Clinical review: Reappraising the concept of immediate defibrillatory attempts for out-of-hospital ventricular fibrillation

Abstract

Despite well developed emergency medical services with rapid response advanced life support capabilities, survival rates following out-of-hospital ventricular fibrillation (VF) have remained bleak in many venues. Generally, these poor resuscitation rates are attributed to delays in the performance of basic cardiopulmonary resuscitation by bystanders or delays in defibrillation, but recent laboratory data suggest that the current standard of immediately providing a countershock as the first therapeutic intervention may be detrimental when VF is prolonged beyond several minutes. Several studies now suggest that when myocardial energy supplies begin to dwindle following more prolonged periods of VF, improvements in coronary artery perfusion must first be achieved in order to prime the heart for successful return of spontaneous circulation after defibrillation. Therefore, before countershocks, certain pharmacologic and/or mechanical interventions might take precedence during resuscitative efforts. This evolving concept has been substantiated recently by clinical studies, including a controlled clinical trial, demonstrating a significant improvement in survival when basic cardiopulmonary resuscitation is provided for several minutes before the initial countershock. Although this evolving concept differs from current standards and may pose a potential problem for automated defibrillator initiatives (e.g. public access defibrillation), successful defibrillation and return of spontaneous circulation have been rendered more predictable by evolving technologies that can score the VF waveform signal and differentiate between those who can be shocked immediately and those who should receive other interventions first.

Figure 1

Comparison of survival rates (successful hospital discharge) in Seattle, USA, during the years when emergency responders made defibrillation attempts their first priority (1990–1993) versus subsequent years (1994–1996), when they provided 90 seconds of basic cardiopulmonary resuscitation before defibrillatory attempts for out-of-hospital cases of ventricular fibrillation. Survival rates and historical comparisons are stratified according to those patients receiving an emergency response within 4 min versus those with response intervals greater than 4 min. The response interval was measured from the time of dispatch of emergency vehicles until the time of arrival at the street address (not time of collapse to arrival at the patient's side). Adapted from Cobb and coworkers [8].

Figure 2

Comparison of out-of-hospital ventricular fibrillation survival rates (successful hospital discharge) with defibrillation attempts provided first versus cases for which there was provision of 3 min of basic cardiopulmonary resuscitation before defibrillation attempts in Oslo, Norway. Survival rate comparisons are stratified according to those patients receiving an emergency response within 5 min versus those with response intervals greater than 5 min. The response interval was measured from the time of dispatch of emergency vehicles until the time of arrival at the street address (not time of collapse to arrival at the patient's side). Adapted from Wik and coworkers [9].