Delaying a shock after takeover from the automated external defibrillator by paramedics is associated with decreased survival.

Abstract

The purpose of this study was to investigate whether the takeover by Advanced Life Support [ALS] trained ambulance paramedics from rescuers using an automated external defibrillator [AED] delays shocks and if this delay is associated with decreased survival after out-of-hospital cardiac arrest [OHCA]. We analyzed continuous ECG recordings of LIFEPAK AEDs and associated manual defibrillator recordings of OHCA of presumed cardiac cause, prospectively collected from July 2005 to July 2009. The primary outcome measure was survival to discharge. Among 693 patients treated with AEDs, 110 had a shockable initial rhythm and a shockable rhythm during ALS takeover. We measured the time interval between the expected shock if the AED would remain attached to the patient and the first observed shock given by the manual defibrillator [shock timing]. Survival was 62% (13/21) if the shock was given early (<-20s), 52% (11/21; odds ratio [OR]=0.68, ns) if given on time (-20 to 20s), 29% (10/34; OR=0.26, 95% confidence interval [CI]=0.08-0.81; P=0.02) if the shock was 20-150s delayed and 21% (7/34; OR=0.16, 95% CI=0.05-0.54; P=0.003) if the shock was delayed >150s. The OR for trend was 0.41, 95% CI=0.25-0.71; P=0.001. The association between shock timing and survival was significant for patients with more than 150s shock delay (OR=0.19; 95% CI=0.04-0.71; P=0.02) or for trend in shock timing (0.42, 95% CI=0.20-0.84; P=0.02) after multivariable adjustment for prognostic factors age and slope of ventricular fibrillation. ALS takeover delays the next shock delivery in almost two-third of cases. This delay is associated with decreased survival.