The QT interval during wake and sleep in patients with ventricular arrhythmias

Eight patients with frequent ventricular ectopy underwent continuous electrocardiographic (ECG) and polygraphic monitoring for 4 days. A complex protocol consisted of normal day-night, activity-nonactivity, cycles for 48 h (nine patients); followed by a 24-h awake bedrest; and finally by a very delayed sleep and inactivity phase in the morning before returning to a normal day-night cycle (eight patients only). ECG tracings showed that the QT intervals during rapid eye movement sleep and nonrapid eye movement sleep increased significantly when compared with active wakefulness. The Bazett's corrected QT (QTc) interval also increased from active wakefulness to rapid eye movement sleep and nonrapid eye movement sleep. Adjusted mean QT intervals computed using the RR [corrected] interval as a covariate were significantly longer during non-rapid-eye-movement (407 ms) and rapid-eye-movement (408 ms) sleep than during active wakefulness (386 ms). The RR-adjusted mean QT intervals during inactive wake were also longer (400 ms) but this clear trend did not reach statistical significance (p = 0.08). Although prolongation of the QT interval during sleep reflects inactivity that may be related to withdrawal of sympathetic tone, we postulate that sleep per se also has an effect on the interval.