LOCALLY PROPAGATED ACTIVATION IMMEDIATELY AFTER INTERNAL DEFIBRILLATION

Background-Electrical mapping studies indicate an interval of 40 to 10 0 ms between a defibrillation shock and the earliest activation that p ropagates globally over the ventricles (globally propagated activation , GPA), This study determined whether activation occurs during this in terval but propagates only locally before being blocked (locally propa gated activation, LPA), Methods and Results-In five anesthetized pigs, the heart was exposed and a 504-electrode sock with lmm interelectrod e spacing was pulled over the ventricles. Ten biphasic shocks of a str ength near the defibrillation threshold (DFT) were delivered via intra cardiac catheter electrodes, and epicardial activation sequences were mapped before and after attempted defibrillation. Local activation was defined as dV/dt less than or equal to-0.5 V/s, Postshock activation times and wave-front interaction patterns were determined with an anim ated display of dV/dt at each electrode in a computer representation o f the ventricular epicardium, LPAs were observed after 40 of the 50 sh ocks. A total of 173 LPA regions were observed, each of which involved 2+/-2 (mean+/-SD) electrodes. LPAs were observed after both successfu l and failed shocks but occurred earlier (P<.0001) after failed (35 +/ - 8 ms) than successful (41+/-16 ms) shocks, although the times at whi ch the GPA appeared were not significantly different. On reaching the LPA region, the GPA front either propagated through it (n=135) or was blocked (n=38). The time from the onset of the LPA until the GPA front propagated to reach the LPA region was shorter (P<.01) when the GPA f ront was blocked (32+/-12 ms) than when it propagated through the LPA region (63+/-20 ms).Conclusions-LPAs exist after successful and failed shocks near the DFT, Thus, the time from the shock to the GPA is not totally electrically silent.