The aim of the study was to investigate the dynamics of experimental parasystole taking into consideration the peculiarities of recurrent arrhythmias recorded in clinical settings.
Material and methods: The experiments were conducted on isolated right atria of seven chinchilla rabbits. Parasystolic arrhythmias using periodical one-site electrostimulation were provoked in one atrium, where the sinus node was not affected, and in two atria with the spontaneous low value activity of pacemakers. The parasystolic arrhythmias by the dual-site periodical pacing were provoked in four atria, in which the spontaneous activity had disappeared, while the membrane potential of cardiomyocytes remained at the level of 70 to 80 mV.
Results: The parasystolic arrhythmias of the shape of single extrapotentials were obtained in atria when the periods of excitation impulses were within the limits of 0.9-1.2 s, and the differences between these periods being relatively small (0.04-0.2 s). The increase of these differences resulted the various allorhythmias. In cases of single extrapotentials, the recurrence periods of arrhythmias reached 5.6-29 s; while in cases of allorhythmias they shortened to 2.4-4.8 s.
Conclusion: The parasystoles in isolated atria of rabbits can be induced by two competitive excitation sources. They may manifest themselves through single extrapotentials or allorhythmias, whose form depends on the duration of the periods of excitation impulses, the difference between these durations, as well as on effective refractory periods of atrial cardiomyocytes. The determination and evaluation of the recurrence period of these arrhythmias can serve in any given clinical situation as a supplementary criterion.