Abstract 12812: In Out of Hospital Cardiac Arrest Due to Ventricular Fibrillation Amplitude Spectral Area, Amsa, and Slope Predict Defibrillation in Shock Resistant Vf but Not Recurrent Vf
Introduction: Patients with out of hospital cardiac arrest (OHCA) due to ventricular fibrillation (VF) may have recurrent VF during resuscitation or VF that fails to defibrillate (shock resistant). While the VF waveform, assessed by the amplitude spectral area (AMSA) and slope, can predict successful defibrillation overall, it is unknown whether AMSA and slope have a similar predictive power for recurrent VF compared to shock resistant VF. This has implications for how to optimize the timing of defibrillation and avoid unnecessary shocks based upon the type of VF, recurrent or shock resistant.
Methods: Patients with OHCA due to witnessed VF as the initial rhythm were included in this study. AMSA and slope were measured immediately prior to each shock. For second or later shocks, VF was classified as either recurrent (if the previous shock had successfully defibrillated VF) or as shock resistant (if the preceding shock had failed to defibrillate VF).
Results: 33 subjects were analyzed who received more than one shock during resuscitation, with 135 shocks delivered for either recurrent VF or shock resistant VF. Defibrillation was more likely to be successful in recurrent VF compared to shock-resistant VF (OR =13, P<0.001). AMSA and slope were both greater in recurrent VF compared to shock resistant VF: AMSA = 31.7 ± 12.4 vs 14.8 ± 8.9, P<0.001 and slope = 3.3 ±1.4 vs 1.4 ± 1.1, P<0.001. If VF was recurrent, AMSA and slope did not predict defibrillation. However, for shock-resistant VF, AMSA and slope predicted defibrillation with OR=1.2 for every 1 mV-Hz increase in AMSA (P=0.016) and OR=4.8 for every 1 mV/s increase in slope (P=0.025).
Conclusions: In witnessed OHCA with VF as the initial rhythm, recurrent VF is likely to be successfully re-defibrillated, and there is no predictive utility in assessing AMSA and slope prior to delivery of a shock. However, when VF is shock resistant, AMSA and slope are highly predictive of an immediately successful defibrillatory shock.
- © 2010 by American Heart Association, Inc.