The right bundle branch of the cardiac conducting system is the continuation of conducting fibres from the atrioventricular bundle of His. It forms within the interventricular septum at the junction of the membranous and muscular parts. It runs to the right within the muscular part of the septum as a fine tract. Reaching the wall of the right ventricle, the fibres run anteriorly and inferiorly towards the apex of the chamber in the subendocardial layer.
Near to the apex, the bundle passes to the right into the septomarginal trabecula. This passes the right bundle branch into the base of the anterior papillary muscle of the right ventricle. From the papillary muscle, the bundle diverges into multiple, fine subendocardial fibres which pass back to the base of the chamber.
Hence, the first contacts between Purkinje cells and contractile myocytes which permits contraction is within the papillary muscle. Prior to this point, the bundle is covered by an insulating layer of connective tissue. This means that:
Histologically, the cells of the left bundle branch are predominantly rapidly-conducting Purkinje myocytes.
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