Patients with an automatic external defibrillator applied by a bystander in a public setting have a strikingly higher frequency of ventricular tachycardia/ventricular fibrillation than observed cardiac arrests in the home

Introduction

The overall incidence of ventricular tachycardia/ventricular fibrillation (VT/VF) as the first recorded electrical rhythm in out-of-hospital cardiac arrest has declined from ~70% to ~25% over the past 30 years. This change has been attributed to primary and secondary prevention of cardiovascular disease and VT/VF. We evaluated whether the incidence of VT/VF as first recorded rhythm differed by location among bystander-applied automatic external defibrillator (AED) patients and emergency medical services (EMS)-witnessed cardiac arrests.

Methods

A prospective cohort study of nontraumatic cardiac arrest from December 2005 to April 2007 in the Resuscitation Outcomes Consortium database from 10 US and Canadian sites. The incidence of an initial shockable rhythm on AED or documented VT/VF was compared among bystander-applied AED patients and EMS-witnessed arrests in public versus private settings.

Results

The first rhythm was known in 13,235 out of 14,059 (94%) adult EMS-treated cardiac arrests. Of the 13,235 with known rhythms, 3,436 (26%) had VT/VF. Among 1,115 EMS-witnessed arrests, 61/161 (38%) had VT/VF in public settings and 224/954 (23%) in private settings. Similarly, for bystander AED applied in the private setting, 39/114 (34%) were shocked. But, in contrast, 125/159 (79%) (P < 0.001 vs. all other) were shocked by the AED in the public setting. Witnessed arrests in both the private setting (vs. public) and in EMS-witnessed cases (vs. bystander AED applied) were more likely to occur in older subjects and females. After adjusting for age and gender via logistic regression models, a significant difference in the odds of having a shockable rhythm in a public versus private location of arrest remained in EMS-witnessed arrests (P < 0.005). The difference also remained in bystander AED-applied arrests (P < 0.001) after adjusting for age, gender, and bystander-witnessed status.

Conclusion

The incidence of VT/VF is far greater in the public setting particularly for bystander-witnessed AED-applied arrests. Patients in the private home setting, even for EMS-observed arrests, are far less likely to benefit from AED application than bystander-witnessed patients in the public setting. Cardiopulmonary resuscitation strategies may need to be tailored by arrest location.