Tricuspid Valve Disease Imaging

Tricuspid valve disease, particularly tricuspid regurgitation, is a highly prevalent condition with a complex pathophysiology and long-term adverse consequences. Although historically neglected, tricuspid valve disease has gained increasing recognition, with important advances in assessment and management of this disorder since the year 2000. Surgical treatment remains the standard of care, but tricuspid valve disease continues to have one of the highest death rates among all cardiac valve–related procedures, and a broad range of patients still do not receive effective therapy for tricuspid valve disease in contemporary clinical practice. Therefore, several alternative, less-invasive technologies for treating patients with severe, native tricuspid valve disease at high surgical risk have been developed, with promising early results. ^[1]

Tricuspid valve disease involves the atrioventricular valve apparatus that separates the right atrium (RA) from the right ventricle (RV). Tricuspid regurgitation (TR) and tricuspid stenosis (TS) are commonly encountered. Isolated tricuspid valve disease is rare. It most often occurs as a secondary condition. Tricuspid regurgitation is more common than tricuspid stenosis and usually develops in association with pulmonary hypertension in patients with mitral stenosis or regurgitation. Most patients with rheumatic tricuspid valve disease present with TR or a combination of stenosis and regurgitation. Rheumatic TS does not occur as an isolated lesion, but it often accompanies mitral and aortic valve disease. Some patients may develop TR in association with trauma or infective endocarditis. Tricuspid stenosis is nearly always rheumatic in origin. However, congenital tricuspid atresia, RA tumors, tricuspid valve vegetation, the presence of a pacemaker lead, or compression caused by extracardiac tumors may produce a clinical picture similar to that of TS. In patients with carcinoid syndrome, endomyocardial fibrosis may lead to obstruction of RV inflow, resulting in a clinical presentation similar to that of TS. ^{[2, 3, 4, 5]}

Transthoracic echocardiography and transesophageal echocardiography, which permit assessment of the tricuspid valve with multilevel imaging, are the techniques of choice for accurate detection and understanding of the etiology and severity of valve regurgitation and for determination of treatment options. These tests provide assistance with timing and guidance during intervention for patients with tricuspid valve disease. ^[6] Echocardiography permits assessment of the dimensions of cardiac chambers, determination of RV and pulmonary pressures, and delineation of associated valvular diseases. ^{[7, 8, 9]}  Three-dimensional echocardiography offers the ability to visualize the entire tricuspid valve and to identify which leaflets are affected by the pathology. ^[6]

Computed tomography (CT) scans of the heart are rarely needed to delineate structural cardiac abnormalities. The degree of confidence is moderate, and rates of false-positive and false-negative findings are low. ^{[7, 10]}  Patients who present with congestive heart failure may require assessment of tricuspid valve and LV function through a first-pass technique (ie, multiple-gated acquisition [MUGA] scanning). The degree of confidence is moderate, and findings may be nonspecific.

Tricuspid valve disease affects millions of patients worldwide. The tricuspid valve has always been considered less relevant than the left-side valves of the heart, but this "forgotten valve" still represents a great challenge for cardiac surgeons, especially in the most difficult symptomatic scenarios. ^[11]

The 2020 American College of Cardiology (ACC)/American Heart Association (AHA) Guidelines for the Management of Patients With Valvular Heart Disease provide recommendations for clinicians to diagnose and manage valvular heart disease, as well as supporting documentation. Many recommendations from earlier valvular heart disease guidelines have been updated with new evidence and newer options for diagnosis and treatment of valvular heart disease. ^[12]  Recommendations include the following:

• In evaluating patients with valvular heart disease, findings on history and physical examination should be correlated with the results of noninvasive tests (ie, ECG, chest x-ray, transthoracic echocardiogram).
• If there is discordance between the physical examination findings and initial noninvasive testing, consider further noninvasive testing (eg, CT, cardiac MRI, stress testing) or invasive testing (transesophageal echocardiography, cardiac catheterization) to determine the optimal treatment strategy.

Several transcatheter tricuspid valve intervention (TTVI) devices have been developed. The particular characteristics of the tricuspid valve (large noncalcific annulus, presence of chief surrounding structures such as the conduction system or the right coronary artery) make multimodality imaging (eg, transesophageal echocardiography, CT) key in the preprocedural assessment of TTVI. According to their mechanisms of action and therapeutic targets, TTVIs include transcatheter repair with coaptation or annuloplasty systems, caval valve devices, and transcatheter tricuspid valve replacement. The initial TTVI experience showed that most procedures were well tolerated, with high procedural success and low in-hospital and early mortality. ^[13]

Very little is known about tricuspid valve disease when compared to other valvular disorders, and tricuspid stenosis (TS) is even more rarely described. Rheumatic heart disease, one of the most common causes of TS, almost always occurs in conjunction with mitral stenosis. Less common causes of TS include congenital abnormalities (Ebstein anomaly) and metabolic or enzymatic abnormalities (Fabry disease, Whipple disease). ^[14]

The rheumatic tricuspid disease is characterized by diffuse fibrous thickening of the leaflets and fusion of 2 or 3 commissures. Leaflet thickening usually occurs in the absence of calcific deposits; the anteroseptal commissure is most commonly involved. Incompletely developed leaflets, shortened or malformed chordae, a small annulus, or an abnormal number or size of papillary muscles may result in TS. The primary result of TS is right atrial pressure elevation and consequent right-sided congestion. ^[14]

Presenting symptoms are generally related to right-sided valve disease, such as reduced exertional capacity, fatigue, or exertional syncope. Patients with severe TS eventually experience hepatic congestion, leg edema, ascites, and deterioration of liver function tests and anasarca.

Tricuspid stenosis accounts for about 2.4% of all cases of organic tricuspid valve disease and is seen most often in young women. ^[14]

Imaging

Radiography

In TS, radiographs may show marked cardiomegaly with conspicuous enlargement of the right atrium (RA) (ie, prominence of the right heart border), which extends into a dilated superior vena cava and azygos vein; conspicuous dilation of the pulmonary artery may be absent. Vascular changes in the lungs characteristic of mitral valvular disease may be masked, with little or no interstitial edema or vascular redistribution; however, left atrial enlargement may be present.

Chest radiographs show a dilated RA without an enlarged pulmonary artery segment.

Electrocardiography

In patients with tricuspid stenosis in sinus rhythm, electrocardiograms (ECGs) show tall right atrium (RA) peaked P waves in leads II, III, and avF consistent with right atrial enlargement and no RV hypertrophy. ^[14]

Echocardiography

Echocardiographic changes of the tricuspid valve in TS resemble those observed in the mitral valve in mitral stenosis. Two-dimensional echocardiography characteristically shows the following:

• Diastolic doming of the valve
• Thickening and restricted motion of leaflets
• Reduction in separation of leaflet commissures
• Diminished tricuspid opening

Hemodynamically significant TS is revealed by the following:

• Tricuspid peak inflow velocity during inspiration of >1 m/s
• Inflow time-velocity integral >60 cm
• Valve area by continuity of ≤1 cm ^{2 [14]}

With transesophageal echocardiography, depiction of details of the valvular structure is improved. On Doppler echocardiography, a delayed slope of antegrade flow is seen; such findings compare well with cardiac catheterization findings in quantification of TS and in assessment of associated TR. ^{[7, 8, 9, 15, 16]}

Computed tomography

The particular characteristics of the tricuspid valve (large noncalcific annulus, presence of chief surrounding structures such as the conduction system or the right coronary artery) make multimodality imaging (eg, transesophageal echocardiography, CT) key in the preprocedural assessment of transcatheter tricuspid valve interventions. ^[17]

Magnetic resonance imaging

Magnetic resonance imaging (MRI) may be helpful in delineating valvular structural abnormalities when echocardiographic assessment is suboptimal. Cardiac MRI is now the preferred method for evaluation of RV size and function. ^[14]

Cardiac catheterization

Tricuspid stenosis is seen as a large right atrial "a" wave of 12-20 mm Hg and a diastolic mean gradient of 4-8 mm Hg across the tricuspid valve. The mean gradient across the tricuspid valve is more significant in TS because an end-diastolic gradient may be absent, with significant obstruction as the result of lower filling pressures on the right side of the heart. Elevated RA pressure with a slow fall in early diastole and a diastolic pressure gradient across the tricuspid valve is characteristic of TS. ^[14]

Angiography

Angiography performed after injection of contrast material into the RA, with imaging in the 30° right anterior oblique projection, characteristically shows the following in patients with TS:

• Thickening of leaflets
• Decreased mobility of leaflets
• Diastolic jet through the constricted orifice
• Thickening of the normal atrial wall

The degree of confidence in angiography is high, and false findings are rare.

Treatment

Loop diuretics may be useful to relieve systemic and hepatic congestion in patients with severe, symptomatic TS. Caution is advised because diuretics may decrease the preload further in patients who have a low output state.

Surgical therapy may be needed in addition to medical management. A decision should be made to treat the patient with a valvotomy or with valve surgery. Tricuspid valve surgery is preferred over percutaneous balloon tricuspid commissurotomy for treatment of symptomatic severe TS because most cases of severe TS are accompanied by TR (rheumatic, carcinoid), and percutaneous balloon tricuspid commissurotomy may create or worsen regurgitation. ^[14]

Prognosis

Tricuspid valve stenosis is a rare disorder that is best managed by an interprofessional team. Most often, mild cases of TS are well tolerated and can be managed medically. Severe cases may require surgery. Although dilation of the leaflets can be undertaken, recurrence is common. In most cases, the valve may need to be replaced. Outcomes for patients with TS depend on the cause. ^[14]

Pathophysiology

Tricuspid regurgitation (TR), also called tricuspid insufficiency, is a relatively common condition that can result from structural abnormalities of any part of the tricuspid valve apparatus. This may involve modifications in valve leaflets, annulus, chordae tendineae, or papillary muscles. ^[17]

Lesions in TR may be categorized as primary, for which intrinsic abnormalities in the tricuspid valvular apparatus are responsible, or secondary, for which right ventricular dilation causes TR. Secondary disorders such as tricuspid annular dilation and/or leaflet tethering in the setting of right ventricular pressure and/or volume overload are largely responsible for TR as compared to primary disorders involving the valve apparatus. ^[17]

Tricuspid regurgitation is defined by the backflow of blood from the right ventricle into the right atrium during systole. In mild to moderate cases of TR, no major hemodynamic consequences are noted because of the comparatively compliant nature of the right atrium. However, in severe cases, right ventricular volume overload eventually results in right-sided congestive heart failure presenting with peripheral edema, ascites, and hepatic congestion. ^[17]

The severity of TR is increased during inspiration. The right ventricle widens during inspiration, which further enlarges the tricuspid valve annulus, hence increasing the effective regurgitant orifice area. ^[17]

Presenting symptoms

Patients present with clinical features of right-sided heart failure. These may consist of painful hepatosplenomegaly, ascites, and peripheral edema. In severe cases, pulsations in the neck from distended and pulsatile jugular veins are noted. Exercise intolerance may be seen. Clinical features of the underlying condition causing TR may be observed. For example, pulmonary hypertension may cause symptoms such as weakness, shortness of breath, and exercise intolerance, or patients with infective endocarditis, a common cause of TR, may present with febrile episodes. ^[17]

Epidemiology

The incidence of tricuspid regurgitation in the United States has been found to be 0.9%. No gender or racial differences in incidence have been noted. ^[17]

Tricuspid regurgitation presents in different age groups depending on its etiology. Ebstein anomaly may be diagnosed at birth and during early childhood. Rheumatic valvular disease is the most common form of TR in patients older than 15 years. ^[17]

Imaging

Several studies have demonstrated that severe tricuspid regurgitation (TR) has a significant negative impact on morbidity and mortality. Nowadays, several therapeutic options are available to treat patients with TR, and patients at high surgical risk can be treated via transcatheter procedures. For management of TR, an accurate assessment of the tricuspid valve and its surrounding structures is of crucial importance and has gained significant interest in the medical community. Different imaging modalities can provide details on the tricuspid valve apparatus, right ventricle, right atrium, and coronary circulation, which are fundamental in defining the timing and anatomic suitability of surgical and percutaneous procedures. ^[18]

Radiography

On chest radiography, the following findings are noted:

• Marked cardiomegaly in severe TR
• Pleural effusions and ascites with diaphragmatic elevation
• Common occurrence of pulmonary arterial and venous hypertension ^[17]

In patients with functional TR, marked cardiomegaly is usually evident and the RA is prominent. Evidence of elevated RA pressure may include distention of the azygos vein and the presence of a pleural effusion. Ascites with upward displacement of the diaphragm may be present. Systolic pulsations of the RA may be evident on fluoroscopy.

In tricuspid valve disease, findings are generally nonspecfic, and false findings are frequent.

Electrocardiography

Electrocardiographic findings are frequently nonspecific. Incomplete right bundle branch block, Q waves in lead V1, and atrial fibrillation are often noted. ^{[15, 16]}

Nonspecific ST and T waves in the right precordial leads reflecting right ventricular dysfunction are seen. If pulmonary hypertension causes TR, the ECG may show right axis deviation indicating RV hypertrophy and tall R waves in V1 to V2. With severe pulmonary hypertension, right atrial hypertrophy and "P-pulmonale" may also be present. ^[17]

Echocardiography

The main modality used to diagnose and evaluate TR is Doppler echocardiography. It is used to precisely contemplate regurgitant blood flow and its flow velocity and to accurately measure systolic pressure in the right ventricle. ^[17]  Pulsed Doppler echocardiography reveals systolic flow from the RV to the RA; it is a sensitive technique for detecting and quantifying TR. Reverse flow may be recorded in the inferior vena cava and the hepatic veins. The peak velocity of TR flow is useful for noninvasive estimation of RV (and pulmonary arterial) systolic pressure. Color flow Doppler imaging is a sensitive and specific method for assessing TR; it is helpful in selecting patients for surgical treatment and in evaluating postoperative results.

Doppler echocardiography shows a prolonged slope of antegrade flow. Doppler echocardiography compares well with cardiac catheterization in quantification of TS and in assessment of associated TR.

The main purpose of echocardiographic imaging is to diagnose TR, assess its severity, and estimate pulmonary arterial pressure and the status of RV function. In secondary TR, clinically significant enlargement of the tricuspid annulus, right atrium, and right ventricle is found. For patients with TR caused by endocarditis, echocardiography may reveal vegetations on the valve or a flail valve leaflet. Transesophageal echocardiography may depict TR vividly. ^{[15, 16]}

The goals of echocardiography are to detect TR, to estimate its severity, and to assess pulmonary arterial pressure and RV function. For patients with TR secondary to dilation of the tricuspid annulus, the right atrium (RA), the right ventricle (RV), and the tricuspid annulus usually appear greatly dilated on echocardiography. Evidence suggests that in patients with TR, RV diastolic overload with paradoxical motion of the ventricular septum occurs to a degree similar to that observed in patients with an atrial septal defect. ^[19]

Exaggerated motion and delayed closure of the tricuspid valve are evident in patients with Ebstein anomaly. Prolapse of the tricuspid valve resulting from myxomatous degeneration may be evident on echocardiography. Echocardiographic indications of tricuspid valve abnormalities, especially TR, as evidenced on Doppler examination, may be seen in most patients with carcinoid heart disease. For patients with TR caused by endocarditis, echocardiography may reveal vegetation on the valve or may show a flail valve.

Transesophageal echocardiography is useful in the detection of TR.

Contrast echocardiography involves rapid injection of saline indocyanine green dye or sonicated human albumin into an antecubital vein while a 2-dimensional echocardiogram is recorded. This injection produces microcavities that are readily visible on echocardiography and that travel normally as a bolus through the circulation. In TR, these microcavities may be seen to travel back and forth across the tricuspid orifice and to pass into the inferior vena cava and hepatic veins during systole.

The degree of confidence in echocardiography is high, and false findings are rare.

(Doppler echocardiograms depicting TR are provided below.)

Cardiac catheterization

Elevated end-diastolic pressures are noted in the right atrium and in the right ventricle. ^[17]

Computed tomography

Particular characteristics of the tricuspid valve (large noncalcific annulus, presence of chief surrounding structures such as the conduction system or the right coronary artery) make multimodality imaging (eg, transesophageal echocardiography, CT) key in the preprocedural assessment of transcatheter tricuspid valve interventions. ^[17]

Magnetic resonance imaging

Magnetic resonance imaging (MRI) may be helpful in delineating valvular structural abnormalities when echocardiographic assessment is suboptimal. In patients with TR, spin-echo (SE) and cine gradient-echo (GRE) imaging may provide important data. ^{[20, 21]} Rates of false-positive and false-negative findings are low. While performing cine GRE imaging, one must remember to keep the echo time somewhat long because with short echo times, the signal void may be difficult. ^{[7, 10]}

SE imaging

The major hemodynamic effect of TR is augmentation of total stroke volume of the RV. Spin-echo (SE) MRI can display the RV myocardium well. Spin-echo MRI may be the preferred technique for accurate assessment of RV function such as measurement of RV end-diastolic, end-systolic, and stroke volumes, as well as of the ejection fraction. When the RV wall is thickened and hypokinetic, particularly with ventricular arrhythmias or syncope, MRI may be used to look for RV dysplasia (transdifferentiation of myocardium to fat). In addition to the RV, SE MRI may show enlargement of the RA, the vena cava, and the hepatic veins.

Spin-echo images may show structural abnormalities other than TR, including Ebstein anomaly, pacemaker leads, valvular vegetation, tricuspid prolapse, and carcinoid syndrome.

Cine GRE imaging

Cine GRE images are used to determine the severity of TR by demonstrating the area of the signal void of the regurgitant jet traveling into the RA in systole. This is best imaged in the 4-chamber view and in the coronal oblique view displaying the RA and the RV.

Velocity-encoded imaging

As with Doppler echocardiography, velocity-encoded (VENC) MRI permits assessment of the severity of regurgitation by determining maximum velocity (V_max) in the regurgitant jet via velocity measurements in a plane parallel to the jet (in-plane measurement). The velocity measurement may then be used to calculate pulmonary arterial systolic pressure (P_PA) by adding RA pressure (P_RA, which is empirically taken to be 10 mm Hg) to the RV and RA pressure gradient (P). For this purpose, the following modified Bernoulli equation is used: P_PA = 10 + (4 × V_max²).

(Echocardiographic images depicting TR are provided below.)

Angiography

For patients with TR, RA and RV end-diastolic pressures are often elevated, whether the condition is the result of organic disease of the tricuspid valve or is secondary to RV systolic overload. The RA pressure tracing usually reveals absence of the x descent and a prominent v or c-v wave (ventricularization of atrial pressure). Absence of these findings essentially excludes moderate or severe TR.

As the severity of TR increases, the contour of the RA pressure pulse increasingly comes to resemble that of the RV pressure pulse. An increase in RA pressure on deep inspiration or no change in RA pressure on deep inspiration, rather than the usual decrease, is a characteristic finding. Measurement of pulmonary arterial (or RV) systolic pressure may be helpful in determining whether TR is primary (ie, caused by disease of the valve or its supporting structures) or functional (ie, secondary to RV dilation).

Pulmonary arterial or RV systolic pressure less than 40 mm Hg suggests a primary cause, whereas pressure greater than 55 mm Hg suggests that TR is secondary. Intermediate values are not helpful. In many instances, right ventriculography may be helpful in the diagnosis and quantitative assessment of TR.

The degree of confidence in angiography is high, and false findings are rare.

Treatment

Treatment preference depends on the severity of tricuspid regurgitation, its etiology, and the presence and extent of associated abnormalities, including pulmonary hypertension, heart failure, and other valve conditions. ^[17]

Management of severe TR includes medical therapy, counseling regarding pregnancy and physical activity, consideration of tricuspid valve surgery, and evaluation and treatment of the underlying cause.

Medical treatment

For patients with TR secondary to left-sided heart failure, adequate control of fluid overload is indicated. Diuretics are suggested in these cases. Loop diuretics are commonly used. Restricted intake of salt is indicated. The head of the bed should be elevated, as this may improve dyspnea. Digitalis, potassium-sparing diuretics, angiotensin-converting enzyme inhibitors, and anticoagulants are indicated for these patients. Atrial fibrillation, if present, can be controlled by starting patients on antiarrhythmics. ^[17]

The following medications may be used:

• Diuretics: Furosemide
• Antiarrhythmics
• Digoxin
• Angiotensin-converting enzyme inhibitors
• Anticoagulants ^[17]

Surgical treatment

For patients with severe TR who are refractory to medical treatment, tricuspid valve surgery is suggested. It is preferred to perform this procedure before the onset of significant right ventricular dysfunction or end-organ damage to the liver and kidney, as recommended in the 2020 American College of Cardiology (ACC)/American Heart Association (AHA) Guidelines for the Management of Patients With Valvular Heart Disease. ^[12]

Indications for tricuspid valve surgery depend upon whether surgery for left-sided (aortic or mitral) valve disease is indicated. ^[17]

Prognosis

Management of severe tricuspid regurgitation includes medical therapy, counseling regarding pregnancy and physical activity, consideration of tricuspid valve surgery, and evaluation and treatment of the underlying cause. ^[17]  

Mild cases are usually managed medically, but severe cases require open heart surgery. The tricuspid valve can be repaired or replaced depending on the status of the leaflets. Because of the risk of thrombosis, all mechanical valves in the tricuspid position need anticoagulation. Patients must be monitored regularly for international normalized ratio. Outcomes of tricuspid regurgitation are usually fair to good. ^[17]