Heart rate at onset and termination of paroxysmal atrial fibrillation in apparently healthy subjects.

Eighteen paroxysms were documented on Holter electrocardiogram both at the onset and the termination of paroxysmal atrial fibrillation in 14 apparently healthy subjects. There were large inter- and intraindividual variations and no definite trend was observed in the time and duration of paroxysms. Heart rate at the onset of paroxysms was consistently higher than that at sinus rhythm immediately before atrial fibrillation started. There were 2 patterns in the sequence of heart rate during paroxysms. One was an almost constant heart rate during paroxysms, and the other was a trend toward a decrease in heart rate from the onset to the termination of paroxysms. The duration of paroxysms was within 2 hours in the former group and more than 2 hours in the latter group. There was a reverse correlation between heart rate at the termination of paroxysms and their duration.