The tricuspid valve regulates blood flow from the right atrium to the right ventricle. It is named for its three leaflets and is an integral component of the right heart structures.
Location and Relations
The tricuspid valve is located between the right atrium and right ventricle. It is positioned inferiorly and slightly to the right of the aortic valve. The valve orifice is approximately 4-5 cm in diameter and is the largest of the four cardiac valves.
The tricuspid valve is related to:
- Superiorly: Right atrium
- Inferiorly: Right ventricle
- Anteriorly: Anterior chest wall (overlying the right sternal border at the fourth intercostal space)
- Medially: Membranous interventricular septum and aortic root
Components of the Tricuspid Valve
Fibrous Annulus
The annulus is a fibrous ring that anchors the valve leaflets. Unlike the mitral annulus, the tricuspid annulus is less well-defined and more dynamic. It changes shape throughout the cardiac cycle:
- Systole: The annulus contracts, reducing the orifice area
- Diastole: The annulus expands, allowing maximal flow
The annulus is not planar; it has a saddle-shaped three-dimensional configuration that is important for valve function. Tricuspid annular dilation is a key mechanism in functional tricuspid regurgitation.
Leaflets (Cusps)
The tricuspid valve has three leaflets:
Anterior Leaflet: The largest leaflet, extending from the infundibulum to the atrioventricular junction. It is triangular and highly mobile.
Posterior Leaflet: The smallest leaflet, with multiple scallops. It is attached to the diaphragmatic wall of the ventricle.
Septal Leaflet: Attached directly to the interventricular septum. It is less mobile than the other leaflets and has chordae tendineae that originate from the septal papillary muscles.
Each leaflet has three zones:
- Basal zone: Attached to the annulus
- Intermediate zone: Contains chordal attachments
- Free edge zone: Thinnest, with smooth surface
Chordae Tendineae
Fibrous cords that connect the papillary muscles to the valve leaflets. They are classified by their insertion pattern:
- Basal chordae: Insert at the base of the leaflets
- Marginal chordae: Insert at the free edge (prevent prolapse)
- Deep chordae: Insert deep into the ventricular surface
Papillary Muscles
Three groups of papillary muscles anchor the chordae:
Anterior Papillary Muscle: Largest, originates from the anterior ventricular wall. Provides chordae primarily to the anterior and posterior leaflets.
Posterior Papillary Muscle: Originates from the inferior wall. May be multiple. Provides chordae to the posterior and septal leaflets.
Septal Papillary Muscle: Smallest, originates from the interventricular septum. Provides chordae primarily to the septal leaflet.
Function
The tricuspid valve opens during ventricular diastole, allowing blood to flow from the right atrium to the right ventricle. During ventricular systole, the valve closes to prevent retrograde flow.
Opening mechanism: As the right ventricle relaxes (diastole), pressure in the ventricle drops below atrial pressure, pushing the valve open.
Closing mechanism: As the right ventricle contracts (systole), ventricular pressure rises, forcing the leaflets together. The papillary muscles contract simultaneously, preventing the leaflets from prolapsing into the atrium.
Tricuspid Valve Area
The normal tricuspid valve area is approximately 4-6 cm². Significant stenosis occurs when the area is less than 1.5 cm².
Clinical Significance
Tricuspid Regurgitation
Incomplete closure of the valve, allowing blood to leak back into the right atrium during systole. Causes include:
- Functional: Annular dilation from right ventricular enlargement (most common)
- Primary: Leaflet prolapse, endocarditis, rheumatic disease, trauma, carcinoid syndrome
- Iatrogenic: Pacemaker lead interference
Physical findings include holosystolic murmur at the left lower sternal border, jugular venous distension, hepatojugular reflux, and pulsatile liver.
Tricuspid Stenosis
Narrowing of the valve orifice, most commonly due to rheumatic heart disease (rare in isolation). Presents with signs of right heart failure and a diastolic murmur at the left lower sternal border.
Ebstein Anomaly
A congenital condition where the septal and posterior leaflets are displaced inferiorly into the right ventricle, resulting in atrialization of the right ventricle. Associated with right heart enlargement and often with atrial septal defect.