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 advance s have been made in the electrophysiologic evaluation and management o f accessory pathways, our understanding of accessory pathway anatomy a nd physiology remains incomplete. Vector mapping has been validated as a method of studying local myocardial activation. Methods. In 28 pati ents with a left-sided or posteroseptal accessory atrioventricular (AV ) pathway referred for ablation, atrial and accessory AV pathway activ ation direction was deter mined during ventricular pacing or orthodrom ic supraventricular tachycardia, or both, by summing three orthogonall y oriented bipolar electrograms recorded from the coronary sinus to cr eate three dimensional vector loops. Atrial and accessory AV pathway a ctivation direction was determined in all patients from the maximal am plitude vectors of the vector loops. Because of beat to beat variabili ty in the directions of the vector loops, data from 8 of 28 patients c ould not be analyzed. Results. At 81 of 83 sites, atrial activation di rection along the long axis of the coronary sinus corresponded with th e 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 pathwa y activation proceeded superiorly and to the right in seven of eight p atients; in one patient with a posteroseptal pathway, accessory AV pat hway activation proceeded superiorly and to the left. Conclusions. 1) Vector mapping is a useful technique for localizing accessory AV pathw ays; 2) left sided accessory AV pathways angle from left to right as t hey traverse the AV groove; and 3) variable activation directions of t he atrial myocardium adjacent to the coronary sinus suggest that acces sory AV pathway insertion into the atrium differs from patient to pati ent.