Mitral regurgitation is the most common valvular abnormality seen in clinical practice. Different disease processes leading to mitral regurgitation may affect different components of the mitral valve. Prevalence of the etiology depends upon surgical or medical series reporting the causes. Below Table gives a list of various disease processes that cause mitral regurgitation.
Pathology
Mitral valve has a complex anatomy and involvement of any of the segments of mitral valve apparatus viz. leaflets, chordae, annulus, papillary muscle or underlying left ventricular muscle may cause mitral regurgitation. Congenital mitral regurgitation may be due to cleft mitral leaflet and is often associated with ostium primum type of ASD. Ostium secundum type is associated with mitral valve prolapse. Rheumatic involvement is the most important cause of mitral regurgitation in our country. Commissural fusion, thickening, calcification, shortening and retraction of leaflets and incomplete coaptation of leaflets characterize the pathology of valve.
Sub valvular pathology with thickened and fused chordae contributes to mitral regurgitation.Only in about 10 per cent of the cases the lesion is a pure regurgitation while in majority of the cases it is a combined mitral stenosis and regurgitation. Myxomatous mitral valve is characterized by deposition of mucopolysaccahrides in the spongiosa layer. This leads to increase in valve area and length causing hooding of the leaflets. Chordal lengthening and tortuosity may be seen and rupture may occur. Chordae may be thick with mucopolysaccahrides deposition but lack strength.
Rupture of chordae results in flail segment of the leaflet. In idiopathic degeneration of chordae usually posterior leaflets are involved and their rupture leads to mitral regurgitation. Sclerosis and calcification of mitral annulus is seen in elderly women who also may have associated hypertension and more often coronary artery disease. Calcific annulus has impaired contraction and also interferes with posterior leaflet coaptation.
Mitral regurgitation is considered secondary if the leaflets and chordae are not directly involved but mitral regurgitation results from changes in annular size or left ventricular geometry as seen in dilated and ischaemic heart disease. In ischaemic heart disease papillary muscle malfunction may be secondary to ischaemia, necrosis or fibrosis of the papillary muscle. Altered geometry with distal displacement of papillary muscle secondary to remodeling also leads to impairedmechanics of mitral valve closure and thereby regurgitation. Venturi effect on anterior leaflet and also certain secondary structural changes of anterior leaflet cause mitral regurgitation in hypertrophic obstructive cardiomyopathy. Chordal and even leaflet encasement in endomyocardial fibrosis causes mitral regurgitation.
Pathophysiology
During left ventricular systole as the pressure rises in left ventricle, blood is pumped simultaneously both into aorta and left atrium. The effective orifice that allows regurgitation is called effective regurgitant orifice. The fraction of total left ventricular stroke volume that regurgitates in to left atrium is regurgitant fraction. In chronic mitral regurgitation compliant left atrium dilates and accommodates the regurgitant blood thus not allowing the mean left atrial pressure to rise. As the blood flow across mitral valve increases during next diastole, end diastolic volume of left ventricle increases. With increased pre load, left ventricular ejection fraction increases and maintains forward stroke volume in spite of regurgitation. During systole as the left ventricle is open to low pressure left atrium, afterload decreases. Thus in chronic mitral regurgitation left ventricular ejection fraction is more than normal due to increased preload and decreased afterload. As the mitral regurgitation progresses, left ventricle and left atrium dilate.
Dilated large left atrium will have areas of fibrosis leading to generation of atrial fibrillation. Dilated chambers with dilated mitral annulus and altered geometry of papillary muscles and posterior left atrial wall lead to aggravation of mitral regurgitation. Hence mitral regurgitation begets mitral regurgitation. Eventually changes take place in left ventricular myocardium causing myocardial dysfunction. As stated earlier, increased preload and decreased afterload of left ventricle allow maintained left ventricular ejection fraction even in the presence of myocardial dysfunction. Left ventricular ejection fraction is not a load independent index of left ventricular systolic function and is not suitable to assess left ventricular systolic function in patients with chronic mitral regurgitation. Removal of the regurgitant orifice through which left ventricle has a low pressure outlet by mitral valve replacement or repair will effectively increase the afterload.
Failing myocardium will now face afterload mismatch and left ventricular ejection fraction actually decreases after surgery. Understanding this concept is of fundamental importance in timing of mitral valve surgery.
Clinical Features
Symptoms
Symptoms depend upon underlying etiology of mitral regurgitation. Patients with mild mitral regurgitation and most of those with even severe mitral regurgitation are asymptomatic. However,patients with secondary mitral regurgitation due to ischaemic heart disease or dilated cardiomyopathy will usually be symptomatic of their underlying myocardial failure. Patients usually have dyspnoea on effort, palpitations and fatigue. Worsening symptoms usually denote worsening of underlying left ventricular dysfunction. Conversely left ventricular dysfunction may progress without any symptoms. Symptoms correlate more with hemodynamic status than severity of mitral regurgitation. Patients may also be asymptomatic as they gradually limit their physical activity. Patients with mitral valve prolapse may complain of chest pain. Sudden worsening of symptoms in a stable patient usually indicates chordal rupture or endocarditis.
Decompensation due to superimposed hemodynamic burden or onset of atrial fibrillation may sometimes bring chronic mitral regurgitation to the clinical notice. Sometimes patients who present with severe symptoms may slowly settle down due to dilatation of left atrium with increased compliance. Symptoms of edema feet denoting right heart failure are usually a late feature.
Physical SignsPulse is of normal character but carotid upstroke may be brisk. Atrial fibrillation is often present in a patient with advanced disease. Blood pressure is normal. Jugular venous pressure is normal in compensated phase. Left ventricle is often dilated with a downward and laterally displaced forcible apex. A systolic left para sternal lift may be palpable as the regurgitant blood enters the left atrium and this is different from para sternal lift due to prominent right ventricle.
Occasionally systolic thrill of mitral regurgitation is palpable. First heart sound (S1) is usually soft in rheumatic mitral regurgitation but it is normal in mitral valve prolapse. Second heart sound (S2) may be widely split. A third heart sound (S3) may be palpable at the apex. A fourth heart sound (S4) may be seen with recent onset severe mitral regurgitations and sinus rhythm. A holosystolic murmur starting with S1 and ending with S2 due to mitral regurgitation is audible at apex. In mitral valve prolapse it is a mid systolic murmur starting after a mid systolic click.
Murmur radiates to axilla and back with a posteriorly directed jet as seen with anterior leaflet abnormalities, ischaemic and dilated cardiomyopathies. It radiates superiorly and medially towards base with posterior leaftlet abnormalities. Patients with severe mitral regurgitation due to valve pathology have loud and long murmurs while soft, short, barely audible early murmurs are present in patients with functional mitral regurgitation. Murmur is often not audible in patients with acute mitral regurgitation. Physical maneuvers like valsalva, squatting and respiration will help in differentiating it form other systolic murmurs. Mid diastolic murmur may follow an S3 especially in rheumatic mitral regurgitation and is unusual in mitral regurgitations of other etiologies.
Investigation
Electrocardiogram
Patients with severe mitral regurgitation often have atrial fibrillation. Left atrial enlargement is a common finding in those with sinus rhythm. Left ventricular hypertrophy with ST segment changes may be seen. Signs of pulmonary hypertensions are seen less often and are usually seen in patients with rheumatic etiology. Non specific ST–T changes may be seen in patient with mitral valve prolapse. Q-waves in Inferior leads and LBBB pattern may be seen in patients with functional mitral regurgitation due to ischaemic and dilated cardiomyopathy respectively.Chest Radiogram Enlarged left atrium is obvious on chest X-ray and it may occupy most of the cardiac silhouette in patients with aneurysmal left atrium. Left ventricular enlargement may also be seen. Mitral annular calcification may be seen left to the vertebral column in elderly women. Signs of left ventricular failure are seen some times but pulmonary artery dilatation and right ventricular enlargement are uncommon.
Echo and Doppler Evaluation
2 D echocardiography will help determine the morphology and etiology of mitral regurgitation.Rheumatic mitral regurgitation is characterized by thickened leaflets and chordae, commissural fusion and limited mobility of posterior mitral leaflet. Leaflets may contract and may not coapt with each other. In patients with SLE small vegetation may be found. In mitral valve prolapse either of the leaflets crosses the plane of mitral annulus in to left atrium during systole. Since the mitral annulus is of saddle shape an assessment should be made in para sternal long axis view than from an apical view. With myxomatous degeneration, mitral leaflets are thickened. Mitral valve prolapse may be present with no or any degree of regurgitation. A flail leaflet is diagnosed when there is complete loss of cooptation and tip of one of the leaflet prolapses in to leaflet atrium during systole. Ruptured chordae are better observed on trans esophageal echo. Mitral annular calcification with varying degrees of involvement of posterior leaflet, vegetations, perforations and cleft leaflets are obvious on 2 D echocardiographic imaging.
In secondary or functional mitral regurgitation, global or regional left ventricular dysfunction is present with normal or mildly thickened mitral leaflets. Characteristic apical displacement of anterior mitral leaflet with tenting due to abnormal tension on the principal chordae results in incomplete leaflet closure with central jet of mitral regurgitation.2 D guided M-mode measurements of left atrium, left ventricle dimensions and ejection fraction should be obtained and recorded at baseline with which future measurements can be compared.With Color flow imaging one can assess the relative sizes of left atrium and mitral regurgitant jet to estimate the severity of mitral regurgitation and this correlates well with the angiographic severity. However, one should keep in mind that color flow imaging depends upon the gain settings, pulsed repetition frequency, field depth, direction of jet and loading conditions. An eccentric MR jet is often underestimated. Doppler echo indices of severe MR include increasedantegrade flow velocities with a large E-wave, dense continuous Doppler wave spectrum of regurgitant jet and systolic flow reversal in pulmonary veins. Vena contracta is the narrowest portion of the mitral regurgitation jet down stream from the orifice and a biplane vena contracta more than or equal to 0.5 cm indicates severe mitral regurgitation. Using volumetric and PISA method, severity of regurgitation, regurgitant volume and fraction and regurgitant orifice area can be measured. Also from the velocity of mitral regurgitation left ventricle to left atrial pressure difference can be obtained which correlates with the left atrial mean pressure.
Severe mitral regurgitation is diagnosed when:
1) There is echocardiographic evidence of disruption of mitral valve apparatus like papillary muscle rupture, flail mitral leaflet etc.,
2) The effective regurgitant orifice area is > 0.40 cm 2,
3) Mitral regurgitation volume > 60 cc,
4) Regurgitant fraction > 55 per cent,
5) Pulmonary vein systolic flow reversal and
6) Mitral regurgitation jet reaches posterior wall of the left atrium.
Severe mitral regurgitation is suggested when:
1) The color flow area is > 40 per cent of LA size,
2) Eccentric mitral regurgitation jet reaches the posterior wall,
3) Dense continuous wave Doppler signal is present,
4) E-wave velocity is > 1.5 m/s for native valves and > 2.0 m/s for prosthetic valves,
5) LV dimension is > 7 cm,
6) LA size is > 5.5 cm
TEE examination gives a superior window and is indicated whenever the etiology and severity can not be assessed accurately with trans thoracic echocardiography. TEE is also helpful in per operative assessment of mitral valve repair.
Cardiac Catheterization
Routine cardiac catheterization is not necessary in patients with mitral regurgitation. It may be done when there is discrepancy between clinical findings and non invasive tests or preoperatively to do coronary angiography before mitral valve replacement in a patient in whom associated coronary artery disease is a possibility. Pressure tracings may show a prominent ‘v’ wave in pulmonary capillary wedge tracings but this in neither a sensitive nor specific finding even in a patient with severe mitral regurgitation as height of ‘v’ wave depends upon left atrial compliance.Exercise hemodynamics may provide additional information. Left ventricular angiography may give a qualitative assessment of mitral regurgitation but this is not an objective method.Quantification of mitral regurgitation has been attempted by measuring forward cardiac output by Fick’s method and stroke volume by left ventricular angiogram, but this is highly erroneous.
However, left ventricular angiogram gives information about left ventricular size, function,severity of mitral regurgitation and regional wall motion abnormalities.
Management Medical Management
Vasodilator therapy to reduce afterload may be beneficial in patients with chronic mitral regurgitation, but there is no evidence to suggest the same in an asymptomatic patient. In a symptomatic patient with primary mitral regurgitation, surgery should be done. Vasodilators should be used in a symptomatic patient with primary or secondary mitral regurgitation not undergoing surgery. Beta blockers, digoxine, calcium channel blockers and even amiodarone may have to be used for rate control in a patient with atrial fibrillation. Diuretics need to be given as required. Oral anticoagulants are indicated in a patient with atrial fibrillation to prevent embolic episodes though the rate of embolic episodes is low and INR in the range of 2.0–2.5 may be sufficient.
Serial Follow Up
Serial follow up will help to identify patients who develop symptoms and left ventricular dysfunction. It is important to identify early signs of left ventricular dysfunction since left ventricular dysfunction may precede symptoms and post-operative outcome depends upon the left ventricular size and function. Patients with mild mitral regurgitation with no left ventricular dilatation need to be followed once in a year. Annual echocardiograms are not indicated unless they develop new symptoms. Patients with moderate mitral regurgitation need annual evaluation including echocardiography. Patients with severe mitral regurgitation should be followed up once in six months to assess symptoms and left ventricular size and function. Even in an asymptomatic patient left ventricular end systolic dimension more than 45 mm and left ventricular ejection fraction less than 60 per cent are indications for mitral valve repair or replacement. When history is not obvious, exercise testing may be done to assess functional capacity objectively.
Indications for Surgery
Surgery is indicated in all symptomatic patients (class II and above) with severe mitral regurgitation and normal or decreased left ventricular function. Surgery is also indicated in an asymptomatic patient with left ventricular ejection fraction less than 60 per cent and or left ventricular end systolic dimension more than 45 mm. In patients with severe mitral regurgitation, even when the patient is asymptomatic, one should not allow left ventricular ejection fraction to fall less then 55 per cent as post operative recovery will not be good. Though left ventricular ejection fraction is a better index to follow than left ventricular end systolic dimension, surgery may be considered even if one of the parameters is satisfied. When left ventricular ejection fraction is less than 30 per cent or end systolic dimension more than 55 mm, mitral valve surgery carries high risk and may not be beneficial. Surgery is indicated in symptomatic or asymptomatic patient with recent onset severe mitral regurgitation and also in patients with atrial fibrillation.With onset of atrial fibrillation patients tend to become symptomatic and left ventricular dysfunction sets in. Atrial fibrillation tends to persistent even after mitral valve surgery if its duration is more than three months. Similarly asymptomatic severe mitral regurgitation patients with pulmonary artery systolic pressure of equal to or more than 50 mm Hg. at rest or equal to or more than 60 mm Hg. with exercise are also candidates for mitral valve surgery. The outcome in patients with ischaemic mitral regurgitation is worse than those with non ischaemic etiology as they have underlying left ventricular dysfunction. In patients with papillary muscle dysfunction due to reversible ischaemia, simple revascularization may be sufficient. Many patients with severe ischaemic mitral regurgitation need mitral valve replacement or repair.
Types of Surgery
Mitral valve repair, mitral valve replacement with preservation of part of or all of the valve apparatus and mitral valve replacement with removal of mitral valve apparatus are three different surgeries that can be performed. When the valve is suitable and surgical expertise is availablemitral valve repair should be the treatment of choice since it avoids the need for chronic anticoagulation, late prosthetic valve failure and preserves post operative left ventricular function.
Preservation of mitral valve apparatus is essential to maintain normal shape, volume and function of mitral valve and it should be preserved as far as possible. Valve or annular calcification,rheumatic and ischaemic involvement, anterior leaflet involvement decrease the chances of repair. Mitral regurgitation due to uncalcified posterior leaflet prolapse due to degenerated mitral leaflets or ruptured chordae tendineae is often repairable. Mitral valve repair rather than mitral valve replacement should be considered seriously in patients with severe left ventricular dysfunction and in asymptomatic patients with good left ventricular function. In the former because any replacement rather then repair will only worsen the dysfunction while in the latter replacement will mandate chronic anticoagulation in otherwise asymptomatic patient.
Natural History
Patients with mild mitral regurgitation and normal left ventricular size and function do well long term, However, those with severe mitral regurgitation with or without left ventricular dysfunction do not de well and their 10 year survival is less than expected to a tune of 50 – 60 per cent in different series. Higher NYHA class, low LVEF, presence of pulmonary hypertension and AF are adverse prognostic factors. Patients who undergo surgery do better and those who undergo surgery at lower NYHA class and those with preserved left ventricular function do better post operatively.
Acute Severe Mitral Regurgitation
Acute severe mitral regurgitation is a medical emergency. Patient presents with breathlessness and low output state. He may be is shock with extreme dyspnoea. There may be features of background disease that led to mitral regurgitation like coronary artery disease usually an inferior wall myocardial infarction, infective endocarditis, or mitral valve prolapse with chordal rupture.
In the absence of time for compensatory left ventricular and left atrial dilatation patient will have an acute decrease in forward output and acute increase in pulmonary wedge pressures leading to pulmonary edema. There will be tachycardia, tachypnoea and extremities may be cold with signs of left ventricular failure. One should not be looking for signs of chronic mitral regurgitation.
Mitral valve has a complex anatomy and involvement of any of the segments of mitral valve apparatus viz. leaflets, chordae, annulus, papillary muscle or underlying left ventricular muscle may cause mitral regurgitation. Congenital mitral regurgitation may be due to cleft mitral leaflet and is often associated with ostium primum type of ASD. Ostium secundum type is associated with mitral valve prolapse. Rheumatic involvement is the most important cause of mitral regurgitation in our country. Commissural fusion, thickening, calcification, shortening and retraction of leaflets and incomplete coaptation of leaflets characterize the pathology of valve.
Sub valvular pathology with thickened and fused chordae contributes to mitral regurgitation.Only in about 10 per cent of the cases the lesion is a pure regurgitation while in majority of the cases it is a combined mitral stenosis and regurgitation. Myxomatous mitral valve is characterized by deposition of mucopolysaccahrides in the spongiosa layer. This leads to increase in valve area and length causing hooding of the leaflets. Chordal lengthening and tortuosity may be seen and rupture may occur. Chordae may be thick with mucopolysaccahrides deposition but lack strength.
Rupture of chordae results in flail segment of the leaflet. In idiopathic degeneration of chordae usually posterior leaflets are involved and their rupture leads to mitral regurgitation. Sclerosis and calcification of mitral annulus is seen in elderly women who also may have associated hypertension and more often coronary artery disease. Calcific annulus has impaired contraction and also interferes with posterior leaflet coaptation.
Mitral regurgitation is considered secondary if the leaflets and chordae are not directly involved but mitral regurgitation results from changes in annular size or left ventricular geometry as seen in dilated and ischaemic heart disease. In ischaemic heart disease papillary muscle malfunction may be secondary to ischaemia, necrosis or fibrosis of the papillary muscle. Altered geometry with distal displacement of papillary muscle secondary to remodeling also leads to impairedmechanics of mitral valve closure and thereby regurgitation. Venturi effect on anterior leaflet and also certain secondary structural changes of anterior leaflet cause mitral regurgitation in hypertrophic obstructive cardiomyopathy. Chordal and even leaflet encasement in endomyocardial fibrosis causes mitral regurgitation.
Pathophysiology
During left ventricular systole as the pressure rises in left ventricle, blood is pumped simultaneously both into aorta and left atrium. The effective orifice that allows regurgitation is called effective regurgitant orifice. The fraction of total left ventricular stroke volume that regurgitates in to left atrium is regurgitant fraction. In chronic mitral regurgitation compliant left atrium dilates and accommodates the regurgitant blood thus not allowing the mean left atrial pressure to rise. As the blood flow across mitral valve increases during next diastole, end diastolic volume of left ventricle increases. With increased pre load, left ventricular ejection fraction increases and maintains forward stroke volume in spite of regurgitation. During systole as the left ventricle is open to low pressure left atrium, afterload decreases. Thus in chronic mitral regurgitation left ventricular ejection fraction is more than normal due to increased preload and decreased afterload. As the mitral regurgitation progresses, left ventricle and left atrium dilate.
Dilated large left atrium will have areas of fibrosis leading to generation of atrial fibrillation. Dilated chambers with dilated mitral annulus and altered geometry of papillary muscles and posterior left atrial wall lead to aggravation of mitral regurgitation. Hence mitral regurgitation begets mitral regurgitation. Eventually changes take place in left ventricular myocardium causing myocardial dysfunction. As stated earlier, increased preload and decreased afterload of left ventricle allow maintained left ventricular ejection fraction even in the presence of myocardial dysfunction. Left ventricular ejection fraction is not a load independent index of left ventricular systolic function and is not suitable to assess left ventricular systolic function in patients with chronic mitral regurgitation. Removal of the regurgitant orifice through which left ventricle has a low pressure outlet by mitral valve replacement or repair will effectively increase the afterload.
Failing myocardium will now face afterload mismatch and left ventricular ejection fraction actually decreases after surgery. Understanding this concept is of fundamental importance in timing of mitral valve surgery.
Clinical Features
Symptoms
Symptoms depend upon underlying etiology of mitral regurgitation. Patients with mild mitral regurgitation and most of those with even severe mitral regurgitation are asymptomatic. However,patients with secondary mitral regurgitation due to ischaemic heart disease or dilated cardiomyopathy will usually be symptomatic of their underlying myocardial failure. Patients usually have dyspnoea on effort, palpitations and fatigue. Worsening symptoms usually denote worsening of underlying left ventricular dysfunction. Conversely left ventricular dysfunction may progress without any symptoms. Symptoms correlate more with hemodynamic status than severity of mitral regurgitation. Patients may also be asymptomatic as they gradually limit their physical activity. Patients with mitral valve prolapse may complain of chest pain. Sudden worsening of symptoms in a stable patient usually indicates chordal rupture or endocarditis.
Decompensation due to superimposed hemodynamic burden or onset of atrial fibrillation may sometimes bring chronic mitral regurgitation to the clinical notice. Sometimes patients who present with severe symptoms may slowly settle down due to dilatation of left atrium with increased compliance. Symptoms of edema feet denoting right heart failure are usually a late feature.
Physical SignsPulse is of normal character but carotid upstroke may be brisk. Atrial fibrillation is often present in a patient with advanced disease. Blood pressure is normal. Jugular venous pressure is normal in compensated phase. Left ventricle is often dilated with a downward and laterally displaced forcible apex. A systolic left para sternal lift may be palpable as the regurgitant blood enters the left atrium and this is different from para sternal lift due to prominent right ventricle.
Occasionally systolic thrill of mitral regurgitation is palpable. First heart sound (S1) is usually soft in rheumatic mitral regurgitation but it is normal in mitral valve prolapse. Second heart sound (S2) may be widely split. A third heart sound (S3) may be palpable at the apex. A fourth heart sound (S4) may be seen with recent onset severe mitral regurgitations and sinus rhythm. A holosystolic murmur starting with S1 and ending with S2 due to mitral regurgitation is audible at apex. In mitral valve prolapse it is a mid systolic murmur starting after a mid systolic click.
Murmur radiates to axilla and back with a posteriorly directed jet as seen with anterior leaflet abnormalities, ischaemic and dilated cardiomyopathies. It radiates superiorly and medially towards base with posterior leaftlet abnormalities. Patients with severe mitral regurgitation due to valve pathology have loud and long murmurs while soft, short, barely audible early murmurs are present in patients with functional mitral regurgitation. Murmur is often not audible in patients with acute mitral regurgitation. Physical maneuvers like valsalva, squatting and respiration will help in differentiating it form other systolic murmurs. Mid diastolic murmur may follow an S3 especially in rheumatic mitral regurgitation and is unusual in mitral regurgitations of other etiologies.
Investigation
Electrocardiogram
Patients with severe mitral regurgitation often have atrial fibrillation. Left atrial enlargement is a common finding in those with sinus rhythm. Left ventricular hypertrophy with ST segment changes may be seen. Signs of pulmonary hypertensions are seen less often and are usually seen in patients with rheumatic etiology. Non specific ST–T changes may be seen in patient with mitral valve prolapse. Q-waves in Inferior leads and LBBB pattern may be seen in patients with functional mitral regurgitation due to ischaemic and dilated cardiomyopathy respectively.Chest Radiogram Enlarged left atrium is obvious on chest X-ray and it may occupy most of the cardiac silhouette in patients with aneurysmal left atrium. Left ventricular enlargement may also be seen. Mitral annular calcification may be seen left to the vertebral column in elderly women. Signs of left ventricular failure are seen some times but pulmonary artery dilatation and right ventricular enlargement are uncommon.
Echo and Doppler Evaluation
2 D echocardiography will help determine the morphology and etiology of mitral regurgitation.Rheumatic mitral regurgitation is characterized by thickened leaflets and chordae, commissural fusion and limited mobility of posterior mitral leaflet. Leaflets may contract and may not coapt with each other. In patients with SLE small vegetation may be found. In mitral valve prolapse either of the leaflets crosses the plane of mitral annulus in to left atrium during systole. Since the mitral annulus is of saddle shape an assessment should be made in para sternal long axis view than from an apical view. With myxomatous degeneration, mitral leaflets are thickened. Mitral valve prolapse may be present with no or any degree of regurgitation. A flail leaflet is diagnosed when there is complete loss of cooptation and tip of one of the leaflet prolapses in to leaflet atrium during systole. Ruptured chordae are better observed on trans esophageal echo. Mitral annular calcification with varying degrees of involvement of posterior leaflet, vegetations, perforations and cleft leaflets are obvious on 2 D echocardiographic imaging.
In secondary or functional mitral regurgitation, global or regional left ventricular dysfunction is present with normal or mildly thickened mitral leaflets. Characteristic apical displacement of anterior mitral leaflet with tenting due to abnormal tension on the principal chordae results in incomplete leaflet closure with central jet of mitral regurgitation.2 D guided M-mode measurements of left atrium, left ventricle dimensions and ejection fraction should be obtained and recorded at baseline with which future measurements can be compared.With Color flow imaging one can assess the relative sizes of left atrium and mitral regurgitant jet to estimate the severity of mitral regurgitation and this correlates well with the angiographic severity. However, one should keep in mind that color flow imaging depends upon the gain settings, pulsed repetition frequency, field depth, direction of jet and loading conditions. An eccentric MR jet is often underestimated. Doppler echo indices of severe MR include increasedantegrade flow velocities with a large E-wave, dense continuous Doppler wave spectrum of regurgitant jet and systolic flow reversal in pulmonary veins. Vena contracta is the narrowest portion of the mitral regurgitation jet down stream from the orifice and a biplane vena contracta more than or equal to 0.5 cm indicates severe mitral regurgitation. Using volumetric and PISA method, severity of regurgitation, regurgitant volume and fraction and regurgitant orifice area can be measured. Also from the velocity of mitral regurgitation left ventricle to left atrial pressure difference can be obtained which correlates with the left atrial mean pressure.
Severe mitral regurgitation is diagnosed when:
1) There is echocardiographic evidence of disruption of mitral valve apparatus like papillary muscle rupture, flail mitral leaflet etc.,
2) The effective regurgitant orifice area is > 0.40 cm 2,
3) Mitral regurgitation volume > 60 cc,
4) Regurgitant fraction > 55 per cent,
5) Pulmonary vein systolic flow reversal and
6) Mitral regurgitation jet reaches posterior wall of the left atrium.
Severe mitral regurgitation is suggested when:
1) The color flow area is > 40 per cent of LA size,
2) Eccentric mitral regurgitation jet reaches the posterior wall,
3) Dense continuous wave Doppler signal is present,
4) E-wave velocity is > 1.5 m/s for native valves and > 2.0 m/s for prosthetic valves,
5) LV dimension is > 7 cm,
6) LA size is > 5.5 cm
TEE examination gives a superior window and is indicated whenever the etiology and severity can not be assessed accurately with trans thoracic echocardiography. TEE is also helpful in per operative assessment of mitral valve repair.
Cardiac Catheterization
Routine cardiac catheterization is not necessary in patients with mitral regurgitation. It may be done when there is discrepancy between clinical findings and non invasive tests or preoperatively to do coronary angiography before mitral valve replacement in a patient in whom associated coronary artery disease is a possibility. Pressure tracings may show a prominent ‘v’ wave in pulmonary capillary wedge tracings but this in neither a sensitive nor specific finding even in a patient with severe mitral regurgitation as height of ‘v’ wave depends upon left atrial compliance.Exercise hemodynamics may provide additional information. Left ventricular angiography may give a qualitative assessment of mitral regurgitation but this is not an objective method.Quantification of mitral regurgitation has been attempted by measuring forward cardiac output by Fick’s method and stroke volume by left ventricular angiogram, but this is highly erroneous.
However, left ventricular angiogram gives information about left ventricular size, function,severity of mitral regurgitation and regional wall motion abnormalities.
Management Medical Management
Vasodilator therapy to reduce afterload may be beneficial in patients with chronic mitral regurgitation, but there is no evidence to suggest the same in an asymptomatic patient. In a symptomatic patient with primary mitral regurgitation, surgery should be done. Vasodilators should be used in a symptomatic patient with primary or secondary mitral regurgitation not undergoing surgery. Beta blockers, digoxine, calcium channel blockers and even amiodarone may have to be used for rate control in a patient with atrial fibrillation. Diuretics need to be given as required. Oral anticoagulants are indicated in a patient with atrial fibrillation to prevent embolic episodes though the rate of embolic episodes is low and INR in the range of 2.0–2.5 may be sufficient.
Serial Follow Up
Serial follow up will help to identify patients who develop symptoms and left ventricular dysfunction. It is important to identify early signs of left ventricular dysfunction since left ventricular dysfunction may precede symptoms and post-operative outcome depends upon the left ventricular size and function. Patients with mild mitral regurgitation with no left ventricular dilatation need to be followed once in a year. Annual echocardiograms are not indicated unless they develop new symptoms. Patients with moderate mitral regurgitation need annual evaluation including echocardiography. Patients with severe mitral regurgitation should be followed up once in six months to assess symptoms and left ventricular size and function. Even in an asymptomatic patient left ventricular end systolic dimension more than 45 mm and left ventricular ejection fraction less than 60 per cent are indications for mitral valve repair or replacement. When history is not obvious, exercise testing may be done to assess functional capacity objectively.
Indications for Surgery
Surgery is indicated in all symptomatic patients (class II and above) with severe mitral regurgitation and normal or decreased left ventricular function. Surgery is also indicated in an asymptomatic patient with left ventricular ejection fraction less than 60 per cent and or left ventricular end systolic dimension more than 45 mm. In patients with severe mitral regurgitation, even when the patient is asymptomatic, one should not allow left ventricular ejection fraction to fall less then 55 per cent as post operative recovery will not be good. Though left ventricular ejection fraction is a better index to follow than left ventricular end systolic dimension, surgery may be considered even if one of the parameters is satisfied. When left ventricular ejection fraction is less than 30 per cent or end systolic dimension more than 55 mm, mitral valve surgery carries high risk and may not be beneficial. Surgery is indicated in symptomatic or asymptomatic patient with recent onset severe mitral regurgitation and also in patients with atrial fibrillation.With onset of atrial fibrillation patients tend to become symptomatic and left ventricular dysfunction sets in. Atrial fibrillation tends to persistent even after mitral valve surgery if its duration is more than three months. Similarly asymptomatic severe mitral regurgitation patients with pulmonary artery systolic pressure of equal to or more than 50 mm Hg. at rest or equal to or more than 60 mm Hg. with exercise are also candidates for mitral valve surgery. The outcome in patients with ischaemic mitral regurgitation is worse than those with non ischaemic etiology as they have underlying left ventricular dysfunction. In patients with papillary muscle dysfunction due to reversible ischaemia, simple revascularization may be sufficient. Many patients with severe ischaemic mitral regurgitation need mitral valve replacement or repair.
Types of Surgery
Mitral valve repair, mitral valve replacement with preservation of part of or all of the valve apparatus and mitral valve replacement with removal of mitral valve apparatus are three different surgeries that can be performed. When the valve is suitable and surgical expertise is availablemitral valve repair should be the treatment of choice since it avoids the need for chronic anticoagulation, late prosthetic valve failure and preserves post operative left ventricular function.
Preservation of mitral valve apparatus is essential to maintain normal shape, volume and function of mitral valve and it should be preserved as far as possible. Valve or annular calcification,rheumatic and ischaemic involvement, anterior leaflet involvement decrease the chances of repair. Mitral regurgitation due to uncalcified posterior leaflet prolapse due to degenerated mitral leaflets or ruptured chordae tendineae is often repairable. Mitral valve repair rather than mitral valve replacement should be considered seriously in patients with severe left ventricular dysfunction and in asymptomatic patients with good left ventricular function. In the former because any replacement rather then repair will only worsen the dysfunction while in the latter replacement will mandate chronic anticoagulation in otherwise asymptomatic patient.
Natural History
Patients with mild mitral regurgitation and normal left ventricular size and function do well long term, However, those with severe mitral regurgitation with or without left ventricular dysfunction do not de well and their 10 year survival is less than expected to a tune of 50 – 60 per cent in different series. Higher NYHA class, low LVEF, presence of pulmonary hypertension and AF are adverse prognostic factors. Patients who undergo surgery do better and those who undergo surgery at lower NYHA class and those with preserved left ventricular function do better post operatively.
Acute Severe Mitral Regurgitation
Acute severe mitral regurgitation is a medical emergency. Patient presents with breathlessness and low output state. He may be is shock with extreme dyspnoea. There may be features of background disease that led to mitral regurgitation like coronary artery disease usually an inferior wall myocardial infarction, infective endocarditis, or mitral valve prolapse with chordal rupture.
In the absence of time for compensatory left ventricular and left atrial dilatation patient will have an acute decrease in forward output and acute increase in pulmonary wedge pressures leading to pulmonary edema. There will be tachycardia, tachypnoea and extremities may be cold with signs of left ventricular failure. One should not be looking for signs of chronic mitral regurgitation.
Cardiomegaly is absent and systolic murmur is often short and may even be inaudible. An S3 and often an S4 are audible. Echocardiography is diagnostic and trans thoracic echo may not completely reveal the extent of mitral regurgitation. Trans esophageal echocardiography is required. This will not only show the severity of mitral regurgitation but also uncover the pathology and anatomy of the mitral valve. This is essential to plan type of surgery. Surgery is often mandatory. Medical management includes use of nitroprusside alone or with inotropic agents like dobutamine. Intra aortic balloon pump preeminently decreases the afterload and improves forward output as well as degree of mitral regurgitation. Whenever possible this should be used prior to planned surgery.
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