COMPUTERIZED 3-DIMENSIONAL ACTIVATION MAPPING STUDY OF SPONTANEOUS VENTRICULAR ARRHYTHMIAS DURING ACUTE MYOCARDIAL-ISCHEMIA IN DOGS - EVIDENCE AGAINST MACROREENTRANT MECHANISM

This study was undertaken to investigate the activation patterns of sp ontaneous ventricular arrhythmias during acute myocardial ischemia in dogs. In 14 open-chest dogs, the left anterior descending coronary art ery was occluded for 2 hours. Three-dimensional activation maps were d erived from 240 bipolar sites by insertion of 60 plunge needle electro des into both ventricles and the septum. Global ventricular activation sequences were displayed in five planes in 10 dogs, whereas the high density regional activation maps of the anterior wall were displayed i n four layers in 4 dogs. Three-dimensional activation maps of 95 sinus beats, 82 premature ventricular complexes (PVCs), and 210 beats of ve ntricular tachycardia (VT) were analyzed. Sinus beats had a uniform ac tivation pattern with total ventricular activation times measuring 42 +/- 4 ms and 67 +/- 8 ms during baseline and ischemia, respectively (P < .05). The PVCs and VTs originated from the subendocardial and intra mural layers, and activation patterns invariably suggested focal excit ation. Macroreentry was not operative because (1) the breakthrough sit es were always remote from the latest activation areas; (2) there was no electrical activity bridging the gap between the termination of a b eat and initiation of the subsequent beat; and (3) impulse conduction was not sufficiently delayed to reexcite the area of impulse origin ev en though functional conduction block was frequently present. In high- density regional activation maps; fragmented activity spanning the dia stolic interval was never found. In conclusion, spontaneously occurrin g PVCs and VTs during acute myocardial ischemia in dogs display focal excitation with no evidence of macroreentry.