NEW YORK (Reuters Health) – During resuscitation of ventricular fibrillation cardiac arrest, keep the pause in compressions to less than 3 seconds before each shock and to less than 6 seconds afterward.

Sticking to these limits leads to a 13-fold increase in the likelihood that spontaneous circulation will return, according to an April 16th online article in Resuscitation.

The pre-shock limit alone increased the odds of resumption of spontaneous circulation by 3-fold, and the post-shock limit on its own increased the odds by 10-fold, Dr. Daniel P. Davis of the University of California at San Diego and his colleagues found.

To define the optimal intervals between compressions and shocks, Dr. Davis and his colleagues looked at electrocardiography (ECG), impedance, and audio recordings for all 36 patients with out-of-hospital cardiac arrest who received care (including 96 defibrillation attempts) by San Diego emergency medical services (EMS) personnel over the course of a month.

Nineteen attempts at defibrillation produced a palpable pulse, the authors said.

The median pre-shock and post-shock pauses were 7.5 and 8.0 seconds. A receiver-operator curve analysis showed the researchers that the optimum pre-shock interval was less than three seconds, while the optimum post-shock interval was below six seconds.

But as Dr. Davis told Reuters Health, EMS personnel don’t have the training to time defibrillation themselves. Instead they must use automatic defibrillators, which can require 10 to 15 seconds to analyze the patient’s heart activity. “Up until recently it’s been OK to let the defibrillator act as an AED, just let the machine do the work,” Dr. Davis added.

Device manufacturers have been working on reducing the pre-shock interval, but analysis still takes around eight seconds.

This isn’t a problem for the post-shock interval, because emergency medical service team can “get back on the chest” immediately after defibrillation, Dr. Davis added.

But some research has suggested that performing compressions once the heart has begun perfusing on its own could be harmful. He and his colleagues are now conducting a study to determine if measuring end-tidal CO2 could offer a different way to determine when reperfusion has been restored and compressions can be halted.

On the front end, Dr. Davis added, device manufacturers are working on developing filtering technology that will allow automatic defibrillators to “read” the heart rhythm as compressions are being done, so there would be no need for emergency personnel to stop compressions in order for the heart rate to be analyzed.

Reference:

Resuscitation 2010.