Unusual Features of Intermediate Septal Bypass Tracts

Abstract

Intermediate Septal Bypass Tracts. Introduction: Intermediate seplal (TS) AV bypass tracts, located uli>n}> the tricuspid annulus hetween the His hund(e and coronary sinus os. lie in close proximity to the AV node. Surgical or catheter ahlation of IS hypass tracts incurs increased risk for development of complete heart hlwk. We report additional unusual features of some IS hypass tracts that distinguish them from typical hypass tracts in other anatomic regions.Methods and Results: We analyzed a consecutive series of 150 patients with a history of Wolff-Parkinson-White syndrome and supraventricular tachycardia who underwent ahiation of hypass tracts. We studied the incidence and characteristics of AV conduction of IS hypass tracts compared with hypass tracts in other locations. Of the 150 patients in the stndy. 21 had an IS hypass tract (all had anterograde \\ conduction). Ten (4KVr) of these 21 IS hypass tracts demonstrated anterograde decremental properties with atrial pacing versus 3 (2%) of 129 non-IS hypass tracts (P < 0.001). During ahlation, a change in delta wave morphology before total loss of conduction in the IS hypass tract also iK'curred in 3 {\49c) of 21 IS hypass tracts versus 0 of I2M non-lS hypass tracts (P = OJMMMl. During ahlation. a change in P wave to delta wave interval occurred in 4 (I9f^) of 21 IS bypass tracts versus 0 of 129 non-IS hypass tracts (P < O.4HK)I). One IS patient exhihited retrograde Wenckehach hlock in the hypass tract, and two IS patients showed loss of retrograde hypass tract conduction after ahlation attempts that first changed the delta wave morphology. No non-IS patient had these features (P < O.OOOI for each comparison).Conclusion: Some IS bypass tracts have unusual properties that distinguish them from hypass tracts in other locations, perhaps due to the presence of multiple ventricular insertions of the bypass tract. It is possible that some cases represent true "nodoventricular" pathways. (J Cardiovasc Electrophysiol. VoL II. pp. 7M)-7S5. July 20()0) Wolff-Parkinson-White syndrome, catheter ablation, preexcitation variantsThis manuscript was prtx'cssed by a guest editor.