Triple Pathway Longitudinal Dissociation in the His Bundle in a Patient with High-degree Atrio-ventricular Block

Abstract

: We reported a patient with high-degree atrio-ventricular block with various QRS complexes. While the ventricular captured beats showed right bundle branch block（RBBB）axis +30°（A）, 2 patterns of escape beats, i.e. RBBB axis +60°（B）and left bundle branch block（LBBB）（C）, were observed with cycle lengths 1.65 and 1.68 sec, respectively. Fusion beats of various degrees between B and C were also observed. When RP interval was＞ 0.89 sec, the P wave depolarized the escape focus antegradely. When RP interval was ≤ 0.88 sec, the P wave did not antegradely depolarize the escape focus but retrogradely depolarized it with some delay, conducting via the lower portion of His bundle transversely. QRS axis of B showed mild rightward shift compared with that of A. With the aforementioned electrocardiographic findings, we concluded that His bundle was functionally dissociated into triple pathway. In addition, the P wave conducting through the bundle connecting to the left posterior bundle branch caused A, and two escape focuses localized in the bundles connecting to the left anterior bundle branch and right bundle branch caused B and C, respectively.