Incessant versus recurrent refractory ventricular fibrillation: classification and prognosis in out-of-hospital...

Refractory ventricular fibrillation sudden cardiac arrest (VF-SCA) can be pragmatically defined as VF requiring ≥3 defibrillation attempts. During resuscitation, cardiac rhythm response to shock is typically assessed two minutes after shock without knowledge of the rhythm's interim evolution. However, treatments might be better directed by defining refractory VF-SCA "subtypes" based on the immediate, shock-specific response: successful defibrillation with VF recurrence (recurrent VF) versus unsuccessful defibrillation without VF termination (incessant VF). We compared two methods for recurrent versus incessant classification to understand their agreement and prognosis.

We conducted a retrospective cohort investigation of VF-SCA. We labeled shock-specific VF subtypes (incessant versus recurrent) using two methods. Method 1 classified VF shocks as recurrent if there were >5 s of non-VF rhythm after shock, while method 2 evaluated the rhythm at 6/8/10-s "snapshots" post-shock to determine if VF was absent (recurrent) or present (incessant). These shock-specific responses generated three patient-level VF groups: recurrent only, mixed (recurrent and incessant), and incessant only. We evaluated the classification agreement between these methods.

Among 1829 VF-SCA patients, 1018 (56%) had refractory VF-SCA of which 48% were recurrent, 36% mixed, and 16% incessant. Agreement between classification methods was greatest using the 8-s snapshot for method 2 (shock-specific kappa = 0.97, patient-level kappa = 0.95). Patient-level refractory VF subtypes had distinct prognoses (favorable survival: recurrent only = 43%, mixed = 36%, incessant only = 22%, p < 0.001 test-for-trend).

Different methods classifying VF shock response produced excellent agreement. Recurrent-mixed-incessant shock responses were associated with progressive decline in favorable outcome, highlighting a measurable phenotype to direct care.