Tricuspid valve (TV) disease is often secondary to, or in association with, mitral or aortic valve disease or left ventricular (LV) disease and receives less attention than the primary left-sided disease. It is frequently labeled "the forgotten valve" because surgical correction is often ignored. Appropriate treatment of the TV disease, even when secondary to left heart diseases, may improve long-term functional outcome.1
The TV is the most apically (or caudally) placed valve with largest orifice among the four valves. The TV apparatus includes leaflets or cusps, chordae and papillary muscles, and tricuspid annulus in addition to the right atrium (RA) and right ventricle (RV).
The tricuspid annulus is oval in shape and becomes more circular when dilated. The annulus has a complex nonplanar shape with the posteroseptal portion being the lowest and the anteroseptal being the highest.2 It tends to become more planar with moderate or severe "functional" tricuspid regurgitation (TR). The annular orifice area is approximately 20% larger than the mitral annulus area, with a major diameter of 3.0 to 3.5 cm in adults. The larger orifice provides for the inflow to occur at lower velocities and lower pressure decreases. Both early and late diastolic velocities are lower than the mitral inflow. The annulus expands in diastole and constricts in midsystole with a nearly 30% reduction in annular area.3
In general, the TV has three distinct leaflets described as septal, anterior, and posterior. The septal and the anterior leaflets are larger. The posterior leaflet is smaller and appears to be of lesser functional significance because it may be imbricated without impairment of valve function. The septal leaflet is in immediate proximity to the membranous ventricular septum, and its extension provides a basis for spontaneous closure of the perimembranous ventricular septal defect. The larger anterior leaflet is attached to the anterolateral margin of the annulus and is often voluminous and sail-like in Ebstein anomaly.
Papillary Muscles and Chordae
There are three sets of smaller papillary muscles; each set is composed of up to three muscles. The chordae tendineae arising from each set are inserted into two adjacent leaflets. Thus, the anterior set chordae insert into half of the septal and half of the anterior leaflets. The medial and posterior sets are similarly related to adjacent valve leaflets.
The diastolic valve opening with expansion of the annular orifice provides for unimpeded inflow. Although systolic narrowing of the orifice is intended to result in effective valve closure; some degree of valvular regurgitation with color Doppler imaging is quite common. Nearly 50% to 60% of young adults exhibit mild TR. A smaller proportion of normal adults, up to 15%, have moderate TR. The significance of mild or moderate TR should be evaluated on the ...