Circadian variations in the electrical properties of the human heart assessed by sequential bedside electrophysiologic testing.

To assess the variability of the currently used electrophysiologic parameters and their possible circadian rhythm, sequential bedside electrophysiologic testing was performed during a 24-hour period, at intervals of 1 to 2 hours, in 12 patients who had normal atrioventricular (AV) conduction times and normal sinus node function. The coefficients of variation during the 24-hour period were: +/- 10.4% for the R-R interval, +/- 10.6% for the sinus node recovery time (SRT) at atrial pacing of 100 bpm, +/- 32.5% for the corrected SRT, +/- 15.1% for the ventriculoatrial (VA) effective refractory period (ERP), +/- 8.3% for the AV nodal ERP, +/- 5.7% for the AH interval, +/- 5.2% for the HV interval, +/- 5.5% for the atrial ERP, +/- 3.3% for the right ventricular ERP, +/- 2.8% for the QT interval, +/- 4% for the VA interval, and +/- 3.4% for the retrograde Kent bundle ERP. Between 12:00 midnight and 7:00 AM, there was significant lengthening of: the sinus node rate (p less than 0.0005), the SRT at atrial paced rates of 100 and 120 bpm (p less than 0.025), the QT interval duration (p less than 0.025), and the ERP of the atria (p less than 0.025), AV node (p less than 0.01), and right ventricle (p less than 0.05). Thus conventional electrophysiologic parameters are subject to daily variability and, like sinus node function, AV nodal and myocardial refractoriness follow a circadian rhythm with an acrophase between 12:00 midnight and 7:00 AM. In addition, prolonged bedside recording of the His bundle potential can be reliably obtained.