I. INTRODUCTION. The tricuspid valve (TV) is a saddle-shaped right-sided heart valve that separates the right atrium (RA) and the right ventricle (RV). The RV is a low-pressure chamber that communicates with a low-resistance pulmonary vascular bed. Hemodynamic abnormalities are often absent until there are significant changes in the pulmonary vascular resistance or tricuspid valvular dysfunction. Disorders of the TV are usually categorized as primary or secondary diseases. This chapter describes the common causes of tricuspid valvular dysfunction, their diagnosis, and current guidelines for treatment.

The highest portion of the TV faces the RA. In anatomic orientation, the TV faces inferiorly and anterolaterally toward the left ventricle. The TV consists of three leaflets, the largest being the anterior leaflet. The septal leaflet is situated in the inferomedial aspect adjacent to the membranous septum, and the posterior leaflet is located in the posterior and inferior aspect of the RV (Fig. 6.1). The tricuspid annulus is an oval-shaped fibrous structure and is larger than the mitral annulus. TV disease affects a large number of patients; however, only a small number of them undergo surgery for correction of valvular regurgitation or stenosis.

Tricuspid stenosis (TS) is the least common of the valvular stenoses owing to the low incidence of rheumatic heart disease (RHD). It is also more often seen in association with mitral stenosis (MS).

The causes of TS include:

RHD-induced TS accounts for >90% of cases and is more often seen in association with MS or aortic valve stenosis. Patients often present with a combination of TS and TR (tricuspid regurgitation). Clinically significant TV disease is present in only 5% of patients with RHD. There is thickening and fibrosis of the valve leaflets, with progression to marked leaflet contracture and commissural fusion in advanced disease.

Carcinoid is a neuroendocrine tumor found in the intestines and does not affect the TV unless there is secondary metastatic spread to the liver. The vasoactive substances (serotonin, histamine, and bradykinin), secreted by the hepatic metastases, fail to be inactivated by the liver, and therefore directly affect the right-sided heart valves. Carcinoid TV disease is characterized by thickened, retracted, shortened, and fixed tricuspid leaflets. Most often, there is significant tricuspid regurgitation associated with carcinoid. The pulmonic valve may also be involved. Mitral and aortic valves are usually spared owing to the clearance of vasoactive substances by the lungs; however, the presence of a significant right-to-left shunt (via an atrial septal defect or patent foramen ovale) may result in left-sided heart valve disease.

TS results in a persistent diastolic pressure gradient between the RA and RV. Augmentation of blood flow across the TV increases, as occurs with inspiration and exercise and results in an increase in this pressure gradient between the RA and RV. In contrast, the gradient decreases when blood flow decreases, such as with expiration (Fig. 6.2).

As a result of the low pressures normally seen in the RA and RV, a mean pressure gradient as low as 2 mm Hg may signal the presence of TS. A gradient as small as 5 mm Hg may result in elevated mean right atrial pressure (RAP) and may produce systemic venous congestion, jugular venous distention, ascites, and peripheral edema. Right atrial “a” wave is increased and may approach the level of right ventricular systolic pressure (RVSP). Resting cardiac output may be reduced and may fail to increase with exercise owing to the limited RV preload. RV preload may also be limited by atrial fibrillation owing to disorganized and suboptimal RA emptying.

Presenting signs and symptoms depend on the severity of stenosis. Fatigue and exercise-induced dyspnea related to low and relatively fixed cardiac output may occur. Severe TS may mask pulmonary venous congestion, paroxysmal nocturnal dyspnea (PND), and orthopnea associated with other valvular lesions, such as MS. Right upper quadrant pain and abdominal distention due to hepatic congestion, hepatomegaly, and ascites may be seen.

Physical exam findings include an elevated jugular venous pressure, hepatomegaly, ascites, and peripheral edema. A low-pitched diastolic murmur heard best along the left sternal border in the third-to-fourth intercostal space or over the xiphoid process is characteristic. The murmur is prominent at end diastole (if the patient is in sinus rhythm). The murmur may be obscured if there is concomitant MS. The intensity of the murmur in TS is usually accentuated by inspiration (Rivero-Carvallo sign) or other maneuvers such as leg raising and squatting, which augment the preload.

An opening snap (OS) may be heard at the left lower sternal border; however, this may be masked by the OS of coexisting MS. A giant a wave in the jugular venous pulse as a result of impaired right atrial diastolic filling.

Owing to the absence of pulmonary venous congestion, there is absence of PND and orthopnea. The discrepancy between the severity of peripheral edema and the absence of pulmonary congestion may help discriminate TS from other valvular lesions.

Respiratory variation in splitting of the second heart sound (S₂) may be absent in TS as a result of the inability to augment diastolic filling of the RV despite increase in venous return with inspiration.

In patients with TS induced by carcinoid syndrome, flushing and diarrhea may be present.

1. Chest X-ray is most notable for right atrial enlargement.

Imaging features of TS include valve thickening and/or calcification, restricted leaflet-to-leaflet separation at peak opening and diastolic doming, leaflet immobility (seen in carcinoid syndrome), and right atrial enlargement.

An increase in transvalvular velocity is recorded by continuous wave Doppler (CWD), which is normally accentuated during inspiration; mean pressure gradient
may range between 2 and 10 mm Hg. Higher gradients may be seen in patients with stenosis and regurgitation.

For calculation of valve area, some have proposed a constant of 190, with valve area determined as 190/T_1/2, where T_1/2 is the pressure half-time in milliseconds. A longer T_1/2 implies a greater TS severity, and T_1/2 >190 may represent hemodynamically significant stenosis.

Valve area may also be calculated using the continuity equation, stroke volume/velocity time interval (VTI_TV): Stroke volume may be obtained from either left or right ventricular outflow, and VTI_TV is the TV inflow recorded by CWD. The main limitation of the method is obtaining an accurate measurement of the inflow volume passing through the TV when there is combined TS and TR. As severity of TR increases, valve area is progressively underestimated by the continuity equation method. In the presence of TR, transvalvular gradient may be clinically more relevant for assessment of severity and decision-making than the actual stenotic valve area.