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Breakthroughs in Emergency Medicine – The Future of Heart Attack Treatment
David Mittelstein
David is a junior majoring in Biomedical Engineering with a focus in Biochemistry at the
University of Southern California. His interest in this topic was sparked by his personal
experience as an emergency medical technician in Los Angeles county and research in a
cardiovascular engineering lab. David hopes to enroll in an MD/PhD program after receiving his
degree.
Heart attacks are the leading cause of death in America, killing over 500,000 people
every year. Current medical practices lead to a survival rate of less than 8% for an outof-hospital heart attack. Three innovative bio-technologies may help emergency medical
personnel respond more promptly to heart attacks and protect heart tissue from
permanent damage. The use of CPR machines to provide effective chest compression, the
administration of perfluorocarbon liquids instead of oxygen gas for “liquid breathing,”
and the application of tissue engineering to generate cardiac tissues for transplant all
have great potential to increase survival outcomes for heart attack victims.
Keywords: Emergency Medicine, Pre-Hospital Care, Heart Attack, Biomedical Engineering,
Cardiovascular, Myocardial Infarction, Cardio-Pulmonary Respiration, Liquid Breathing,
Perflurocarbons, Tissue Engineering
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A BATTLE AGAINST TIME
Heart attacks are the leading cause of death in America and an immense public health
concern. Over 500,000 Americans die suddenly every year from heart attacks [1]. Despite the
development of emergency medical strategies to quickly diagnose, assess, and treat heart attacks,
the survival rate for an out-of-hospital heart attack is less than 8% [2].
When treating a heart attack victim, medical personnel are engaged in a battle against
time. The American Heart Association states that the chances of survival for a heart attack
victim drop significantly with any delay in treatment. A “fast response is critical” to have any
hope to prevent irreversible tissue damage [3]. As such, medical care for heart attack treatment
focuses on providing effective care in as time-efficient a means as possible.
Now, recent innovations in biomedical engineering may give emergency personnel an
advantage in treating heart attacks quickly and effectively. Novel technologies and
methodologies may improve pre-hospital care, delay the death of heart muscle and brain cells, or
even replace damaged tissue. This article will discuss the background of heart attacks, identify
certain challenges in the clinical treatment of this condition, and then present engineering
solutions to said challenges.
WHAT IS A HEART ATTACK?
Normally, the lungs and heart are in continual operation to bring oxygen into the
bloodstream and pump it throughout the body. Without this constant flow of oxygen, the organs
of the body will malfunction and ultimately die [4]. The brain and heart are particularly
vulnerable; tissue death in these organs may occur only minutes after oxygen deprivation [5].
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A heart attack occurs when the coronary arteries – small blood vessels that supply the
powerful heart muscles with blood – become clogged. Fat-heavy diets, smoking, age, and many
other factors contribute to the build-up of plaque in these arteries. In a heart attack, this plaque
may suddenly “rupture,” causing a clot to form. This blocks the artery and cuts off blood flow to
a section of heart muscle. The oxygen starved heart tissue will begin dying while producing the
painful chest crushing sensation commonly associated with heart attacks [4]. If severe enough,
this muscle death may prevent the heart from pumping altogether.
Figure 1: Blood clots in coronary arteries may block blood flow to heart muscle. The death of
heart muscle due to inadequate blood flow may cause a heart attack.
Image from National Heart Lung and Blood Institute
http://www.nhlbi.nih.gov/health/health-topics/images/heart_coronary_artery.gif
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CURRENT TREATMENT OF HEART ATTACKS
Cardiac conditions are among the most severe conditions treated in the field of
emergency medicine. Medical personnel have thus devised what can be roughly considered a
three-point strategy: keep blood pumping through the heart with CPR, delay the onset of oxygen
starvation through artificial ventilation, and finally re-open blocked coronary arteries at the
hospital [6]. For the purposes of this article, other steps involved in heart attack response process
will not be discussed.
Emergency medical personnel can maintain blood flow through a stopped heart by using
cardiopulmonary resuscitation – better known as CPR. By rhythmically pressing the chest
downward about 1 ½ to 2 inches at 100 compressions per minute, medical personnel can
simulate the pumping action of the heart [7]. CPR can more than double a patient’s probability
of survival from a heart attack when provided promptly and effectively [8]. However, this is
only a stop-gap measure to be performed as the patient is transferred to a hospital for more
appropriate care.
As time passes without a proper heartbeat, the body begins to suffer from a lack of
oxygen. To delay this, emergency personnel use a portable ventilator to breathe 100% oxygen
into the victim’s lungs. Despite the best efforts of the emergency medical team to simulate the
actions of the heart and lungs through CPR and artificial ventilation, typically heart attack
victims worsen with time until hospital medical intervention can take place [6].
Medical personnel may also administer drugs to “jump-start” the heart, such as atropine,
or use a defibrillator to “shock” a heart back into an appropriate rhythm. However, the definitive
care for heart attacks occurs in hospitals. There, physicians administer clot-busting medications
or perform the necessary surgeries to restore the correct blood flow to the coronary arteries [6].
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Unfortunately, even if these medical procedures save the patient’s life for the moment, heart
attacks irreversibly damage the heart. Heart function is substantially decreased, and the heart is
very prone to a subsequent, potentially fatal, heart attack [3].
INNOVATING NOVEL SOLUTIONS FOR EMERGENCY CARE
These three strategies of heart attack treatment undoubtedly help many victims survive
heart attacks. However, each of these current solutions suffers from inherent limitations that
have kept the overall survival rate of heart attacks below 8%. In this sense, the public health
crisis that heart attacks present also poses a challenge to biomedical engineers – to design
devices or medical procedures that improve a heart attack victim’s chance for survival. This
paper will discuss three answers to this challenge that give medical personnel an advantage in
their battle against time to save heart tissue.
Automatic CPR Machines
Manual CPR is difficult to perform and physically taxing, even for trained medical
personnel. According to a recent study, about 35% of patients receiving professional CPR did
not receive chest compressions of a sufficient depth [8]. Without continuous and proper
compressions, the blood flow throughout the body will falter, starving tissues of oxygen.
This challenge has a remarkably simple engineering solution: an automatic CPR machine.
These devices perform the same function of compressing the chest cavity as manual CPR
without suffering from human limitations in technique and stamina. A CPR machine may
rhythmically compress the victim’s chest using a band [9] or piston [10] that distributes the force
uniformly across the chest cavity. This leaves the hands of the emergency personnel free to
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provide artificial ventilation or use a defibrillator to shock the heart into normal rhythm.
Furthermore, the added efficiency of having a device perform CPR may allow for a speedier
transfer to the hospital for definitive care.
<SUGGESTED FIGURE: animation of automatic CPR devices. Animator may use these videos
for reference: LUCAS Heart Thumper (http://www.youtube.com/watch?v=znIidvdmqso), ZOLL
AutoPulse (http://www.zoll.com/medical-products/cardiac-support-pump/autopulse/video/)>
Figure 2: Piston-based and band-based automatic CPR devices deliver chest compressions of the
appropriate depth and rhythm without tiring.
To be functional in a heart attack situation, these automatic CPR devices must be
portable, rapidly deployable, and function off of supplies available to emergency medical teams.
Some machines take advantage of a power source available to nearly all emergency responders –
oxygen tanks. These tanks are highly compressed and thus store a great deal of energy. By
using the energy of the oxygen released from the tank, the CPR machine can effectively perform
compressions without requiring an additional power source [10].
As these devices become more frequently used by emergency medical practices, studies
published in Resuscitation and JAMA suggest that such machines can provide safe and effective
CPR while improving overall outcome of heart attack victims.
Liquid Breathing
One innovative technique to provide oxygen to a heart attack victim, involves filling the
victim’s lungs of with liquid perflurocarbons. New research in “liquid breathing” methods
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indicate that these liquid compounds may be even better at delivering oxygen to the patient’s
lungs than pure oxygen gas [11].
At room pressure, molecules in a gas are very dispersed. As such, there is an upper limit
on the concentration of oxygen that medical personnel can administer through a gas – even 100%
oxygen gas has a limited amount of oxygen per volume. However, when dissolved into a liquid
solution such as a perflurocarbon (PFC), oxygen molecules can be much more concentrated [11].
Since PFCs do not irritate the lung tissue as water does, introducing liquid PFC into the
lungs is not as damaging as one would expect. Amazingly, a mouse submerged in PFC can
comfortably respire, literally breathing the oily liquid solution in and out of its lungs [11], as
shown in Figure 3 below. When in the lungs, the oxygen leaves the PFC and enters the blood
stream through simple diffusion, just as it would from oxygen gas. However, with the PFC
solution’s higher concentration of oxygen, this diffusion process is more efficient and complete
[11]. For a heart attack victim, the oxygen-rich PFC liquid may be lifesaving.
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Figure 3: A mouse completely submerged in liquid perfluorocarbon breathes normally.
Photo from Brown University
http://biomed.brown.edu/Courses/BI108/BI108_2005_Groups/10/pictures/web/PFC6.gif
Perfluorocarbons offer another great advantage for the emergency treatment of heart
attacks: the administration of chilled PFC liquid can lower the body temperature and induce mild
hypothermia. In fact, lowering the body temperature by just 6 °C can minimize brain damage
from low oxygen conditions [12]. This can give rescuers the few extra minutes they need to
ensure a patient can be brought to a hospital for treatment.
As incredible as “liquid breathing” sounds, physicians have already used partial liquid
ventilation, in which the lung is filled 40% with the PFC solution, on pre-term neonates with
insufficient respiratory systems [13]. The neonatal staff can perform liquid ventilation using the
existing air-based artificial respirators after pouring PFC solution into the lungs of the patients.
While not yet implemented, total liquid ventilation with perfluorocarbons has the
potential to revolutionize the emergency medicine response to heart attacks. Hypothetically, on
the scene of a heart attack, medical personnel could use endotracheal intubation – a common
medical procedure in pre-hospital care – to fill the lungs of a heart attack victim with chilled
PFC. During patient transport, a pump may draw deoxygenated PFC out of the lungs to be
saturated through an oxygenator, cooled by a thermostat, and reintroduced into the lungs through
the endotracheal tube. This would provide quick relief to oxygen-starved tissues and delay tissue
death while the medical personnel transport the patient to the hospital for definitive care.
Researchers have demonstrated that this emergency medical use of total liquid ventilation
can be effective through animal trials. One such trial verified that the rapid endotracheal
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introduction of PFC into the lungs of a dog slowed the progression of brain damage from a heart
attack [12]. With further research and refinement, total liquid ventilation with chilled PFCs may
serve as an effective field-solution to provide oxygen and delay tissue damage in a heart attack
victim.
Custom-Made Heart for Transplant
Even after a successful heart attack surgery, the heart has likely suffered irreversible
damage. A potential solution may be to replace the damaged heart with a functional one.
Unfortunately, this is fraught with complications. Though heart transplantation surgeries have
been well established since the 1970s, the short shelf-life of donated hearts makes it very
unlikely that one can be provided for a heart-attack victim in time. Of the few hearts that are
available, most will have different immunological markers than the heart attack victim. These
hearts are unsuitable for transplant as the body’s immune system will recognize the new heart as
foreign and reject it [14].
However, recent advancements in tissue engineering may make it possible to grow new
hearts that match the victim’s immunological markers as needed. Instead of harvesting hearts
from the very recently deceased, tissue engineers can revitalize hearts taken from cadavers.
Rather than waiting for a compatible donor to be located, medical personnel may simply retrieve
dead hearts from cold storage, digest away everything but the heart’s tissue scaffold, and then
apply the victim’s own stem cells to grow a new functional heart [15]. This capacity to custombuild replacement organs may revolutionize the field of tissue transplantation. By removing the
limitation of transplant tissue scarcity, this bioengineering method can make replacement organs
far more accessible to those who may need it.
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Researchers at the University of Minnesota have actually implemented this theory, using
the heart tissue scaffold from a dead mouse to create a new heart from the stem cells of another
mouse. The researchers reported that the newly regenerated mouse heart was beating selfsufficiently [16], see Figure 4.
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<Suggested figure – could use video from (http://www.youtube.com/watch?v=j9hEFUpTVPA)
to make brief repeating animation of heart beating, perhaps around 0:55 or 1:43>
Figure 4: Tissue engineering with adult stem cells has revitalized a dead rat’s heart. The newly
formed heart can beat independently and is ready for transplant into another rat.
Photo from thestar.com
http://media.thestar.topscms.com/images/f1/f8/ba31dbfb4f6f87c941d2ee357240.jpeg
With this proof of concept in rats, the researchers aim to adapt this method to develop
hearts from pig scaffolds. Because pig hearts are very similar to human hearts, this method may
open the door for the harvesting of dead pig hearts for transplant into human heart attack victims.
This is a great milestone for the development of replacement hearts from relatively common
resources and holds great promise for future implementation.
BEATING THE CLOCK WITH HEART ATTACK TREATMENTS
The treatment for heart attack is inherently a race against time. By employing
engineering solutions to secure precious minutes or even reverse tissue damage in the heart
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attack response system, patient outcomes can be significantly increased. With the three
technological innovations discussed above, future medical personnel will have a more effective
arsenal to both keep tissue damage from oxygen deprivation at bay and potentially cure the
damage caused by heart attacks.
CITATIONS
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[10] H. Bonnemeier et al. (2011, Feb). Continuous mechanical chest compression during inhospital cardiopulmonary resuscitation of patients with pulseless electrical activity. Resuscitation
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