1008-9 Atrioventricular Nodal “Slow Pathway” Conduction Time is Due to the Length of the Pathway

Abstract

The determinants of atrioventricular (AV) nodal “slow pathway” conduction remain controversial. We hypothesized that anterograde “slow pathway” conduction time depends on the length (rather than functional properties) of the pathway. Therefore, we studied 19 patients (4 men and 15 women, mean age 51 ± 4 years) with typical AV nodal reentrant tachycardia (AVNRT) who underwent successful radiofrequency ablation (RFA) of the “slow pathway”. As a measure of the pathway length we determined two distances in both RAO and LAO projections: I) coronary sinus (CS) os to the His bundle and 2) mapping catheter tip at the successful ablation site to the His bundle. These distances were correlated with the conduction time of the “slow pathway” (AH interval) during programmed atrial stimulation following coupling intervals longer than the functional “slow pathway” refractory period and during AVNRT. RFA was initially attempted in the posteroseptal area of the right atrium close to the CS os and was delivered at progressively superior and anterior locations (closer to the compact AV node) only when inferior RFA applications were unsuccessful. There was a significant correlation between the anterograde “slow pathway” conduction time (AH) and the distance between the mapping catheter tip (MAP) and the His bundle (HIS) in both LAO (Fig.) and RAO projections (p < 0.001). This was true when slow pathway conduction time was measured either during programmed atrial stimulation or during AVNRT. “Slow pathway” conduction time did not correlate with tle distance between the CS os and the His bundle. In this study, AV nodal “slow pathway” conduction time was related to the distance between the “slow pathway” atrial insertion site and the His Bundle. This supports the hypothesis that “slow pathway” conduction time is in part due to pathway length and may not be due to functional properties.