The timing of ventricular premature complexes initiating chronic ventricular tachycardia.

Prematurity index (PI), defined as the ratio of the coupling to QT intervals of isolated ventricular premature complexes (VPC) and those initiating ventricular tachycardia (VT) on 24-hour ambulatory ECG recording, was examined in 496 episodes of VT occurring in 122 patients. The PI of VPC initiating VT was less than 1 in only 62 (13%) of the VT episodes and occurred in 14 patients. Although the range of PI was similar for isolated VPC and those initiating VT, for individual patients the PI of VPC initiating VT was significantly longer than the PI of isolated VPC (P less than 0.01). This relationship was not affected by age, sex, presence of absence of heart disease, or drug therapy. The coupling interval of the first VT complex was longer than the first interectopic interval of the VT (VT1-VT2) in 88 (72%) patients; and, the VT1-VT2 interval correlated strongly with the average R-R during VT (r = 0.75), (p less than 0.001). The VT was irregular in 48 patients with 300 episodes of VT. Irregularity of the VT was significantly associated with shorter duration of VT (p less than 0.05). These results show that, for individual patients, the PI of VPC initiating VT tends to be longer than that of isolated VPC, and that the rate of VT is usually predictable from the duration of the first interectopic interval of the VT. These results may have mechanistic implications.