Predictors of resuscitation in a swine model of ischemic and nonischemic ventricular fibrillation cardiac arrest: Superiority of amplitude spectral area and slope to predict a return of spontaneous circulation when resuscitation efforts are prolonged

Objective: We have demonstrated that a return of spontaneous circulation in the first 3 mins of resuscitation in swine is predicted by ventricular fibrillation waveform (amplitude spectral area or slope) when untreated ventricular fibrillation duration or presence of acute myocardial infarction is unknown. We hypothesized that in prolonged resuscitation efforts that return of spontaneous circulation immediately after a second or later shock with postshock chest compression is independently predicted by end-tidal CO₂, coronary perfusion pressure, and ventricular fibrillation waveform measured before that shock in a swine model of ischemic and nonischemic ventricular fibrillation arrest. Design: Animal intervention study with comparison to a control group. Setting: University animal laboratory. Subjects: Twenty swine. Interventions: Myocardial infarction was induced by steel plug occlusion of the left anterior descending coronary artery. Ventricular fibrillation was untreated for 8 mins in normal swine (n = 10) and acute myocardial infarction swine (n = 10). Measurements and main results: End-tidal CO₂, coronary perfusion pressure, and ventricular fibrillation waveform characteristics of amplitude spectral area and slope were analyzed before second or later shocks. For an amplitude spectral area >35 mV-Hz, the odds ratio for achieving return of spontaneous circulation after that shock was 72 (95% confidence interval, 3.8-1300; p = .004) compared with an amplitude spectral area <28 mV-Hz and with an area under the receiver operator characteristic curve of 0.86. For slope >3.6 mV/s, the odds ratio for achieving return of spontaneous circulation was 36 (95% confidence interval, 2.7-480; p = .007) compared with slope <2.72 mV/s with an area under the curve of 0.86. End-tidal CO₂ and coronary perfusion pressure were not predictive of return of spontaneous circulation after a shock, although coronary perfusion pressure was significantly related to both amplitude spectral area (p < .001) and slope (p < .001). Conclusions: In prolonged untreated ventricular fibrillation arrest, the waveform characteristics of amplitude spectral area and slope predict the attainment of return of spontaneous circulation with a second or later shock. This has implications for the ideal means to customize the timing of shocks and chest compressions when return of spontaneous circulation is not promptly obtained.