Delaying shock for cardiopulmonary resuscitation: does it save lives?

Out-of-hospital cardiac arrest claims more than 450,000 lives annually in North America. Many communities have dedicated significant resources to provide rapid defibrillator response for patients in ventricular fibrillation. In spite of these efforts, mortality from out-of-hospital cardiac arrest has not improved significantly. Emerging evidence suggests some patients in ventricular fibrillation arrest may be harmed by immediate defibrillation.

Recent laboratory studies have shown benefit in performing a period of chest compressions (cardiopulmonary resuscitation) prior to defibrillation in models with more than 4 minutes of induced ventricular fibrillation. During the initial 4 minutes the heart is more amenable to electrical defibrillation. Between 4-10 minutes, chest compressions create some coronary perfusion and fill the left ventricle to prepare the heart for electric shock. These findings, in conjunction with most emergency medical service response times reported to be 5-8 minutes, have prompted human investigation into a strategy of chest compression first. A recent randomized controlled trial reported a fivefold increase in survival for patients with more than 5 minutes of VF who received 3 minutes of chest compressions prior to defibrillation compared with those who had not.

Current guidelines call for rapid defibrillation as the most important 'link' in the 'chain of survival'. For most ventricular fibrillation patients who have professional rescuers arrive after 5-8 minutes of ventricular fibrillation, however, immediate defibrillation is likely to be ineffective. Counterintuitively, these patients may benefit from a period of chest compressions prior to being shocked.