Isolated Conduction Within the Left His-Purkenje System During Sinus Rhythm and Idiopathic Left Ventricle Tachycardia

BACKGROUND: Functionally, left His-Purkenje system (HPS) is insulated from the adjacent myocardium and exhibits isolated conduction during sinus rhythm (SR), but in vivo human study is rare. Meanwhile, whether the isolated conduction also exists during idiopathic left ventricle tachycardia (ILVT) is not clearly defined. The current study aimed to delineate the activation sequence and gross anatomy of left HPS during SR and ILVT. METHODS AND RESULTS: The study involved 25 consecutive patients with ILVT. During SR, left HPS exhibited antegrade activation sequence, and its surrounding myocardium depolarized after HPS in an apical to base direction. During ILVT, the earliest retrograde presystolic potentials were mainly located at the middle portion of left posterior fascicle (0.5±0.1 [95% confidence interval, 0.46-0.58] of its full length) with an average of 29.5±6.0 mm (19.8-41.5) away from the His position. Left posterior fascicle was depolarized from the earliest retrograde presystolic potentials via 2 opposite wavefronts with significantly shorter activation time than that during SR (15.1±2.1 versus 30.0±3.2 ms; P<0.001). The left anterior fascicle was depolarized after left posterior fascicle with an antegrade activation sequence and comparable activation time with that during SR (21.9±2.9 versus 22.0±4.1 ms; P=0.932). The depolarization of ventricle septum also occurred after HPS in an apical to base direction. CONCLUSIONS: During SR, isolated conduction within the HPS is demonstrated by documenting the reverse activation sequence with its surrounding myocardium. During ILVT, the earliest retrograde presystolic potentials were usually recorded at the middle segment of left posterior fascicle, and the isolated conduction within the HPS remained.