Transverse interconnection
Song-Yun Chu et al. describing the LBBP as a choice to correct the RBBB in a case report putting forward an intriguing theory that unipolar pacing captured the intra-Hisian LBB then recruited the distal RBB through transverse interconnection fibers (TF). TF, connecting the left and right bundle branches, can transmit the electrical signals from LBB to RBB, thus correcting the distal RBBB and causing a narrower QRS complex 17. (Figure 3 C) Back in the 1970s, Lazzara et al. stimulated the incised His bundle intracellularly and found that the native conduction restored, which suggested that functional transverse interconnection (FTI) exists in the His bundle and the bundle branches and can transmit an electrical signal across fibers18. Transverse interconnection challenges the traditional theory of longitudinal dissociation that the LBB and RBB are longitudinally separated by collagen sheaths within the His bundle, making conduction better “end to end” than “side to side” within the His bundle. 19. The limitation of transverse interconnection has been noticed before, if transverse connections coexist with longitudinal dissociation, then the native conduction would circumnavigate the structure block 20. We suspected that if there is indeed a transverse connection between bundle branches, the excitation generated by LBBP would bypass the block to RBB and then conduct forward through RBB and Purkinje fibers to excite the RV with no paced morphology of RBBB pattern. Besides that, the anatomical structure of these fibers has not been clearly reported before, which requires further studies, especially in the human body 21.