[Electrophysiological mechanisms of atrial tachyarrhythmia].

Both supraventricular and ventricular arrhythmias are generated by one of the following 2 mechanisms: increased automaticity and reentry. In this paper we will refer about the mechanisms of the commonest atrial tachyarrhythmias. Atrial parasystole: it is determined by an automatic focus protected by entrance block. In some cases the focus is only partially protected owing to a partial block or to the electrotonic influence of the sinus rhythm. Atrial tachycardia: it can be due both to increased automaticity and to reentry. Atrial flutter: it is generated by a counterclockwise macroreentry localized in the right atrium. The left atrium is passively activated. A critical delay of the circuit is present near the ostium of the coronary sinus. The lesion of this area by surgery or catheter ablation can interrupt and prevent the arrhythmia. Atrial fibrillation: it is generated by multiple wavelets which continuously change site and direction. The functional multiple reentry is made possible by dispersion of atrial refractoriness and by the existence of areas having delayed conduction. It is noteworthy that the same arrhythmia and the same atrial electrophysiologic alterations are present in many clinical conditions having very different anatomic backgrounds: subjects with no evident heart disease and normal atria, subjects with large atria, subjects with an anomalous pathway. These data suggest that some important informations are probably lacking about the genesis of this arrhythmia.