Fig. 7. Initiation of a reentrant ventricular tachycardia after a 100-mJ contusion in the left ventricular epicardium. (Top ) Electrogram recorded during induction of ventricular tachycardia using rapid pacing (S1). Numbers above the recorded electrogram indicate time interval (in milliseconds) between two ventricular activations. Four consecutive activation maps are given and show the spread of depolarization. Numbers indicate local activation times in milliseconds. Isochrones are drawn at 10-ms intervals. The thick isochrones indicate local conduction blocks. Arrows indicate direction of activation. Double bars indicate the stop of influx propagation in the direction considered. The closed circle represents the pacing site. The hatched area corresponds to the impact contusion zone with no electrical activity. (A , B ) Correspond to the epicardial depolarization after the regular pacing cycle (S1–S1 = 145 ms). A  was recorded immediately after contusion (T0), B  was recorded 16 min after contusion impact. The first beat of the sustained ventricular tachycardia (first VTB) is shown in C . The pattern of the depolarization during sustained monomorphic ventricular tachycardia (second VTB) is shown in D . All maps present the same frontal view of the heart. FW = ventricular free wall; LAD = left anterior descending coronary artery. (See text for further descriptions.)