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Monday, June 20, 2011

Pause between CPR, defibrillation can be deadly

PUBLIC HEALTH REPORTER— From Tuesday's Globe and Mail

Published Monday, Jun. 20, 2011 4:00PM EDT
Last updated Monday, Jun. 20, 2011 4:43PM EDT

The research, published in Tuesday’s edition of the medical journal Circulation, indicates that minimizing the brief period it takes to move from cardiopulmonary resuscitation to administering an electric shock with a defibrillator is a key predictor for survival.

“If your preshock pause is over 20 seconds, the chances of surviving to reach a hospital, be treated and be discharged are 53 per cent less than if the pause is less than 10 seconds,” said Sheldon Cheskes, medical director of the Sunnybrook Osler Centre for Prehospital Care in Brampton, Ont., and lead author of the study. “Those seconds matter.”

He said he hopes the findings will encourage paramedics to move more quickly. In particular, he said, using defibrillators in manual mode halves the delay. Dr. Cheskes said that manufacturers of lifesaving equipment also need to update software to ensure that the time required to analyze a patient’s heart rhythm and charge the defibrillator before delivering a shock is minimal.

The new study is based on data from 815 people who suffered out-of-hospital cardiac arrest between 2005 and 2007 across Canada and the United States. Their average age was 64, and 80 per cent were men.

All of the people included in the research suffered either ventricular fibrillation (abnormal heart rhythm) or pulseless ventricular tachycardia (no effective cardiac output), conditions that can be reversed with an electric shock. They were treated promptly – paramedics arrived, on average, in less than six minutes – and received CPR and defibrillation. The patients received at least one shock but required, on average, five jolts to restart their heart.

Dr. Cheskes and his colleagues in the research group known as the Resuscitation Outcomes Consortium found the time that passed between stopping CPR and defibrillation ranged from 0 to 107 seconds. The median time required for the transition was 22 seconds.

The researchers found that when the pause was less than 20 seconds, 32.6 per cent of patients survived; between 20 and 39 seconds, the survival rate was 31.9 per cent. But when the pause exceeded 40 seconds, the survival rate fell to 20.3 per cent.

“If you minimize interruptions, you maximize survival,” Dr. Cheskes said. He stressed, however, that the study focused on just one element in a chain of events that needs to occur when a person suffers cardiac arrest.

“We looked at the work of paramedics but don’t forget that without bystander CPR – people doing CPR before the paramedics arrive – very few people survive,” Dr. Cheskes said. “Any delay in blood flow to the brain is detrimental for survival.”

In 2010, new CPR guidelines were published that urge people to push hard and fast – at least 100 compressions a minute. While assisting with breathing (mouth-to-mouth in common parlance) is still important, it is considered secondary because it discouraged many people from intervening.

In addition to chest compressions, people are urged to call 911 and ask for another bystander to locate a public access defibrillator. PADs are automated and will not “shock” a patient unless there is no heart rhythm.

In the new study, in 52 per cent of cases, a bystander performed CPR before paramedics arrived, but a PAD was used in fewer than 1 per cent of cases.

Time matters - it's really important

Contact: Tagni McRae
American Heart Association

Shorter pause in CPR before defibrillator use improves cardiac arrest survival

A shorter pause in CPR just before a defibrillator delivered an electric shock to a cardiac arrest victim's heart significantly increased survival, according to a study in Circulation: Journal of the American Heart Association.

Researchers found the odds of surviving until hospital discharge were significantly lower for patients whose rescuers paused CPR for 20 seconds or more before delivering a shock (the pre-shock pause), and for patients whose rescuers paused CPR before and after defibrillation (the peri-shock pause) for 40 seconds or more, compared to patients with a pre-shock pause of less than 10 seconds and a peri-shock pause of less than 20 seconds.

"We found that if the interval between ending CPR and delivering a shock was over 20 seconds, the chance of a patient surviving was 53 percent less than if that interval was less than 10 seconds," said Sheldon Cheskes, M.D., principal investigator of the study and assistant professor of emergency medicine at the University of Toronto. "Interestingly there was no significant association between the time from delivering a shock to restarting CPR, known as the post-shock pause, and survival to discharge. This led us to believe that a primary driver for survival was related to the pre-shock pause interval."

The team also found that patients with peri-shock pauses of more than 40 seconds had a 45 percent decrease in survival when compared to those who had peri-shock pauses of less than 20 seconds.

Based on previous studies, American Heart Association resuscitation guidelines advise minimizing interruptions to chest compressions to 10 seconds or less. However, previous studies didn't measure how such pauses in CPR affected survival to hospital discharge.

According to this study, emergency medical services (EMS) in the United States treat nearly 300,000 cardiac arrest cases a year that occur outside the hospital. Less than 8 percent survive.

Cheskes and colleagues used data gathered by the Resuscitation Outcomes Consortium (ROC), a group of 11 U. S. and Canadian Emergency Medical Services that carry out research studies related to cardiac arrest resuscitation and life-threatening traumatic injury.

Between Dec. 1, 2005, and June 30, 2007, 815 patients suffered a cardiac arrest and were included in the study. They were treated by EMS paramedics in Toronto and Ottawa, Ontario; Vancouver, B.C.; Seattle/King County, Wash. and Pittsburgh, Pa. The patients were treated with either an automated external defibrillator (AED) or a manual defibrillator.

Other findings from the study:

The length of the post-shock pause showed no significant survival difference between the two groups.
AEDs were used to treat 40 percent of the cardiac arrests; 20 percent received shocks from a manual defibrillator.
Patients treated with AEDs had pre-shock pause times nearly double those treated in the manual mode, a median of 18 seconds versus 10 seconds. This likely resulted from the time required for an AED to analyze the patient's rhythm as well as the time required to charge it prior to delivering a shock.
The study findings could prompt EMS providers and defibrillator manufacturers to adopt changes likely to increase the number of successful cardiac arrest resuscitations, researchers said. These include:

Paramedics should minimize all CPR interruptions; preferably defibrillate patients in manual mode to limit the pre-shock pause to an "optimal time" of five seconds.
Manufacturers should modify defibrillator software to quicken the assessment of a patient's heart rhythm, and allow devices to deliver more timely shocks while in AED mode. "If these changes occur, I think you have at least the potential to see a greater number of patients surviving cardiac arrest," Cheskes said.
Although the study was not a randomized controlled trial, researchers said their findings confirm those of other smaller observational studies and that it would be very difficult to perform a randomized controlled trial given the evidence to date. Furthermore, higher rates of bystander witnessed cardiac arrest and bystander-provided CPR occurred in the study group which may have resulted in a selection bias. Although the study controlled for a large number of resuscitation variables, the potential for other components of CPR such as compression rate and depth may have also confounded the findings.

Study co-authors and funding sources are listed on the manuscript.

Statements and conclusions of study authors published in American Heart Association scientific journals are solely those of the study authors and do not necessarily reflect the association's policy or position. The association makes no representation or guarantee as to their accuracy or reliability. The association receives funding primarily from individuals; foundations and corporations (including pharmaceutical, device manufacturers and other companies) also make donations and fund specific association programs and events. The association has strict policies to prevent these relationships from influencing the science content. Revenues from pharmaceutical and device corporations are available at

NR11 – 1088 (Circ/Cheskes)

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