Anatomy of the Right Ventricular Outflow Tract

Before describing variations in coronary arterial anatomy, it is imperative to have a clear understanding of the anatomy of the pulmonary valve, specifically of the components of the pulmonary infundibulum (Figure 40.1). Excellent work in this area was published many years ago,2'3 and will be amplified here.

The pulmonary valve is, in most cases, a trileaflet valve supported by a muscular infundibulum. The infundibulum has two com ponents, a free-standing component existing in a plane superior to the muscle of the right ventricular (RV) wall and an "internal" component below the surface of the RV wall.The pulmonary valve therefore, sits higher than the RV mass, since it is supported by this free-standing infundibulum. When excising the autograft, the dissection is carried down from superiorly and stops when the RV mass is encountered. The height of this free-standing infundibulum is remarkably consistent, both in normal hearts and those with aortic pathology, ranging from 5 to 10 mm in length (5 mm—20%, 6 mm—30%, 7mm—30%, 8-10mm—20%). There were no differences in this anatomy between the two groups.

The pulmonary valve has not received as much interest as the aortic valve, but it's interrelationships and anatomy are crucial to both the Ross procedure and also the arterial switch operation. As already discussed, the pulmonary valve is, in most cases, a trileaflet valve. Its suitability as a systemic valve should always have been assessed preoperatively using an echocardiograph.

The three leaflets are right and left facing relative to the right and left coronary leaflets of the aortic valve, and the non-facing or lateral leaflet (Figure 40.2). In both the normal and abnormal hearts examined, these leaflets were equal in their circumferential extent. As with the aortic valve,4 there is no true basal collage-nous annulus supporting the valvar subcomponents. Instead the overall structure is similar to the aortic valve, with sinuses, leaflets and a

Aortic Valve Annulus Size
pulmonary valve.
Outflow Tract Anatomy

Figure 40.2. The atrioventricular junction viewed valve. Two leaflets of these valves always face each from its atrial aspect after removal of the atrial other, permitting the normination of right-facing and chambers and great arteries. It shows the relation- left-facing leaflets of the pulmonary valves. ship of the leaflets of the pulmonary valve and aortic

Figure 40.2. The atrioventricular junction viewed valve. Two leaflets of these valves always face each from its atrial aspect after removal of the atrial other, permitting the normination of right-facing and chambers and great arteries. It shows the relation- left-facing leaflets of the pulmonary valves. ship of the leaflets of the pulmonary valve and aortic supporting infundibulum with three fibrous interleaflet triangles. The free surface of the leaflets is thickened at the point of coaptation to form a lunula. This is not as discrete a structure as in the aortic valve, nor is there such a well-developed sino-tubular ridge. A possible explanation for this is the lower pressures to which the right ventricular outflow tract is exposed, or the more proximal bifurcation of the pulmonary tract.

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