VENTRICULAR-TACHYCARDIA IN HEALING CANINE MYOCARDIAL-INFARCTION - EVIDENCE FOR MULTIPLE REENTRANT MECHANISMS

Prior studies have demonstrated that unimorphic VT, sometimes due to e picardial reentry, can be induced in healing canine MI; however, the c haracterization of the types of reentry involved has differed among pr ior studies. The purpose of this study was to further characterize the spectrum of epicardial reentrant circuits during induced VT in experi mental canine MI. Experimental MI was created by total occlusion of th e LAD in dogs. Five days later, programmed stimulation tvas used to in duce VT, which was mapped on the epicardium using a combination of vec tor and isochronal techniques. Pathological analysis was used to deter mine regions of transmural MI. Epicardial reentrant circuits were iden tified in eight dogs. The mean cycle length of induced VT was 212 +/- 32 ms. In 3 of 8 experiments, a region of transmural MI was present, w hich formed at least a portion of a central zone of block around which reentrant impulses circulated. In five experiments, reentry was funct ional in nature, although the characteristics of the region of functio nal conduction block were variable. Long lines of functional block, sh ort lines of block with slow conduction transverse to fiber orientatio n, and leading circle reentry were each observed in different experime nts. Although a zone of slow conduction was identified in seven of the experiments, slow conduction transverse to fiber orientation appeared crucial in maintaining reentry in only three experiments. Multiple re entrant mechanisms of VT may be present in this single canine infarcti on model. Although a zone of slow conduction is usually present, the c haracteristics of the region of block are highly variable. However, ep icardial reentry accounted for only a minority of induced arrhythmia e pisodes.