Ambulatory ventricular tachycardia: characteristics of the initiating beat

One hundred ten 24-hour Holter ECG recordings from 82 ambulatory patients with 341 episodes of ventricular tachycardia (VT) were analyzed. Most VT was precipitated by ventricular premature beats (VPBs) with prematurity indices (coupling interval/QT) between 1.0 and 2.0. However, a disproportionate number of VPBs initiating VT occurred early and late in the cardiac cycle compared with isolated VPBs. VT rate was not related to preceding heart rate, but faster basic rates appeared to protect against VT of extended duration. Approximately 80% of episodes of VT were initiated by VPB forms also seen in isolation. Of the 20% of VT initiated by a VPB of new morphology, one third occurred late in the cardiac cycle; almost none were early cycle.