[Electrophysiology of the atrioventricular node during atrial fibrillation. I. Ventricular rhythm].

Atrial fibrillation (AF) occurs in 0.9% of the population, in 6% of persons over 65 and in 10% of persons over 80. It is an important independent risk factor for thromboembolism, especially cerebral infarctions. The functions of the atrioventricular (AV) node are: (a) optimal adjustment of the time between the contractions of atria and ventricles; (b) protection of the ventricles against excessively high frequencies of atrial tachycardia; (c) a pacemaker function in case of atrial arrest. AF is an irregular, disorganized electrical activity of the atria. On the ECG, P waves are absent and the baseline shows wavelets constantly changing in shape, duration, amplitude and direction. Development and existence of AF are correlated with a sufficiently large number of myocardial cells and a sufficient degree of difference between the electrical properties of the myocardial cells. In the absence of an AV conduction block, the resulting ventricular rhythm is completely irregular. The constant irregularity of the ventricular rhythm is independent of ventricular frequency and independent of cardiac and other characteristics of the patient. Electrical stimulation of the right ventricle leads to complete AV block.