Phase image triangulation of accessory pathways in patients undergoing catheter ablation of posteroseptal pathways.

The outcome of posteroseptal accessory pathway ablation by direct current (DC) shocks delivered just outside the os of the coronary sinus was studied in 21 patients. Electrocardiographic and electrophysiological parameters as well as phase image patterns of equilibrium multiple-gated blood-pool scintigrams were studied to determine their usefulness in predicting the success of ablation. A second free-wall pathway was documented by electrophysiological or surgical findings in six patients, and the value of phase images in detecting this second pathway was studied as well. Ablation was successful in 57%. The cumulative mean energy of DC shocks amounted to 524 +/- 170 joules and was not predictive of ablation outcome, neither was the mean ventriculoatrial (VA) conduction time. The predictive value of the 12-lead maximally preexcited electrocardiogram was poor in the 15 patients with a single posteroseptal bypass tract. A new method to triangulate the site of the earliest phase angle on the atrioventricular (AV) valve plane successfully localized the bypass pathway in 14 of those patients. No specific phase pattern predicted successful ablation except for a symmetrical, concentric peripheral phase progression found to be predictive of ablation success in the four patients who showed this pattern. Phase analysis was able to localize the second, nonposteroseptal pathway in four of six patients. This study showed that a concentric peripheral phase progression in the gated blood-pool scintigrams is predictive for ablation success in patients with posteroseptal pathways. A free-wall localization of the earliest phase angle is suggestive of a second bypass tract in this area.