Dynamics of T-U wave in patients with idiopathic ventricular tachycardia originating from the right ventricular outflow tract.

Postextrasystolic U wave augmentation is observed in patients with long QT syndrome and those with organic heart disease. This phenomenon is considered a marker of increased risk of arrhythmia. However, the characteristics of the U wave have not been evaluated in patients with idiopathic VT originating from the right ventricular outflow tract (RVOT-VT). The present study evaluated the dynamic change in the T-U wave in patients with RVOT-VT. Holter ECGs obtained from 14 patients with RVOT-VT and 11 healthy control subjects were analyzed. The amplitude of T and U waves (Tamp and Uamp) and preceding RR intervals were measured during stable sinus rhythm (rate dependent change) and in the postextrasystolic sinus complex (pause dependent change). Uamp correlated negatively and significantly with the preceding RR interval in 13 (93%) RVOT-VT patients but in only 2 (18%) control subjects. The average value of the slope of the Uamp/RR relationship was negative (-0.22 +/- 0.10 mV/s) in the RVOT-VT group, but was positive (0.04 +/- 0.07 mV/s, P < 0.001) in the control group. Pause dependent U wave augmentation was observed in 12 (86%) of 14 patients. Increased frequency of consecutive preceding premature ventricular contractions (PVCs) was associated with a larger postextrasystolic Uamp. PVC or the first ventricular beat of VT arose from near the peak of augmented U waves. The dynamic changes in the T-U wave were observed in patients with RVOT-VT. Further investigations are required to elucidate the precise role of the U wave in arrhythmogenesis in those patients.