SITE-DEPENDENT INTRAATRIAL CONDUCTION DELAY - RELATIONSHIP TO INITIATION OF ATRIAL-FIBRILLATION

Background Atrial dysrhythmia patients have exaggerated intra-atrial c onduction delays and prolonged relative refractoriness in response to atrial premature depolarizations (APDs). Furthermore, atrial fibrillat ion (AF) is more readily inducible by APDs from the high right atrium (HRA) than the coronary sinus (CS). In this study, we postulated that site-specific intra-atrial conduction delays can explain why AF is ini tiated more from the HRA than from the CS. Methods and Results We exam ined 17 patients (age, 49 +/- 22 years) without a history of atrial fl utter, AF, or structural heart disease. Programmed stimulation was car ried out from the HRA and distal CS, and bipolar recordings were made at the HRA, His bundle, posterior triangle of Koch, and CS. More prolo ngations in conduction and relative refractoriness in all intra-atrial sites were observed during HRA than CS APDs. AF was induced in 8 pati ents after HRA and not CS stimulation. During HRA stimulation, patient s with AF inducibility exhibited significant prolongation of conductio n to the posterior triangle of Koch and marked broadening of the poste rior triangle of Koch electrogram compared with CS stimulation. In pat ients without AF inducibility, the posterior triangle of Koch electrog ram width was the same during HRA and CS stimulation. Conclusions The existence of site-dependent intra-atrial conduction delays and site-de pendent dispersion of refractoriness appears to be a common property o f the atrial myocardium and does not necessarily forecast AF inducibil ity. However, the presence of nonuniform anisotropic characteristics o f the posterior triangle of Koch may be critical for AF induction.