Vectorcardiographic analysis of prefibrillatory ventricular tachycardia in the rabbit

In 10 urethan anaesthetized rabbits, VCG of acontine induced VT was studied. At the beginning of VT, both QRS and T loops arise and end regularly at the e point. Then, QRS loop opens and its end moves outside the E point, as a result of changes in ST segment. Later on, when ST segment disappears completely owing to an initial overlapping of the depolarization and repolarization processes, no arrest of the trace is observed between QRS and T loops. Lastly, immediately before the appearance of ventricular fibrillation, a progressive increase of the rate of VT above 400/min produces a fusion between the end of the T and the initial part ofn the next QRS loop. At this stage, no E point can be recognize. The results suggest that the transformation of VT into VF occurs through a delay and an overlapping of the depolarization-repolarization sequence.