral transmission, some of which can prove fatal or preclude transplantation.
When bleeding occurs, it impacts the one year Kaplan-Meier mortality. In addition
to complexity of the patient population and the complexity of these procedures
contributing to bleeding, the devices themselves may contribute to the severe
coagulopathy that can ensue when these devices are implanted. Critical in the
management of bleeding in the early hours after implantation or explantation
is to adequately evacuate the post-surgical blood from around the
heart and lungs to prevent retained blood from contributing to the need for
reoperation to wash out clot that can compress the device features and
contribute to post operative shock. Preventing chest tube clogging during
this period is critical to recovery. Because the devices generally result in
blood flowing over a non-biologic surface, predisposing the blood to
clotting, there is need for anticoagulation measures. One device,
the HeartMate XVE, is designed with a biologic surface derived from fibrin and
does not require long term anticoagulation; unfortunately, this
biologic surface may also predispose the patient to infection through selective
reduction of certain types of leukocytes.
New VAD designs which are now approved for use in the European Community and
are undergoing trials for FDA approval have all but eliminated mechanical
failure. VAD-related infection can be caused by a
large number of different organisms: Gram positive bacteria
Gram negative bacteria Fungi. especially Candida species
Treatment of VAD-related infection is exceedingly difficult and many patients
die of infection despite optimal treatment. Initial treatment should be
with broad spectrum antibiotics, but every effort must be made to obtain
appropriate samples for culture. A final decision regarding antibiotic therapy
must be based on the results of microbiogical cultures.
Other problems include immunosuppression, clotting with
resultant stroke, and bleeding secondary to anticoagulation. Some of the
polyurethane components used in the devices cause the deletion of a subset
of immune cells when blood comes in contact with them. This predisposes the
patient to fungal and some viral infections necessitating appropriate
prophylactic therapy. Considering the multitude of risks and
lifestyle modifications associated with ventricular assist device implant, it is
important for prospective patients to be informed prior to decision making. In
addition to physician consult, various Internet-based patient directed
resources are available to assist in patient education.
List of implantable VAD devices This is a partial list and may never be
completeReferenced additions are welcome See also
Intra-aortic balloon pump Gus Rosenberg
References External links
LifeFlow LVAD at the University of Virginia
Nader Moazami, Patrick M. McCarthy Temporary Circulatory Support
Eugene L. Kukuy, Mehmet C. Oz, Yoshifumi Naka Long-Term Mechanical Circulatory
Support – a review of the subject as at 2003.
Mechanical Circulatory Support Resource Center
Health Center Online VAD Mayo Clinic VAD
Life without a pulse — news story about Canadian man with VAD
Heart Pump Design Could Give Patients New Hope — A new counter-flow heart pump
developed by Queensland University of Technology
Heart pump improves quality of life in congestive heart failure patients A
rapid review of the medical literature and specialist opinion as at December
2005 NATIONAL INSTITUTE FOR HEALTH AND
CLINICAL EXCELLENCE Interventional procedures overview – short-term
circulatory support with left ventricular assist devices as a bridge
to cardiac transplantation or recovery A rapid review of the medical literature
and specialist opinion as at December 2005
Courtney J. Gemmato,Matthew D. Forrester,Timothy J. Myers,O.H.
Frazier,Denton A. Cooley Thirty-Five Years of Mechanical Circulatory Support
at the Texas Heart Institute Tex Heart Inst J 2005;32:168-77
MyLVAD.com Non branded site with video, news, and community discussions on
VAD's. Ventricular Assist Device Center for
Heart Failure – Northwestern Memorial Hospital
[1] Website Hannover Medical School. LVAD FAQ.