Mitral Valve Anatomy
The Common Vein Copyright 2008
The mitral valve is a complex, bileaflet finely coordinated structure that guards the inlet of the left ventricle and is usually located cephalad in comparison with the tricuspid valve.
Structurally the mitral valvular complex comprises of the fibro elastic annulus, the two leaflets, the tendinous cords, the two papillary muscles with their left ventricular attachments and the less appreciated left atrial wall.
Functionally it serves to prevents backflow to the left atrium during ventricular systole.
Diseases of the mitral valve may be either due to obstruction as in mitral stenosis or incompetence as in mitral regurgitation, both of which may be either congenital or acquired.
Diagnosis of a mitral valvular disease is suspected in patients presenting with symptoms of exertional dyspnea, fatigue, orthopnea , paroxysmal nocturnal dyspnea, chest pain or palpitations. On examination a tapping apical impulse with a low pitched mid diastolic rumbling murmur in the apical area is heard in mitral stenosis, while a high pitched pan systolic murmur is heard in mitral regurgitation. On chest radiography, the characteristic findings of mitral stenosis are pulmonary congestion, enlargement of the main pulmonary arteries, and enlargement of the left atrium without cardiomegaly while that of mitral regurgitation is cardiomegaly. An electrocardiogram (ECG) may reveal evidence of left atrial enlargement or atrial fibrillation in both conditions. Two dimensional echocardiogram is the noninvasive diagnostic test of choice for both lesions.
Medical therapy for congestive heart failure or infective endocarditis, minimally invasive techniques and surgical options are available.
The complex mitral valve includes a tensor apparatus ( Fibrous annulus, LV myocardium between the annulus and attachment of base of papillary muscles, papillary muscles and the chordae) and a valvular apparatus ( two mitral leaflets )
Mitral leaflets: The term “mitral” was introduced by Andreas Vesalius3 to describe the orientation of the two leaflets of the left atrioventricular valve owing to their resemblance to a plan view of the bishop’s mitre.
The two leaflets anterior (aortic) and posterior (mural)are notably different in shape and circumferential length with neither attached to the septum , unlike the tricuspid valve which has a septal leaflet1 . The anterior (aortic) leaflet has a rounded free edge, occupies a third of the annular circumference and a base to free edge length 2 or more times the posterior. Consequently, the anterior leaflet is more mobile, while the posterior leaflet fulfills a secondary or supporting role. The posterior mural leaflet is long and narrow lining the remainder of the circumference. However Both leaflets are thick at the bases and tips, with central thinning and with nearly identical surface ares.
The Carpentier nomenclature2 is commonly used and provides uniformity in communicating . The anterior leaflet is termed A, and divided into three parts: lateral third (A1), middle third (A2), and medial third (A3). The posterior mitral leaflet termed P comprises of a lateral(P1), middle (P2), and medial scallop (P3).
The two leaflets meet to form an arch shaped closure line that is obliquely situated. Each end of the closure line is referred to as a commissure and is identified by the attachment of the commissural fan chordae. As seen through an atriotomy the lateral commissure is called anterior and the medial is called the posterior2.
Papillary muscles and LV myocardium: The papillary muscle and adjacent LV myocardium serve as a single functional muscular unit. The chordae arise from the tips of the papillary muscles. There are two papillary muscles – anterolateral and posteromedial2. The anterior papillary muscle, located on the anterolateral wall of the LV has a dual blood supply-first obtuse marginal branch from the left circumflex and the first diagonal branch from the left anterior descending artery. The posterior papillary muscle is supplied by a single artery arising from either the right coronary artery or from the third obtuse marginal of the left circumflex artery2.
Alterations in the size and shape of the left ventricle can distort the locations of the papillary muscles, resulting in valvular dysfunction1. Similarly rupture of the papillary muscle subsequent to infarction will lead to mitral regurgitation.
Tendinous Cords: These are fine fibrous strings radiating from the papillary muscles and attaching to the ventricular surface of corresponding halves of the anterior and posterior mitral leaflets in an organized pattern. .The absent septal attachment of the chords of the mitral valve allows it to be distinguished from the tricuspid valve on cross sectional echocardiography. There are numerous classifications 1of the tendinous cords based on their thickness and site of attachment (Toronto classification – leaflet cords, commissural cords and cleft cord, earlier classification3– first order , second order and third order) . The thinnest ones are attached to the free leaflet margin while thickest ones are attached quite away from the free margin. This arrangement serves to distribute systolic stress.
Mitral Annulus : The mitral annulus is an fibrous ellipsoidal , D shaped tissue serving as a fulcrum for the leaflets and also exhibiting sphincteric contraction in systole that serves to decreases the size of the mitral orifice1. The straight border accommodates the aortic valve allowing the latter to be wedged between the ventricular septum and the mitral valve1. Posteriorly its thin nature contributes to dilatation in pathological conditions, chordal tears and calcifications. The anterior mitral annulus is more rigid.
During systole the annulus is elliptical in shape and round in diastole, with maximal dimensions in end-diastole (area 7.1 cm2, diameter 3.0 cm, circumference 9.3 cm)2.
The outflow tract
The anterior leaflet of the mitral valve
When the closed valve is seen in profile, the major part of the closure line lies below the plane of the atrioventricular junction rising toward the commissures at the peripheral ends so that the atrial surface of the leaflets has a saddle-like configuration1. The line of coaptation in a normal valve does not extend above the level of the junction during ventricular systole. Prolapse of the mitral valve is the situation in which the leaflets extend above the plane of the atrioventricular junction during ventricular systole1.
A normally functioning mitral valve opens to pressure from the superior surface of the valve, allowing blood to flow into the left ventricle during left atria systole , and closes at the end of atrial contraction to prevent blood from back flowing into the atria during left ventricle systole.
More on flow across the mitral valve will be discussed in the physiology section of the heart module.
|3D Mitral – Anterior leaflet acting as the boundaries of Inflow|
|47824 heart cardiac ascending aorta shape aortic tuck mitral valve to aortic fibrous continuity AV MV normal anatomy CTscan Davidoff MD|
|3D Mitral – Aortic fibrous Continuity|
|47823 heart cardiac ascending aorta shape aortic tuck mitral valve to aortic fibrous continuity AV MV normal anatomy CTscan Davidoff MD|
1.Ho SY. Anatomy of mitral valve. Heart 2002;88(Suppl IV):iv5–iv10.
2.Condado JA and Gimon MV. Catheter-Based Approach to Mitral Regurgitation. (J Interven Cardiol 2003;16:523–534.
- Walmsley T. The heart. In: Sharpey-Schafer E, Symington J,Bryce TH, eds. Quain’s Elements of Anatomy, 11th ed. Vol 4,part 3. London: Longmans, Greens & Co, 1929, p. 42.