MULTIPLE RECORDING DURING ELECTRICALLY INDUCED ATRIAL FIBRILLATION.

Abstract

1. Atrial fibrillation was induced in dogs by single electrical shocks. Close bipolar direct electrograms were taken from various parts of the atrium; as many as 22 electrograms and a standard lead II electrocardiogram were recorded simultaneously. Initial phase and recovery phase of fibrillation were analyzed. 2. In the initial phase of atrial fibrillation, local firing consisting of rapid tachysystole of 996 to 3000 per minute was observed near the stimulating point in most experiments. Except for the leads showing local firing, the interval between beats at each recording point tended to be constant, and a time gap between two successive beats was observed. A propagation pattern could be plotted which seemed to start from the origin of local firing; some beats were conducted only locally, and others (every second, third or fourth discharge) were conducted widely. The cause of atrial fibrillation was considered to be local firing of one small area of the atrium, i.e., the unifocal theory of the origin of atrial fibrillation was supported. 3. During recovery from atrial fibrillation, features similar to those seen in the initial phase often appeared, although local firing disappeared. In some experiments, the atrium was separated electrically into a few groups of cells beating independently, and in others a "circus pathway" appeared to exist in the last beat. It seems that electrical separation of the atrium into many parts and circus movements, or multiple re-entry, may develop during the course of fibrillation, and that these phenomena perpetuate atrial fibrillation. 4. During the last beat of atrial fibrillation, the time required for all cells to depolarize was occasionally less than the duration of the normal sinus beat. A similar phenomenon was sometimes observed in the premature beats following atrial fibrillation.