POWER SPECTRAL-ANALYSIS OF HEART PERIOD VARIABILITY OF PRECEDING SINUS RHYTHM BEFORE INITIATION OF PAROXYSMAL ATRIAL-FIBRILLATION

Time domain analysis of heart period variability in patients without s tructural heart disease demonstrated increased parasympathetic modulat ion before paroxysmal atrial fibrillation (AF) occurring predominantly at night. However, diurnal differences in autonomic activity precedin g AF episodes in a diverse patient population have not been assessed. Accordingly, we performed spectral analysis of heart period variabilit y on Holter recordings during sinus rhythm preceding AF in 29 patients , 17 with night and 12 with day episodes. Samples taken 5, 10, and 20 minutes before AF onset were compared. Normalized high-frequency (HF) spectral power change was greater when comparing the interval 10 to 5 minutes with 20 to 10 minutes preceding AF in 26 of 29 patients (0.09 +/- 0.07 vs 0.03 +/- 0.02; p <0.0001). HF spectral power increased bef ore 3 of 12 AF episodes during the day compared with 15 of 17 BF episo des during the night (p = 0.001). Nocturnal AF episodes were preceded by increased HF spectral power in the 5- versus the 20-minute sample e xpressed as natural logarithm-transformed values (5.6 +/- 4.8 vs 4.2 /- 4.0; p <0.005) and normalized values (0.19 +/- 0.09 vs 0.10 +/- 0.0 7; p <0.02), a decrease in low-frequency/HF ratio (1.05 +/- 0.61 vs 2. 21 +/- 1.75; p <0.05) and heart rate (60 +/- 13 vs 71 +/- 13 beats/min ; p = 0.06). Structural heart disease was more common with daytime tha n nocturnal AF episodes (58% vs 18%, p <0.05). In conclusion, HF spect ral power change was increased preceding most AF episodes. However, di urnal differences were demonstrated. Contrary to daytime AF, increased parasympathetic activity preceded predominantly nocturnal AF, mostly in younger patients with structurally normal hearts. (C)1998 by Excerp ta Medica, Inc.