title: 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, and Royal Oak into a new cardiac arrest database. We used classification and regression 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, and absence 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, and absence of BCPR may be useful in predicting which VF patients are likely to have failed first shocks and would thereby benefit from a CPR-first strategy. Stacked rescue shocks most often fail, and this outcome can also be predicted.
authors.affiliation: Department of Emergency Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA. menegazzijj@upmc.edu
authors.forename: James J
authors.initials: JJ
authors.lastname: Menegazzi
authors.forename: Margaret
authors.initials: M
authors.lastname: Hsieh
authors.forename: James T
authors.initials: JT
authors.lastname: Niemann
authors.forename: Robert A
authors.initials: RA
authors.lastname: Swor
mesh_terms: D016887:Cardiopulmonary Resuscitation; D003661:Decision Support Techniques; D004554:Electric Countershock; D004634:Emergency Medical Technicians; D006801:Humans; D015141:Los Angeles; D008824:Michigan; D010414:Pennsylvania; D012044:Regression Analysis; D017211:Treatment Failure; D014218:Triage / Q000379:methods*; D014693:Ventricular Fibrillation / Q000175:diagnosis / Q000628:therapy*