Tricuspid Valve Anatomy

The right atrioventricular valve complex (the tricuspid valve) is made up of the 3 valve leaflets, the annulus, the supporting chordae tendineae, and the papillary muscles. The atrial and ventricular masses, conduction system tissue, and support structure of the fibroelastic cardiac skeleton allow coordinated actions of the tricuspid valve. ^[1] See the following images.

Surface anatomy of the heart. A = aortic valve; M = mitral valve; P = pulmonic valve; T = tricuspid valve.

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Heart valves, superior view.

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The tricuspid valve is often called the "forgotten valve" or "lost valve," because it is understudied relative to the other cardiac valves; variations in anatomic structures have been reported in the literature. The tricuspid valve has been described as having as few as 2 and as many as 6 leaflets, ^[2] whereas the papillary muscles have been reported to number from 2 to 9. ^[3]

The tricuspid valve is located between the right atrium and right ventricle and has a valve area of 4-6 cm ² (see the following image and video). ^[4] The valve is nearly vertical and is approximately 45° to the sagittal plane. The valve itself is slightly inclined to the vertical so that the margins of the valve are anterosuperior, inferior, and septal, and the cusps take their name from these attachment sites. ^[1]

The tricuspid valve (TV) as viewed from the right atrium (RA).

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The anterosuperior (anterior or infundibular) cusp is the largest cusp of the 3 and is located between the conus arteriosus and atrioventricular orifice. The posterior (marginal) cusp is the next largest cusp and is named for its relative posterior position and is connected to the posterior aspect of the right ventricle. The third and smallest cusp, the septal (medial) cusp, is attached to the right and left fibrous trigones and the atrial and ventricular septa. These fibrous attachments make the septal cusp relatively immobile; therefore, most of the tricuspid annular descent takes place along the margins of the anterior and posterior cusps. ^{[1, 4]} During diastole, the major cusps (anterior and posterior) move like sails and meet to join the smaller septal leaflet. Thus, functionally, the tricuspid valve acts more like a bicuspid valve. ^[1]

The tricuspid subvalvular apparatus consists of anterior, posterior, and septal papillary muscles and their true chordae tendineae. False chordae can connect 2 papillary muscles, connect a papillary muscle to the ventricular wall, or connect points on the ventricular walls. The true chordae typically originate from the apical third of the papillary muscle but can originate from the ventricular walls, as is the case for the septal leaflet.

The anterior papillary muscle is the largest, the posterior is often bifid or trifid, and the septal is the smallest. These papillary muscles supply the chordae for the adjacent components of the cusps they support. The anterior papillary muscle provides chordae to the anterior only or the anterior and septal leaflet; the posterior papillary muscle provides chordae to the posterior and septal leaflets; and the septal papillary provides chordae to the septal and anterior leaflets. ^[5] Characteristically, the septal leaflet is also supported by chordae that arise from the ventricular septum. ^{[1, 4, 6]} .

Functionally, the papillary muscles contract just prior to the onset of right ventricular systole so as to increase tension in the chordae tendinae and maximize coaptation of the 3 cusps, thereby reducing regurgitation across the tricuspid valve.  ^[7]

The tricuspid valve is formed in weeks 5-6 of embryonic development. After the atrioventricular (AV) endocardial cushions fuse, each atrioventricular orifice is surrounded by local proliferations of mesenchymal tissue, from which the AV valves form and are attached to the ventricular wall by muscular cords. Finally, muscular tissue in the cords degenerates and is replaced by dense connective tissue with the valve itself covered by endocardium. ^[8]

The following image shows the AV valve leaflet and its attachment to the fibrous skeleton of the heart. The AV valve leaflet is formed by a fold or duplication of the endocardium; a dense connective tissue core forms the central part of the valve leaflet. The upper or atrial surface of the valve is thick and resembles atrial endocardium, and the lower or ventricular surface of the valve is thin and resembles ventricular endocardium.

Atrioventricular valve (AV) histology.

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Ebstein anomaly

Ebstein anomaly occurs in approximately 1 in 200,000 live births, accounts for less than 1% of all congenital heart diseases, and is associated with maternal lithium use during the first trimester of pregnancy. Ebstein anomaly is characterized by the following ^[9] : (1) adherence of the septal and posterior leaflets to the underlying myocardium; (2) apical displacement of the functional annulus; (3) dilatation of the "atrialized" portion of the right ventricle with thinning of the wall; (4) redundancy, fenestration, and tethering of the anterior leaflet; and (5) dilatation of the true tricuspid annulus. (See Ebstein Anomaly.)

Tricuspid atresia

Tricuspid atresia may be defined as a congenital absence or agenesis of the tricuspid valve; this is the third most common cause of cyanotic congenital heart defects. There are 6 forms of tricuspid atresia with differing underlying anatomic pathology; see Tricuspid Atresia for more information.

Congenital tricuspid stenosis

Congenital tricuspid stenosis has several manifestations. The tricuspid valve may have incompletely developed leaflets, shortened or malformed chordae, small annuli, abnormal size and number of the papillary muscles, or any combination of these defects. ^[10] Congenital tricuspid stenosis is rare and is usually associated with other anomalies, such as severe pulmonary stenosis or atresia and secondary hypoplasia of the right ventricle. ^{[11, 10]}

Congenital cleft of the anterior leaflet

Congenital cleft of the anterior leaflet of the tricuspid valve is rare and usually associated with perimembranous ventricular septal defects, pulmonary stenosis, or atrial septal defects. ^[12]