Prolongation of the Q-T interval in man during sleep

Kevin F. Browne, Eric Prystowsky, James J. Heger, Donald A. Chilson, Douglas P. Zipes

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186 Scopus citations


Parasympathetic blockade shortens the duration of the Q-T interval and ventricular effective refractory period independent of heart rate change. Since relative parasympathetic effect increases during sleep, it was determined whether sleep was associated with a change in the Q-T interval. Fifteen patients receiving no drugs underwent 3 to 6 days of continuous electrocardiographic recordings. Tracings were sampled every 30 minutes and recorded at a paper speed of 25 mm/s. This provided 12,000 Q-T and R-R intervals that were measured. Comparison of R-R intervals that had similar durations during sleep and awake states revealed that the duration of the Q-T interval was longer during sleep in all 15 patients (p < 0.001). Eight patients had sufficient range of overlap of R-R intervals to compare linear regression lines of Q-T intervals recorded while awake with Q-T intervals recorded while asleep. The regression lines during sleep exhibited a mean intercept change of 38 ± 37 ms and mean slope change of -0.021 ± 0.040 ms when compared with the regression lines during the awake state. The difference in Q-T interval between awake and sleep states was 19 ± 7 ms when calculated at a heart rate of 60 beats/min. These statistical comparisons of the relationship of the Q-T interval to R-R interval indicate that the Q-T interval is longer during sleep than during the awake state at the same heart rate. Prolongation of the Q-T interval during sleep may reflect increased vagal tone or sympathetic withdrawal. These changes in repolarization may be related to the diurnal variation of some ventricular arrhythmias.

Original languageEnglish (US)
Pages (from-to)55-59
Number of pages5
JournalThe American journal of cardiology
Issue number1
StatePublished - Jul 1983

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine

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    Browne, K. F., Prystowsky, E., Heger, J. J., Chilson, D. A., & Zipes, D. P. (1983). Prolongation of the Q-T interval in man during sleep. The American journal of cardiology, 52(1), 55-59.