Stable microreentrant sources as a mechanism of atrial fibrillation in theisolated sheep heart

Background-Atrial fibrillation (AF) has traditionally been described as ape riodic or random. Yet, ongoing sources of high-frequency periodic activity have recently been suggested to underlie AF in the sheep heart. Our objecti ve was to use a combination of optical and bipolar electrode recordings to identify sites of periodic activity during AF and elucidate their mechanism . Methods and Results-AF was induced by rapid pacing in the presence of 0.1 t o 0.5 mu mol/L acetylcholine in 7 Langendorff-perfused sheep hearts. We use d simultaneous optical mapping of the right and left atria (RA and LA) and frequency sampling of optical and bipolar electrode recordings (including a roving electrode) to identify sites having the highest dominant frequency (DF). Rotors were identified from optical recordings, and their rotation pe riod, core area, and perimeter were measured. In all, 35 AF episodes were a nalyzed. Mean LA and RA DFs were 14.7+/-3.8 and 10.3+/-2.1 Hz, respectively . Spatiotemporal periodicity was seen in the LA during all episodes. In 5 o f 7 experiments, a single site having periodic activity at the highest DF w as localized. The highest DF was most often (80%) localized to the posterio r LA, near or at the pulmonary vein ostium. Rotors (n=14) were localized on the LA. The mean core perimeter and area were 10.4+/-2.8 mm and 3.8+/-2.8 mm(2), respectively. Conclusions-Frequency sampling allows rapid identification of discrete site s of high-frequency periodic activity during AF. Stable microreentrant sour ces are the most likely underlying mechanism of AF in this model.