The time it takes for an AED to analyze a cardiac arrest victim’s electrocardiogram, charge and deliver a shock is called the “hands-off” interval because cardiopulmonary resuscitation (CPR) chest compressions must stop then. Researchers found indications that the shorter the time between stopping chest compressions and when a shock is delivered, the better a person’s chance of surviving ventricular fibrillation. Ventricular fibrillation is the chaotic heart rhythm that causes cardiac arrest and sudden cardiac death.
According to the American Heart Association, about 250,000 people a year die of coronary heart disease without being hospitalized. That’s about half of all deaths from coronary heart disease – more than 680 Americans each day. Most of these are sudden deaths caused by cardiac arrest. “Our study suggests that not only do you need to act quickly to get an AED on the scene of a cardiac arrest, but you also should move as quickly as possible from CPR to defibrillation,” says study author Trygve Eftestol, Dr. Ing., an associate professor at Stavanger University College, Stavanger, Norway.
To determine the link between the hands-off interval and survival, researchers studied 634 hands-off intervals in 156 patients with ventricular fibrillation in which AEDs were used for resuscitation attempts. The duration of hands-off intervals varied by a median of 20 seconds.
Researchers grouped cardiac arrest victims according to their initial probability (high, medium or low) of return of spontaneous circulation (ROSC), which was estimated from the starting point of the ECG readings of their hands-off intervals.
These ECG readings show a person’s cardiac activity from the beginning of the hands-off interval – when chest compressions are stopped – until delivery of a shock. During this interval, the AED analyzes the heart rhythm and determines if a shock is needed, charges to the proper shock dose, and prompts the rescuer to deliver a shock. The probability of successful defibrillation with return to spontaneous circulation was also estimated at 5, 10, 15 and 20 seconds into each of the hands-off intervals.
Researchers compared the calculated probabilities with the actual rates of ROSC for the medium-level and high-level groups. From this comparison they found that the shorter the hands-off interval, the greater the chance of a cardiac arrest victim regaining spontaneous circulation. People with the highest initial chance of ROSC would have received the most benefit from a shorter hands-off interval—if they had received a shock immediately, they might have had a ROSC rate as high as 50 percent, says Eftestol. Within five seconds, their estimated ROSC rate dropped to 25 percent; after 15 seconds to 15 percent; and after 20 seconds, it was 8 percent. For those with a medium initial probability of ROSC, shock delivery after a five-second hands-off period resulted in ROSC in 24 percent; after 15 seconds, 17 percent; and at 20 seconds it was 11 percent.
Finally, the group with the lowest probability of ROSC had only about a 5 percent estimated chance of ROSC throughout the intervals. “This study is extremely important for several reasons,” says Mary-Fran Hazinski, R.N., M.S.N., former chair of the American Heart Association’s emergency cardiovascular care committee. “First, it reaffirms the importance of CPR training and the important role of CPR with the use of AEDs. Second, it provides very solid data that supports the need to shorten the time required for AED rhythm analysis and charging. AED manufacturers are already working to shorten this hands-off interval. Finally, it emphasizes the need for CPR-AED rescuers to practice their skills to ensure the most efficient time to shock delivery – seconds saved can mean improved survival.”
Co-authors include Kjetil Sunde, M.D., Ph.D., and Petter Andreas Steen, M.D., Ph.D.
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