Derivation of Clinical Predictors of Failed Rescue Shock During Out-of-Hospital Ventricular Fibrillation

Abstract

Background. Failed rescue shocks have been shown to decrease the likelihood of survival in the treatment of out-of-hospital ventricular fibrillation (VF). Avoidance of failed shocks may improve survival. Objective. We sought to derive clinical predictors that could be used by emergency medical services (EMS) personnel to identify a subset of VF patients whose first rescue shock is likely to fail, making them candidates for a cardiopulmonary resuscitation (CPR)-first strategy. Methods. After gaining institutional review board approval from all three institutions, we merged data from Los Angeles, Pittsburgh, andRoyal Oak into a new cardiac arrest database. We used classification andregression tree (CART) analyses to build the model. We defined a failed first rescue shock as one in which there was no return of spontaneous circulation (ROSC); the postshock electrocardiographic (ECG) rhythm was VF, pulseless electrical activity (PEA), or asystole; or subsequent shocks were delivered (indicating that the first shock had failed). Results. The database contains 5,046 cases, of which 1,777 (35%) had VF as the initial ECG rhythm. Sufficient data were present for 748 cases. Using unwitnessed collapse, a response time of >6 minutes, andabsence of bystander CPR (BCPR) on EMS arrival as predictors, 35 of 35 (100%, 95% confidence interval [CI] 100–91.4%) cases had failed first rescue shocks. Second shock failure was predicted in 162 of 164 (99%) cases. Conclusions. Unwitnessed collapse, response time >6 minutes, andabsence of BCPR may be useful in predicting which VF patients are likely to have failed first shocks andwould thereby benefit from a CPR-first strategy. Stacked rescue shocks most often fail, andthis outcome can also be predicted.

Key words:

• predictors
• ventricular fibrillation
• rescue shocks, failure
• cardiopulmonary resuscitation