eMedicine Specialties > Pediatrics: Cardiac Disease and Critical Care Medicine > Cardiology

Mitral Valve Insufficiency

Author: Jason T Su, DO, Assistant Professor, Department of Pediatric Cardiology, Primary Children's Medical Center, University of Utah
Contributor Information and Disclosures

Updated: Apr 28, 2009

Introduction

Background

Mitral regurgitation (MR) occurs when the mitral valve allows reversal of blood flow from the left ventricle (LV) to the left atrium.¹

The presentation of MR varies and largely depends on etiology, severity, and rate of onset. In acute severe MR, the patient may present in heart failure or cardiogenic shock. In chronic MR, depending on the degree of regurgitation, patients may be asymptomatic and may remain so for many years. As the volume of regurgitation increases, the LV also increases in size. Progressive LV dilation eventually leads to impaired contraction, increased afterload, reduced cardiac output, and, finally, left heart failure. Major factors in management include determining when to start therapy and what kind of intervention is needed. Prognosis in patients with MR varies with the timing of presentation and the severity of associated congenital defects.

Embryology and anatomy

Formation of the atrioventricular valve is completed early in embryologic development. The mitral valve is formed from endocardial cushions that originate both at the atrioventricular orifice and from muscular tissue of the ventricular wall. This process creates the 4 major components of the mitral valve, which are the mitral annulus, the mitral leaflets, the chordae tendineae, and the papillary muscles.²

The mitral annulus is derived from the fibrous skeleton of the heart. The mitral valve leaflets (anterior, posterior) consist of collagenous fibrosa and spongiosa peripherally and mucoid myxomatous tissue centrally. The anterior leaflet is one third of the mitral valve and attaches to the mitral annulus, whereas the posterior leaflet attaches to the posterior lateral free wall of the LV. The chordae tendineae are a complex network of collagenous cordlike structures that extend from the free edges of the mitral valve leaflets to the papillary muscles. These papillary muscles arise from the ventricular wall.

These 4 anatomic components function to allow unobstructed blood flow from the left atrium to the LV during diastole and to maintain competent closure during systole. The leaflets open fully during the early rapid-filling phase of diastole. They begin to close passively as LV pressure and volume increase. Then, the leaflets reopen briefly as atrial contraction occurs, adding additional volume to the LV. During atrial contraction, annular contraction begins, effectively decreasing the circumference of the mitral valve by 20-30% throughout systole. Contraction of the papillary muscles serves to maintain the length of the chordae under the pressure that develops during systole. In the event that one or more of the 4 components is rendered nonfunctional or developmentally abnormal, MR results.

Pathophysiology

Normal blood flow from the left atrium to the LV and, subsequently, to the systemic circulation, is altered in MR. In the presence of MR, blood flows antegrade from the LV into the aorta, and the regurgitant volume flows retrograde from the LV into the left atrium. This causes a proportionate increase in LV ejection volume. The regurgitant fraction reenters the LV, producing left ventricular volume overload. The LV compensates via the Frank-Starling mechanism, resulting in a greater ventricular stroke volume. The volume of the regurgitant fraction depends on several factors, including size of the orifice allowing regurgitation and the pressure gradient between the left ventricle and left atrium. This volume also depends on ventricular systolic pressure; therefore, the regurgitant volume increases in situations that increase afterload, such as hypertension or aortic stenosis.

The natural history and time course of MR varies, but MR can develop in 3 distinct stages (ie, acute, chronic compensated, chronic decompensated) that are clinically significant. The stages depend on acuity of onset, regurgitant volume, and compliance of the left atrium.

Acute MR stage

Acute MR causes sudden volume overload of the left atrium and LV. Initially, the undilated left atrium restricts the regurgitant volume at the expense of increase in both left atrial and LV end-diastolic pressures.

Although total ventricular stroke volume increases compared to normal, total forward stroke volume usually decreases, thereby lowering cardiac output. In the acute situation, rapidly increasing left atrial pressure results in elevated pulmonary venous pressure causing pulmonary congestion and, eventually, pulmonary edema (see Media file 1).

In this stage, the LV compensates by allowing greater diastolic filling and developing LV enlargement to augment forward stroke volume. More importantly, the left atrium dilates in response to the increased volume. Compensation for the increased volume can occur without resulting in increased pressure in the pulmonary circulation and the right heart. Left atrial compliance decreases the afterload on the LV, whereas LV dilation and hypertrophy increases contractility. These important changes keep the overall afterload on the left heart normal or unchanged. Although the regurgitant fraction may be high, the larger stroke volume compensates, maintaining a nearly normal forward cardiac output (see Media file 2).

Chronic decompensated stage

This stage occurs when the LV is unable to sustain adequate forward cardiac output. As LV contractility begins to decrease, end-systolic volume gradually increases, thereby increasing LV end-diastolic pressure. The resulting increased pressure in the left atrium creates increased afterload, which further impairs LV ejection, thereby creating a repeating cycle. Whereas the end-diastolic and end-systolic volumes increase, pulmonary congestion eventually results if the cause of the MR is left untreated. Although the forward LV ejection fraction is reduced compared to the compensated phase, the overall ejection fraction could remain normal because of a large regurgitant flow.

As the degree of MR worsens, the total ejection fraction falls, indicating increasing ventricular dysfunction. Pulmonary hypertension may develop under long-standing increased pulmonary venous pressure, and, ultimately, it can lead to right heart failure (see Media file 3).

Clinical

History

The nature and severity of symptoms in patients with mitral regurgitation (MR) relates to etiology, rate of onset and progression, left ventricle (LV) function, pulmonary artery pressure, and the presence of preexisting valvular or myocardial diseases.

• Children with minor degrees of MR are usually asymptomatic. With increased amounts of MR, fatigue may be reported, but children can tolerate more severe MR surprisingly better than adults can.
• Once pulmonary hypertension develops, complaints such as tachypnea and dyspnea with light activity become more prominent.
• With the most severe MR, children may experience limited growth and failure to thrive. Hemoptysis can develop during the later stages.
• Children may remain asymptomatic with no complications of MR until the second or third decade of life.
  • An indolent course of MR may be deceptive because of the ability of the heart to compensate for the altered hemodynamics. This occurs because of changes in cardiac pump loading such that increased diastolic filling increases preload, whereas LV ejection, in part into the left atrium, reduces afterload.
  • By the time symptoms become apparent, serious and irreversible LV dysfunction may have developed.

Physical

Vital signs are usually normal, although heart and respiratory rates may be slightly increased. Patients with mild MR may reveal no signs other than a characteristic apical systolic murmur.

• The cardiac impulse may be displaced to the left, and, in more advanced disease, a double impulse is felt.
  • A left atrial lift is a second impulse resulting from the increased volume that is displaced into the left atrium during systole.
  • The second impulse should be felt near the time of the second heart sound.
  • This sign is most helpful in thin children and young adults because their chest diameters are smaller and their hearts are closer to the chest wall.
  • In patients with severe MR, arterial pulse has been characterized as having a small volume with a sharp upstroke.
• On auscultation, the first heart sound is usually slightly diminished, whereas the second heart sound usually is split.
• The sound of the typical MR murmur is characterized as blowing and high pitched, and it is loudest over the apex with radiation to the left axilla. The murmur is often pansystolic, beginning immediately after the first heart sound, and it may continue beyond the aortic component of the second heart sound, thus obscuring the murmur. This murmur increases with increased afterload (squatting) and decreases with decreased preload (standing). Occasionally, radiation toward the sternum occurs when posterior leaflet abnormalities are present.
  • Little correlation is noted between intensity of the murmur and severity of MR.
  • The murmur occasionally may be confined to late systole only. The degree of MR in these patients is usually mild.
• With more severe MR, a third heart sound and a mid diastolic low frequency murmur may be present, caused by increased ventricular filling.
• When pulmonary hypertension develops, the pulmonary component of the second heart sound becomes louder and occurs earlier (as long as right ventricular function is not significantly impaired), reducing the splitting interval.

Causes

Although the pathophysiology resulting from MR is similar throughout all age groups, the specific cause of MR differs. Most MR in the pediatric population is congenital in origin.

• In older adolescent and adult patients, MR is likely to be acquired. In these patients, MR can result from numerous problems, including the following:
  • Infection - Endocarditis and myocarditis
  • Inflammation -Rheumatic heart disease and systemic lupus erythematosus (SLE)
  • Structural disorders - Ischemic heart disease and trauma
• The cause of MR in children may include some causes seen in adults, but MR in children is usually the result of a congenital defect.
  • Most cases of MR result from abnormalities in embryologic development that produce not only MR but other cardiac anomalies as well.
  • Most cases of congenital MR are part of a developmental abnormality rather than an isolated phenomenon, although a few conditions are noted in which MR is isolated. These congenital conditions include mitral valve clefts, myxomatous degeneration of the mitral valve, double orifice mitral valve, and anomalous mitral arcade.
• Acute causes of MR are as follows:
  • Mitral annulus disorders
    • Infective endocarditis (abscess formation)
    • Trauma (valvular heart surgery)
    • Paravalvular leak resulting from suture interruption (surgical technical problems, infective endocarditis)
  • Mitral leaflet disorders
    • Infective endocarditis (perforation or interference with valve closure by vegetation)
    • Trauma (tear during percutaneous mitral balloon valvotomy or penetrating chest injury)
    • Tumors (atrial myxoma)
    • Myxomatous degeneration
    • SLE (Libman-Sacks lesion)
    • Acute rheumatic fever
  • Rupture of chordae tendineae
    • Idiopathic (eg, spontaneous)
    • Myxomatous degeneration (mitral valve prolapse, Marfan syndrome, Ehlers-Danlos syndrome)
    • Infective endocarditis
    • Acute rheumatic fever
    • Trauma (percutaneous balloon valvuloplasty, blunt chest trauma)
  • Papillary muscle disorders
    • Coronary artery disease (causing dysfunction and, rarely, rupture)
    • Acute global LV dysfunction
    • Infiltrative diseases (amyloidosis, sarcoidosis)
    • Trauma
• Chronic causes of MR are as follows:
  • Congenital disorders
    • Mitral valve clefts or fenestrations
    • Parachute mitral valve abnormality
    • Part of any associated congenital heart disease (endocardial cushion defects, cardiomyopathy, transposition of the great arteries, anomalous origin of the left coronary artery)³
  • Inflammatory disorders
    • Rheumatic heart disease
    • SLE
    • Scleroderma
  • Degenerative disorders
    • Myxomatous degeneration of mitral valve leaflets (Barlow click-murmur syndrome, prolapsing leaflet, mitral valve prolapse)
    • Marfan syndrome
    • Ehlers-Danlos syndrome
    • Pseudoxanthoma elasticum
    • Calcification or mitral valve annulus
  • Infective disorders - Infective endocarditis affecting normal, abnormal, or prosthetic mitral valves
  • Structural disorders
    • Ruptured chordae tendineae (spontaneous or secondary to myocardial infarction, trauma, mitral valve prolapse, endocarditis)
    • Rupture or dysfunction or papillary muscle (ischemia, myocardial infarction)
    • Dilation of mitral valve annulus and LV cavity (congestive cardiomyopathies, aneurysmal dilation of the LV)⁴
    • Hypertrophic cardiomyopathy
    • Paravalvular prosthetic leak

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