Longitudinal dissociation in the His bundle. Bundle branch block due to asynchronous conduction within the His bundle in man.

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Abstract
Electrophysiological data in 27 patients (of a series of 110) which suggest longitudinal dissociation in the His Bundle (BH) were presented. Patients (25) showed left bundle branch block (LBBB) which was rate related in 3, and 2 had isolated left axis deviation (LAD) with narrow QRS complexes. BH recordings were performed via the right heart, and in each patient the same electrode catheter was used for stimulation of the BH at different sites. The H-V time was prolonged (range 50-70 ms, mean 59) in all 22 patients with constant LBBB, in 1 of the 3 of the rate related LBBB and in 1 of the 2 with isolated LAD; and remained unchanged throughout. In all 25 patients with LBBB proximal BH stimulation exhibited QRST complexes identical to those with normal sinus rhythm with a PI[pacing impulse]-R interval equal to the H-V time. BH stimulation at a constant cycle length, but at a slightly distal site, abolished the LBBB (constant or rate related) and resulted in narrow QRS complexes (.ltoreq. 95 ms) with a PI-R interval shorter than the H-V time by 5-20 ms. In the 2 patients with isolated LAD, BH stimulation abolished LAD with a PI-R interval identical to the H-V time. A bundle branch block pattern and/or axis deviation may result from a focal lesion or an area of altered refractoriness within the BH. The duration of the QRS complexes and/or a shift in QRS axis was normalized by BH stimulation distal to the lesion due to synchronous impulse conduction to both bundle branches.