Anatomy of the atrioventricular conduction system.

To the Editor: I am writing regarding the article by Racker and Kadish1 that appeared in a previous issue of Circulation . Their statement that “the atrioventricular (AV) node and AV bundle consist of myocardial fascicles, not myofibers”1 is inappropriate.2 Dorland’s Illustrated Medical Dictionary defines fascicle as “a small bundle or cluster, especially of nerve or muscle fibers.” The human conduction system has more collagenous connective tissue and elastic tissue than the surrounding myocardium, and this may be considered the hallmark of the conduction system histologically.2 Lev et al2 did not mention anything about nerves in their work cited by Racker and Kadish. Racker and Kadish’s interpretation of Figures 1 and 4 from the article by Lev et al2 needs further clarification.1 They state that “Lev et al’s Figure 1 partially overlooked the proximal AV bundle, as seen in schematic AV junction region tissue blocks.”1 This statement is inaccurate. Figure 1 …