Zoom into inlet valves

Siew Yen Ho
Hideki Uemura
Royal Brompton Hospital
London, UK

This review of the atrioventricular valves examines first the normal structures of the tricuspid and mitral valves and then discusses various congenital malformations of these valves in hearts with biventricular atrioventricular connections. The format of the review is live video-demonstration of heart specimens followed by comments and discussions.
　Atrioventricular valves are characterized by having leaflets that are attached to the atrioventricular junctions at the hingelines(annuli) and to papillary muscles via tendinous cords. The papillary muscles are then inserted into the ventricular walls. Tendinous cords may also insert directly into the ventricular walls or septum. Normal functioning of the atrioventricular valves depends on normal structures and integrity of all the valvar elements from the hingelines through to the papillary muscle insertions into ventricular myocardium. The tricuspid and mitral valves have their distinctive features and inherent morphological differences. Other than differences in leaflet arrangement or numbers, the tricuspid valve can be recognized on account of its septal leaflet whereas the mitral valve lacks a septal leaflet and its leaflets are attached exclusively to two distinct groups of papillary muscles.
　Congenital malformations of the atrioventricular valves can be considered in terms of variations in valvar orifices (number/size/imperforate), leaflets (number, shape, thickness, integrity), tendinous cords (attachments, lengths, intercordal spaces), papillary muscles (number, form, attachment), affecting each entity or in combinations. Thus, valvar malformations may result in stenosis (or atresia at the extreme end) or a combination of stenosis and incompetence. We will review some examples of cases with mitral atresia, mitral stenosis, mitral dysplasia, mitral regurgitation, tricuspid stenosis, straddling tricuspid valve, and Ebstein malformation.
　Common atrioventricular valve exemplified by atrioventricular septal defect will also be reviewed. There are two major forms of these valves in the setting of atrioventricular septal defect: those with common valvar orifice and those with separate valvar orifices. In both forms, the basic common valve has five leaflets; two of them are shared between the left and the right ventricles and are known as bridging leaflets. Thus, the portion of the common valve opening to the morphologically right ventricle has 4 leaflets (including 2 bridging leaflets) and the portion opening to the morphologically left ventricle has 3 leaflets (including 2 bridging leaflets). It is fusion between the two bridging leaflets that differentiates the valve with separate valvar orifices from that with a common valvar orifice. The division of the common valvar orifice into two does not confer on the right or left portion of the valve distinctive properties that can justify calling them mitral or tricuspid.