Session C1 Bioengineering
2333
THE IMPROVEMENT OF AN UNHEALTHY HEARTH WITH THE
HEARTMATE II LVAD
Patrick Devlin (pjd40@pitt.edu), Patrick Bianconi (pab99@pitt.edu)
Abstract—This paper will describe the significance of
Thoratec’s Heartmate II Left Ventricular Assist Device
(LVAD) and other ventricular assist devices (VAD) of the
like, and how these devices are improving the lives of the
many sufferers of heart failure. This paper will also explain
how the Heartmate II compensates for an injured hearts’
inability to pump blood at an efficient rate. The wide range
of eligible patients and potential costs will be assessed. The
benefits of this device and existing clinical outcomes will
also be discussed with great detail. Such benefits include
durability of the device, longevity of the device, and success
of the device [10]. This paper aims to educate the reader
about heart failure, and how the innovative design and the
efficient processes of the Heartmate II can sustain the life of
a patient with this condition. First, the significance of heart
failure and the methods of improving inept heart function
will be discussed. Second, the mechanical design and the
reliability of the Heartmate II will be described. Lastly, the
results of clinical trials and the ethical issues surrounding
artificial organs and machines will be debated. All in all the
Heartmate II is affecting the lives of thousands and will
continue to improve the lives of millions.
through the aorta. If one of the ventricles fails to operate
correctly, a ventricular assist device would be a sufficient
solution to the overbearing problem [1].
Clinical research studies have showed Thoratec’s Heartmate
II Left Ventricular Assist Device to be safe and effective,
with improved quality of life and survival compared with
historical norms for heart-failure patients [2]. The Heartmate
II is not the only ventricular assist device on the market, but
comparisons shall be made between this device and devices
of the like, including total artificial hearts. The advantages
and disadvantages of these devices will be discussed in
detail, in order to explain why most attention should be paid
to Thoratec’s Heartmate II Left Ventricular Assist Device.
HEALING AN UNHEALTHY HEART
Currently about six million patients in the United States are
suffering from heart failure with an additional six hundred
thousand cases arising annually [1]. About fifty percent of
these sufferers die within only five years of the initial
diagnosis [3]. After the initial diagnosis, about a quarter of
the patients proceed to advanced heart failure. Advanced
heart failure consists of the final two stages of the four
stages of heart failure. The first two stages involve little or
no limitation to physical activity. During stage three the
patient is considered to have advanced heart failure and
experiences fatigue from normal physical activity. Unlike
the previous three stages, the patient experiences cardiac
insufficiency while at rest during the fourth stage and has
trouble doing any sort of physical activity. Less than thirty
percent of patients who are suffering from advanced heart
failure fail to survive more than a year.
One may think that a simple solution to this crisis would
be the transplantation of a heart from a donor. Unfortunately,
there are less than three thousand donor organs available
world-wide per year [1]. These organs could potentially
save, if not severely help the lives of those suffering with
any stage of heart failure. In 1964, research and development
of artificial heart technologies had gone underway and
continues to progress in a positive direction [4]. This
information alone should be evidence enough as to why
further research and development of implementing artificial
heart technologies should be continued, in hopes of healing
the many unhealthy hearts, not only in America, but around
the world.
Key Words—total artificial heart, Heartmate II, heart
failure, left ventricular assist device (LVAD), transplant,
THE SIGNIFICANCE OF HEART FAILURE
Every year, hundreds of thousands of individuals are
diagnosed with heart failure, and on top of that, millions are
already suffering from this condition [1]. Heart transplants
may be the best option for a healthy future, but unfortunately
there are a very limited number of donor organs available
and for most patients, only specific areas of the heart are in
need of medical attention [1]. One may think that total
artificial hearts hold the key to a healthy life for many, but
this is not necessarily true. Total artificial hearts are much
less common than ventricular assist devices due to the fact
that not all patients qualify for one, or need a totally new
heart for that matter.
The heart is a muscular organ that pumps blood to all
parts of the body. Oxygen rich blood from the lungs enters
the heart and fills the left atrium. As blood fills up the left
atrium, the mitral valve is pushed open and blood flows in
the left ventricle. As the heart beats, the ventricles contract,
and the blood is forced into the aorta. The aorta is the largest
artery in the body, and it has the power to supply the whole
body with oxygenated blood. If problems arise in the left
ventricle, insufficient blood will be supplied to the body
Artificial Heart Technologies
Before Thoratec’s Heartmate II LVAD hit the market, other
left ventricular assist devices and total artificial hearts were
University of Pittsburgh
Swanson School of Engineering
Twelfth Annual Freshman Conference
April 14, 2012
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Patrick Devlin
Patrick Bianconi
the main focus of artificial heart technologies [4]. Both
VADs and TAHs have the potential to be used as long term
heart support or as bridges to heart transplantation. Different
devices work better for the specific purpose they are serving.
The main goal of all of these devices is to support a human
life with sufficient blood flow throughout the body. Without
this sufficient flow of blood, multiple organ failure occurs
[4].
The obvious difference between VADs and TAHs is the
severity of implantation. Although both procedures are
invasive, the implantation of a TAH is much more
dangerous, and involves a complex procedure of completely
withdrawing the patient’s heart in an attempt to insert a
totally artificial machine. One major drawback of TAHs is
that most of devices on the market are intended for inpatient
use only [4]. This severely limits the patient’s mobility and
social life. Along with residing in the hospital, the patient
has to wait until a heart is available for transplantation. Very
few of the devices offer an option for destination therapy.
A total artificial heart is a complex machine and is made
up of multiple moving parts. Due to the complexity, many
problems have the potential to occur [4]. This requires
severe surveillance of the patient, such as hemodynamic
management and anticoagulation. Routine care is also
conducted and includes supporting and recovering end-organ
function, respiratory and ventilator management, infection
control, maintenance or nutrition, pain control, and gradual
mobilization [4].
A VAD is a much simpler device in comparison and the
surgery is much less invasive. The patient does not lose his
or her heart, but rather has this miniscule machine assist the
ventricular flow in an ordinary manner. Ventricular assist
devices represent a method of providing temporary support
for those patients not expected to survive until a heart
becomes available for their transplant [5]. Due to the
scarcity of donor hearts available, improvements have been
made, allowing patients to use an assist device in a hospital
setting or even as an outpatient. These improved devices are
surgically placed entirely within the thoracic and abdominal
cavity and are connected to the power source by a drive line
that passes through the torso with an open wound. This
poses obvious problems such as infection and the risk of
damaging the power line. Devices like these are intended for
long-term use (at least a year), but devices specifically for
short term use are available for patients who are unable to
use a device for the long term. Many VADs are used as
bridge to transplant, but the Heartmate II in particular is
FDA approved for both bridge to transplant and destination
therapy. Patient management is required after implantation,
but this management is not nearly as extensive as the
management required after the implantation of a TAH [6].
Food and Drug Administration for transplant-ineligible
heart-failure patients [7]. This device was originally
approved for “bridge to transplant” in 2008, but on January
20th, 2010, the device was approved for destination therapy
for patients with end-stage heart failure who are not suitable
for cardiac transplant [7]. This allows for a course of
treatment for a patient who has no option of being provided
with a heart for transplantation. Now less sick sufferers of
heart failure can significantly increase their quality of life
with the Heartmate II without using the device as a bridge to
transplantation.
Aside from being available to suit two different needs of
patients with heart failure, the Heartmate II is very reliable
and can fit a wide variety of patients in need. The current
model is smaller than previously approved LVADs, meaning
that it can be implanted in women and even children. The
device covers the full output of a heart by pumping up to 10
liters of blood per minute and is much easier to implant than
previous LVAD devices [8]. The Hearmate II is implanted
alongside a patient’s heart and takes over the pumping
ability of the weakened heart. Unlike total artificial hearts
and even previous LVADs for that matter, the Heartmate II
is made up of only one moving part and operates more
simply [8]. This allows for the device to be used much
longer and operate much more quietly than previous devices.
A study was conducted to determine whether results with
the Heartmate II LVAD in a commercial setting are
comparable to other available devices for the same
indication [9]. Many characteristics were similar in the
results of the Heartmate II versus the other devices, except
that creatine and blood urea nitrogen levels were lower in
the patients with the Heartmate II. The percentage of
patients reaching transplant, cardiac recovery, or ongoing
LVAD support by six months was 91% for the Heartmate II
and 80% for the control group [10]. At one year, survival for
the Heartmate II was at 85% versus the 70% of the control
group [10]. This information is strong evidence as to how
the Hearmate II is very reliable in comparison to other
similar devices. These data suggest that after approval, the
technology has been associated with continued excellent
results. The simple complexity of this device separates the
Heartmate II from all other LVADs on the market. For being
the first LVAD approved for destination therapy and as a
bridge to transplantation, the Heartmate II can brighten the
future of the many sufferers of advanced heart failure.
How It Works
The Heartmate II is about the size of a D-cell battery, weighs
375 grams and incorporates an electromagnetic DC
brushless motor to provide rotation to the dual cup-socket
ruby bearing supported impeller which has demonstrated a
five year service life. The pump is made of titanium and the
knitted polyester graft is reinforced with a titanium ring and
a rubber sleeve [8].
THE HEARTMATE II LVAD
Thoratec’s Heartmate II LVAD is the first-continuous flow
left ventricular assist device approved by the United States
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The Heartmate II operates with a continuous flow rotary
pump. Continuous flow pumps have the distinct advantages
of small size and superior mechanical longevity [11]. The
direction in which the blood enters and leaves the impeller
of the Heartmate II is termed axial flow. Axial flow rotary
blood pumps are small and contain an impeller that can spin
at speeds between 6000 and 15,000 rotations per minute to
deliver blood flow to the circulatory system [11]. Suitable
hemodynamic pressures and flows are typically produced at
about 9000 rotations per minute [11].
The pump lies parallel to the diaphragm and may be
placed within the muscles of the abdominal wall. The only
part that moves on the pump is the rotor and it spins on inlet
and outlet ball-and-cup bearings. The motor of the device
creates a spinning magnetic field that spins the rotor and
imports torque to its internal cylindrical magnet. Blood
flows from the inlet tube into the pump, past three airfoilshaped guide vanes that straighten the flow of blood as it is
picked up by the rotor. The rotor consists of three curved
blades. As the rotor spins, kinetic energy is supplied to the
blood flow as it moves toward the outlet vanes and into the
aorta where it embarks on its journey through the circulatory
system [11]. Since the approval for bridge to transplant in
2008, and destination therapy in 2010, more than 5000
patients worldwide have been implanted with the Heartmate
II [12].
After the initial surgery to implant the device, 86% of the
participants with the Heartmate II and 76% of people with
the Heartmate XVE were released from the hospital after
about twenty-seven days. Throughout the trial, patients with
the Heartmate II spent 88% of the time outside the hospital
as opposed to 74% of the Heartmate XVE. All the patients
were tested at regular intervals to judge their health and
quality of life. A six-minute walk test was done at one
month, three months, and then every six months after until
the end of the trial to study the patient’s energy and strength
[12].
After two years, eighty percent of the patients who
survived with the Heartmate II had only stage one or stage
two NYHA symptoms and could double their six-minute
walk distance of two years prior. Questionnaires were
distributed to all of the surviving patients to describe their
quality of life with the devices. Results of the questionnaires
showed a much higher improvement of quality of life with
the Heartmate II rather than the Heartmate XVE [12].
After the entire trial was over, results of the Heartmate II
continuous flow left ventricular assist device were compared
the results of the pulsatile flow Heartmate XVE. The
Heartmate II proved to be superior to the Heartmate XVE.
The Heartmate II achieved higher percentages of primary
end points and actual survival rates, better quality of life
assessments, and lower cases of adverse events like stroke,
right heart failure, respiratory failure, and renal failure. The
durability of the Heartmate II was exceedingly better than
the Heartmate XVE. Only six out of every 100 Heartmate
II’s needed replacement compared to forty-eight out of a 100
for the Heartmate XVE [12]. This trial’s results thoroughly
detailed the preeminence of the continuous flow Heartmate
II.
Clinical Results
The continuous flow Heartmate II LVAD was placed in a
trial with the pulsatile flow Heartmate XVE LVAD to
compare the Heartmate II’s clinical results with a device that
has been previously tested. The Heartmate XVE has already
proven that it increases the quality of life and survival rates
compared to medical therapy alone. Throughout the trial, the
Heartmate II surpassed the Heartmate XVE in almost every
way [12].
The trial consisted of two hundred patients with advanced
heart failure randomly being assigned to two groups. The
first group contained one hundred and thirty-four patients
receiving the Heartmate II, and the second group had sixtysix patients being implanted with the pulsatile flow
Heartmate XVE. Due to its smaller size, more women were
placed into the Heartmate II group. The median age of the
patients was 64 years old, with ages ranging from twenty-six
to eighty-one years of age. Every trial has primary and
secondary endpoints that they use to determine the
effectiveness of the device that is being studied. In this trial,
the primary endpoint was two years of use of the device
without any incapacitating stroke, operation to fix or replace
the device. Secondary endpoints included quality of life,
survival, and functional capacity. By the end of the trial,
46% of the patients on the Heartmate II achieved the
primary endpoint as opposed to only 11% of the patients on
the Heartmate XVE. The Heartmate II had over double the
actual survival rate of the Heartmate XVE, at 58% [12].
Comparability
What separates the Heartmate II LVAD from LVADs of the
past is the continuous flow system that is utilized. Previous
devices contained a pulsatile flow. The pulsatile output
closely simulates the ventricular action of the heart. It
provides physiological advantages in blood flow for
perfusion in cardiovascular and hemodynamic studies [10].
The pulsatile flow was favored in the medical community
for years, and when the smaller-sized continuous flow
devices surfaced, there was initial skepticism [13]. The
skepticism concerned the long-term physiological effects of
a ‘non-pulsatile’ pump, such as the formation of a blood clot
[10].
A study was conducted comparing the results of pulsatile
flow rotary pumps versus continuous flow rotary pumps.
The primary outcome showed that the survival free from
stroke or reoperation to repair or replace the device was 46%
for the continuous flow group and 11% for the pulsatile flow
group [12]. Both types of devices improve the quality of life
and functional capacity, but the continuous flow LVAD
improved the probability of survival free from stroke and
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device failure at two years compared with a pulsatile device
[11].
Another advantage of the continuous flow pump is that it
is smaller and thus requires less surgical dissection for
implantation [11]. The continuous flow group in the study
had about half the amount of device-related infections in
patients than in the pulsatile flow group [11].
Continuous flow rotary pumps can be further specified
into axial flow or radial flow. As stated before, this is the
method in which the blood enters and leaves the impeller of
the device [10]. In axial flow pumps, the fluid flows spirally
along the axis and is nicknamed the “propeller pump”. In
radial flow pumps, the fluid flows outward at a right angle to
its axis. The Heartmate II utilizes the axial flow pump, and
as stated before this axial pump is very small in size, can be
implanted in a wide range of patients, and can spin at speeds
between 6000 and 15,000 rotations per minute [10]. The
radial, or centrifugal, flow pump is slightly larger in
diameter and spins at slower speeds than the axial pump.
These radial pumps are suitable for long-term cardiac
assistance due to the lower rotational speed and higher
hydraulic efficiency [11]. Both types of pumps provide full
circulatory support and can be implanted in such a way that
will aide the heart as a bridge to transplant or even as
destination therapy.
Devices that use the radial flow pump are currently
undergoing clinical trials for FDA approval in the United
States. The future looks bright for radial flow in devices, but
approval by the FDA must happen first, and when/if it does,
the Heartmate II could possibly utilize this method of flow
[11]. Until the approval of radial flow, axial flow remains to
be the most reliable and efficient way to direct the flow of
blood in LVADs. This allows for the assertation to be made
that the Heartmate II is currently the best LVAD available
on the market.
across the room. Patients with the Heartmate II have
reported significantly more energy even after only a few
months of receiving the machine. After recovering from
surgery, the patient is able to go about their day almost as if
they did not have heart problems. People have been reported
to participate in snowboarding and other sports with the
Heartmate II, proving that the machine can provide a level of
energy similar to that of a healthy heart. The quality of life
for a patient, without the Heartmate II, who barely has the
energy to walk is far inferior compared to a patient with the
Heartmate II who can play sports [14].
In the NPSE code of ethics for engineers, one of the
canons states that engineers must work for the safety, health,
and welfare of the public [15]. The Heartmate II gives
patients an opportunity to not only leave the hospital, but
also enough energy to go about the day as though they have
a normal, healthy heart. An obvious positive aspect to the
patient’s health is that the patient’s heart is working at full
capacity. A not so obvious positive aspect that also comes
with the Heartmate II is the psychological health benefits
that come hand in hand with living a normal healthy life
outside of the hospital. Patients can experience a typical day
with their friends and family that they would never have the
opportunity to experience if it wasn’t for the Heartmate II.
The importance of psychological health should never be
underestimated. Some may argue that it is as important as
physical health.
Artificial organs are a controversial topic. Some people
do not like the idea of people living with artificial organs
that are basically machines. Many cases from the past have
involved intense debates regarding the ethical nature of a
person being kept alive by a machine. For instance when a
patient who has suffered brain damage is put into a
permanent vegetable like state, that person requires
machines to feed, control their breathing, and other functions
that they would not be able to sustain life without. In those
cases, the patients themselves are in a state which they
cannot make the decision for themselves. This raises more
ethical issues as to who has the power to decide what is best
for them. In the cases involving the Heartmate II however,
the patient has the ability to decide if the machine is right for
them. Also, left ventricular assist devices are only assisting
the patient’s existing, normal heart. This is very similar to
the way that an inhaler assists the lungs of a person with
asthma.
The Heartmate II has also been known to be used as a
method of myocardial recovery. Myocardial recovery
means the machine slowly helps the natural organ begin to
function on its own again. In some cases , the Heartmate II
has strengthened the ventricles of the heart enough that
they had begun to work properly on their own without the
aid of the LVAD. Ideally, this would be the best possible
outcome, but sadly, it does not happen nearly enough.
PROBLEMS OF THE REALITY IN RETROSPECT
Heart disease is currently plaguing the lives of millions of
people and hundreds of thousands more each year. Clearly,
new technologies and advancements must be made to fight
this horrible disease. Biomedical engineers have been
working to find solutions to save millions from heart related
problems. The first goal for engineers is to design a device
that will keep the patient with heart failure alive. This used
to require constant hospitalization with no hope of leaving
the hospital and experiencing a normal day. Engineers
began to develop artificial hearts and ventricular assist
devices in hopes of giving patients a chance at a normal life
again. Total artificial hearts are slowly becoming capable of
discharging patients from the hospital, but not nearly at the
capacity of LVADs. The Heartmate II is the best left
ventricular assist device on the market to give a patient the
opportunity for a normal life. Heart Disease has been known
to drastically reduce the energy of sufferers. In most cases,
patients barely have the energy to get out of bed and walk
Common Issues
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The Heartmate II is an incredible device that has the
potential to save millions of lives, but like almost every
machine that has been designed, it has flaws. Users of the
Heartmate II, and all continuous-flow VADs for that matter,
will appear to not have a pulse. The user must carry around
documentation indicating that the lack of a pulse does not
mean the person is dead. Other than being rather eerie, this
problem does not affect the well-being of the patient.
In a normal heart, there is a balance between the amount
of blood the right ventricle supplies to the left ventricle in
order to be distributed throughout the body. With an LVAD
in place, Right Ventricular Failure has the potential to occur.
This happens because the right ventricle stops working
properly and does not provide an adequate reservoir of blood
to the left side, so the LVAD does not have a sufficient
amount of blood to pump.
Another possible issue with LVADs occurs when the
device is pumping blood at too fast of a pace and the device
becomes displaced thus preventing proper functioning. This
is called Cannula Obstruction. As a possible result of
Cannula Obstruction and as a pre-cursor to Right Ventricular
Failure, Arrhythmias involves unnatural rhythmic blood
flow. Normally the left ventricle can compensate for the
unbalance, but the right ventricle can’t handle it in
comparison with the LVAD in place. This then leads to
Right Ventricular Failure.
One factor that can negatively contribute to the success of
the device is the clotting of blood in the bearing of the
device that leads into the left ventricle. These clots can build
up in the bearing and break off and flow into the aorta,
which in turn can lead to a stroke by cutting off proper blood
supply. Similar to this is aortic stenosis, where calcium
deposits build up in the aorta thus increasing the pressure in
the cardiovascular system which can also lead to a stroke
and even gastrointestinal bleeding [13].
Possibly the largest problem with the Heartmate II and
many of the other LVADs on the market is the percutaneous
drive line that supplies power to the device. This constant
exposure to the wound can lead to a wide range of serious
infections that can in turn plague the user of the device. It is
also of utmost importance that special care and attention is
paid to the open wound, because if it is bumped, the power
supply can potentially get cut off and the open wound can be
harmed, leading to infection.
One of the more limiting factors of the Heartmate II, is
the amount of strenuous activity the user’s heart and LVAD
can handle. A manual control system is in place to allow the
user to operate the speed at which the impeller of the device
rotates. This seemingly helpful function can lead to serious
consequences if not properly operated by the user [14].
The Heartmate II is not a cheap machine when used as a
bridge to transplantation. The LVAD costs around $150,000
plus more bills for hospitalization and drugs.
After
receiving the Heartmate II, patients are discharged from the
hospital after about one month and are capable of staying out
of the hospital for long amounts of time if no adverse events
occur. Hypothetical, with its ability to keep the patient out
of the hospital for long periods of time, the Heartmate II
could save money if used as destination therapy. The device
is not used long enough as a bridge to transplantation to
save money on hospital bills that would accumulate if the
patient stayed in the hospital as opposed to receiving the
device. Although cost may be an issue when deciding to use
the Heartmate II, the survival rates and improvement of
quality of life that come with the machine outweigh the
monetary cost of the device [16]. A price tag cannot be put
on the positive psychological effects of living a normal life
outside of the hospital.
THE FUTURE OF ARTIFICIAL HEART
TECHNOLOGIES
Biomedical engineers are constantly designing new products
that are far superior to their predecessors. Creating new,
more effective artificial organs is a process
much like
designing a building or even writing a paper. Each time a
device is created, it is the best version of the idea, but newer,
more efficient models will eventually be designed. Devices
relating to failing hearts are no exception. As stated before,
the current top model of left ventricular assist devices is
Thoratec’s Heartmate II. This is the only device that is FDA
approved for both bridge to transplant and destination
therapy.
The approval backs the reliability of the device, and
clinical results have agreed as well. The success of
Thoratec’s device should inspire the company to continue
making improvements and come out with newer, more
efficient models that will greater improve the quality of life
of a heart failure patient.
Currently undergoing design is the Heartmate III and the
Heartmate X. These devices hold promising outcomes in the
future of artificial heart technologies. The devices aim to
make such improvements as the reduction of clotting, a
smaller pump, and a less of a requirement of energy,
enabling the battery life to last longer. The newer devices
will hopefully contain a transcutaneous power source, rather
than having a driveline connect to the external power source
through an open wound in the side of the patient. This will
eliminate the chance of infections entering the body through
that wound [8].
As time continues to change, and new advancements are
made in the medical and technological fields, further
improvements can be made to any future artificial heart
device. Currently, the Heartmate II LVAD reigns at the top
of the ventricular assist device totem pole, supplying the
weakened heart with the appropriate aide to pump blood
throughout the body. With such a complex device dealing
with such a complex problem, the Heartmate II may have its
flaws. The improvement of the quality of life, compared to
life without the device, however, fully compensates for these
flaws. All in all the Heartmate II is affecting the lives of
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Patrick Bianconi
Device.” The New England Journal of Medicine. [Online].
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W.
(2012).
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thousands and will continue to advance as a leading device
in fighting heart failure, thus improving the lives of millions.
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ADDITIONAL RESOURCES
(2012, January 27) “America’s Heart Disease Burden”
National Center for Chronic Disease Prevention and Health
Promotion.
[Online]
Available:
http://www.cdc.gov/heartdisease/facts.htm
(2012) “Heartmate II Left Ventricular Assist System”
Thoratec
Corporation
[Online].
Available:
http://www.thoratec.com/medical-professionals/vadproduct-information/heartmate-ll-lvad.aspx
(2011) “Questions about HF.” Heart Failure Society of
America.
[Online].
Available:
http://www.abouthf.org/questions_stages.htm;
(2010) “The SynCardia Total Artificial Heart: What to
Expect” SynCardia Systems Inc. [Online]. Available:
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ACKNOWLEDGMENTS
We would like to thank Dr. William Weiss, the Engineering
0012 professors, the writing instructors, the reader who is
reading this, and most important of all, the suffers of heart
failure for fighting through their tough times.
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