Introduction

Mitral regurgitation can be categorized as organic or functional, depending on the architecture of the valve and remainder of the heart.

Organic mitral regurgitation refers to disease of the valves themselves, e.g., after rheumatic heart disease or infective endocarditis. The remainder of the heart is often structurally normal initially, but remodeling subsequently occurs to compensate for the valvular dysfunction.

Functional mitral regurgitation is where the valve's architecture is normal, but has been distorted by remodeling of the surrounding heart muscle, resulting in regurgitation. Ischemic heart disease is the most common culprit.

Asymptomatic

Patients with mitral regurgitation are initially asymptomatic, as the heart is able to maintain sufficient cardiac output for a prolonged period.

However, despite the lack of symptoms, a dysfunctional mitral valve reduces the heart's efficiency and triggers remodelling. Over time, this leads to heart failure and conduction abnormalities.

Symptoms of heart failure

Symptoms of heart failure include exertional dyspnea, paroxysmal nocturnal dyspnea, orthopnea, and peripheral edema.

In mitral regurgitation, the effective output of the heart is reduced because a proportion of the ejection fraction is expelled back into the left atrium. To maintain the circulating volume, dilation of the left ventricle occurs (in accordance with the Starling's law).

However, once the left ventricle has dilated beyond a certain point, progressive systolic dysfunction results; this culminates in overt heart failure. Dilation may also worsen the mitral regurgitation by distorting the ventricular architecture.

Symptoms of infective endocarditis

Symptoms of infective endocarditis include fever, weight loss, lethargy and night sweats. Septic embolization may result in infections in atypical locations (e.g., discitis or cerebral abscesses).

Infective endocarditis is a complication of organic mitral regurgitation, with the structurally abnormal valves conferring an increased risk of bacterial colonization. Note that the absolute risk of infective endocarditis is still fairly small.

Symptoms of atrial fibrillation

Atrial fibrillation is often seen as a complication of mitral regurgitation. When it develops it can present as palpitations; an acute reduction in exercise tolerance, due to the switch from sinus rhythm to fibrillation; or as chest pain, due to the increased heart rate causing reduced myocardial perfusion.

This is a result of the progressive left atrial remodeling that occurs in chronic mitral regurgitation.

Past rheumatic fever

Rheumatic heart disease is a consequence of rheumatic fever, an autoimmune complication of group A streptococcus infection. The autoimmune response causes inflammation of the cardiac valves, with the mitral valve often affected. Mitral regurgitation may result.

Family history of mitral valve prolapse

Mitral valve prolapse is a known cause of mitral regurgitation. In this condition, changes in elasticity result in prolapse of one or more valvular leaflets into the left atrium during systole. This can progress into overt mitral regurgitation over time; chordal rupture can also occur.

Mitral valve prolapse has been shown to have a genetic component; it is also linked to a number of connective tissue disorders.

History of connective tissue disorders

Individuals with connective tissue disorders such as Ehlers-Danlos syndrome and Marfan syndrome have an increased incidence of mitral valve prolapse; this predisposes them to developing mitral regurgitation.

History of infective endocarditis

Infective endocarditis involving the mitral valve is a known cause of mitral regurgitation. This tends to occur due to rupture of the chordae tendinae that maintain the valve's structure.

Note that most cases tend to present acutely and severely. However, in others, the valve's architecture is altered only slightly; it may be years before symptoms appear.

Systolic thrill

The presence of a systolic thrill indicates a significant regurgitant jet through the mitral valve; this is a marker of severe disease.

Displaced apical impulse

A displaced apical impulse implies cardiomegaly, suggesting at significant remodelling of the heart. This may be secondary to a primary valvular lesion, or due to functional mitral regurgitation secondary to remodelling of the papillae and mitral annulus.

Pansystolic murmur

A pansystolic murmur is a typical finding in mitral regurgitation. This is best heard in the mitral area, with radiation into the left axilla.

Soft S1 sound

A soft S1 sound is common. This is because the end-diastolic left ventricular pressure is higher than normal.

Audible S3 sound

The presence of an audible S3 sound is believed to indicate rapid ventricular filling into a compliant ventricle.

This is a consequence of the increased left atrial volume secondary to dilatation; and of the increased left ventricular compliance due to remodeling.

Mid-systolic click

A mid-systolic click indicates concomitant mitral valve prolapse. A late systolic murmur may also be present.

Signs of heart failure

These include an elevated jugular venous pressure, bilateral ankle edema, and bibasal crackles.

Ischemic heart disease

Ischemic cardiomyopathy can give rise to functional mitral regurgitation and heart failure; this can mimic the signs and symptoms of organic mitral regurgitation.

Pointers towards this diagnosis include a previous diagnosis of ischemic heart disease, or signs and symptoms suggestive in this regard. Echocardiography may show signs suggestive of ischemia, include myocardial scarring, wall thinning, and wall motion abnormalities.

Definitive diagnosis can be made by coronary angiography showing ≥75% stenosis of the left main stem, proximal left anterior descending artery, or two or more epicardial coronary arteries.

Dilated cardiomyopathy

Dilated cardiomyopathy also give rise to both functional mitral regurgitation and heart failure, thus mimicking the clinical presentation of organic mitral regurgitation.

Echocardiography allows for differentiation; typical findings include global left ventricular hypokinesis and annular dilatation giving rise to functional mitral regurgitation.

Echocardiography

Echocardiography is usually the key diagnostic study. This can both confirm the presence of mitral regurgitation, determine the severity of regurgitation, assess the size of the left atrium and ventricle, and visualize the vavular architecture.

Echocardiography is also helpful to determine the presence of complications such as systolic heart failure and pulmonary hypertension.

Cardiac MRI

Cardiac magnetic resonance imaging (CMR) is an alternative in patients in whom echocardiography has been equivocal or of poor quality, due to factors such as obesity.

EKG

Electrocardiography (EKG) may detect atrial fibrillation, left bundle branch block, and left ventricular hypertrophy.

Coronary angiography

Coronary angiography helps determine the extent of any associated ischemic heart disease.

This is typically performed before mitral valve surgery, so as to identify patients who might benefit from coronary bypass grafting, which can be done as a combined operation.

ACE inhibitors and ARBs

Angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) reduce cardiac remodelling.

In the case of organic mitral regurgitation, this slows disease progression and delays the development of complications. In patients with functional mitral regurgitation, the severity of regurgitation may also be reduced.

Beta blockers

Beta blocker therapy has been shown to reduce left ventricular dysfunction and reduce the severity of functional mitral regurgitation.

In left ventricular dysfunction the body tries to compensate by increasing inotropy (i.e. cardiac contractility) and chronotropy (the heart rate). These mechanisms are initially helpful, but over time lead to counterproductive remodelling of the left ventricle. Beta blockers help prevent or reduce remodelling.

Diuretics

Diuretics provide symptomatic relief via reducing fluid overload; this is more pronounced in severe cases. The degree of regurgitation seen on echocardiography may also diminish, due to reduction of left-ventricular pressures. Note that the underlying disease process is not affected.

Vasodilators

Vasodilators help reduce the regurgitant volume by decreasing afterload, i.e. systemic vascular resistance.

While their benefit is well-established in patients with acute mitral regurgitation, this is less clear in individuals with chronic mitral regurgitation.

Treatment of complications

Isolated mitral regurgitation is usually asymptomatic. Most patients presenting with symptoms related to one or more complications, including heart failure, and atrial fibrillation.

These conditions should be managed appropriately.

Treatment of the causative etiology

Where mitral regurgitation is secondary a condition such as ischemic heart disease or infective endocarditis, this should be treated as appropriate.

Mitral valve repair

Mitral valve repair involves removal of sections of the valve leaflet; the annulus is sutured to return it to its premorbid dimensions and shape. Currently, this is the preferred surgical technique, due to its lesser morbidity and mortality, and comparable outcomes.

Repairing the valve retains the existing anatomy, maintains natural shape and function, and reduces the need for anticoagulation; the native value often has greater durability than a prosthesis. Repair may also be undertaken in combination with other cardiac surgery (e.g., coronary artery bypass grafting).

Outcomes are better in patients with organic regurgitation, as they often have a normal ventricular structure. This is as compared to individuals with functional regurgitation, who often have extensive ventricular remodelling which continues postoperatively.

Mitral valve replacement

Surgical replacement of the mitral valve is preferred over repair if both leaflets are involved, or where the disease is extensive enough to make a successful repair infeasible.

The native valve is replaced by either a biological or mechanical prosthesis; the former have a shorter lifespan but lower embolic risk than mechanical valves.