Abstract 419: Incidence of True Refractory Ventricular Fibrillation in Patients Meeting a Pragmatic Definition of Refractory Ventricular Fibrillation

Abstract

Introduction: Refractory VF, pragmatically defined as a shockable presenting rhythm that is still observed after three shocks and associated 2-minute CPR cycles, is often encountered in out-of-hospital cardiac arrest (OHCA) and is associated with worse outcomes. A recent clinical trial tested alternative strategies for treating patients meeting this definition of refractory VF. It is unknown how often standard defibrillation truly fails to terminate VF in these patients. Methods: Using the prospective AmsteRdam REsuscitation STudies (ARREST) registry of OHCA patients, we examined termination of VF in patients meeting the pragmatic definition of refractory VF between 2016 and 2019. All patients received standard defibrillation. We reviewed ECG waveforms from all AEDs and manual defibrillators to analyze termination of VF to a non-shockable rhythm at five seconds after each of the first 3 shocks. Refibrillation was defined as recurrence of VF after a shock terminated VF. Results: Out of 1573 OHCAs with an initial shockable rhythm, we analyzed the 453 cases (29%) that met the pragmatic definition of refractory VF. Median time to first shock was 8.0 (IQR 6.3-9.7) minutes; in 65% an AED was used. The first three shocks terminated VF at least once in 96% of the patients, at least twice in 81%, and all three times in 57%. Altogether, VF was terminated by 78% of all individual shocks. In 4% of patients all three shocks failed to terminate VF (Figure). Median time to refibrillation was 32 (IQR 12-61) seconds. ROSC at any time occurred in 59% of patients; 27% survived to discharge. Conclusions: In patients meeting a pragmatic definition of refractory VF, true refractory VF without termination of the shockable rhythm by any of the first three shocks was rare. Instead, VF was successfully terminated by most shocks and recurred during the ensuing CPR cycle. Therefore, the mechanism of benefit from alternative defibrillation strategies in these patients is unclear.