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length of the myofibers

Source: Compiled from ref. 2. DAVB, distal atrioventricular bundle.

Source: Compiled from ref. 2. DAVB, distal atrioventricular bundle.

atrial appendage; or (3) radially within the noncoronary cusp of the aortic valve (13-15,17,37).

Today, His potentials are commonly mapped to provide a landmark for ablation of the atrioventricular node and to assess atrial-to-ventricular conduction timing. In addition to direct electrical mapping, much can be learned about the general anatomical and functional properties of the cell lying within the bundle via attempts to stimulate it directly. For example, direct stimulation of the His bundle produces normal ventricular activation because of the initiation of depolarization into the intrinsic conduction pathway (13,14,16). Thus, if attempts to stimulate the His bundle selectively frequently fail, pathological changes may be assumed (17).

The His bundle has historically been thought to act only as a conduit for transferring depolarization. Ventricular escape rhythms have been known to emanate from the His bundle, but it was thought generally a relatively simple structure. To the contrary, evidence indicates that at least two general sources serve as inputs to the His bundle, and that it functions as at least two functionally distinct conduits. Using alternans (alternate beat variation in the direction, amplitude, and duration of any component of the electrocardiogram), the duality of its electro-physiology was demonstrated in isolated preparations from the region of the triangle of Koch in rabbit hearts (37).

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