Abstract
There is considerable confusion as to how best describe the components of the arterial valves. It is hardly surprising, therefore, that similar uncertainties apply to concepts for their development. In this review, we describe the anatomy of the arterial valves as seen in the postnatal heart. We suggest that their working components are best described as leaflets, housed in supporting arterial sinuses. The roots surrounding the leaflets, which are hinged in semilunar fashion, can then be defined as extending from a virtual ring at their base to the sinutubular junction. We also discuss the problems related to definition of the valvar “annulus”. Understanding the development of the arterial roots, which are formed in the central part of the embryonic outflow tract, is facilitated by considering the outflow tract itself as possessing three components, as opposed to the traditional “conus” and “truncus”. These three parts can be described as being distal, intermediate, and proximal. The distal part is separated to form the intrapericardial arterial trunks, while the proximal part becomes the ventricular outflow tracts. It is the intermediate component that houses the developing arterial valves, and their supporting valvar sinuses. The distal parts of the cushions that separate the outflow tract into aortic and pulmonary components, along with the intercalated cushions, excavate to form the leaflets. The walls of the sinuses are formed by growth of non-myocardial tissues from the heart-forming area. We then show how these features can be used to interpret the anatomy and development of congenitally malformed arterial valves.
Highlights
It is difficult currently to find a coherent and unified account of the development of the arterial valves
In describing the appearance of the intercalated cushions, Kramer showed how the arterial valves are developed in the intermediate component of the embryonic outflow tract
Why Kramer should have suggested that the outflow tract is best described in bipartite rather than tripartite fashion, since this begs the question as to whether the valves themselves, and their supporting sinuses, should be considered to belong to the “truncus” or the “conus”
Summary
It is difficult currently to find a coherent and unified account of the development of the arterial valves. A unifying nomenclature is essential if we are to correlate the normal and abnormal structure of the valves. By reviewing these aspects, we offer a vocabulary for use in this arena. The valves within the heart guard, on the one hand, the junctions between the atrial and ventricular chambers, and on the other hand, those between the ventricles and the arterial trunks These sets of valves, can be considered collectively as being atrioventricular and arterial. Because of this semilunar shape, the leaflets are attached through a significant length of the outflow tract It is difficult, to describe a specific “level” for the valves. They occupy the intermediate parts of the outflow channels (Figure 1)
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