Characterization of the nodal slow pathway in patients with nodal reentrant tachycardia: clinical implications for guiding ablation.

INTRODUCTION AND OBJECTIVES: Nodal slow pathway ablation is the treatment of choice for nodal reentrant tachycardia. No demographic, anatomic, or electrophysiologic variables have been reported to predict an exact location of the slow pathway in the atrioventricular node or its proximity to the fast pathway. The purpose of this study was to analyze these variables. METHODS: The study prospectively included 54 patients (17 men; mean age, 55 [16] years) who had undergone successful slow pathway ablation. The refractory periods of both pathways and their differential conduction time were measured, and calculations were performed to obtain the distance from the His-bundle region (location of the fast pathway) to the coronary sinus ostium (to estimate the anteroposterior length of the triangle of Koch) and to the slow pathway area. RESULTS: The differential conduction time (139 [98] ms) did not correlate with the His-coronary sinus distance (19 [6] mm; P=.6) or the His-slow pathway distance (14 [4] mm; P=.4). When the His-coronary sinus distance was larger, the His-slow pathway distance was also larger (r=0.652; P<.01) and the anatomic correlation between the triangle dimensions and the separation between the two pathways was confirmed. In patients older than 70 years, smaller triangle sizes and a shorter distance between both pathways were observed (P<.001). CONCLUSIONS: A greater anteroposterior dimension of the triangle of Koch is associated with a slow-pathway location farther from the fast pathway. In elderly patients the two pathways are closer together (higher risk of atrioventricular block).