Association Between Delay to First Shock and Successful First-Shock Ventricular Fibrillation Termination in Patients With Witnessed Out-of-Hospital Cardiac Arrest

Abstract

Background: In patients with out-of-hospital cardiac arrest who present with an initial shockable rhythm, a longer delay to the first shock decreases the probability of survival, often attributed to cerebral damage. The mechanisms of this decreased survival have not yet been elucidated. Estimating the probability of successful defibrillation and other factors in relation to the time to first shock may guide prehospital care systems to implement policies that improve patient survival by decreasing time to first shock.

Methods: Patients with a witnessed out-of-hospital cardiac arrest and ventricular fibrillation (VF) as an initial rhythm were included using the prospective ARREST registry (Amsterdam Resuscitation Studies). Patient and resuscitation data, including time-synchronized automated external defibrillator and manual defibrillator data, were analyzed to determine VF termination at 5 seconds after the first shock. Delay to first shock was defined as the time from initial emergency call until the first shock by any defibrillator. Outcomes were the proportion of VF termination, return of organized rhythm, and survival to discharge, all in relation to the delay to first shock. A Poisson regression model with robust standard errors was used to estimate the association between delay to first shock and outcomes.

Results: Among 3723 patients, the proportion of VF termination declined from 93% when the delay to first shock was <6 minutes to 75% when that delay was >16 minutes (P_trend<0.001). Every additional minute in VF from emergency call was associated with 6% higher probability of failure to terminate VF (adjusted relative risk, 1.06 [95% CI, 1.04-1.07]), 4% lower probability of return of organized rhythm (adjusted relative risk, 0.96 [95% CI, 0.95-0.98]), and 6% lower probability of surviving to discharge (adjusted relative risk, 0.94 [95% CI, 0.93-0.95]).

Conclusions: Every minute of delay to first shock was associated with a significantly lower proportion of VF termination and return of organized rhythm. This may explain the worse outcomes in patients with a long delay to defibrillation. Reducing the time interval from emergency call to first shock to ≤6 minutes could be considered a key performance indicator of the chain of survival.

Keywords: cardiopulmonary resuscitation; defibrillators; electric countershock; emergency medical services; heart arrest; out-of-hospital cardiac arrest; ventricular fibrillation.

Figure 1.

Flowchart of the study population. EMS indicates emergency medical services; ICD, implantable cardioverter defibrillator; OHCA, out-of-hospital cardiac arrest; PEA, pulseless electrical activity; VF, ventricular fibrillation; and VT, ventricular tachycardia.

Figure 2.

Rhythm 5 seconds after the first shock in patients with a witnessed out-of-hospital cardiac arrest with ventricular fibrillation as initial rhythm. A, Rhythm 5 seconds after the first shock in patients with a non–emergency medical services (EMS)–witnessed out-of-hospital cardiac arrest (OHCA) with ventricular fibrillation (VF) as initial rhythm. Rhythm 5 seconds after first shock in relation to the time interval between emergency call and first shock. The 49 patients within the <0 category are patients in whom an automated external defibrillator shock was delivered before the call to the dispatch center was received. χ² for trend P<0.001. B, Rhythm 5 seconds after the first shock in patients with an EMS-witnessed OHCA with VF as initial rhythm. Rhythm 5 seconds after first shock in relation to the time interval between initiation of VF and first shock in patients with an EMS-witnessed OHCA. χ² for trend P=0.007.

Figure 3.

Estimated adjusted relative risk in outcomes per additional minute of delay to first shock. Estimated risk ratios (RRs) in outcomes per additional minute of delay to first shock compared with the reference category and adjusted for sex, age, rural or urban area, public or residential, and time of day using Poisson regression model with robust standard errors. Reference categories: nonshockable rhythm 5 seconds after first shock; no return of organized rhythm 5 seconds after first shock; 1 prehospital shock delivered during resuscitation; no sustained return of spontaneous circulation (ROSC) before transport; deceased before hospital discharge. aRR indicates adjusted relative risk.

Figure 4.

Total number of prehospital shocks in patients with a non–emergency medical services–witnessed out-of-hospital cardiac arrest. Total number of shocks delivered during the resuscitation attempt in the prehospital phase using any defibrillator (automated external defibrillator or emergency medical services defibrillator) in relation to the time interval between call to the dispatch center and first shock. The 49 patients within the <0 category are patients in whom an automated external defibrillator shock was delivered before the call to the dispatch center was received. χ² for trend P<0.001. *Data of 1 patient were missing. †Data of 2 patients were missing.

Figure 5.

Return of spontaneous circulation in relation to delay to first shock in patients with a non–emergency medical services–witnessed out-of-hospital cardiac arrest with ventricular fibrillation as initial rhythm. Percentages of patients with return of spontaneous circulation (ROSC), patients who were transported to the hospital with ongoing cardiopulmonary resuscitation, or patients who died on scene in relation to delay to first shock. The 49 patients within the <0 category are patients in whom an automated external defibrillator shock was delivered before the call to the dispatch center was received. χ² for trend P<0.001. *Data of 3 patients were missing. †Data of 1 patient were missing.