Abstract 189: Changes in Initial Quantitative VF Score as a Function of EMS Response Time

Introduction: EMS response intervals have been correlated with increased return of spontaneous circulation (ROSC), as well as improved survival to hospital admission and discharge. Response intervals have also been associated with increased likelihood of ventricular fibrillation (VF) as the presenting rhythm, as well as crude VF waveform amplitude. The role of bystander CPR (B-CPR) has been extensively studied, with some studies suggesting a more limited contribution to survival. We sought to analyze correlations between EMS response time, B-CPR and VF waveform properties. Methods: We performed a retrospective analysis of data derived from an international randomized controlled trial utilizing a VF waveform algorithm in patients with out of hospital cardiac arrest (OOHCA). Standard Utstein definitions were used. EMS response times were calculated from the time calls were received until EMS personnel arrived at the incident location. Quantitative VF scores were calculated using a proprietary algorithm. Results: There were a total of 752 bystander-witnessed VF arrests for which B-CPR and EMS response times were known. Those patients who received B-CPR (n=290) had a mean normalized VF score of 0.13 (sd=0.07), while those not receiving B-CPR (n=462) had a mean initial VF score of 0.11 (sd=0.07), (p Conclusions: Bystander CPR improves the likelihood that OOHCA patients will present with VF characteristics amenable to immediate shock. EMS response time was not associated with increased quantitative VF score when B-CPR occurred. These findings suggest a physiologic explanation through which B-CPR may contribute to improved outcomes that has not been previously described. Further research regarding this relationship may aid strategies for optimizing B-CPR and its contribution to OOHCA survival.