6.7: Mitral regurgitation

Mitral valve regurgitation results from inadequate mitral leaflet coaptation during systole. This allows the systolic regurgitation of blood from the high-pressure LV to the normally low-pressure LA. The regurgitating volume depends on both the size of the regurgitant orifice and the pressure gradient between the left ventricle and the left atrium. In primary mitral regurgitation, inadequate mitral leaflet coaptation results from an abnormality in any of the functional components of the mitral apparatus. Secondary or functional mitral regurgitation results from left ventricle disease and remodeling.

During systole, combined papillary muscle contraction and contraction of the dynamic annulus promote leaflet coaptation. Calcification of the annulus may hinder the sphincter-like contraction of the annulus allowing regurgitation. Secondary mitral regurgitation due to annulus dilation may be caused by ischemic or dilated cardiomyopathy. The regurgitant volume causes left ventricular enlargement and contractile dysfunction. Left ventricle dilation may cause enlargement of the mitral annulus and the regurgitant orifice, increasing the mitral regurgitation. Positive inotropes, diuretics and vasodilators reduce the size of the left ventricle and the regurgitant orifice, and decrease the regurgitant flow.

Etiology

Three different types of primary mitral regurgitation can be defined; leaflet retraction from fibrosis and calcification, annular dilatation and chordal abnormalities (including rupture, elongation, or shortening). Functional mitral regurgitation results from LV dysfunction with or without annular dilation. Mitral regurgitation was classified by Carpentier into three types based on leaflet and chordal motion: normal leaflet motion (type I), leaflet prolapse or excessive motion (type II), and restricted leaflet motion (type III).[46]

Chronic Mitral Valve Regurgitation

Degenerative mitral valve disease is the most common cause of mitral regurgitation in Europe.

Myxomatous mitral valve degeneration is also known as floppy mitral valve or mitral valve prolapse. Prolapse is defined as excursion of one or both leaflets above the plane of the annulus during systole.[47] Prolapse of the middle portion of the posterior leaflet is the most common finding in degenerative MR.[48]

Mitral regurgitation in Barlow syndrome or parachute mitral valve is due to annular dilatation and extensive hooding of leaflets with large amounts of excessive leaflet tissue. In mitral regurgitation, the mass-to-volume ratio of the enlarged, thin walled left ventricle is less than one.[38]

Clinical Presentation

Patients with mild to moderate compensated chronic mitral regurgitation may remain asymptomatic for many years. The adapted left ventricle maintains normal forward cardiac output. The left ventricle ejection fraction in chronic mitral regurgitation may be greater than normal due to the compensatory cardiac adaptations. Progression of severity depends on etiology of regurgitation; in patients with connective tissue disease regurgitation tends to progress more rapidly than patients with mitral valve prolapse or rheumatic mitral regurgitation. Progression in acute rheumatic fever is often rapid. Acute progression may by caused by endocarditis or chordae rupture.

Gradual progression and eventually decompensation results in decreased cardiac output with physical activity and pulmonary congestion. Patients present with weakness, fatigue, palpitations, dyspnea on exertion. Hepatomegaly, peripheral edema and ascites due to right sided heart failure can be associated with rapid clinical deterioration.

Acute mitral regurgitation is associated with sudden pulmonary congestion and edema.

On physical examination the apical impulse is displaced laterally, indicating left ventricular enlargement. S1 is normal or diminished. S₂ may be single, closely split, normally split, or even widely split as a consequence of the reduced resistance to LV ejection. A widely split S2 is often audible, due to shortening of LV systole and early closure of the aortic valve. The P2 component of the second heart sound may be increased if pulmonary hypertension has developed. The apical systolic murmur is typically holosystolic and radiates to the axilla, depending on the direction of the regurgitant jet. It can be blowing, moderately harsh, or even soft. An S3 gallop often is present, reflecting the transmitral diastolic flow during the rapid filling phase.

Early in the disease process of patients with Barlow syndrome, a characteristic midsystolic click can be appreciated, followed by a late systolic murmur; with disease progression the murmur becomes holosystolic, and the midsystolic click may become inaudible.[46]

Acute Mitral Valve Regurgitation

Immediate intervention is often necessary in acute mitral regurgitation. Etiology can be organic or functional. Organic causes include rupture of a major chorda tendinea (in myxomatous mitral valve disease) or papillary muscle (due to myocardial infarction), leaflet perforation (of endocarditic origin), and dysfunction of a prosthetic valve due to endocarditis or paravalvular regurgitation. Regurgitation of functional etiology results from left ventricular abnormalities such as dyskinetic wall due to ischemia or dilated ventricle due to cardiomyopathy.

Acute mitral regurgitation is associated with dyspnea and orthopnea, caused by sudden pulmonary congestion and edema. Acute papillary muscle rupture may mimic the presentation of a patient with a postinfarction ventricular septal defect.[49]

On physical examination no signs of cardiac compensatory mechanisms are present. The increase in left atrial pressure diminishes the pressure gradient between the left ventricle and left atrium by midsystole. The murmur of mitral regurgitation is shortened and of decreased intensity, it may be soft, short of even inaudible. An S3 gallop usually is present. The volume overload is increasing the severity of MR over time, and leads to a greater percentage of the LV stroke volume being ejected in a retrograde fashion.

Diagnostic Options

Chest Radiography

In chronic mitral regurgitation chest radiography demonstrates enlargement of the left ventricle and atrium. The mitral annulus may be calcified. In acute mitral regurgitation, no adaptive left atrium or ventricle enlargement has developed. Signs of interstitial or alveolar pulmonary edema may be present.

Electrocardiography

Signs of left ventricular hypertrophy and left atrial enlargement due to chronic volume overload may be seen on the electrocardiogram. Atrial fibrillation is a common finding late in the natural history of the disease. Q-waves may be seen in ischemic mitral regurgitation. In patients with acute mitral regurgitation, left atrial and ventricular enlargement may not be evident and the electrocardiogram may be normal or show only nonspecific findings. The resting electrocardiogram of patients with asymptomatic mitral valve prolapse is normal. A variety of ST-T-wave changes, including T-wave inversion and sometimes ST-segment depression, particularly in the inferior leads, can be found in patients with symptomatic mitral valve prolapse.

Echocardiography

Mitral valve pathology and pathophysiology is primary assessed by echocardiography. Left atrial and ventricular dimensions can be quantified. The etiology and mechanism of mitral regurgitation can be identified by echocardiography. Leaflet abnormalities and chordal morphology and function is assessed by echocardiography. Fused subvalvular apparatus due to rheumatic valvulitis and leaflet destruction due to endocarditis can be visualized by echocardiography. Myxoid degeneration of the mitral valve is characterized by an excess of tissue and by leaflets of more than 5mm thickness. Annular dilatation is characterized by a ratio of >1.3 anterior–posterior diameter of the annulus to the length of the anterior leaflet in diastole. The regurgitation caused by annular dilatation and incomplete leaflet coaptation is directed straight back into the left atrium.

In ischemic MR, the apical displacement of the leaflets can be quantified by measuring the tenting area and the leaflet opening angles.

Color doppler analysis can be used to grade the severity of the regurgitation and permits visualization of the origin, extent, direction, duration, and velocity of disturbed backward flow of the regurgitant leak or leaks into the left atrium.[46] MR is considered severe when the jet area is >10cm2 or >40% of the left atrial area.

Cardiac Catheterization

Coronary ischemic causes of mitral regurgitation can be identified by cardiac catheterization.

Treatment

Surgical

The hemodynamic overload on the heart caused by mitral regurgitation can ultimately only be corrected by surgically restoring valve competence. For all valve surgery timing of surgery is essential. Irreversible left ventricular dysfunction will result in suboptimal results indelayed surgery. Due to the operative risk and risk of valve prosthesis surgery should however be delayed as long as possible

Mitral valve regurgitation is surgically corrected by mitral valve replacement or repair. Mitral valve repair is generally found to be superior to replacement, with preservation of left ventricular function and part of the mitral valve apparatus [50] [51] [52] [53] and without the use of a prosthesis. In mitral valve regurgitation indication for valve surgery is influenced by symptomatic status, ventricular functional status, and the procedure to be performed. Repair might be considered in asymptomatic patients with normal left ventricular function or patients with severe impairment of left ventricular function who might not be candidates for mitral valve replacement.

For most patients, mitral valve surgery is performed for the relief of symptoms or to prevent worsening of asymptomatic left ventricular dysfunction.