VF or VT – Earlier Defibrillation Is Better?

Written by Samuel Rouleau

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In a retrospective study of 142 patients with an initial shockable rhythm and 4 to 5 episodes of recurrent/refractory ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT), shorter duration of VF and pVT was associated with higher rates of ROSC. 

VF or VT arrest in the air? Ride the Lightning!
This retrospective study included adult patients who had out-of-hospital cardiac arrest from presumed medical etiology. They had an initial shockable rhythm and then had 4–5 additional VF/pVT episodes. Paramedics used a Zoll defibrillator that interprets rhythms during chest compressions, and, if there is a shockable rhythm, the local protocol was to pre-charge the defibrillator, stop chest compressions, and deliver the shock. The primary outcome was ROSC (either sustained or non-sustained) within 20 seconds of shock. 

Out of all 891 shocks, 243 (27%) were deemed inappropriate. When analyzing the 622 shocks correctly delivered as the study unit, 204 shocks (32.8%) resulted in ROSC. The ROSC group had a shorter duration of VF/pVT (0.83 min) compared to no ROSC (1.28 min). When analyzing the 142 patients as the study unit, ROSC was achieved in 70 patients (49.3%), and 32 (22.5%) survived to discharge with good neurologic outcome. The authors used a special logistic regression model (generalizing estimating equations) to determine the impact of covariates. Unsurprisingly, longer durations of VF and pVT were less likely to be associated with ROSC (OR 0.81, 95%CI 0.7–0.93). The statistical methodology used, and this odds ratio is how the authors concluded, “for each one-minute increase in VF/pVT duration, the odds of achieving ROSC decrease by 19%.” 

How will this change my practice?

• This study suggests that we should continue to shock VF/pVT quickly and without delay.
• I am intrigued by rhythm analysis during chest compressions allowing for earlier defibrillation. However, an error rate of 27% is too high for me to feel confident about this technology. 
• While not statistically significant in this study, limiting epinephrine in patients with recurrent or refractory VF/pVT may confer a benefit (refer to Table 2 in the manuscript).

Editor’s note: Agree with Sam that the performance of adaptive filters to interpret the rhythm during chest compressions was lackluster. However, the principle of early defibrillation fits with current BLS and ACLS recommendations. If VF/pVT persists after the first shock, I wonder if we might resume CPR for 1 minute instead of 2 minutes before confirming the rhythm and delivering the next shock. There is no evidence for what I just said. I am just wondering if this might be beneficial based on this study. ~Clay Smith

Source 
The impact of time to defibrillation on return of spontaneous circulation in out-of-hospital cardiac arrest patients with recurrent shockable rhythms. Resuscitation. 2024;201:110286. doi:10.1016/j.resuscitation.2024.110286. PMID: 38901663.