Chronotopography of excitation during beginning of cholinergic atrial fibrillation in intact dog heart

Generation of atrial fibrillation in human being may be due to enhanced vagal tone. To determine space-time relations of spontaneously arising extrasystolic beats which trigger vagally-induced atrial fibrillation and to describe the picture of activation in beginning of such atrial fibrillation we carried out total epicardial mapping (254 unipolar electrodes) of the first 10 cycles of atrial fibrillation, arising spontaneously in opened-chest dog hearts (n=10) under the influence of trains 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 increased 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 pacemakers in atria. In most oases of atrial fibrillation one leading and stable source of excitation was established after second-third heart or after some previous interaction of unstable sources of arrhythmia. We determined three main types of atrial fibrillation development depending on activation picture and kind of leading source of excitation. They are the following: obvious re-entry, conditional focal and septal. Basing on indirect indications we can suggest that all determined excitation sources had circulation origin, but these sources were mapped from epicardium to electrode templates In different manner. All cases of obvious re-entry had functional origin. Although only small number of unstable re-entry circuits (<3) and momentary passive turbulent activities (<2) were possible at the same time, most of sustained cholinergic atrial fibrillations were accounted for by one leading stable re-entry circuit and were characterized by rather regulated picture of atrial activation.