Heart valves permit forward flow of blood through the cardiac chambers when open and prevent backward leakage when closed. Mitral regurgitation is characterized by abnormal backflow of blood through the mitral valve during the systolic period of the cardiac cycle. The left ventricle (LV) must pump additional volume to compensate for the amount regurgitated. As mitral regurgitation becomes severe, the continued hemodynamic burden may lead to ventricular dysfunction, heart failure, and sudden death.
See the images below depicting mitral regurgitation.
Mitral regurgitation may be acute or chronic. Common causes of severe acute mitral regurgitation include ruptured chordae tendineae, ischemic papillary muscle dysfunction or rupture, and infective endocarditis. Chronic severe mitral regurgitation is commonly caused by myxomatous degeneration of the valve, rheumatic heart disease, or mitral annular calcification.
Echocardiography has emerged as the diagnostic imaging modality of choice. It can provide vivid images of the LV and the mitral valve, and it may provide clues to the mitral-valve abnormalities responsible for the regurgitation. The Doppler echocardiographic technique is excellent for determining the severity of mitral regurgitation.
Acute mitral regurgitation often requires prompt surgical correction. However, symptomatic patients with chronic mitral regurgitation may be initially treated with digitalis, afterload reduction, and diuretics. After the LV function begins to deteriorate, clinical and echocardiographic parameters may be used to determine the timing for surgical reconstruction or replacement of the mitral valve. [1, 2, 3]
The electrocardiogram (ECG) may exhibit an LA abnormality, LVH, and, in some patients, atrial fibrillation. ECG evidence of LV enlargement occurs in about one third of patients with severe mitral regurgitation. In approximately 15% of patients, the ECG shows evidence of RV hypertrophy.
Although the heart may not be enlarged in patients with acute mitral regurgitation, severe pulmonary edema is frequently present as a result of left-sided cardiac failure. In cases involving chronic mitral regurgitation, the LA and the LV border appears enlarged, and it may be massive because of volume overload and increased pressure. When the LA is enlarged, it may extend toward the right side, and it may appear as a double shadow along the right atrial border. Coexistent pulmonary arterial hypertension or tricuspid regurgitation may cause dilation of the right atrium and ventricle, as well as enlargement of the pulmonary arteries.
Echocardiography is the preferred examination. It demonstrates the extent of LA and LV enlargement, as well as the presence and severity of mitral regurgitation. Two-dimensional (2D) echocardiography or transesophageal echocardiography (TEE) with Doppler echocardiography and color flow Doppler imaging enables detailed assessment of the structure and function of the mitral valve. [4, 5, 6, 7, 8, 9, 10, 11]
In the past, the use of echocardiography resulted in overestimations of the prevalence of MVP. Early studies suggested a prevalence of as high as 21% in healthy young women. In early studies, normal bowing of the mitral valve was interpreted as representing an MVP.
Magnetic resonance imaging
MRI can demonstrate the abnormality of the valve apparatus, and it may be useful in evaluating the amount of regurgitant flow with velocity encoding (VENC) and with model-independent measurements of stroke volumes of RV and LV. [12, 6]
Cardiac catheterization is often needed. In patients older than 40 years or in those with symptoms suggestive of coronary disease, cardiac catheterization should include coronary arteriography. The main indications for catheterization include (1) the need to evaluate a discrepancy between echocardiographic findings and the clinical presentation, (2) the need to detect other associated valvular lesions and to assess the severity of those lesions, and (3) the need to determine whether coronary artery disease is present and, if so, to assess the extent of disease.
Limitations of techniques
The limitations are minimal. Color-flow Doppler echocardiography of the valve helps in determining the severity of regurgitation, but because this technique measures flow velocity rather than actual flow, it is subject to error in interpretation.
The Doppler technique is good for excluding mitral regurgitation and for differentiating between mild and severe degrees of the condition. However, color-flow Doppler examination may not be sufficient for more exact quantification of mitral regurgitation or for determining whether the lesion is severe enough to cause LV dysfunction.
Chest radiography is useful in evaluating mitral regurgitation in several ways, but it mostly reveals nonspecific findings.
The chest radiograph usually shows an enlarged cardiac silhouette. The heart is increased in size secondary to enlargement of both the LA and the LV. The absence of cardiomegaly indicates that the mitral regurgitation is either mild or acute.
The enlarged atrial appendage may be seen along the middle portion of the left cardiac border. Also, a double shadow may be present on the right cardiac border, indicating an increase in the size of the LA.
In patients with combined mitral stenosis and mitral regurgitation, overall cardiac enlargement and particularly LA dilatation are prominent findings. Relatively mild cardiomegaly and clinically significant changes in the lung fields suggest predominant mitral stenosis. In comparison, predominant mitral regurgitation is most likely when the heart is greatly enlarged and when the changes in the lungs are relatively inconspicuous.
Calcification of the mitral annulus, an important cause of mitral regurgitation in the elderly, is most prominent in the posterior third of the cardiac silhouette. The lesion is best visualized on chest radiographs in the lateral or right anterior oblique projections, on which it appears as a dense, coarse, C -shaped opacity.
Pulmonary interstitial edema with Kerley B lines is usually seen in patients with progressive LV failure and chronic mitral regurgitation.
In acute mitral regurgitation, the chest radiograph reveals pulmonary edema, moderate or no enlargement of the LA, and little if any cardiac enlargement.
CT can show the cardiac silhouette and chamber sizes with clarity. However, because of the widespread use of echocardiography, CT is rarely performed in the evaluation of mitral regurgitation. The degree of confidence is moderate in mitral regurgitation. False findings are rare in mitral regurgitation.
Magnetic Resonance Imaging
Accurate measurement of the degree of mitral regurgitation is critical. Doppler echocardiography provides an estimate of the area and depth of the regurgitant jet, but the finding is only semiquantitative. A direct quantitative, noninvasive measurement of the mitral regurgitant volume can be precisely determined by using MRI. [8, 11]
Spin-echo (SE) images show structural consequences of mitral regurgitation, such as an enlarged LV and LA.
Cine gradient-echo MRI
Cine gradient-echo (GRE) images may be used to assess the severity of mitral regurgitation by calculating the regurgitant fraction. The procedure involves mapping the area of the signal void starting from the mitral valve and extending into the LA. The signal void of mitral regurgitation is best seen on the 4-chamber and the coronal oblique views.
Another way to calculate regurgitant fraction involves estimation of the ventricular volumes. This method is usable only if the mitral valve is the sole regurgitant valve.
VENC (encoding velocity) MRI is another method for determining the severity of mitral regurgitation. In this method, the diastolic inflow across the mitral annulus is compared with systolic outflow across the ascending aorta. In cases of mitral regurgitation, the LV inflow is increased. As an alternative, regurgitant volume may be determined by measuring flows in the ascending aorta and pulmonary artery. In fact, the best way to quantify the mitral regurgitant volume is to combine the ventricular volume calculations obtained by using cine GRE sequences with the estimated forward flow in aorta obtained with VENC MRI.
Degree of confidence
The degree of confidence is high. MRI is the most accurate technique for measuring regurgitant flow, and it provides measurements that are well correlated with those of quantitative Doppler imaging. MRI is also the most accurate noninvasive technique that enables the measurement of ventricular EDV, ESV, and mass.
Errors may occur when cine GRE imaging is used to measure the area of the mitral annulus and the mitral flow velocity, owing to the constant motion of the atrioventricular valves during each cardiac cycle.
In patients with severe mitral regurgitation, 2D echocardiography shows enlargement of the LA and LV. The cause of mitral regurgitation may often be apparent on the transthoracic echocardiogram. Potential causes include rupture of the chordae tendineae; MVP; a flail leaflet; vegetations; and LV dilatation. Calcification of the mitral annulus, which appears as a band of dense echoes, may be seen between the mitral valve and the posterior wall of the heart.
Three-dimensional (3D) transthoracic echocardiography (TTE) and 3D color Doppler imaging may be helpful in elucidating the mechanism of mitral regurgitation. The imaging of the mitral valve is excellent on TEE, and the images offer clues to the mitral valve abnormalities responsible for the regurgitation (see the image below). 
Color-flow Doppler imaging
Color-flow Doppler imaging of the valve helps in semiquantitatively determining the severity of regurgitation (see the images below). This technique measures flow velocity rather than actual flow; therefore, it is sometimes subject to error.
The severity of mitral regurgitation is directly proportional to the size of the regurgitant jet within the left atrium. The size of the jet is typically indexed to the size of the left atrium. Jets that are peripheral impinge on a wall, rather than the center, causing predictable problems with assessment of severity. Owing to the Coanda effect, a regurgitant jet impinging on a wall results in a color-flow area smaller than an equivalent central regurgitant volume. A jet impinging on a wall leads to underestimations of the regurgitant volume by approximately 40%.
In cases of moderate and severe mitral regurgitation, flow in the pulmonary veins may reverse direction in systole. A variation on this finding is attenuation of normal forward flow in the pulmonary vein during ventricular systole. Three-dimensional reconstruction of mitral regurgitation jets has been shown to be feasible. The incremental value of this method has not yet been demonstrated. [13, 14, 15, 16, 17, 18, 19, 8, 10]
In cases of mitral regurgitation, Doppler echocardiography characteristically reveals a high-velocity jet in the LA during systole. The severity of the regurgitation is a function of the distance from the valve at which the jet can be detected and the size of the LA.
In estimating the severity of mitral regurgitation, both color-flow Doppler and pulsed Doppler results are used. Color Doppler imaging involves measurement of the area of the mitral jet. If the area of the jet is greater than 8 cm2, the mitral regurgitation is considered severe. Findings that indicate that mitral regurgitation is severe include reversal of flow in the pulmonary veins during systole and a high peak mitral inflow velocity. 
TEE is better than TTE in imaging the regurgitant mitral valve. Angiographic assessments of mitral regurgitation are well correlated with the color-flow mapping obtained by using TEE rather than TTE.
Mitral valve prolapse
Echocardiography is useful in diagnosing MVP, in determining the severity of associated mitral regurgitation, and in showing the pathologic anatomy of the mitral valve. An extreme form of MVP involves myxomatous degeneration of the valves with leaflet thickening (>3-5 mm), marked symmetrical bowing of the valve behind the annular plane, and/or highly asymmetrical buckling of 1 or both leaflets into the LA associated with mitral regurgitation. Because of the eccentric leaflet buckling, the mitral regurgitation jet may be eccentric rather than central.
Acute mitral regurgitation after acute myocardial infarction
Two complications of myocardial infarction that produce confusing clinical signs are mitral insufficiency caused by rupture of an infarcted papillary muscle and a ventricular septal defect that occurs after infarction and necrosis of the septum. These are easily identified by noting the intracardiac flow patterns seen on cine GRE images.
Degree of confidence
The degree of confidence is high in mitral regurgitation. False findings are rare. Color-flow Doppler examination may not be sufficient for exactly quantifying mitral regurgitation or for determining whether the severity of the lesion is sufficient to cause eventual LV dysfunction.
Radionuclide angiography may be useful in assessing mitral regurgitation, and gated blood-pool nuclear imaging or first-pass angiography may reveal an increased EDV.
The regurgitant fraction may be estimated from the ratio of LV stroke volume to RV stroke volume. In patients with mitral regurgitation and impaired LV function, the ejection fraction fails to rise normally during exercise.
Radionuclide angiograms are useful for interval follow-up, and progressive increases in ventricular EDV and/or ESV often suggest that surgical treatment is necessary.
Radionuclide angiography is good for assessing LV function. False findings are unusual in mitral regurgitation.
LV angiography may be performed to evaluate mitral regurgitation.
The immediate appearance of contrast material in the LA after its injection into the LV indicates mitral regurgitation. The regurgitant volume may be determined from the difference between the total LV stroke volume, which is estimated by using angiocardiography, and the simultaneous measurement of the effective forward stroke volume, which is determined by using the Fick method.
In patients with severe mitral regurgitation, the regurgitant volume may approach the effective forward stroke volume; in rare instances, it may even exceed this volume. Qualitative but clinically useful estimates of the severity of mitral regurgitation may be made by means of cineangiographic observation of the degree of opacification of the LA and the pulmonary veins after the injection of contrast material into the LV (see the image below).
The cause of the regurgitation (eg, MVP) and a flail leaflet may often be distinguished by using angiography. Mitral regurgitation secondary to rheumatic heart disease is angiographically characterized by a central regurgitant jet and by thickened leaflets that have reduced motion. In regurgitation resulting from other conditions, particularly dilatation or calcification of the mitral annulus or ruptured chordae tendineae and papillary muscles, the systolic jet may be eccentric; in such cases, the valves consist of thin filaments that display excessive motion.
Degree of confidence
The degree of confidence in mitral regurgitation is excellent. False findings are rare in mitral regurgitation.