[Electrophysiologic mechanisms of atrial rhythm disorders. I. Atrial fibrillation].
Atrial fibrillation (AF) is a frequent finding in clinical practice. In advanced age its incidence is rising and according to the literature the prevalence is as high as 3.2-11%. AF doubles the mortality and brings a fivefold risk of the most frequent embolic complication--a cerebrovascular attack. The typical electrophysiological feature are intra-atrial defects of the conduction and the absence of refractory period adaptation with regard to the cycle length. In 1962 Moe, based on experimental work, postulated the hypothesis on multiple independent wavelets which move in a random fashion through the myocardium round several islets or strips of refractory tissue. Modern mapping studies confirmed the reentry concept as the mechanism of atrial fibrillation. Two forms of reentry were observed: the leading circle reentry and the random reentry. The main factors which facilitate the development of AF are dilatation of the atria, reduced rate of conduction of the impulse and shortening of the refractory. A combination of these factors leads to a reduction of the size of the wave which is a multiple of the refractory period and rate of the impulse. This leads to the formation of smaller waves which may co-exist in greater number in the dilated atria. Persistence of AF depends on the number of waves present. A small number of waves can disappear at a certain moment or change into one wave and this leads to the development of sinus rhythm or atrial flutter.