Defibrillation and refractory ventricular fibrillation

Abstract

Of patients with out-of-hospital cardiac arrest (OHCA) presenting in ventricular fibrillation (VF), the majority require multiple shocks.1 Guidelines recommend chest compressions be resumed immediately after the shock without a rhythm check.2 In current practice, when VF is present at consecutive rhythm checks, it is uncertain whether previous shocks repeatedly failed to terminate VF (refractory VF) or VF recurred after successful shocks. Alternative defibrillation strategies have been studied in patients found to be in VF at three consecutive rhythm checks.3 We studied the incidence of refractory and recurrent VF in patients receiving multiple consecutive standard shocks and the time to refibrillation in cases with recurrent VF. In this observational study, we analysed data from patients from the ARREST (AmsteRdam REsuscitation STudies) registry who received four or more consecutive standard shocks separated by 2-min cardiopulmonary resuscitation (CPR) cycles. We included all OHCA cases between January 2016 and December 2019 with a medical cause and VF as initial rhythm. We excluded patients in whom the automated external defibrillator (AED) or emergency medical service (EMS) defibrillator recordings were not available, in whom a stacked shock strategy was used, and who received a shock from an implantable cardioverter-defibrillator. Details on data collection by ARREST have previously been reported.4 In brief, ARREST collects a comprehensive data set on all consecutive OHCAs in the study region and follows the Utstein resuscitation template for OHCA.5 All AEDs are manually accessed by the study team on site, and data from EMS defibrillators are sent digitally to the study site. For this study, all rhythm strips from both AEDs and EMS manual defibrillators were analysed to determine the pre- and post-shock rhythms and time of refibrillation. All cases were analysed separately by two assessors with experience in reviewing defibrillator recordings and electrocardiogram interpretation. The primary outcome was the proportion of patients with refractory VF, defined as the proportion of OHCA patients with VF as initial rhythm, and three shocks administered at the first three rhythm checks, in whom the first three shocks all failed to terminate VF. Successful termination of VF was defined as the presence of a non-shockable rhythm 5 s after the shock.6 Patients in whom at least one of three shocks successfully terminated VF were considered to have recurrent VF. Refibrillation was defined as recurrence of VF following successful termination of VF. From a total of 4993 OHCA cases, 1640 (33%) had a shockable initial rhythm. Of the 436 (27%) that met the inclusion criteria, 88% were male, mean age 64 ± 14 years, 86% were witnessed, and 86% received basic life support before EMS arrival. Median time from initial EMS call to the first shock was 8.0 [interquartile range (IQR), 6.3–9.7] min. An AED was connected in 66% of cases, and 641 of the 1308 (49%) initial three shocks were delivered by an AED. In 22 cases (5.0%, 95% confidence interval, 3.2%–7.5%), all of the first three shocks failed to terminate VF. The remaining 414 patients (95.0%) had recurrent VF. Altogether, VF was terminated in 1006 of the 1308 (77%) first three shocks combined. The first three shocks terminated VF at least once in 414 patients (95%), at least twice in 351 patients (81%), and with all three shocks in 241 patients (55%) (Figure 1). (A) Sankey plot showing ventricular fibrillation termination success for each defibrillation. Green (upper ribbons) changing to red indicates cases in whom the rhythm 5-s post-shock was non-shockable and in whom refibrillation occurred during the ensuing 2-min cardiopulmonary resuscitation (CPR) cycle. Red (lower ribbons) indicates cases in whom the rhythm 5-s post-shock was shockable and the shock was therefore classified as unsuccessful. (B) Cumulative percentage of the time to refibrillation after the first three 773 successful defibrillations. VF, ventricular fibrillation The time of refibrillation could be determined in 773 of 1006 successful shocks (77%). Median time to refibrillation for the first three shocks combined was 27 (IQR, 14–60) s. By 60 s after the shock, refibrillation occurred in 75% of all cases with recurrent VF, which increased to 87% at 90 s after the shock. This study showed that, in OHCA patients receiving standard shocks at the first three consecutive rhythm checks during resuscitation, the incidence of refractory VF was only 5%. Even when patients needed multiple shocks, VF termination rate was high throughout all defibrillation attempts. In patients with recurrent VF, the median time to refibrillation was 27 s. Our results are in line with results from earlier studies. The rate of successful termination of VF at the first shock is typically high at around 67%–96%, remaining high even after multiple shocks.1,7–9 Our findings shed a different light on the findings of the recent DOSE-VF trial.3 This clustered randomized trial found that in patients with perceived refractory VF, survival to hospital discharge occurred more frequently among those in the dual sequential external defibrillation (DSED) group or vector-change defibrillation group than among those in the standard defibrillation group.3 That trial was designed based on the hypothesis that continuing with standard defibrillation after the first three shocks is usually unsuccessful at terminating VF. In our study, we applied inclusion criteria similar to those of DOSE-VF and found that 95% of the cases who would have been perceived to have refractory VF actually had recurrent VF. The majority of patients (56%) even had successful termination of VF by all three standard shocks. This may partly be explained by the high rates of bystander CPR and shorter time to first shock found in our study as compared with the DOSE-VF trial. Thus, although the populations and study methods are different, our findings suggest that the vast majority of the DOSE-VF patients must have been in recurrent VF rather than in refractory VF and that many of the standard shocks in the DOSE-VF study already had successfully terminated VF. Therefore, alternative explanations for the positive results of the DOSE-VF trial are needed. In cases who were cluster randomized to DSED, the survival benefit may have resulted from the additional care provided by a second EMS team, which provided the second defibrillator. Another explanation might be that DOSE-VF was terminated early and included only 405 of the required 930 patients (45%), which increased the likelihood of a false-positive result (type 1 error). Differences in possible co-determinants between randomized groups then may be exaggerated by chance. Future research should focus on the prevention and treatment of recurrent VF. These may include efforts to reduce the time to first shock, alternative antiarrhythmic drug strategies, and detection of recurrent VF during CPR followed by immediate defibrillation, reducing the total VF burden.10 We thank Rudolph W. Koster, MD, PhD (Amsterdam UMC location University of Amsterdam, Heart Center, Department of Clinical and Experimental Cardiology) for providing valuable comments on the manuscript. Authors R.G.W., T.G.T., R.M., and F.W.C. reported being full-time employees of Stryker Emergency Care. L.C.D., M.M.E., R.S., and H.v.S. report funding from Stryker Emergency Care to their institution. All other authors reported no conflicts of interest. The data underlying this article will be shared on reasonable request to the corresponding author. All authors declare no funding for this contribution. The Institutional Ethical Review Board of the Academic Medical Center approved the ARREST data collection, including the use of data from deceased individual patients and the use of a limited anonymous data set from survivors who refused consent. None supplied.

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