Distinctive time course of ventricular vulnerability to fibrillation during and after release of coronary ligation

Release of left anterior descending coronary artery ligature was performed in 32 dogs after periods of ligation ranging from 3 to 45 minutes. Spontaneous ventricular tachycardia or fibrillation occurred during occlusion in 9 of 20 dogs, developing during the first 8 minutes of occlusion in 8 of the 9. Ventricular tachycardia or fibrillation was evoked by release of occlusion in 3 of 7 dogs after a short-term occlusion of 3 to 6 minutes, and in 9 of 13 dogs after release of a long-term occlusion of 15 to 45 minutes. Thresholds for induced ventricular tachycardia or fibrillation were obtained using a train of gated stimuli (100 Hz for 250 msec). During short-term occlusions, average thresholds for ventricular tachycardia or fibrillation were reduced from 32.4 ma (control) to 3.4 ma ( P < 0.001); during long-term occlusions, thresholds returned to normal (control 29.6 ma, occlusion 18.6 ma; difference not significant). Immediately after release of both short- and long-term occlusions, thresholds were not significantly different from control values. No correlation was found between mechanical and electrical abnormalities during the release phase since the magnitude of tension prolongation after release of both short- and long-term ligations was the same and thus did not correspond with the electrical differences of these states. Our data suggest the following conclusions: (1) The time course of spontaneous ventricular vulnerability to fibrillation during coronary occlusion differs from that of ligature release, the former diminishing and the latter increasing with the duration of occlusion. (2) This observation and the lack of correlation between thresholds of induced ventricular tachycardia or fibrillation and spontaneous vulnerability to fibrillation after ligature release suggest different electrophysiologic mechanisms for ventricular tachyarrhythmias during and after release of coronary ligation.