Site-dependent intra-atrial conduction delay. Relationship to initiation of atrial fibrillation.

BACKGROUND: Atrial dysrhythmia patients have exaggerated intra-atrial conduction delays and prolonged relative refractoriness in response to atrial premature depolarizations (APDs). Furthermore, atrial fibrillation (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 initiated more from the HRA than from the CS. METHODS AND
RESULTS: We examined 17 patients (age, 49 +/- 22 years) without a history of atrial flutter, AF, or structural heart disease. Programmed stimulation was carried out from the HRA and distal CS, and bipolar recordings were made at the HRA, His bundle, posterior triangle of Koch, and CS. More prolongations in conduction and relative refractoriness in all intra-atrial sites were observed during HRA than CS APDs. AF was induced in 8 patients after HRA and not CS stimulation. During HRA stimulation, patients with AF inducibility exhibited significant prolongation of conduction to the posterior triangle of Koch and marked broadening of the posterior triangle of Koch electrogram compared with CS stimulation. In patients without AF inducibility, the posterior triangle of Koch electrogram width was the same during HRA and CS stimulation.
CONCLUSIONS: The existence of site-dependent intra-atrial conduction delays and site-dependent dispersion of refractoriness appears to be a common property of the atrial myocardium and does not necessarily forecast AF inducibility. However, the presence of nonuniform anisotropic characteristics of the posterior triangle of Koch may be critical for AF induction.