Cardiac Arrest Linking Lifelines to Beat the Odds

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 - Minneapolis Heart Institute Foundation
Thermal hypothermia mitigates brain damage that may occur when blood flow is restored to the brain after cardiac arrest and resuscitation.
Source: Minneapolis Heart Institute Foundation
Annually, an estimated 295,000 people in the U.S. experience out-of-hospital cardiac arrest, and only 6 to 10 percent survive (Circ 2011;123:e18-e209). Another 200,000 hospitalized patients suffer cardiac arrest each year, with only 25 percent surviving to discharge (Crit Care Med 2011, online). These overall survival statistics have seemed mired in the low digits for decades. But strengthening the American Heart Association (AHA) Emergency Cardiovascular Care's "chain of survival" may lead to improvements in outcomes for both out-of-hospital and inpatient cardiac arrest victims.

Last year, the chain of survival became longer if not immediately stronger when the AHA updated its Cardiopulmonary Resuscitation (CPR) and Emergency Cardiovascular Care guidelines (Circulation 2010;122:S640-S933). The previous guidelines listed four series of events as crucial to cardiac arrest survival: an emergency response, CPR, defibrillation and advanced cardiac life support. Recent studies that showed promising results from the use of therapeutic hypothermia (TH) prompted the committee to add integrated care after resuscitation to the chain. Early indications suggest that the fifth link could tip survival rates in patients' favor.

A prompt response, continuous CPR  

Survival rates for patients with out-of-hospital cardiac arrest vary widely, depending on circumstances, particularly emergency medical service (EMS) systems and hospitals. One key factor is whether the event is witnessed, followed by a prompt response. For instance, Valenzuela et al reported one of the highest survival to discharge rates—53 percent—among patients who experienced cardiac arrest at a casino and were treated by security personnel trained in CPR and the use of automated external defibrillators (N Engl J Med 2000;343:1206-1209). The authors attributed the high survival rate in part to the events occurring in a public area with surveillance cameras.

But only about 20 percent of cardiac arrests occur in public settings, making rapid response by EMS personnel more difficult, especially when the patient is in a hard-to-reach location such as an elevator, says Ian G. Stiell, MD, chair of emergency medicine research at the Ottawa Hospital Research Institute in Ontario, Canada. In a large-scale cluster-randomized study, Stiell and colleagues in the Resuscitation Outcomes Consortium (ROC) found that EMS personnel failed to follow the study's protocol duration of CPR in 36 percent of the patients, despite training.

The findings reflect the complex clinical circumstances that EMS face, the researchers wrote. ROC currently is testing in the real-world setting, which is fast paced and sometimes chaotic, Stiell says. "This is not a laboratory."

The 2010 guidelines emphasized early CPR and rapid defibrillation, but they don't resolve conflicting results in studies that, on one side, support a brief period of CPR followed by first analysis of cardiac rhythm, and on the other, call for prolonged CPR before first analysis.

Stiell and his ROC colleagues designed their study to try to clarify the issue. The trial enrolled 9,933 patients assigned to either early analysis in which EMS administered CPR for 30 to 60 seconds before first analysis of cardiac rhythm, or later-analysis, with CPR administration lasting three minutes before first cardiac rhythm analysis.

The researchers found no advantage in the longer duration group: 5.9 percent of patients survived to hospital discharge with satisfactory functional status in both groups. Patients with a first rhythm of ventricular tachycardia or ventricular fibrillation who first were given CPR by a bystander had poorer survival if they were in the later-analysis group.

"There is no point in performing a lot of additional CPR," Stiell insists. "For resuscitation, CPR should be started immediately and should be continued with minimal interruptions."

On the surface, the ROC's findings of a 5.9 percent survival rate reinforced the gloomy forecast for cardiac arrests. But the study included a wealth of measurements that ROC investigators are analyzing to identify practices that improve survival outcomes. "This is a major issue for the pre-hospital part of this equation," Stiell says. "We're learning a lot of what's right and wrong and how to correct it."

In-hospital cardiac arrests

Location counts most when it comes to in-hospital cardiac arrests, according to research by Demetrios J. Kutsogiannis, MD, of the division of critical care medicine at the University of Alberta in Edmonton, Canada, and colleagues. In two separate studies, Kutsogiannis et al explored survival outcomes after cardiac arrest in ICUs and non-ICU hospital wards.

Among the ICU patients, 59.6 percent were resuscitated and 26.9 percent survived to discharge from the hospital. Non-ICU patients fared worse. About 30 percent of those patients regained a pulse and only 13 percent survived to hospital discharge.

Just as visibility helped patients in the casino study, the ICU's standard 24-hour monitoring may have benefited the ICU patients—even though they were sicker, Kutsogiannis and colleagues noted. He says their findings demonstrate that adding more nurses or monitoring devices in other wards may increase chances for survival for in-hospital cardiac arrests.

"This speaks to the bigger issue of resource allocation," Kutsogiannis says. "Perhaps, we should be monitoring sicker people who are on the wards."

Post-cardiac care varies among hospitals as well, according to Brenda G. Carr, MD, of the department of emergency medicine at University of Pennsylvania School of Medicine in Philadelphia, and colleagues. In a study of 39 hospitals between 2002 and 2005, they found that inpatient mortality ranged from 41 to 81 percent. Carr et al also observed no relationship between type of hospital and mortality, but survival rates were higher at high-volume hospitals (Resuscitation 2009;80[1]:30-34).

Effective post-cardiac arrest care

Animal studies have shown TH mitigated brain damage that can result when cerebral blood flow is restored after cardiac arrest and resuscitation. In 2002, two clinical trials pushed the strategy to the forefront by concluding that cooling cardiac arrest patients' body temperature to 32 to 34 degrees Celsius improved outcomes.

One study compared the effects of moderate TH with standard treatment at normal temperatures in comatose patients resuscitated after cardiac arrest (N Engl J Med 2002;346-557-63). Almost half of the hypothermia group survived to discharge compared with a quarter of the other group. And the second study reported favorable neurologic outcomes in resuscitated patients who received mild TH after cardiac arrest due to atrial fibrillation (N Engl J Med 2002;346:549-56).

"They were landmark papers," says Bradley A. Maron, MD, of the division of cardiovascular medicine at Brigham and Women's Hospital in Boston. "They exposed the utility of this therapy to preserve neurological function and to improve outcome." Since then, the International Liaison Committee on Resuscitation and the AHA have endorsed TH post-resuscitation care for comatose adults with witnessed out-of-hospital with ventricular fibrillation arrest.

While uptake has been slow, several hospitals now have programs, such as the Minneapolis Heart institute's Cool It initiative, which makes TH a standard of care for resuscitated cardiac arrest patients. Also, EMS in some urban areas, including New York City and Boston, have put policies in place to transport resuscitated cardiac arrest patients to hospitals that perform TH, even if they are farther away. In some regions, trained EMS personnel initiate cooling with ice packs for cardiac arrest patients with restored circulation, no matter what the presenting rhythm.

Maron partnered with his father, Barry J. Maron, MD, and his brother, Martin S. Maron, MD, at the Minneapolis Heart Institute and Tufts University School of Medicine in Boston, respectively, to assess TH as a treatment strategy for patients whose cardiac arrest was not from ischemic heart disease but another form of heart disease that did not affect cardiac output. They selected hypertrophic cardiomyopathy, which is a major cause of sudden cardiac death in young athletes.

"It is important to note that most, if not all of the trials, assessing therapeutic hypothermia have not fractionated with therapy by the cardiac disease," Maron says. "These studies have included patients solely on the presence of cardiac arrest, typically of ventricular arrhythmia."

They identified seven relatively young out-of-hospital cardiac arrest patients with hypertrophic cardiomyopathy who received TH between 2006 and 2010 for their study group. All seven fully recovered with preserved neurological and cardiac functions (JACC 2011;57[24]:2454-560). Typical survival rates for this patient population are about 25 percent, Maron says.

Their study potentially extends the use of TH to a broader patient population that includes younger people and a spectrum of heart diseases. If early results hold up, then TH therapy may galvanize the fifth link in the chain of survival and improve survival outcomes.