Initial defibrillation versus initial chest compression in a 4-minute ventricular fibrillation canine model of cardiac arrest

Objective: Previous laboratory and clinical studies have demonstrated that chest compression preceding defibrillation in prolonged ventricular fibrillation (VF) increases the likelihood of successful cardiac resuscitation. The lower limit of VF duration when preshock chest compression provides no benefit has not been specifically studied. We aimed to study the effect of order of defibrillation and chest compression on defibrillation and cardiac resuscitation in a 4-minute VF canine model of cardiac arrest. Design: Prospective, randomized animal study. Setting. Key Laboratory of Cardiovascular Remodeling and Function Research and Department of Cardiology, QiLu Hospital. Subjects. Twenty-four domestic dogs. Interventions: VF was induced in anesthetized and ventilated canines. After 4 minutes of untreated VF, animals were randomly assigned to receive shock first or chest compression first. Animals in the shock-first group received an immediate single countershock of 360 J for <10 seconds, then 200 immediate compressions before pulse check or rhythm reanalysis. The ratio of compression to ventilation was 30:2. Interruptions to deliver rescue breaths were eliminated in this study. Animals in the chest compression-first group received 200 chest compressions before a single countershock; the other interventions were the same as for the shock-first group. End points were restoration of spontaneous circulation (ROSC), defined as spontaneous systolic arterial pressure >50 mm Hg, when epinephrine (0.02 mg/kg intravenously) was given, and resuscitation, defined as maintaining systolic arterial pressure >50 mm Hg at the 24-hour study end point. Measurements and Main Results: In the shock-first group, all animals achieved ROSC, and ten of 12 survived at the 24-hour study end point. In the chest compression-first group, 11 of 12 animals achieved ROSC, and nine of 12 survived at the 24-hour study end point. Conclusions: In this 4-minute VF canine model of cardiac arrest, the order of initial defibrillation or initial chest compression does not affect cardiac resuscitation. (Crit Care Med 2009; 37:2250-2252)