Abstract Body: Introduction: Rapid termination of ventricular fibrillation (VF) has long been recognized as the cornerstone of effective cardiac arrest resuscitation. In recent years, amplitude spectral area (AMSA) has been shown to be highly associated with defibrillation success, and AMSA has been experimentally used to personalize defibrillation timing and strategy. However, questions remain about whether the interpretation of AMSA holds uniformly in varied conditions, such as ultra-early or prolonged cardiac arrest or after anti-arrhythmic administration.

Hypothesis: AMSA is greater after 20 seconds of untreated VF compared to 50 seconds of untreated VF; a higher AMSA predicts greater first-defibrillation success.

Methods: VF was induced in adult swine (n = 3) with a bipolar pacing catheter placed in the right ventricle. Animals were randomized to 20- or 50-second-long episodes of VF (n = 123), followed by standard 150 J biphasic defibrillation. In MATLAB, AMSA was calculated as the summed product of frequency and square root of power after Fast Fourier Transform for the four second period of VF immediately prior to defibrillation. Results were analyzed by a two-sided Chi-squared test or ANOVA with Tukey’s HSD in R; a p-value < 0.05 was considered significant.

Results: First shock success was lower in the 20-second-VF group compared to the 50 second group (31/78 (39.7%) vs 31/45 (68.8%), p = 0.003). The AMSA at 20 seconds was significantly higher for successful compared to unsuccessful first defibrillation (8.20 vs. 7.31 mV-Hz, p = 0.034). The AMSA at 50 seconds was not statistically different between successful and unsuccessful defibrillations (6.32 vs. 5.67 mV-Hz, p = 0.470). Evaluating the AMSA after a duration of VF irrespective of shock success, AMSA was higher at 20 seconds compared to 50 seconds (7.66 vs 6.12 mV-Hz, p < 0.001).

Conclusion(s): AMSA decreases from 20 to 50 seconds of untreated VF, and higher AMSA at a given time point is associated with greater first defibrillation success. However, first defibrillation success was higher after 50 seconds of untreated VF compared to 20 seconds, raising questions about special cases, such as edge effects, that may influence AMSA interpretation.