567 QT prolongation during ventricular stimulation is entirely dependent on QRS widening

Abstract

Conditions that prolong the QT interval (QTi) on the ECG can increase the risk of polymorphic ventricular tachycardia. The recognition of the normal and augmented Qti is important to prevent sudden death. In patients with bundle branch blocks, the augmentation of the Qti is totally caused by the prolongation of the depolarization (QRS duration). In these patients, formulas of QT correction have been developed which exclude the QRS duration. Alternatively, the JT interval (Jti) can be used. Criteria to evaluate the Qti in patients stimulated by a ventricular pacemaker have not been established. The extrinsic stimulation changes the QRS duration, and also the vectors of depolarization. The purpose of this study is to evaluate whether the depolarization time (JT) prolongs during ventricular pacing. In six consecutive pacemaker clinics, we searched our ECG database to find patients who had at least one ECG showing ventricular stimulation and one with intrinsic ventricular activation. We compared the paired (intrinsic vs stimulated) QTi, QRS duration and JTi of 71 patients (33 females, 68.7 ± 11 years old). As expected, the QRS complexes were wider with stimulation (105 ± 27 ms vs 163 ± 21 ms, P < 0.0001). QTi were also longer during ventricular pacing (430 ± 35 ms vs 493 ± 35 ms, P < 0.0001) but the JTi was not statistically different (325 ± 28 ms, 330 ± 32 ms, P = 0.29). There is a prolongation of the QTi with ventricular stimulation. This seems to be completely dependent on the prolongation of the QRS. The formula for QTi correction developed for patients with intraventricular conduction abnormalities is probably also useful for stimulated patients. This will be further confirmed in a prospective study.