ATRIAL AND ACCESSORY PATHWAY ACTIVATION DIRECTION IN PATIENTS WITH ORTHODROMIC SUPRAVENTRICULAR TACHYCARDIA - INSIGHTS FROM VECTOR MAPPING

Objectives. The purpose of this study was to utilize vector mapping to investigate atrial and accessory pathway activation direction during orthodromic supraventricular tachycardia. Background. Although advances have been made in the electrophysiologic evaluation and management of accessory pathways, our understanding of accessory pathway anatomy and physiology remains incomplete. Vector mapping has been validated as a method of studying local myocardial activation. Methods. In 28 patients with a left-sided or posteroseptal accessory atrioventricular (AV) pathway referred for ablation, atrial and accessory AV pathway activation direction was deter mined during ventricular pacing or orthodromic supraventricular tachycardia, or both, by summing three orthogonally oriented bipolar electrograms recorded from the coronary sinus to create three dimensional vector loops. Atrial and accessory AV pathway activation direction was determined in all patients from the maximal amplitude vectors of the vector loops. Because of beat to beat variability in the directions of the vector loops, data from 8 of 28 patients could not be analyzed. Results. At 81 of 83 sites, atrial activation direction along the long axis of the coronary sinus corresponded with the direction suggested by activation time mapping. Activation direction along the anteroposterior and inferosuperior axes was variable, poten tially due to variations in the level of the atrial insertion of the accessory AV pathway and in the depth or angling of pathway fibers in the AV fat pad. In eight patients, at least one recording was obtained at the site of an accessory AV pathway potential. Accessory AV pathway activation proceeded superiorly and to the right in seven of eight patients; in one patient with a posteroseptal pathway, accessory AV pathway activation proceeded superiorly and to the left. Conclusions. 1) Vector mapping is a useful technique for localizing accessory AV pathways; 2) left sided accessory AV pathways angle from left to right as they traverse the AV groove; and 3) variable activation directions of the atrial myocardium adjacent to the coronary sinus suggest that accessory AV pathway insertion into the atrium differs from patient to patient.