The ventricular fibrillation waveform in relation to shock success in early vs. late phases of out-of-hospital resuscitation

Background: The amplitude spectrum area (AMSA)of the ventricular fibrillation (VF)waveform predicts shock success and clinical outcome after out-of-hospital cardiac arrest (OHCA). Recently, also AMSA-changes demonstrated prognostic value. Until now, most studies focused on early shocks, while many patients require prolonged resuscitations. We studied AMSA and its changes in relation to shock success, for both the early and later phase of resuscitation.

Methods: Per-shock VF-waveform analysis of a prospective OHCA-cohort (Nijmegen, The Netherlands). The absolute AMSA and relative AMSA-changes (ΔAMSA)were calculated from three-second VF-segments prior to defibrillation. Shocks were categorised as early (#1–3)or late (#4–8). Shock success was defined as return of organised rhythm.

Results: Shock success was 46% for early (131/286)and 52% for late shocks (85/162), p = 0.18. Early shock success varied from 23% to 70% with increasing quartiles of AMSA (p-trend<0.001). For late shocks, there also was an association with AMSA, with a narrower range in shock success from 43% to 68% (p-trend = 0.04). Higher values of ΔAMSA were associated with shock success in the early, but not in the later phase.

Conclusion: AMSA relates to shock success during the entire resuscitation, but associations were most apparent for early shocks. AMSA-changes were also associated with shock success, but only in the early phase of resuscitation. In an era of smart defibrillators, absolute AMSA and relative changes hold promise for studies on early guidance of resuscitation, whereas additional studies are warranted to further characterize shock prediction in the later phase.