The mitral valve is made up of the annulus, anterior and posterior leaflets, and chordae, which attach the leaflets to their respective papillary muscles. A normally functioning valve allows blood to flow unimpeded from the left atrium to the left ventricle during diastole and prevents regurgitation during systole. Normal mitral valve function is dependent not only on the integrity of the underlying valvular structure, but on that of the adjacent myocardium as well.

This chapter reviews three types of mitral valve disease: mitral stenosis (MS), mitral regurgitation (MR), and mitral valve prolapse (MVP). Recent 2014 practice guidelines published jointly by the American College of Cardiology (ACC) and the American Heart Association (AHA) for the management of patients with valvular heart disease are referenced in this chapter.¹ Where relevant, we refer in the text to the ACC/AHA evidence grading for diagnostic and therapeutic procedures, as follows:

• Class I: There is evidence and/or general agreement in favor of a given procedure or treatment.

• Class II: There is conflicting evidence and/or a divergence of opinion about the efficacy of a given procedure or treatment.

• Class IIa: The weight of evidence or opinion is in favor of efficacy.

• Class IIb: Efficacy is less well established by evidence or opinion.

• Class III: There is evidence and/or general agreement that the procedure or treatment is not useful and in some cases may be harmful.

Mitral stenosis

Definition and Etiology

MS refers to narrowing of the mitral valve orifice, resulting in impairment of filling of the left ventricle in diastole. It is usually caused by rheumatic heart disease. Less common causes include severe calcification of the mitral annulus, infective endocarditis, systemic lupus erythematosus, rheumatoid arthritis, and carcinoid heart disease.

Staging of Mitral Stenosis (as per New Guidelines of 2014)¹

Patients identified as having mild valve doming during diastole are considered at risk of MS (Stage A). Those with more advanced (progressive) rheumatic valve changes such as commissural fusion and at least moderate diastolic doming of the mitral valve leaflets are defined as Stage B. Severe MS is now defined by a mitral valve area (MVA) of 1.5 cm² or less (normal valve area 4-5 cm²) and is staged according to whether patients are asymptomatic (Stage C) or symptomatic (Stage D). This new valve staging classification (similar to how heart failure [HF] is classified) provides a means to integrate all forms of valve disease in a unified way.

Prevalence and Risk Factors

Although the incidence of rheumatic heart disease has steeply declined during the past 4 decades in the United States, it is still a major cause of cardiovascular disease in developing countries. It is estimated that 15.6 million people suffer from rheumatic heart disease worldwide, with approximately 282,000 new cases and 233,000 related deaths each year.²

Pathophysiology and Natural History

Patients with MS typically present more than 20 years after an episode of rheumatic fever. Single or recurrent bouts of rheumatic carditis cause progressive thickening, scarring, and calcification of the mitral leaflets and chordae (Figure 1). Fusion of the commissures and chordae decreases the size of the mitral opening (Figure 2). This obstruction results in the development of a pressure gradient across the valve in diastole and causes an elevation in left atrial and pulmonary venous pressures. Elevated left atrial pressures lead to left atrial enlargement, predisposing the patient to atrial fibrillation and arterial thromboembolism. Elevated pulmonary venous pressure results in pulmonary congestion and pulmonary edema. In advanced MS, patients develop pulmonary hypertension and right-sided HF.

Signs and Symptoms

Patients with MS may present with exertional dyspnea, fatigue, atrial arrhythmias, embolic events, angina-like chest pain, hemoptysis, or even right-sided HF. Previously asymptomatic or stable patients may decompensate acutely during exercise, emotional stress, pregnancy, infection, or with uncontrolled atrial fibrillation.

The characteristic findings of MS on auscultation are an opening snap, a mid-diastolic rumble and an accentuated first heart sound. The first heart sound may be diminished in intensity if the valve is heavily calcified, with limited mobility. If the patient is in sinus rhythm, there is presystolic accentuation of the murmur during atrial contraction. With increasingly severe stenosis, the duration of the murmur increases and the opening snap occurs earlier during diastole as a result of higher left atrial pressure. There is accentuation of P₂ when pulmonary hypertension is present. If flow across the mitral valve is reduced because of HF, pulmonary hypertension, or aortic stenosis, the murmur of MS may be reduced in intensity or may be inaudible. Left atrial myxoma may be distinguished from MS by the presence of a “tumor plop” versus an opening snap in early diastole.

Diagnosis

An electrocardiogram may reveal evidence of left atrial enlargement; in more advanced disease, atrial fibrillation and/or right ventricular (RV) hypertrophy consistent with pulmonary hypertension may be present. On chest radiography, characteristic findings of MS are enlargement of the left atrium without cardiomegaly, enlargement of the main pulmonary arteries, and pulmonary congestion (Figure 1). Transthoracic echocardiography is indicated for all patients with suspected MS to establish the diagnosis, quantify hemodynamic severity (mean pressure gradient, MVA, and pulmonary artery pressure), assess for concomitant valvular lesions, and demonstrate valve morphology to determine suitability for mitral commissurotomy (Class I).¹ Characteristic findings of MS include valve thickening, restricted valve opening, anterior leaflet doming, and fusion of the leaflets at the commissures. The mean pressure gradient across the mitral valve on Doppler echocardiography (echo) in MS is at least 5 mm Hg; in severe stenosis, it is usually higher than 10 mm Hg. Because the gradient across the mitral valve is flow dependent, the severity of MS is more accurately defined by the MVA. The valve area may be measured by tracing the mitral valve opening in cross section by 2D or 3D echo. Alternatively, the MVA is calculated using the pressure half-time (P × ½t), which is the amount of time it takes for the transmitral pressure to fall to one half its initial value (MVA = 220/[P × ½t]).

Echocardiography also allows assessment of pulmonary artery pressures, detection of other valve disease, visualization of left atrial thrombus, and identification of important differential diagnoses, such as left atrial myxoma. Trans-esophageal echo should be performed in patients considered for percutaneous mitral balloon commissurotomy (PMBC) to assess the presence or absence of left atrial thrombus and to further evaluate the severity of MR (Class I).¹ Exercise testing with Doppler or invasive hemodynamic assessment is recommended to evaluate the response of the mean mitral gradient and pulmonary artery pressure in patients with MS when there is a discrepancy between resting Doppler echocardiographic findings and clinical symptoms or signs Class I).¹

Summary

• Transthoracic echocardiography is necessary to diagnose and determine the severity of mitral stenosis.

• Transesophageal echocardiography is indicated in patients before percutaneous mitral balloon valvotomy.

• Stress echocardiography and cardiac catheterization might be helpful in those cases in which there is a discrepancy between the severity of symptoms and baseline echocardiographic findings.

Treatment

Medical Treatment

Medical therapy has no role in altering the natural history or delaying the need for surgery in patients with MS. Medical treatment is directed toward alleviating pulmonary congestion with diuretics, treating atrial fibrillation, and anti-coagulating patients who are at increased risk of arterial embolic events.

Tachycardia is typically poorly tolerated in patients with MS and can lead to an acute deterioration as diastolic filling time may be inadequate. In particular, heart rate control can be beneficial in patients with MS and atrial fibrillation and fast ventricular response (Class IIa).¹ However, heart rate control may also be considered for patients with MS in normal sinus rhythm and symptoms associated with exercise (Class IIb).¹ Beta blockers, calcium channel blockers, digoxin and ivabradine have been used to control ventricular rate. An attempt to restore sinus rhythm with direct current electrical cardioversion or antiarrhythmic drugs may be considered. Anticoagulation with warfarin is indicated to prevent thromboembolism when atrial fibrillation is present, if there is a prior history of thromboembolism, or if a thrombus is detected in the left atrium (Class I).¹ Anticoagulation may also be considered if the left atrium is markedly dilated (5.0-5.5 mm) or if there is spontaneous contrast on echocardiography (Class IIb).^1,3,4 The efficacy of novel oral anticoagulant agents in preventing embolic events has not been studied in patients with MS. Antibiotic therapy is important for the secondary prevention of rheumatic carditis, de-novo rheumatic valvular disease or worsened rheumatic valvular disease. Patients with a history of rheumatic fever are at high risk of recurrence. Long-term secondary prophylaxis, preferentially with penicillin, is therefore recommended for all patients with a history of rheumatic fever, rheumatic carditis or rheumatic valve disease. The duration of prophylaxis depends on a number of factors, including time since the last attack, the age of the patient, the extent of cardiac involvement, and the patient’s risk of exposure to streptococcal infections.^1,5 Routine antibiotic prophylaxis for endocarditis is no longer recommended for patients with MS.⁶

Surgery

Three invasive options are available for patients with MS: PMBC, surgical mitral commissurotomy, and mitral valve replacement (MVR).

PMBC is a catheter-based technique in which a balloon is inflated across the stenotic valve to split the fused commissures and increase the valve area. Hemodynamic as well as clinical improvements may be seen immediately and the results are typically comparable with those achieved with open mitral commissurotomy, although less invasive and less costly.^7,8 Mitral valve morphology is an important predictor of successful PMBC. Severe valve calcification and/or significant thickening/calcification of the subvalvular apparatus on echocardiography before PMBC is associated with a higher complication rate and a greater risk of recurrence. PMBC should also not be performed in patients who have left atrial thrombus or more than 2+ (moderate) MR, because the degree of MR usually increases following the procedure. PMBC is the initial procedure of choice in experienced centers and should be considered for those with symptomatic severe MS and favorable valve morphology in the absence of contraindications (Class I).¹ PMBC is also indicated for symptomatic patients with less valve stenosis (MVA >1.5 cm²) if there is evidence of hemodynamically significant MS during exercise, e.g., if PCWP >25 mm Hg (Class IIb).¹ If valve anatomy is suboptimal, PMBC may also be considered but only for those with severe MS that have more advanced symptoms (New York Heart Association [NYHA] class III-IV) who are either not candidates or at high risk for surgery (Class IIb).¹ PMBC is indicated in asymptomatic patients if they have either very severe MS (MVA ≤1 cm², Class IIa) or severe MS and new onset atrial fibrillation (Class IIb).¹ Complications of PMBC include severe MR (3%), thromboembolism (3%), and residual atrial septal defect with significant shunting (<5%). Mortality with the procedure is lower than 1% in experienced hands. At 7 years after PMBC, 50% to 69% of patients remain free of cardiovascular events and up to 90% of patients remain free of re-intervention.^8,9

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Surgical mitral commissurotomy was first performed in 1925 as a closed technique (which does not necessitate the use of full cardiopulmonary bypass and is performed through an incision in the left atrial appendage) and is still widely used in many developing countries. Open surgical mitral commissurotomy involves the use of cardiopulmonary bypass and the surgical repair of a diseased mitral valve by direct visualization. It may be considered in patients with MS if the valve anatomy is unsuitable for PMBC, in the presence of a left atrial thrombus or significant MR, or for patients that require surgery for other concomitant valvular disease or coronary artery disease. Surgical mitral commissurotomy (either open or closed) may be carried out through a median sternotomy or left thoracotomy incision.

PMBC and surgical mitral commissurotomy are palliative procedures and, in most cases, further intervention is eventually required, usually in the form of a MVR. In addition, MVR may be necessary as a first line procedure in patients with either heavily calcified valves, or significant MR. Both mechanical and biological prostheses are used for MVR; the choice of valve often depends on factors such as age, need for concomitant anticoagulation, and left ventricular (LV) size. Morbidity and mortality are higher with prosthetic valve replacement than with surgical or balloon valvotomy. MVR surgery is indicated in severely symptomatic patients (NYHA class III/IV) with severe MS who are not high risk for surgery and who are not candidates for or failed previous PMBC (Class I).¹ Concomitant mitral valve surgery is indicated for patients with severe or moderate MS undergoing other cardiac surgery (Class I and Class IIb, respectively).¹ Mitral valve surgery and excision of the left atrial appendage may also be considered for patients with severe MS who have had recurrent embolic events while receiving adequate anticoagulation (Class IIb).¹ In general, the threshold for mitral valve surgery (commissurotomy or MVR) is higher than for PMBC in patients with MS, and commissurotomy or repair is preferable to MVR, if feasible. The new guidelines stress the importance of dedicated centers of excellence in which “Heart Valve Teams” of relevant specialists with expertise come together to guide complex decision making and to provide care particularly for high-risk patients.

A more detailed discussion of the management of MS may be found in the AHA/ACC guidelines.¹

Summary

• Medical therapy in patients with mitral stenosis includes diuretic therapy, heart rate or rhythm control, anticoagulation to prevent thromboembolism, and antibiotic prophylaxis against recurrent rheumatic carditis.

• For patients with severe mitral stenosis, percutaneous mitral balloon commissurotomy and surgical commissurotomy provide equivalent immediate and long-term outcome results and delay the need for mitral valve replacement.

Prevention and Screening

Antibiotic therapy of group A streptococcal tonsillo-pharyngitis, even delayed 9 days after the onset of symptoms, can prevent rheumatic fever and rheumatic carditis.¹⁰Antibiotic therapy also reduces transmission to contacts. Routine screening or treatment of asymptomatic contacts of persons with group A streptococcal tonsillo-pharyngitis is not recommended.

Patients with MS should at a minimum be followed-up with yearly history and physical examinations. Repeat echo should be considered every 3 to 5 years for those with progressive MS (MVA >1.5 cm²), while for asymptomatic patients with severe MS, serial echocardiography is advised every 1 to 2 years for those with MVA 1.0 to 1.5 cm² and every year for those with MVA <1.0 cm².

Special Populations

Pregnancy causes increased plasma volume, decreased afterload, and increased heart rate. These features will tend to increase the transmitral gradient (sometimes to double that of baseline), leading to increased left atrial pressures and elevated pulmonary pressures, which can result in pulmonary edema. Increased left atrial pressures often lead to atrial arrhythmias (such as atrial fibrillation), which are not well-tolerated by patients with MS, frequently resulting in clinical decompensation. Indeed, patients with asymptomatic moderate to severe MS may decompensate during periods of increased physiologic stress, such as pregnancy or non-cardiac surgery.

Before pregnancy, all patients with severe MS should undergo pre-pregnancy counseling by a cardiologist with the relevant expertise including a discussion of the risks and benefits of potential operative interventions, including mechanical prosthesis, bioprosthesis, and valve repair (Class I).¹ Valve intervention is recommended before pregnancy for symptomatic patients with severe MS and for asymptomatic patients with severe MS who have valve morphology favorable for PMBC (Class I).¹ Pregnant patients with severe MS should be monitored in a tertiary care center with a dedicated Heart Valve Team of cardiologists, surgeons, anesthesiologists, and obstetricians with expertise in the management of high-risk cardiac patients during pregnancy (Class I).¹ PMBC is reasonable for pregnant patients with severe MS with valve morphology favorable for PMBC who remain symptomatic with NYHA class III to IV HF symptoms despite medical therapy (Class IIa).¹ Valve operation is reasonable for pregnant patients with severe MS and valve morphology not favorable for PMBC only if there are refractory NYHA class IV HF symptoms (Class IIa). ¹ Of note, in asymptomatic patients with severe MS whose valve morphology is not favorable for PMBC, it may be reasonable to proceed with moderate-risk elective non-cardiac surgery coupled with appropriate intraoperative and postoperative hemodynamic monitoring (Class IIb).¹

During pregnancy, women with MS should receive appropriate medical therapy, including beta-blockers (Class IIa) and in certain cases, diuretics (Class IIb), but never angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers (Class III), due to their teratogenic potential. Those at risk for thromboembolization should be anticoagulated (Class I). In general, this is accomplished with warfarin during the 2nd and 3rd trimesters, with a transition to unfractionated heparin prior to labor and delivery.¹

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Mitral regurgitation

Definition and Causes

MR is leakage of blood from the left ventricle backwards into the left atrium during systole. It is caused by various mechanisms related to structural or functional abnormalities of the mitral apparatus (primary) or the left ventricle (secondary) (Figure 3). The most common causes of MR in the United States are myxomatous degeneration, chordal rupture, rheumatic heart disease, infective endocarditis, coronary artery disease, and cardiomyopathy.

Staging of Mitral Regurgitation (as per New Guidelines)¹

Primary

Patients identified as having mild abnormalities of mitral valve structure or function (mild prolapse, thickening or leaflet restriction) are considered at risk of MR (Stage A). Those with more severe valvular abnormalities (severe prolapse, rheumatic changes with loss of central coaptation, or prior infective endocarditis) are considered as having progressive MR (Stage B). Severe MR is classified as at least Stage C1 unless both LV enlargement (LVESD ≥40 mm) and impairment of LV function ([left ventricular ejection fraction] LVEF ≤60%) are present, in which case the patient is termed Stage C2. A symptomatic patient is classified as Stage D.

Secondary

Patients with coronary disease or cardiomyopathy with normal mitral valve anatomy are considered at risk of MR (Stage A). Those with regional wall motion abnormalities with mild mitral leaflet tethering or annular dilation with mild loss of central coaptation of the mitral leaflets are considered as having progressive MR (Stage B). Reflecting the significant impact of what would have previously been considered lesser degrees of MR in the setting of LV dysfunction, secondary MR is now considered severe if the effective regurgitant orifice area (EROA) is ≥0.2 cm² and the regurgitant volume is ≥30cc (Stage C) or if the patient is symptomatic (Stage D).

It is worth highlighting that the definition of severe MR is now different based upon etiology (as above), since severe primary MR requires an EROA ≥0.4 cm² while severe secondary MR only requires an EROA ≥0.2 cm². The rationale for this was largely based upon the clear adverse prognostic impact of even lesser degrees of secondary (vs. primary) MR. However, this may be a moot point as prognosis in secondary MR is more related to the underlying pathology than the degree of MR—typically prognosis alters little even if you fix secondary MR. A criticism of this guideline change has been that MR is now the only valve disease where you first need to describe the etiology before you can assess the severity. How widespread this change will be adopted is as yet unclear and it also remains to be seen whether the American Society of Echocardiography will also adopt this change in their echocardiographic definition of severe MR in their upcoming new valve guidelines.

Prevalence and Risk Factors

Significant mitral valve regurgitation occurs in about 2% of the population with a similar prevalence in males and females.¹¹Myxomatous disease is the most common cause of primary MR in the United States (Figure 4).

Pathophysiology and Natural History

Significant MR leads to volume overload of the left ventricle, because it has to accommodate both the stroke volume and regurgitant volume with each heartbeat. To compensate, the left ventricle becomes hyperdynamic. In acute severe MR, the left atrial and pulmonary venous pressures increase quickly, leading to pulmonary congestion and pulmonary edema. In chronic MR, a gradual increase in left atrial size and compliance compensate so that left atrial and pulmonary venous pressures do not increase until late in the course of the disease. Then, progressive LV dilation eventually leads to an increase in afterload, contractile dysfunction, and HF. Left atrial enlargement predisposes the patient to atrial fibrillation and arterial thromboembolism. In long-standing MR, patients may develop pulmonary hypertension and right-sided HF.

Signs and Symptoms

Patients with chronic, severe MR may remain asymptomatic for years because the regurgitant volume load is well tolerated as a result of compensatory ventricular and atrial dilation. When symptoms do develop, the most common are dyspnea, fatigue, orthopnea, paroxysmal nocturnal dyspnea, and palpitations caused by atrial fibrillation. Acute severe MR, as occurs with chordal rupture or papillary muscle rupture, is almost always symptomatic because the sudden regurgitant volume load in the nondilated left ventricle and atrium leads to pulmonary venous hypertension and congestion.

The characteristic finding in a patient with MR is a blowing holosystolic murmur heard best at the cardiac apex. When ventricular enlargement is present, the apical impulse may be diffuse and laterally displaced, and a third heart sound may be heard.

Diagnosis

An electrocardiogram may reveal evidence of left atrial enlargement; in more advanced disease, atrial fibrillation and/or RV hypertrophy consistent with pulmonary hypertension may be present. The chest radiograph may demonstrate left atrial enlargement and/or cardiomegaly.

Transthoracic echocardiography is indicated for all patients with suspected MR to confirm its presence, assess etiology (e.g., the presence of myxomatous mitral valve disease and leaflet prolapse, or evidence of underlying dilated cardiomyopathy), and determine its severity (Class I).¹ Evaluation of MR severity by echo requires an integrated assessment of several parameters, including etiology (primary vs. secondary), regurgitant jet size by color Doppler, regurgitant jet density by continuous-wave Doppler, pulmonary vein and mitral valve inflow by pulse-wave Doppler, as well as EROA (the area through which the valve leaks in systole) and regurgitant volume.¹²Transesophageal echocardiography is indicated for patients who are not adequately imaged by transthoracic echocardiography and before surgery to assess feasibility of repair (Class I).¹ Cardiac magnetic resonance imaging is also indicated in patients with chronic primary MR to assess LV and RV volumes, function, or MR severity and when these issues are not satisfactorily addressed by transthoracic echocardiography (Class I).1

Exercise treadmill testing can be useful in patients with chronic primary MR to establish symptom status and exercise tolerance (Stages B and C, Class IIa).¹ Exercise hemodynamics obtained with either Doppler echocardiography or cardiac catheterization is reasonable for symptomatic patients with chronic primary MR in whom there is a discrepancy between symptoms and the severity of MR at rest (Stages B and C, Class I).¹ Noninvasive imaging (stress echocardiography, stress nuclear/positron emission tomography, cardiac computed tomography angiography, cardiac magnetic resonance imaging) or cardiac catheterization with coronary arteriography, may also be useful to establish the etiology of chronic secondary MR (Stages B to D) and/or to assess myocardial viability, which in turn may influence management of functional MR (Class I).¹

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Summary

• Determining the severity of mitral regurgitation requires knowledge regarding the underlying etiology of the mitral regurgitation and an integrated assessment of several echocardiographic parameters.
• Additional noninvasive and invasive testing is useful as part of a complete preoperative assessment of patients with severe mitral regurgitation.

Treatment

Medical Treatment

In patients with acute severe MR, afterload reduction with intravenous nitroprusside and nitroglycerin reduces the regurgitant fraction and pulmonary pressures. Placement of an intra-aortic balloon pump also helps stabilize these patients. However, these are temporary measures before urgent mitral valve repair or replacement.

In patients with chronic asymptomatic MR caused by primary valve disease, there is no evidence for the routine use of vasodilator therapy given normotension and normal systolic LV function.¹³ The management of these patients is focused on deciding the appropriate timing of surgery, before the development of irreversible LV dysfunction as discussed below.

In patients with ischemic heart disease or dilated cardiomyopathy, MR portends a poor prognosis.¹⁴ MR in these patients is called functional or secondary MR and is caused by global or regional changes in LV geometry as well as annular dilation. Patients with chronic secondary MR (Stages B to D) and HF with reduced LVEF should receive standard guideline-determined medical therapy for HF, including angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers, beta blockers, and/or aldosterone antagonists as indicated (Class 1).¹ Biventricular pacing has also been shown to decrease the degree of MR in dilated cardiomyopathy.¹⁵

Routine antibiotic prophylaxis for endocarditis is no longer recommended for patients with MR.⁶

Surgery

Primary. For symptomatic patients with chronic severe primary MR, mitral valve surgery is recommended if LVEF >30% (Class I); and reasonable if LVEF ≤30% (Class IIb, Figure 4).¹

For asymptomatic patients with chronic severe primary MR, surgery is recommended in the presence of LV dysfunction (LVEF 30%-60%) and/or dilation (LVESD ≥40 mm, Class I); and reasonable in the absence of LV dysfunction/dilation if the likelihood of a successful and durable repair without residual MR is >95% with an expected mortality <1% when performed at a Heart Valve Center of Excellence (Class IIa); mitral valve repair is also reasonable for such patients given a high likelihood of a successful and durable repair, a nonrheumatic etiology with preserved LV function and either new onset of atrial fibrillation or resting pulmonary hypertension (pulmonary artery systolic arterial pressure >50 mm Hg, Class IIa).¹

Mitral valve repair is always recommended over MVR when a successful and durable repair can be accomplished (Class I), because of the improved outcomes.¹Concomitant mitral valve repair or replacement is indicated in patients with chronic moderate (Class IIa) or severe (Class I) primary MR undergoing other cardiac surgery.¹

Percutaneous mitral valve repair may be considered for severely symptomatic patients (NYHA class III-IV) with chronic severe primary MR (Stage D) who have a reasonable life expectancy, but a prohibitive surgical risk because of severe comorbidities (Class IIb, Figure 5).¹

Secondary. Mitral valve surgery is reasonable for patients with chronic moderate (Class IIb) or severe (Class IIa) secondary MR if they are undergoing concomitant cardiac surgery.¹ Isolated mitral valve surgery should be considered in the setting of chronic severe secondary MR only if patients are severely symptomatic (NYHA III-IV) as while symptoms may improve, a survival benefit has not been demonstrated (Class IIb).¹

A more detailed discussion of the management of MR may be found in the AHA/ACC guidelines.¹

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Summary

• Medical therapy has no role to specifically treat primary mitral regurgitation while it is the mainstay of treatment in patients with secondary mitral regurgitation.
• In patients with primary mitral regurgitation, surgery is indicated in the presence of symptoms or, in asymptomatic patients, if there is evidence of secondary left ventricular dysfunction.
• Mitral valve repair is the procedure of choice for the surgical management of mitral regurgitation and is associated with lower mortality and better preservation of left ventricular function.

Prevention and Screening

Patients with established MR should at a minimum be followed-up with yearly history and physical examination. Repeat echo should be considered every 3 to 5 years for those with mild MR and every 1 to 2 years for those with moderate MR. For asymptomatic patients with severe MR, serial echocardiography every 6 to 12 months to assess LV size and systolic function is important for optimal timing of surgery (Class I).¹

Special Populations

Patients with MR generally tolerate pregnancy better than patients with MS do, because the decrease in after-load means that increased cardiac output does not necessarily cause a rise in ventricular filling pressures or pulmonary pressures. However, patients with severe pre-existing regurgitation who are already symptom-limited, have a reduced LVEF or pulmonary hypertension may develop HF symptoms because of the volume load of pregnancy. Thus, all patients with suspected valve regurgitation should undergo a clinical evaluation and transthoracic echocardiogram before pregnancy (Class I).¹ Valve repair or replacement is recommended before pregnancy for symptomatic women with severe valve regurgitation (Class I).¹ Valve repair before pregnancy may be considered in asymptomatic patients with severe MR but only after detailed discussion with the patient about the risks and benefits of the operation and its outcome on future pregnancies (Class IIb).¹ During pregnancy, given the high maternal and fetal risk, such surgery is only recommended if refractory NYHA IV symptoms are present (Class IIa).¹ Finally, acute severe MR (such as that caused by papillary muscle or chordal rupture) is generally not well-tolerated during pregnancy, often causing flash pulmonary edema and rapid clinical decompensation. These patients require hemodynamic stabilization in the cardiac intensive care unit as emergent surgery is arranged.

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Mitral valve prolapse

Definition and Causes

MVP is the systolic billowing of one or both mitral leaflets into the left atrium during systole.¹⁶ It may occur in the setting of myxomatous valve disease or in persons with normal mitral valve leaflets.

Prevalence and Risk Factors

MVP is the most common valvular disorder in the United States, occurring in 2% to 3% of the general population. There is a similar prevalence in men and women, with a greater risk of complications in men.¹⁷

Pathophysiology and Natural History

Many patients with MVP have normal mitral leaflets, with little or no MR, and a benign prognosis. Survival rates among affected patients are similar to those of age- and gender-matched individuals without MVP.¹⁸ In other patients, MVP is caused by myxomatous valve disease, with typical findings of elongated and thickened leaflets, interchordal hooding, and chordal elongation (Figure 6). Patients with myxomatous MVP are at increased risk for cardiovascular complications, particularly when prolapse is associated with at least moderate MV or LV dysfunction. Although most patients with MVP do not develop severe MR, MVP is a common underlying cause of progressive MR, often necessitating mitral valve repair or replacement.¹⁹

The causes of myxomatous mitral valve disease are not certain, but appear to involve dysregulation of extracellular matrix proteins. Myxomatous mitral valve disease usually occurs sporadically, although there are well-described cases of familial clustering that involve an autosomal dominant mode of inheritance.¹⁶ Three genetic loci for autosomal dominant myxomatous mitral valve disease have been described, but the precise genes and mutations have not yet been identified. Myxomatous MVP also may occur in conjunction with certain connective tissue disorders, such as Marfan syndrome and Ehlers-Danlos syndrome.

Signs and Symptoms

Most patients with MVP are asymptomatic. In the past, multiple nonspecific symptoms (atypical chest pain, dyspnea, palpitations, anxiety, and syncope) and clinical findings (low body weight, low blood pressure, and pectus excavatum) were associated with MVP and termed mitral valve prolapse syndrome. Prospective testing has failed to confirm most of these associations.¹⁷ The classic findings of MVP on physical examination are a mid-systolic click, with a late systolic murmur from MR (Figure 7), heard best at the cardiac apex.

Diagnosis

Transthoracic echocardiography is the most important test for diagnosing MVP (Class I).¹ The diagnosis is made when there is displacement of one or both mitral leaflets by 2 mm or more into the left atrium during systole (Figure 8). Because the mitral annulus is known to have a saddle shape, a normal mitral valve can appear to prolapse in certain echocardiographic views, most notably in the apical two- and four-chamber views. Therefore, the diagnosis of MVP should be based on a parasternal long-axis or apical three-chamber view. In patients with MVP, echocardiography is also useful in determining the presence and severity of MR and assessing left atrial and ventricular chamber size, LV function, and leaflet thickening and redundancy. Unless severe MR is present, findings on the chest radiograph and electrocardiogram are typically unremarkable.

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Summary

• Mitral valve prolapse is present if there is more than 2 mm displacement of the mitral valve leaflets into the left atrium during systole in a parasternal long-axis or apical three-chamber view on echocardiography.

Treatment

Medical Treatment

Asymptomatic patients require no specific treatment and they should be reassured of their excellent prognosis. Although antibiotic prophylaxis for endocarditis was once advocated for certain patients with MVP, more recent guidelines do not recommend antibiotic prophylaxis in this group of patients.^1,6 Beta blockers may be useful for alleviating symptoms of palpitations, anxiety, and chest pain in certain patients.

Patients with MVP but without MR should be evaluated every 3 to 5 years. Echocardiography should be performed if the patient has new cardiovascular symptoms or if the physical examination suggests that significant MR has developed. Patients with severe MR or high-risk features should be reviewed with an echocardiogram yearly or more often if their clinical condition warrants it.

Surgery

In MVP patients with severe MR, the indications for mitral valve surgery are similar to those for patients with other primary causes of severe regurgitation. When surgery is required, mitral valve repair is usually feasible. Repair is characterized by low mortality and long-lasting durability; the 10-year reoperation-free survival rate ranges between 93% and 96%.²⁰ A more detailed discussion of the MVP may be found in the AHA/ACC guidelines.¹

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Summary

• Mitral valve prolapse is a benign condition in most cases with similar surgical indications as those for patients with other causes of primary mitral regurgitation.

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Suggested Readings

• Bonow RO, Carabello B, Chatterjee K, et al. ACC/AHA 2006 Guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Valvular Heart Disease).  Circulation. 2006, 114: e84-e231.
• Enriquez-Sarano M, Avierinos JF, Messika-Zeitoun D, et al. Quantitative determinants of the outcome of asymptomatic mitral regurgitation. N Engl J Med. 2005, 352: 875-883.