Circadian behavior of P-wave duration, P-wave area, and PR interval in healthy subjects

Background: The prolongation of P-wave duration has long been shown to indicate the presence of high risk for atrial fibrillation. The circadian variation of P-wave characteristics and their dynamic adaptation to heart rate changes was not tested before. Methods: To evaluate the diurnal pattern of P-wave duration, P area, and PR interval and of their linearly fitted relation with RR interval, 50 healthy volunteers (25 men, mean age 34 +/- 10 years) underwent 24-hour ambulatory electrocardiographic (ECG) recording with digital 12-lead Holter recorders. The median P-wave duration, P area, and PR interval were calculated from the average 12-lead ECG constructed from each 10-second ECG recording. Single harmonic regression analysis was performed to reveal the presence of circadian variation in the aforementioned ECG parameters. Results: The P area (P < 0.0001, R-2 = 0.78), the PR interval (P < 0.0001, R-2 = 0.92), the P area / RR slope (P < 0.0001, R-2 = 0.55), and the PR/RR slope (P < 0.0001, R-2 = 0.42) showed a highly significant circadian variation while the periodic nature of P-wave duration (P = 0.016, R-2 = 0.32) and of the P duration / RR slope (P = 0.011, R-2 = 0.18) was only indicated by harmonic regression analysis. Conclusions: P-wave duration, P area, and PR interval show a significant circadian variation in healthy subjects. The relations between P area/RR, PR/RR, and P duration/RR also demonstrate a significant diurnal pattern.