972-106 Intramural Activation Patterns of Focal Ventricular Tachycardia Induced by Programmed Stimulation During Experimental Subacute Myocardial Infarction

The purpose of this study was to elucidate the three dimensional (3-D) activation patterns of focal excitation during induced ventricular tachycardia (VT) in subacute myocardial infarction in canines. In 30 dogs 5 days after LAD occlusion and reperfusion, intramural electrograms were simultaneously recorded from 240 bipolar sites through 60 plunge needles inserted into both ventricles. Computerized 3-D color-coded isochronal activation maps were generated. At the given resolution, focal VT was diagsnosed when the site of latest activation was anatomically remote from the site of impulse origin. In 12 of 26 experiments, reproducibly induced sustained monomorphic VTs were attributed to a focal mechanism. Activation patterns were the following: 1) Radial spread of excitation (n = 5). Ventricular activation was completed in approximately 100 ms followed by about 100 ms of electrical quiescence. 2) Progressive slow conduction (n = 2). A focal excitation pattern was associated with progressive prolongation of intramural conduction times. 3) Presystolic activity and unidirectional exit block(n = 2). The site of impulse origin was surrounded by areas of unidirectional conduction block with intramural conduction delay. 4) Pan diastolic activity (n = 3). Myocardial activation was present throughout the entire systolic and diastolic intervals without regional slow conduction or block. In conclusion, multiple intramural activation patterns are present in focal VTs induced by programmed stimulation. Delayed diastolic activity does not constitute a direct evidence for macro-reentry. Triggered activity with or without conduction delay may be the underlying mechanism of these induced arrhythmias.