The Tricuspid Valve
SECTION 1 THE TRICUSPID VALVE AT THE BEDSIDE AND THE ECHOCARDIOGRAPHY AND CARDIAC CATHETERIZATION LABS
Of the four valves, the tricuspid valve may produce the most visible signs of dysfunction. Manifestations of dysfunction of the tricuspid are visible from the head to the ankles. Individuals with severe tricuspid regurgitation sometimes have visible pulsatile veins on their forehead, systolic propulsion of the eyeballs, moving earlobes, distended external jugular veins, pulsating internal jugular veins, ascites, and peripheral edema.
A careful look at the patient at 30° elevation is revealing and can suggest the presence of severe tricuspid regurgitation. A search for the other signs follow, and the echocardiogram then can be used to define, quantitate, and explore etiologies.
In the cardiac cath laboratory, transducers from femoral sheaths demonstrate large systolic valves, and the pulse wave tracings in the right atrium show similar configurations as are found in the right ventricle.
In the echocardiography laboratory, the right atrium is filled with color on Doppler tracings, the inferior vena cava and hepatic veins are full and have flow reversal, and various abnormalities of the valve are visualized. The right ventricle dilates and takes away the interventricular septum from the left and has a configurational change from triangular to rounded. As the right ventricle dilates, the tricuspid annulus dilates in a direction opposite to the interventricular septum, and the tricuspid valve line of coaptation is pulled apart and tricuspid regurgitation of various degrees follows.
SECTION 2 ANATOMY OF THE TRICUSPID VALVE
The tricuspid valve consists of anterior, posterior, septal leaflets and the tricuspid annulus. The right ventricle supports the papillary muscles and the chordal structures. The atrium also supports the annulus. The annulus of the tricuspid valve is nonplanar with two high points: one in the anterior septal region and the other on the opposite side of the annulus. Viewed from above the plane of the annulus, it is elliptical in shape. It is subject to being dilated by various conditions. The interventricular component does not dilate since it abuts the ventricular septum, so the remainder of the circumference of the annulus dilates in response to such conditions as volume and pressure overload of the right ventricle.
The anterior and posterior leaflets of the tricuspid valve are opposed, and the septal leaflet coapts with a portion of each of them creating three commissures. The anterior leaflet is the largest of the three, the posterior leaflet the smallest, and the septal leaflet in between in size. The posterior leaflet sometimes has scallops. The septal leaflet is the most variable in size. There are generally three papillary muscle groups with the anterior that is the largest. The anterior papillary muscle has its origin in the region of the moderator band. The anterior papillary muscle sends chords to the anterior and posterior leaflets and the posterior papillary muscle sends chords to the posterior and septal leaflets. The septal papillary muscles may be just chordae that course from the interventricular septum to the septal leaflet, and sometimes a few of these connect to the anterior leaflet.1,2,3
Abnormal function of the tricuspid valve results from various conditions such as the annulus becoming dilated (the most common cause), inflammatory and infectious processes, mechanical influences by pacer and defibrillator leads, and congenital abnormalities.
The tricuspid valve is depicted in Figure 6.1. The anterior leaflet is quite variable. Papillary muscles to the anterior leaflet (larger red circle) arise from the moderator band, and their chordal structures extend to the anterior leaflet and septal leaflet (large red circle). The smaller posterior papillary muscle (smaller red circle) sends chordal structures to the posterior leaflet and the septal leaflet. The septal leaflet has chords (red lines) that arise from the septum itself and usually do not have muscle attached.
Usually on 2D echocardiography, all three leaflets cannot be visualized simultaneously because of the nonplanar configuration. The anterior leaflet is the most obvious from the mitral inflow view and the apical four-chamber view. Next, the septal leaflet can be visualized with the anterior leaflet in the easily obtained RV inflow view. The posterior leaflet is the most elusive but can be visualized from the RV inflow view with a more posterior angulation. On live 3D echocardiography all three of the tricuspid leaflets can frequently be visualized simultaneously. As with the mitral valve annulus, there is a saddle shape to the tricuspid annulus with high points at the aorta and an opposite position on the other side of the annulus (blue circles). Low points are on the opposite poles. When the tricuspid annulus dilates, it can only do so laterally (green arrows). The septal region does not expand.
In the apical four-chamber view the tricuspid annulus measures 28 ± 5 mm in diastole and a significantly dilated tricuspid annulus is >35 mm. A systolic diameter of >3.2 cm and a diastolic annular diameter of >3.4 cm are markers of significant TR. Physiologically, the tricuspid annulus may decrease its annular area by 25%, so this is a dynamic structure. Surgeons take into account the size of the tricuspid annulus when performing mitral surgery and in deciding which type of surgical procedure might be most appropriate.4
SECTION 3 THE NORMAL TRICUSPID VALVE
ABNORMALITIES OF THE TRICUSPID VALVE
The most common etiology of tricuspid valve abnormalities that result in tricuspid regurgitation is a secondary cause. When the right ventricle dilates in response to a pressure and/or a volume overload, then the tricuspid annulus dilates in a lateral fashion (see stick diagram) since the septal portion of the annulus cannot dilate. This may be in response to abnormalities in the pulmonary vasculature from pulmonary vascular disease or something else such as pulmonary embolus. In addition, as the left-sided structures develop abnormalities, they reflect back to the right side. For example as mitral stenosis worsens the right sided pressures elevate and the right ventricle dilates resulting in the tricuspid valve failing. Infective endocarditis is always a threat to the tricuspid valve especially in the setting of IV drug use or in the presence of foreign bodies such as central lines and pacemaker leads. The list is long of conditions that can result in tricuspid regurgitation.
The tricuspid valve leaflets are vulnerable to various abnormalities that range from rheumatic inflammatory changes and myxomatous changes to trauma or even compromise from a cardiac tumor. Humoral substances that arise from the GI tract may result in scarred, retracted leaflets as seen in the carcinoid syndrome or from systemic-taken diet drugs. Pacemaker leads can prop the valve leaflets open, or adhesions may develop that scar the leaflets to the point of causing functional abnormality. Trauma can rupture a leaflet or chord and result in severe regurgitation.
There is a long list of abnormalities that cause tricuspid regurgitation and a shorter list that cause tricuspid valve stenosis. Rheumatic disease can produce tricuspid stenosis as an associated abnormality with rheumatic mitral stenosis. See Table 6.1.