Accessory Atrioventricular Pathways

B y definition, accessory atrioventricular pathways are aberrant muscle bundles that connect the atrium to a ventricle outside of the regular atrioventricular conduction system.Clinically, they may manifest as substrates for ventricular preexcitation.The first accessory pathway in a patient who suffered from Wolff-Parkinson-White syndrome was described in 1943 by Wood, Wolferth, and Geckler. 1 Shortly after, Öhnell created a reconstruction of an accessory pathway that very elegantly showed the close proximity of the pathway to the fibrous attachment of the mitral valve and its relationship with the sulcus coronarius (Figure , A). 2 Subsequent histological studies have demonstrated unequivocally that these pathways are the anatomic substrates for the classical Wolff-Parkinson-White variety of preexcitation. Article p 1508Accessory atrioventricular pathways are found most often in the parietal atrioventricular junctional areas, including the paraseptal areas.They breach the insulation provided by the fibrofatty tissues of the atrioventricular groove (sulcus tissue) and the hingelines (fibrous annulus) of the valves.They are rarely found in the area of fibrous continuity between the aortic and mitral valves because in this area, there is usually a wide gap between the atrial myocardium and ventricular myocardium to accommodate the aortic outflow tract.On the left parietal side, the accessory pathways tend to pass close to the hingeline of the mitral valve (Figure , B).In the right atrioventricular junction, the atrioventricular groove is much deeper than on the left side, and the accessory muscle bundles can cross at any depth.Cardiac surgeons have suggested that the deep groove may itself allow the atrial wall to fold over the ventricular wall, thereby producing atrialventricular myocardial continuity.3 Most of the pathways identified through the use of microscopy have been working myocardium, with only a few reported to contain histologically specialized cells.4 Whether comprising working myocardium or abnormal myocytes, these pathways have normal gap junctions with a pattern suggestive of working ventricular myocardium.5 Morphologically, these threads of musculature