Mitral valve regurgitation, also known as mitral valve insufficiency or mitral valve incompetence, is a valvulopathy that describes leaking of the mitral valve during systole that causes blood to flow in the reverse direction from the left ventricle into the left atrium.
According to one study of the United States of America, mitral regurgitation affects approximately 2% of all adults 1. Furthermore, the prevalence of mitral regurgitation increases with age 1.
Presentation is dependent on whether the mitral valve disease represents acute or chronic regurgitation 1,2.
Acute mitral regurgitation
Acute mitral regurgitation presents with signs and symptoms of acutely decompensated congestive heart failure 1,2. Depending on the severity of the regurgitation, there may be a progression into cardiogenic shock 1,2.
Chronic mitral regurgitation
In chronic mitral regurgitation, there may be relative compensation with limited signs and symptoms 1,2. However, these patients tend to be very sensitive to small changes in intravascular volume and prone to cardiac failure 1,2.
Clinical examination classically reveals a volume loaded (‘thrusting’) apex beat and a pansystolic (holosystolic) murmur that is heard on praecordial auscultation 1,2. The murmur may radiate to the left axilla in posterior leaflet disease or to the back in anterior leaflet disease 1,2.
Patients with chronic mitral regurgitation, in the initial stages of the disease, compensate with more complete left ventricular emptying, resulting in a supraphysiological ejection fraction 1,2. In order to maintain sufficient forward cardiac output, this compensatory mechanism is met with an increased diastolic volume 1,2. This, over time, results in increased compliance of the walls of the left atrium and ventricle as they respond to volume overload in both chambers 1,2. In particular, left atrial enlargement can be responsible for the development of arrhythmias and symptoms of atrial mass-effect on adjacent structures 1,2.
Eventually, this mechanism fails, and the left ventricle can not compensate for the volume overload 1,2. This causes the stroke volume to decrease and the cardiac output to decrease 1,2. This volume overload eventually causes a drop in forward flow 1,2. This results in an increased end-systolic volume and pressure, causing pulmonary venous hypertension and heart failure 1,2. It is at this point where the ejection fraction may fall, signifying severe mitral regurgitation 1,2.
In contrast, in acute mitral regurgitation, sudden regurgitant volume enters into a relatively normal left atrium that does not have years to develop the compliance seen in chronic mitral regurgitation 1,2. This results in a sudden increase in left atrial pressure and pulmonary venous pressures 1,2. Thus, acute pulmonary edema is a common manifestation in acute mitral regurgitation. Interestingly, because the reflux of blood through the mitral valve in acute mitral regurgitation preferentially moves rightwards posterosuperiorly, the pulmonary edema is often most noticeable in the upper and middle lobes of the right lung 3.
Mitral regurgitation can be caused by damage to any of the mitral valve leaﬂets, the annulus, the chordae tendineae, the papillary muscles, and the subjacent myocardium 2. Thus, the causes of mitral regurgitation are protean, and, as such, there is no single group of patients who are affected 1,2.
Mitral regurgitation can be divided into acute and chronic forms, which have differing etiologies and imaging features 1,2. Furthermore, causes and mechanisms can be divided into primary causes (i.e. degenerative) or secondary causes (i.e. functional) 1,2.
Causes and mechanisms include 1,2:
- acute mitral regurgitation
myocardial infarction with a papillary muscle rupture
- the anterolateral papillary muscle is supplied by both the left anterior descending artery (via a diagonal branch) and left circumflex artery (via an obtuse branch), while the posteromedial papillary muscle is only supplied by the posterior descending artery (which originates from the right coronary artery in most cases), hence most acute mitral regurgitation in myocardial infarcts occur due to posteromedial papillary muscle rupture in inferior myocardial infarcts
- infective endocarditis
- chordae tendinae rupture seen in myxomatous degeneration (e.g. due to mitral valve prolapse, Marfan syndrome, Ehlers-Danlos syndrome, etc.)
- prosthetic mitral valve dysfunction
- myocardial infarction with a papillary muscle rupture
- chronic mitral regurgitation
- annular calcification
- myxomatous degeneration (same underlying causes as in acute mitral regurgitation)
- previous infective/inflammatory illness
- congenital valvular malformation (e.g. parachute mitral valve in the Shone complex)
- dilated cardiomyopathy
- hypertrophic obstructive cardiomyopathy
Typical chest radiographic features of chronic mitral regurgitation include 4,5:
left atrial enlargement
- convexity or straightening of the left atrial appendage just below the main pulmonary artery (along left heart border)
- double density sign: the right side of the enlarged left atrium pushes into the adjacent lung and creates an addition contour superimposed over the right heart
- elevation of the left main bronchus and splaying of the carina
- walking man sign on lateral projections
- upper zone venous enlargement due to pulmonary venous hypertension
- left ventricular enlargement is also eventually present due to volume overload
- features of congestive heart failure may also be present
In acute mitral regurgitation, pulmonary edema is often seen 3-5. Occasionally, it may be unilateral pulmonary edema, sometimes localized to the right upper lobe 3. In acute mitral regurgitation, radiographic signs of left atrial enlargement are often absent 5.
Echocardiography is useful for evaluating the cause of mitral regurgitation, for assessing the regurgitant volume, and for assessing the left ventricle 6. Various parameters are used in order to determine severity, such as 6:
- the central jet has a width <20% of the left atrial area, or <4 cm2
- vena contracta <0.3 cm
- no or minimal flow convergence
- regurgitant volume <30 mL per beat
- regurgitant fraction <30%
- effective regurgitant orifice area <0.20 cm2
- measurements are worse than mild mitral regurgitation but do not meet criteria for severe mitral regurgitation
- the central jet has a width >40% of the left atrial area and vena contracta ≥0.7 cm
- large flow convergence
- systolic reversal in pulmonary veins
- regurgitant volume ≥60 mL per beat
- regurgitant fraction ≥50%
- effective regurgitant orifice area ≥0.40 cm2
Cross-sectional imaging is rarely used to evaluate mitral regurgitation, however, demonstrates the same radiographic features appreciated on plain film and echocardiography, but in greater detail 1,7.
In particular, cardiac MRI (CMR) may be particularly useful for accurate measurements pertaining to the valve, regurgitant volume, and underlying etiology 1,7.
Regurgitant volumes of the mitral valve can be obtained by subtracting the antegrade flow volume across the aortic valve from either the volumetric measured left ventricular stroke volume, the diastolic inflow across the mitral valve or the difference between left and right ventricular stroke volumes obtained from volumetric cine images.
One study suggested the following threshold for cardiac MRI as a risk for progression to symptomatic mitral regurgitation and other indications for mitral valve replacement 11,12:
- regurgitant volume > 55 mL/beat
- regurgitant fraction > 40%
Treatment and prognosis
Treatment depends on whether the mitral regurgitation is acute or chronic.
Acute mitral regurgitation
If mitral regurgitation is acute and secondary to papillary rupture, the treatment of choice is mitral valve replacement 8. If there is concurrent hypotension (i.e. cardiogenic shock), an aortic-balloon pump can be used to increase organ perfusion and decrease the degree of mitral regurgitation 8. In normotensive patients, vasodilators help to decrease afterload 8.
Chronic mitral regurgitation
In chronic mitral regurgitation, vasodilators are used to decrease afterload, e.g. ACE inhibitors 8-10. Hypertension is aggressively treated, antiarrhythmics are given where necessary and if there is concomitant mitral valve prolapse or atrial fibrillation, chronic anticoagulation is initiated 8-10.
- congestive heart failure
- pulmonary hypertension
- mass-effect from left atrial enlargement (e.g. Ortner syndrome, dysphagia megalatriensis)
- atrial fibrillation
- sudden cardiac death from other arrhythmias
- tricuspid regurgitation
The main radiographic differential is that of mitral stenosis which also leads to enlargement of the left atrium. Unlike mitral regurgitation, mitral stenosis does not have left ventricular enlargement and usually has less striking enlargement of the left atrium 2.
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