Myocardial Substrate in Secondary Ventricular Fibrillation: Insights from Quantitative Waveform Measures

Abstract

Background. Some patients presenting with nonshockable cardiac arrest rhythms will subsequently manifest ventricular fibrillation. Their prognosis remains poor despite transition to a shockable rhythm. Quantitative waveform measures assess the electrophysiologic status of the fibrillating heart and predict outcome. Objective. To use waveform measures to compare those who presented initially with ventricular fibrillation (primary group) with those who manifested ventricular fibrillation after initially presenting with a nonshockable arrest rhythm (secondary group). Methods. We conducted an observational study using a convenience sample to compare waveform measures of amplitude spectrum area (AMSA), cardioversion output predictor (COP), and detrended fluctuation analysis (DFA) prior to initial shock between the primary (n = 178) and secondary (n = 28) groups. We produced a primary group matched to the secondary group based on the average waveform values to evaluate the observed versus expected outcomes in the secondary group. Results. Survival was 42% in the primary group and 0% in the secondary group. There was a trend toward more favorable waveform values in the primary compared with the secondary group (9.48 versus 9.29, p = 0.10 for AMSA; 13.75 versus 14.12, p = 0.003 for COP; and 0.36 versus 0.44, p = 0.09 for DFA). The restricted, matched primary group experienced a survival of 37%, compared with 0% for the secondary group. Conclusions. Taken together, the findings suggest that the electrophysiologic status of the heart may be suitable for resuscitation in at least some secondary ventricular fibrillation cases and that other pathophysiology may contribute substantially to the poor prognosis. Alternately, waveform measures may not predict clinical outcomes in secondary ventricular fibrillation.