Refractory ventricular fibrillation in out-of-hospital cardiac arrest: shock characteristics, predictors and clinical outcomes.

BACKGROUND

In patients with out-of-hospital cardiac arrest (OHCA) who receive multiple shocks, it is often unclear whether they are experiencing refractory or recurrent ventricular fibrillation (VF). Understanding into the cause of refractory VF is limited and the foundational evidence for alternative defibrillation strategies are lacking. To gain further insight into these patients we studied the incidence and possible predictors of refractory VF, and compared outcomes between patients with recurrent VF and those with refractory VF.

METHODS

Using the ARREST registry, we included patients with VF at the first three rhythm checks between 2016 and 2019. ECG waveforms were analysed for successful termination of VF at five seconds after each shock delivered. Patients were classified as having refractory VF if all three shocks failed to terminate VF. The remaining patients were classified as having recurrent VF. Outcomes and possible predictors between both groups were compared.

RESULTS

Out of 436 patients who met the inclusion criteria, 22 (5%) had refractory VF and 414 (95%) had recurrent VF. Rates of return of spontaneous circulation (ROSC) and 30-day survival were 9/22 (41%) vs 243/409 (59%) (RR 0.69 [95% CI, 0.41-1.15]) and 5/22 (23%) vs 187/408 (46%) (RR 0.49 [95% CI, 0.23-1.08]) in patients with refractory and recurrent VF, respectively. Predictors for refractory VF were absence of CPR and AED use before emergency medical services arrival, a longer delay to the first shock, and a lower amplitude spectral area value.

CONCLUSIONS

The small group of refractory VF patients were characterised by unfavourable resuscitation characteristics. Clinical outcomes in refractory VF versus recurrent VF patients remain uncertain due to low patient numbers.