CIRCADIAN VARIATION IN ATRIAL-FIBRILLATION IN PATIENTS WITH FREQUENT PAROXYSMS

Determinants of the duration of episodes of atrial fibrillation (AF) i n patients with paroxysmal atrial fibrillation (PAF) are poorly unders tood. However, autonomic tone shows circadian variation and is known t o affect atrial electrophysiology, We therefore compared the duration of episodes of AF with an onset during the day (08:00 - 22:00) to thos e with an onset during the night in a database of 24-hour ECG recordin gs in patients with frequent symptomatic PAF. The heart rate in the 30 seconds prior to AF onset was also compared. From 42 recordings, 296 episodes of AF > 30 seconds duration and preceded by > 60 seconds sinu s rhythm were identified. The 165 nocturnal episodes tended to be shor ter (median = 1.15 min) than the 131 diurnal episodes (median = 1.5 mi n) and the distribution of nocturnal and diurnal durations was signifi cantly different (P = 0.007; Kolgomorov-Smirnov test). This was also t rue in recordings containing at least 1 diurnal and at least 1 nocturn al episode. The mean heart rate prior to AF onset was lower at night ( 62.2 +/- 11.8 vs 75.6 +/- 16.4 beats/min; P < 0.0001 Wilcoxon test). T hese findings suggest that in patients with frequent symptomatic PAF, autonomic influences affect the duration of episodes of AF and has pat hphysiological and therapeutic implications.