The Conduction System

The sinus node is located on the anterolateral aspect of the junction between the superior vena cava and right atrium. It can sometimes be seen as a white nodule in this area. It is superficial, lying just beneath the epicardial surface. The AV node lies on the right atrial side of the central fibrous body (right trigone) between the muscular and membranous portions of the AV septum. It is just anterosuperior to the ostium of the coronary sinus in the triangle of Koch (Fig .1.2). The triangle of Koch is formed by the tricuspid annulus, the coronary sinus, and the tendon of Todaro (a continuation of the eustachian valve from the inferior vena cava). The bundle of His passes through the right part of the right trigone and the central fibrous body, and this area is just inferior to the commissure between the septal and anterior leaflets of the tricuspid valve. It is this area which is in most danger of injuring conduction tissue when stitches are placed in the tri-cuspid annulus. The bundle of His then courses along the border of the membranous septum giving out fibers forming the left bundle branch. This region of the junction of the septal and anterior leaflet of the tricuspid valve is exactly the location between the right coronary cusp of the aortic valve and noncoronary cusp of the aortic valve in the anterior commissure and it is precisely this region which is in most danger of injuring the bundle of His when performing an aortic valve replacement (Fig. 1.1).

The left bundle branch fans over the left ventricular septum surface and is subdivided into an anterior and posterior subdivisions, the anterior one going to the anterolateral papillary muscle and the posterior one going towards the pos-teromedial papillary muscle.

The right bundle branch originates from bundle of His and fans out to supply the wall of the right ventricle.

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