Shock outcome is related to prior rhythm and duration of ventricular fibrillation

Several different ventricular fibrillation (VF) analysis features based on ECG have been reported for shock outcome prediction. In this study we investigated the influence of the time from VF onset to shock delivery (VF duration) and the rhythm before onset of VF, on the probability of return of spontaneous circulation (ROSC). We also analysed how these factors relate to the VF analysis feature median slope.

ECG recordings from 221 cardiac arrest patients from previously published prospective studies on the quality of CPR were used. VF duration and prior rhythm were determined when VF occurred during the episode. Median slope before each shock was calculated.

The median VF duration was shorter in shocks producing ROSC, 24 seconds (s) versus 70s (P<0.001). VF duration shorter than 30s resulted in 27% ROSC versus 10% for those longer than 30s (OR=3.5 [95% CI: 2.2-5.4]). The prior rhythm influenced the probability of ROSC, with perfusing rhythm being superior, followed by PEA, asystole, and "poor" PEA (broad complexes and/or irregular/very slow rate), respectively. The probability of ROSC corresponded well with the average median slope value for each group, but the correlation between median slope and VF duration was very poor (r2=0.05).

Based on our findings, detection of VF during ongoing chest compressions might be valuable because VF of short duration was associated with ROSC. Further, the rhythm before VF affects shock outcome with a perfusing rhythm giving the best prospect. The median slope can be used for shock outcome prediction, but not for determining VF duration. A combination could be beneficial and warrants further studies.