Atrioventricular Nodal Electrophysiology Still Exciting After All These Years

The anatomical atrioventricular node was first de-scribed by Tawara in 1906.1 Although some surmisedthe node to be the region responsible for delay between contraction of atria and ventricles, Erlanger in 1912 localized the major portion of delay to a latency at the transition between atrial and nodal fibers.2 Nearly a century of research on properties of the atrioventricular (AV) node has substantiated the suggestion of Hoffman and Cranefield3 in 1960 that the term “atrioventricular node ” should be used to describe “the entire complex of fibers functionally inter-posed between atrial fibers proper and His bundle fibers proper ” (page 132) and not just the compact node of Tawara, since nodal-like properties have been found outside the compact node.4–8 Thus, the posterior nodal extension, the focus of the study by Dobrzynski et al9 in this issue of Circulation Research, is now included as part of the electro-physiological AV node. Identified as a nodal structure by it