ECG Criteria for Accurate Localization of Left Anterolateral and Posterolateral Accessory Pathways

Background: Left lateral accessory pathway (AP) location along the mitral annulus (MA) can influence ablation strategy, including choice of a transseptal or retrograde aortic approach and the use of deflectable sheaths and/or bidirectional catheters. We aimed to develop electrocardiographic (ECG) criteria to accurately localize a left lateral AP, hypothesizing that the relationship of QRS amplitudes in limb leads II and III could be used to differentiate left anterolateral (LAL) from left posterolateral (LPL) AP locations.Methods: The ECGs from patients who underwent ablation of a left‐sided AP between 2001 and 2008 were evaluated for the relationship of QRS amplitudes in limb leads II and III. A LAL‐AP was defined by successful ablation between 12 and 3 o’clock on the MA, as seen in left anterior oblique (LAO) fluoroscopic projection. A LPL‐AP was defined by successful ablation between 3 and 6 o’clock in the LAO projection.Results: In 249 consecutive patients undergoing AP ablation, 23 met the prespecified inclusion criteria: manifest preexcitation due to single AP, ablated successfully in a LAL or LPL location. The ratio of dominant QRS amplitude in lead II to lead III was ≥1 in 10/11 patients with LAL‐AP, compared with 3/12 patients with a LPL‐AP (P = 0.002). Using these criteria, two blinded reviewers predicted a LAL or LPL location with 87% accuracy and 100% interobserver agreement.Conclusions: We report new ECG criteria that can be used to accurately predict the anterior and posterior location of a left lateral AP. Such localization may facilitate procedural planning. (PACE 2012;35:1444–1450)