Abstract
STUDY OBJECTIVE: Effectiveness of a resuscitation strategy may vary across communities. We hypothesize that a strategy that prioritizes initial emergency medical services (EMS) rhythm analysis (analyze early) will be associated with survival advantage among EMS systems with lower baseline (pretrial) ventricular fibrillation survival, whereas a strategy that prioritizes initial EMS cardiopulmonary resuscitation (analyze late) will be associated with survival advantage among systems with higher ventricular fibrillation baseline survival. METHODS: We conducted a secondary, post hoc study of a randomized trial of out-of-hospital cardiac arrest. Subjects were stratified according to randomization status (analyze early versus analyze late) and EMS agency baseline ventricular fibrillation survival. We used a mixed-effects model to determine whether the association between favorable functional survival to hospital discharge and trial intervention (analyze late versus analyze early) differed according to EMS agency baseline ventricular fibrillation survival (<20% or >20%). RESULTS: Characteristics were similar among patients randomized to analyze early (n=4,964) versus analyze late (n=4,426). For EMS agencies with baseline ventricular fibrillation survival less than 20%, analyze late compared with analyze early was associated with a lower likelihood of favorable functional survival (3.8% versus 5.5%; odds ratio [OR]=0.67 [95% CI 0.50, 0.90]). Conversely, among agencies with a ventricular fibrillation survival greater than 20%, analyze late compared with analyze early was associated with higher likelihood of favorable functional survival (7.5% versus 6.1%; OR=1.22 [95% CI 0.98, 1.52]). In the multivariable-adjusted model, for every 10% increase in baseline ventricular fibrillation survival, analyze late versus analyze early was associated with a 34% increase in odds of favorable functional survival (OR=1.34 [95% CI 1.07 to 1.66]). CONCLUSION: The findings suggest that system-level characteristics may influence resuscitation outcomes.