Evolution of activation dynamics during early stages of electrically-induced ventricular fibrillation

Previous studies suggest that the organization of epicardial activation patterns (EAP) during ventricular fibrillation (VF) changes over both time and space. To investigate whether organization of EAP changes during the first few seconds of electrically-induced VF, we recorded unipolar electrograms [V(t)] from 504 epicardial recording sites (21×24, 1 mm separation) during multiple runs of VF in three open-chest pigs. Activation intervals (temporal difference between local activation times defined by selecting dV/dt_max within 25 ms window) were determined at nine of the epicardial sites during 2 s segments of data taken 1, 5 and 10 s after VF induction. Activation intervals (mean ± SD) became longer and more regular as VF duration increased from 1-3 s (110 ± 17 ms) to 10-12 s (115 ± 15). The spatial distribution of SD over the mapped region tended to decrease over this same time period. These findings may have important implications related to therapeutic strategies which attempt to produce regional control of myocardial activation patterns during VF.