Mitral Valve

Mitral Valve Anatomy

The Common Vein Copyright 2008

Definition

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.

Structural Considerations

 

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).

Leaflets of the Mitral Valve
The mitral valve consists of two leaflets; an anterior shield shaped leaflet that extends deep into the LV, and a posterior leaflet that occupies a greater percentage of the circumference of the annulus, but is more shallow in its extension into LV.
code cardiac heart normal MV mitral valve anatomy Courtesy of Ashley Davidoff M.D.32116
Anterior Leaflet of the Mitral Valve
The anatomic specimen taken from the left atrium through the mitral annulus shows the broad anterior leaflet of the mitral valve ..
Courtesy of Ashley Davidoff M.D. code cardiac heart normal MV mitral valve anatomy 32106

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.

Normal LVOT
This anatomic specimen shows the LV with septal side to the patients right and free wall side to the patients left. Note the relatively smooth walled septal surface and the papillary muscle apparatus attached to the free wall side. There are two groups of papillary muscles neither of which are attached to the septum. The anterior leaflet of the MV is in full view and note that it is in fibrous continuity with the left and non coronary cusps of the aortic valve.
Courtesy Ashley Davidoff MD 01817

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.

Chordae
The anatomic specimen taken from the left ventricle alongside the pillars of the papillary muscles and chordae and the waterfall of blood as it comes from the left atrium into the left ventricle is conceptualized.
32118b03 heart papillary muscles chordae tendinae left ventricle maid of the mist mitral valve sounds of the blood flow Davidoff art Davidoff photography copyright 2019 

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

Clinical consideration:

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.

Functional Considerations

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.

2D Echo
The Normal Mitral Aortic Complex
This gray scale echo of the heart shows the left ventricle, anterior and posterior leaflets of the mitral valve, the aortic valve and the base of the aorta. The echo demonstrates the intimate anatomic and physiological relationship of the anterior leaflet of the mitral valve (light pink) and the left aortic cusp(dark pink)..
( Courtesy Philips Medical Systems 33132 code cardiac heart echo LV MV aorta mitral aortic complex normal anatomy 33132c02.8s

Normal LV Angiogram
This normal left ventriculogram is taken in the classical right anterior oblique (RAO) projection, enabling an excellent profile for the LV and the mitral valve plane. The annulus of the valve is inferred as a white ring in the color overlay.
Courtesy of Ashley Davidoff M.D.32120

CT scan

Sagittal View of the Normal LV
Thickness
The sagittally reconstructed CT study of the heart demonstrates the normal LV thickness, chamber size, mitral valve with continuity to the aortic valve.  The smaller of the two hollow tubes to the left of the aorta represents the left atrial appendage and the larger more superior structure represents the main pulmonary artery
.
Davidoff MD 47823 copyright 2009 all rights reserved

 

CT scan of the Endocardium
The reconstructed CT scan is the left ventricle (LV), left atrium (LA) and right atrium (RA). The thin endocardium (white arrows) throughout the heart is one continuous sheet of tissue connected across the whole circulatory system and it is more fibrous in nature. The thin white layer is seen in the left atrium, left atrial appendage (LAA) over the posterior leaflet of the mitral valve (pl) in the left ventricle (LV) and in the right atrium. The surface of the left ventricle, left ventricular outflow tract (LVOT) and right atrium are also lined by the endothelium.Davidoff, M.D.
47824c02.8s
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

MRI

Mitral Valve and Tricuspid Valve in Systole and Diastole   In the gated MRI, systole and diastole can be differentiated and so standard measurement to thickness and volume can be applied, for evaluation of size. This MRI series demonstrates the heart in systole and diastole. Image 1 demonstrates ventricular systole. The atrial chambers are full, the A-V valves (tricuspid valve and mitral valve) are closed and the ventricular chambers are contracted. Image 3 is a color overlay of the closed A-V valves of image 1. Image 2 demonstrates ventricular diastole. The atrial chambers are emptying, the A-V valves are open and the ventricular chambers are full. Image 4 is a color overlay of the open A-V valves of image 2.  32062
THE MITRAL VALVE IN SYSTOLE AND DIASTOLE
CONGESTIVE CARDIOMYOPATHY
61 male, with alcoholic congestive cardiomyopathy.
MRI of the heart in short axis, shows the LV in systole (above) with the mitral valve (MV) closed and in diastole (below) with the open mitral valve.
Ashley Davidoff MD

Diseases

Endocarditis with Mitral Vegetation
The four chambered echocardiogram of the heart shows an echogenic mass representing a mitral valve vegetation characteristic of endocarditis.
key words
heart cardiac MV mass SBE bacterial endocarditis vegetation infection imaging cardiac echo overlay
Courtesy of Philips Medical Systems, Ultrasound, and modified by Ashley Davidoff M.D 32121

 

VSD of the A-V canal type
Complete Endocardial Cushion Defect
The pathology specimen shows a complete endocardial cushion defect with a cleft mitral valve and a VSD.  The atrial chambers can be seen through the cleft of the mitral valve and a ASD primum was present as well
Key words
heart cardiac LV left ventricle IVS interventricular septum mitral valve endocardial cushions complete AV canal defect cleft mitral valve VSD endocardial cushion defect congenital heart disease gross pathology Courtesy Ashley Davidoff MD 01863b01

 

Treatment

Mitral Valve and ASD Secundum Repair
This anatomical specimen is from an unfortunate pediatric patient who had a mitral valve replaced and an ASD secundum closed. The pink overlay in b shows a suture line opposing the borders of the ASD secundum. A prosthetic mitral valve is noted.
key words
heart mitral valve atrial septal defect secundum repair treatment surgery Courtesy Ashley Davidoff MD copyright 2019  06704c01.8s

 References:

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.

  1. 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.

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