Three‐Dimensional Mapping of Earliest Activation after Near‐Threshold Ventricular Defibrillation Shocks

Three‐Dimensional Pattern of Earliest Postshock Activation. Introduction: Following shocks with a 50% defibrillation success (DFT 50 ) delivered from electrodes at the right ventricular (RV) apex and superior vena cava (SVC), the earliest epicardial postshock activation always appears focally in the left ventricular (LV) apex for both successful and failed shocks. Because the heart is a three‐dimensional (3D) structure, questions remain whether this activation truly arises from a focus or the focal pattern represents epicardial breakthrough resulting from intramural reentry. To answer these questions, 3D electrical mapping was performed.Methods and Results: In six pigs, 60 to 84 epoxy fiberglass needles (0.7‐mm‐diameter), each containing six electrodes 2 mm apart, were inserted into the LV with 3‐ to 5‐mm spacing around the apex and 5‐ to 10‐mm spacing near the base. Ten DFT 50 shocks (RV→SVC, biphasic, 6/4 msec) were delivered after 10 seconds of fibrillation in each animal. The first five activations after each shock were mapped. Of 60 DFT 50 shocks, 31 were successful, of which the first postshock cycle was a sinus beat in 13. In the other 18 successful shock episodes, the first postshock activation was detected63 ± 16msec after the shock, which was not significantly different from the58 ± 23msec postshock interval for the 29 failed shock episodes. In these 47 successful and failed shock episodes, the earliest postshock activation always arose focally from the LV apex. Its origin was in the subepicardium in76%± 17%, midmyocardium in16%± 12%, and subendocardium in8%± 6%of cases .Conclusion: Following near‐DFT 50 shocks, the first postshock cycles did not arise by macroreentry. Instead, they originated from a true focus or microreentry, most commonly near the epicardium.