Rapid cooling technique may save victims of sudden cardiac death
May 9, 2001
Rapid Cooling Technique May Save Victims of Sudden Cardiac Death
Fifty percent of victims could be saved
May 10, 2001
Then the heart and brain are cooled to low temperatures, patients can survive without any blood flow for an extended period of time. A rapid cooling technique could be extremely helpful in the treatment of sudden cardiac death, according to Lance B. Becker, MD, a leading expert in emergency medicine.
"In Russia, people are packed in ice, cooled until the heart stops, and then have open heart surgery without blood flow, while in the United States, cardiopulmonary bypass is used during heart surgery," says Dr. Becker, Director of the Emergency Resuscitation Center at the University of Chicago and Argonne National Laboratory in Argonne, Ill., and Associate Professor of Medicine at the University of Chicago.
Dr. Becker spoke May 10 at an American Medical Association media briefing on heart disease.
One of the treatments being developed for sudden cardiac death puts patients into stasis (a suspended animation-like state of reduced heart rate and body function similar to that experienced by mammals during hibernation) through hypothermia (the lowering of core body temperature) instead of restarting their hearts immediately. For hypothermic stasis to work for a victim of sudden death, the cooling has to be done very early and very rapidly. When paramedics are confronted by sudden cardiac death, they do not have any methods to cool a person down rapidly enough to be effective, according to Dr. Becker.
"A new technology for human cooling is being developed at the University of Chicago and Argonne National Laboratory based on a new phase-change microparticulate ice slurry technology that looks promising at least in the theoretical sense," Dr. Becker announces. "One of the coolant slurries we are working with is based on perfluorocarbon, a liquid that can deliver oxygen to the lungs (also portrayed fictionally in the movie The Abyss as the liquid a diver breathed while descending on a very deep dive). The trick is to create a partial liquid/partial solid ice-slurry that can flow easily into a patient because these slurries are high capacity coolants. They have the ability to transfer a lot of heat for a small amount of volume because they will absorb about eight times the amount of heat compared with water (without slurry) at zero degrees Celsius (or 32ºF). We aim to make these coolants biologically compatible and we have done some preliminary animal testing which suggests we are on the right track."
In the future, paramedics might administer this slurry coolant through a breathing tube to patients in cardiac arrest to cool the heart and brain rapidly. "If we can introduce something cold and non-toxic into the lungs of sudden death victims, then when you do cardiopulmonary resuscitation (CPR), the blood cooled in the lungs is pumped first to the heart and then into brain," describes Dr. Becker. "This methods looks promising in terms of giving paramedics the ability to cool the targeted organs of the brain and heart before a patient gets back to the hospital. Once the patient is in the emergency department, we have other cooling techniques that can be used but take some time to get working. We hope by cooling in the field, we will buy time for additional therapies that can be lifesaving. This cooling technology may also benefit diseases other than heart attack such as stroke," he concludes.
Restarting the heart usually fails after cardiac arrest
There is now emerging science to suggest that there might be an even better approach to restarting the heart after prolonged cardiac arrest, according to Dr. Becker. It has been assumed that when heart or brain tissue are without blood flow--and therefore oxygen--tissue and cellular damage is taking place. Therefore, it was believed the best thing to do for that tissue is to immediately give it back as much oxygen-rich blood as possible. But Dr. Becker has learned from his laboratory research that cells appear to die not during the lack of oxygen, but during the restoration of oxygen and blood flow.
"Restarting hearts is what I try to do every day in the emergency room, and it works fantastically if it is accomplished in three to four minutes after the patient collapses. But the patients we typically see are not so lucky--they have had too long a time period without bloodflow; about 90 percent of those patients die even after I've successfully restarted their hearts," comments Dr. Becker. "They die from an injury that is different than the cardiac arrest that originally stopped the heart. We are just beginning to learn that the cause of death appears to be a form of injury that is, in some part, due to the way we resuscitate the person. It appears that significant additional damage takes place during the time when we rapidly reintroduce oxygen and nutrients back into the cells and stimulate the heart to beat. This is called reperfusion injury--and it may be possible to avoid this and still eventually restart the heart. But we may need to give the heart a rest."
During a cardiac arrest when blood has ceased circulating oxygen to the body's cells, precursors to harmful free radicals build up in critical heart and brain tissue. When resuscitation begins, oxygen and nutrients are delivered to the heart and brain cells and powerful drugs are used to force the heart to begin to work (i.e. to contract and beat). The result is a large burst of destructive free radicals--which may make the tissue even sicker--extending this reperfusion injury. "The question is," according to Dr. Becker, "even if we agree that reperfusion injury may be bad, what is the alternative therapy for a person whose heart has stopped beating? By cooling the heart and brain, we can both protect the tissues and prevent the heart from prematurely restarting, as long as we provide both cooling and artificial circulation by some other means (such as a cardiac bypass machine)."
"I predict that in the future we will simply not immediately restart the heart when a person has suffered prolonged lack of blood flow. Instead, our paramedics will rapidly cool patients and put them into a stasis state. The patients will come to an emergency department where they can be placed on cardiopulmonary bypass--this will provide additional cooled circulation. We will allow the heart and the brain to rest and recover for a brief time (maybe an hour) while the external machine does the work of the heart. If our theory works, the tissues should have regenerated more normal physiology before we re-warm and restart the beating of the heart. This method would allow tissues to initially focus all the cell's energy into repair, rather than on working (i.e. contracting)--thus tissue recovery could be much greater," according to Dr. Becker.
"Most importantly, with research funding these methods can be developed right now and I cannot imagine how we can fail to invest in science to save people's lives," he articulates. "We lose approximately 1,000 lives a day in our country to sudden expected death, and the true tragedy is that with the appropriate therapy, we could save around 50 percent of those people. Right now our national survival rate is below 5 percent. We are all guilty of tolerating a lot of unnecessary deaths."
Many more lives can be saved with current technology
"There have been many breakthroughs in the fight against sudden death and we know absolutely that we can do far better--right now--in saving people's lives from cardiac arrest. It is exciting that there is a growing movement now in this country trying to bring all these breakthroughs to the victims of sudden death," says Dr. Becker. "By combining the best of basic science with the best of new technologies (such as automated external defibrillators) plus CPR, we could make a major difference in the world."
Automated external defibrillators (AEDs) are new devices that make it possible for a lay rescuer to rapidly shock and restart the heart of a cardiac arrest victim and have been shown to make a significant difference in the survival of life threatening heart arrhythmias. According to the American Heart Association (AHA), survival rates are highest (from 9 percent to 30 percent) in cities where AEDs are available to first responders and where CPR training is widespread and emergency medical service (EMS) response is rapid. Markedly lower longer-term survival rates (from 1 percent to 2 percent) are seen in cities in which high-rise buildings and traffic congestion delay EMS response times and bystander CPR is infrequent. The challenge in these locations is getting rapid defibrillation to a victim.
After equipping police vehicles and training the police to defibrillate with AEDs, Rochester, Minn., saw an improved survival rate of 21 of out 44 victims (48 percent). That compares to a survival rate in New York of 26 out of 2,329 victims (1 percent), according to AHA figures.
By installing AEDs, Chicago airports have increased their survival rates from approximately 2 percent to greater than 60 percent. Several other public locations including casinos and airplanes have done the same thing, according to Dr. Becker. With rapid defibrillation, as can be provided with AEDs, other public places may also be able to improve survival rates.