[Initiation mechanism of the first extrasystole in short-term atrial arrhythmia]

Excitation propagation during arrhythmias induced by electric stimulation into the vulnerable phase was studied on rabbit' left auricle bands by mapping (in 80-150 points). Arrhythmias were initiated under normal conditions and at acetylcholine background (0.2 mg/l). Recording of the electrical activity was realized by surface electrodes. The first extrasystole wave was shown to be conditioned as a result of the appearance of one or several point or ring-like excitation sources on the myocardium surface. There is no continuous circulation of the excitation wave on the surface of the cardiac tissue. Probable mechanisms of the appearance of such sources are discussed. Excitation circulation in the myocardium thickness (intramural re-entry) is considered as a more probable mechanism.