CHRONOTOPOGRAPHY OF EXCITATION DURING BEG INNING OF CHOLINERGIC ATRIAL-FIBRILLATION IN INTACT DOG HEART

Generation of atrial fibrillation in human being may be due to enhance d vagal tone. To determine space-time relations of spontaneously arisi ng extrasystolic beats which trigger vagally-induced atrial fibrillati on and to describe the picture of activation in beginning of such atri al fibrillation we carried out total epicardial mapping (254 unipolar electrodes) of the first 10 cycles of atrial fibrillation, arising spo ntaneously in opened-chest dog hearts (n=10) under the influence of tr ains of vagal stimulation (10 - 50 Hz, I ms, 10 - 17 V, 5 sec. trains) . Atrial fibrillation developed in 8 out of 10 dogs (54 cases of which 49 were mapped). Probability of atrial fibrillation initiation increa sed when frequency of vagal stimulation was increased from 10 Hz to 40 Hz and then became stable. Most of atrial fibrillations were induced after first extrasystolic beat with range of coupling interval from 70 to 209 ms. Triggering beat sites were located outside of intervenous region (mostly in right atrium auricle) in 75% of atrial fibrillations , i.e. they were ectopic. This suggests wide distribution of latent pa cemakers in atria. In most Gases of atrial fibrillation one leading an d stable source of excitation was established after second-third beart or after same previous interaction of unstable sources of arrhythmia. We determined three main types of atrial fibrillation development dep ending on activation picture and kind of leading source of excitation. They are the following: obvious re-entry, conditional focal and septa l. Basing on indirect indications we can suggest that all determined e xcitation sources had circulation origin, but these sources were mappe d from epicardium to electrode templates in different manner. All case s of obvious re-entry had functional origin. Although only small numbe r of unstable re-entry circuits (<3) and momentary passive turbulent a ctivities (<2) were possible at the same time, most of sustained choli nergic atrial fibrillations were accounted for by one leading stable r e-entry circuit and were characterized by rather regulated picture of atrial activation.