INTRODUCTION — The mitral valve was the first structure to be identified by echocardiography (figure 1) [1,2]. Technical advances have enabled echocardiography to identify almost any anatomic or functional abnormality of the mitral valve. The appearance of the normal mitral valve and the more commonly encountered mitral valvular abnormalities will be reviewed here.
NORMAL MITRAL VALVE — A standard transthoracic echocardiographic (TTE) examination of the mitral valve consists of an M-mode tracing, multiple 2D views, and Doppler flow evaluation. If clinically indicated (eg, technically difficult TTE or evaluation of prosthetic paravalvular leak), a transesophageal echocardiogram (TEE) may be performed. Together, these elements form an integrated examination of the mitral valve that can reliably define its function and evaluate the severity of abnormalities [3].
Anatomically, the orientation of the anterior leaflet of the mitral valve places this broad surface toward the anterior chest wall, making it an ideal sound reflecting target. Furthermore, because of its relatively large margin-to-base ratio, the anterior leaflet is highly mobile (figure 2).
The mitral valve can be recorded by ultrasound through a variety of anatomic windows in the precordium, apical, and subxiphoid regions, all of which should be used in its examination.
M-mode echocardiogram — The M-mode examination is performed from the precordium and guided from the 2D long and short axis views. Normally, the anterior mitral leaflet exhibits a motion pattern that reflects the phasic nature of ventricular filling and produces a familiar M-shaped pattern (figure 3). The posterior leaflet moves in a nearly mirror image "W" pattern with a smaller excursion.
●The initial large opening diastolic movement of the valve, which culminates in the E-point, is the result of rapid left ventricular (LV) filling.
●The valve assumes a nearly closed position during the middle of diastole (F point), reflecting the deceleration of inflow as the pressure gradient between atrium and ventricle is reduced. On the M-mode echocardiogram, this mid-diastolic closure is measured as the E-F slope, which is usually >60 mm/sec.
During this mid-diastolic phase, in spite of the appearance of closure, there continues to be flow of blood from pulmonary veins to the LV. This period of filling is known as the conduit phase because the atrium briefly functions as a passive channel rather than a reservoir [4].
●Following atrial contraction, the valve opens for a second time (A point), completing the second peak of the letter M.
●Final closure is probably the combined effect of deceleration of atrial inflow and isometric LV contraction.
Two-dimensional echocardiogram — The 2D appearance of the normal mitral valve on TTE depends somewhat upon the imaging plane from which it is viewed. In the parasternal short axis plane, the valve presents itself as an ovoid (fish mouth) orifice (image 1), while in parasternal long axis and apical views, it resembles clapping hands, with the anterior hand longer and more mobile than the posterior (image 2A-B). In general, the normal mitral valve should appear as a mobile, two leaflet structure that moves freely enough to respond to the normal flux of diastolic filling but forms a stable coaptation plane in systole without breaking the plane defined by the mitral annulus and entering the body of the left atrium.
Anatomically, the mitral valve leaflets are thin and translucent; the rough attachment points of its chordae to their free margins are thicker than their smooth bellies. The chordae from each leaflet connect to both papillary muscles. On M-mode, each leaflet is represented by no more than two linear echoes. On 2D imaging, the valve appears homogeneous and thin, <4 mm in thickness. However, the perception of leaflet thickness also depends upon the transducer frequency.
Many sonographers prefer 2.5 mHz for imaging because it allows adequate images in difficult patients and is superior for Doppler flow. At this lower frequency, some normal valves can appear mildly thickened. For this reason, if an abnormality is suspected, the valve should be imaged with a higher frequency before being designated as "thickened." In order to exclude valve pathology, fundamental (non-harmonic) imaging at 3.5 mHz or higher should be used. As a general rule, when imaged fundamentally, a normal mitral valve is thinner than a normal aortic root imaged under the same conditions.
Other anatomic features of the mitral apparatus that are appreciated on 2D echocardiographic examination include the papillary muscles, chordae, and the mitral annulus.
●The papillary muscles can be seen in the parasternal short axis at approximately four o'clock (anterolateral) and eight o'clock (posteromedial) orientations, and their fine anatomy is highly variable.
●The mitral annulus is receiving increasing attention because three-dimensional (3D) imaging has revealed it to be highly dynamic [5]. On 2D imaging, the examination is limited to measuring the diameter of the mitral annulus and inspecting it for calcification (image 3 and image 4 and waveform 1).
Mitral leaflet anatomy can be identified by location on standard imaging views. In the parasternal long axis, the A2 and P2 segments are visualized. A1 and P1 segments are adjacent to the left atrial appendage, which is seen on the right side of the image in the standard parasternal short-axis view (with the near field at the top of the image). In the two-chamber view, segments P1, A2, and P3 are visualized from right to left in the transthoracic image, with P1 adjacent to the anterior annulus. By TEE in the zero-degree plane, A1 and P1 are seen first as the probe is advanced; with deeper insertion, A2 and P2 come into view, and subsequently A3 and P3 are visualized.
Doppler echocardiogram — Doppler examination of the normal mitral valve reveals that the velocity pattern of blood entering the LV during diastole closely resembles the M-shaped pattern of the M-mode of that structure; blood flow is most rapid during the early (E) phases of filling, falls to very low levels during the mid-diastolic conduit phase, and accelerates again during atrial (A) contraction. Transmitral flow is sampled from the apical four chamber view; the sampling site used to obtain this signal is the space between the tips of the open mitral valve (waveform 2). When transmitral flow is used to quantitate flow volume, the sample volume is placed in the mitral annulus. The normal peak flow velocity across the mitral valve is usually just under 1 m/sec and the normal mitral valve area is 4 to 6 cm2.
Many measurements are derived from the transmitral wave form. The most reliable and relevant measurements are the ratio of the E to A waves, the isovolemic relaxation time, and the deceleration time. These values give insight into diastolic function and into the function of the valve.
Three-dimensional echocardiogram — Three-dimensional echocardiography has improved the understanding of the anatomy and function of the hyperbolic paraboloid mitral valve. Three-dimensional TTE image acquisition is performed from the parasternal and apical views, using zoomed or full-volume feature. Changing the display enables visualization of the mitral valve from either the LV or the left atrium ("surgical") perspective and allows for precise lesion localization. Additionally, 3D echocardiography allows for accurate LV measurements as it avoids LV foreshortening [6]. Subvalvular apparatus can be seen from the LV perspective (movie 1) [7]. Three-dimensional TEE has superior resolution compared with 3D TTE and is a critical aid in percutaneous mitral valve repair [8].
Role of cardiac magnetic resonance in mitral regurgitation — Cardiac magnetic resonance (CMR) can be clinically useful in the assessment of mitral regurgitation, including identifying the mechanism of mitral regurgitation, quantifying its severity, and determining its cardiac consequences including LV and left atrial volumes. Several studies have compared CMR with TTE in the assessment of mitral regurgitation and have found a role for CMR [9,10]. However, CMR and echocardiographic findings can be discordant, and an integrated approach should be used with caution. In instances where CMR and echocardiographic findings are discrepant, careful history and auscultation may be helpful [11].
MITRAL VALVE LESIONS CAUSING INFLOW OBSTRUCTION — The most common lesion of the mitral valve that causes inflow obstruction is mitral stenosis, which is usually acquired as the result of rheumatic heart disease. Less common causes include left atrial myxoma and other tumors, severe mitral annular calcification, left-sided carcinoid heart disease, and congenital disorders. (See "Clinical manifestations and diagnosis of rheumatic mitral stenosis" and "Carcinoid heart disease".)
Mitral stenosis — In mitral stenosis, the normal, rapid, biphasic motion of the valve is altered because the valve opens only partly and as a single unit. Anatomically, the commissural separation between the anterior and posterior or mural leaflets is diminished by partial fusion and the subvalvular apparatus is altered by chordal foreshortening. Immobility of the posterior leaflet is a common early finding with a "hockey stick/knee bend" appearance to the anterior mitral leaflet due to leaflet tethering. Doming of the anterior leaflet corresponds temporally to the opening snap on auscultation.
These changes cause a limiting orifice that obstructs diastolic transit of blood from atrium to ventricle. One hemodynamic consequence of this alteration is a holodiastolic pressure gradient between the left atrium and left ventricle (LV).
Transthoracic echocardiography (TTE) can identify the pathologic entity of mitral stenosis and quantitate its severity with sufficient accuracy to make reliable decisions about the suitability for catheter-based balloon valvotomy or the need for surgery. Quantitation of mitral stenosis severity can be accomplished by direct methods and its qualitative estimation by a number of indirect observations.
The 2014 American Heart Association/American College of Cardiology (AHA/ACC) guideline for valvular heart disease gave a Class I recommendation for the use of TTE in diagnosing the presence and evaluating the severity of mitral stenosis [12].
M-mode echocardiography — M-mode confirmation of the altered pattern of mitral motion in mitral stenosis remains a useful tool. Mitral stenosis alters the appearance of the M-mode tracing of the mitral valve so that its normal early diastolic closure is delayed or abolished. The early diastolic closure slope, the E-F slope, produces an easily recognized pattern and can also be quantitated to separate normal atrial inflow from obstructed and to differentiate among the degrees of obstruction (figure 4A-C and movie 2). Although this method is the least reliable means of quantitating the severity of obstruction, a slope of less than 10 mm/sec (normal is >60 mm/sec) from a valve recording made during suspended respiration is evidence for severe mitral stenosis [13]. In normal valves, the posterior leaflet moves in a mirror image pattern to the anterior; in mitral stenosis, the posterior leaflet moves forward in diastole, paralleling the anterior. Reversal of diastolic motion from the normal pattern makes the M-mode of the posterior leaflet one of the most valuable means of identifying mitral stenosis.
The opening snap (OS) of the mitral valve coincides with the initial peak opening (E) of the valve (picture 1).
Two-dimensional TTE — Mitral stenosis alters the appearance of the valve on 2D echocardiography because it partially fuses the normally independent leaflets and creates a persistent gradient between the LV and left atrium. This gradient keeps the stenotic diastolic orifice opened to its maximum and causes the entire valve to dome or bulge into the ventricle throughout diastole (image 5 and movie 3 and movie 4 and movie 5). The elevated gradient initiates the opening motion in an abrupt manner, generating the opening snap and a characteristic "knee bend" appearance on the precordial long axis view (image 6 and movie 6).
In the parasternal short axis plane, the opening of the valve can be imaged just above the tips of the papillary muscles. From this orientation, its maximum diastolic opening area can be measured by direct planimetry of the 2D image. This method is a reliable means of judging the severity of obstruction [13,14]. A mitral valve area (MVA) of less than 1.0 cm2 is considered severe, regardless of the method used to calculate its size.
Other features of mitral stenosis on the 2D echocardiogram include chordal foreshortening and atrial thrombi; the latter are rarely seen in echocardiograms taken from the precordial windows.
Doppler echocardiography — Doppler methods provide a constellation of measurements by which the severity of mitral stenosis is gauged. These variables include the gradient across the valve at rest and with exercise, the inferred area by the pressure half-time method, the continuity equation or the proximal flow convergence method, and the pulmonary pressure at rest and during exercise from the tricuspid regurgitant jet velocity [15-17].
Doppler methods can measure the velocity of mitral inflow. In mitral stenosis, this velocity increases at rest from a normal value of less than 1 m/sec to greater than 1.5 m/sec. The algorithm to convert Doppler velocity into pressure gradient is the modified Bernoulli equation. The peak gradient between two reservoirs connected by a narrow orifice or pipe (in this case the LV and the left atrium connected by the stenotic mitral valve) can be calculated by the modified Bernoulli formula, taking the square of the peak velocity of fluid flowing between them (in this case, blood) and multiplying by four (movie 7 and movie 8 and waveform 3).
Peak gradient, in mmHg = 4 x peak velocity(2)
Thus, a peak velocity of 1 m/sec indicates a peak gradient of 4 mmHg; a peak velocity of 2 m/sec indicates a peak gradient of 16 mmHg; 3 m/sec indicates a peak gradient of 36 mmHg.
The mean transmitral gradient can be measured by tracing the area-under-the-curve of the mitral E and A waves obtained by continuous wave Doppler. With severe mitral stenosis, the mean transmitral gradient is >10 mmHg in sinus rhythm at heart rates between 60 and 80 bpm [18].
The most frequently used measurement for the determination of the mitral valve area is the pressure half-time, which is derived from hemodynamic data (figure 5A-B). The pressure half-time is the time required for the gradient between the left atrium and the LV to fall to one-half of its initial value. In order to convert Doppler velocity into a pressure gradient, the initial flow velocity is divided by 1.41 (square root of 2), because velocity bears a second order relationship to pressure. Empirically, a pressure half-time of 220 msec is equivalent to a valve area of 1.0 cm2; therefore:
MVA = 220 ÷ pressure half-time
Calculating the MVA using the pressure half-time may be an inaccurate approach whenever abrupt changes in the transmitral gradient occur for reasons other than inflow obstruction. An example of such a change is additional ventricular filling from aortic regurgitation.
Among the methods for estimating rheumatic mitral stenosis severity, direct planimetry of the orifice is probably the most accurate when performed correctly with good image quality and without severe distortion of valve anatomy [18]. However, in a clinical setting, limitations are frequently present and it is the universal practice to achieve cross validation by applying the full array of methods.
Indirect methods to identify the severity of mitral stenosis include observing the degree of foreshortening of the chordae tendineae, estimating the extent of leaflet calcification, noting the degree of left atrial enlargement, noting the degree of LV underloading (ie, volume decrease), noting the presence of right ventricular and atrial dilatation, and noting the degree of tricuspid regurgitation and pulmonary hypertension, as determined by Doppler of tricuspid regurgitant jet.
The 2014 AHA/ACC guideline for valvular heart disease defined severe mitral stenosis as having an MVA ≤1.5 cm2 (MVA ≤1.0 cm2 with very severe MS) and diastolic pressure half-time ≥150 ms (diastolic pressure half-time ≥220 ms with very severe MS), along with severe left atrial enlargement and pulmonary artery systolic pressure >30 mmHg (table 1) [12].
Stress echocardiography — Documentation of elevation of transmitral gradient and pulmonary pressure during exercise is useful in patients whose symptoms do not seem concordant with the degree of mitral stenosis at rest [12]. In patients who cannot exercise, dobutamine has been used to increase heart rate [19]. The 2014 AHA/ACC valve guideline recommended exercise echocardiography in evaluating the severity of mitral stenosis when there is a discrepancy between the resting echocardiographic findings and clinical findings [12]. (See "Overview of stress echocardiography", section on 'Indications'.)
Three-dimensional echocardiography — Three-dimensional echocardiography (echo) has been evaluated for its utility in assessing mitral stenosis [20,21]. This technique can provide an en-face cross sectional view of the mitral orifice, to which planimetry can be applied to determine the MVA. Compared with 2D echocardiography, it performs better when cardiac catheterization derived MVA is used as the reference standard. (See "Three-dimensional echocardiography", section on 'Valvular heart disease'.)
Echocardiography in balloon valvuloplasty — The role of echocardiography in mitral stenosis has become even more demanding with the development of catheter-based palliative interventions. These interventions require a transseptal puncture to deliver a dilating balloon across the obstructed mitral orifice. When successful, these techniques offer dramatic relief of symptoms and may avoid surgery. (See "Percutaneous mitral balloon valvotomy for mitral stenosis".)
The likelihood of success of balloon valvotomy can be judged with TTE by grading the severity of involvement of elements of the mitral valve on scale of 1 through 4, with a score of 1 representing normal [22,23]. The four elements are the mobility of the anterior leaflet, the severity of subvalvular disease, the calcification of the anterior leaflet, and the thickness of the anterior leaflet. The value for each of these four scores is added together for a total "splitability index" of 4 to 16, with a score of 8 or less indicating a higher probability of success.
Other studies have proposed an alternate means of judging suitability for valvotomy by the location and distribution of calcium around the stenotic orifice [24]. Mitral regurgitation is not included in any of these indices, but a degree of mitral regurgitation more than mild is considered a relative contraindication to the procedure. Indeed, severe mitral regurgitation, occurring as a complication of the procedure, often requires urgent valve replacement.
Mitral annular calcification — Mitral annular calcification is a common echocardiographic finding associated with aging, renal failure and other conditions. It is discussed in detail separately. (See "Clinical manifestations and diagnosis of mitral annular calcification".)
Other — Congenital conditions that cause mitral stenosis are rarely encountered in adults. Parachute mitral valve (single papillary muscle), supravalvular mitral ring, and cor triatriatum are congenital conditions that obstruct mitral inflow.
Cor triatriatum — Cor triatriatum is among the rarest of all congenital cardiac anomalies and is often a hemodynamically mild incidental finding. The membrane of cor triatriatum appears as a linear echo bisecting the left atrium, from right to left, into an upper chamber (embryonic common pulmonary vein) containing the pulmonary veins and a lower chamber (embryonic left atrium) leading to the mitral inflow tract. Color flow mapping usually demonstrates mild increases in velocity, suggesting minimal obstruction. This lesion may be resected in childhood, as it may eventually lead to atrial dilation and symptomatic arrhythmia.
Left atrial myxoma — Left atrial myxoma, when mobile, may cause inflow obstruction by interposing its bulk in the mitral orifice (movie 9 and movie 10 and movie 11 and movie 12 and movie 13). When these rare tumors are encountered on 2D imaging, Doppler examination detects the degree of mechanical inflow obstruction. (See "Cardiac tumors" and "Echocardiography in detection of cardiac and aortic sources of systemic embolism".)
Other cardiac tumors — Primary malignant tumors of the heart, such as angiosarcomas and lymphomas, may mechanically deform and obstruct the mitral valve. Advanced lymphoma may engulf much of the mitral apparatus. (See "Cardiac tumors".)
Carcinoid heart disease — Carcinoid heart disease is a rare disease that, in most patients, involves only valves on the right side of the heart. However, left-sided involvement (mitral stenosis) can occur when there are bronchial metastases [25]. (See "Carcinoid heart disease".)
ABNORMALITIES ASSOCIATED WITH MITRAL REGURGITATION — Whereas stenotic lesions alter the diastolic motion pattern of the mitral valve and are readily identifiable by M-mode and 2D imaging, lesions associated with mitral regurgitation are often associated with subtle abnormalities of the valve elements. However, when the valve is obviously disrupted or partially flail, mitral regurgitation is likely to be severe (movie 14 and movie 15 and movie 16 and waveform 4). Competent mitral leaflets typically have a coaptation surface (coaptation length) of 8 to 10 mm (compared with 4 to 9 mm for tricuspid valve) [26]. While 2D transthoracic echocardiography (TTE) is not accurate in measuring coaptation surface, 3D transesophageal echocardiogram (TEE) or cardiac magnetic resonance (CMR) imaging is more reliable [26].
In contrast to anatomic imaging methods, Doppler flow imaging is highly sensitive in detecting mitral regurgitation of all severities and is the most important part of the ultrasound examination for mitral regurgitation. In addition, echocardiographic assessment should include evaluation of regurgitation (particularly when clinically significant) and should include identification of the mechanism and possible etiology, as this affects the severity of regurgitation, cardiac remodeling, and management, as noted in the 2017 American Society of Echocardiography (ASE) guidelines for evaluation of native valvular regurgitation [26]. A precise description of the lesions, using segmental and functional anatomy according to the Carpentier classification [27], should be performed to determine disease severity and assess the feasibility of repair (table 2).
Determination of severity — Over 20 variables for judging the severity of mitral regurgitation have been described [3]. Employing this approach, severe lesions are readily recognized, but distinguishing among the intermediate grades of mitral regurgitation (mild to moderate, moderate to severe mitral regurgitation) is more difficult. To sort out this clinical problem, it is frequently useful to perform supine bicycle exercise to evaluate for an exaggerated rise in pulmonary pressure that typifies the more advanced degrees of mitral regurgitation [28]. Resting pulmonary artery systolic pressure >50 mmHg is a class IIa indication for intervention by both ACC and European Society of Cardiology (ESC) guidelines [29,30]. While exercise-induced increase in pulmonary artery systolic pressure >60 mmHg has been proposed as a criterion for intervention [31], our lab uses >65 mmHg as a cutoff in older patients, as 60 mmHg is often upper limits of normal during exercise.
The 2017 ASE consensus statement on echocardiographic quantification of valvular regurgitation [26], corroborated by the 2017 AHA/ACC valve guideline [29], recommended using multiple parameters when determining the severity of mitral regurgitation (table 2 and table 3). These include structural, qualitative Doppler, and quantitative Doppler parameters. In addition, TTE enables measurement of mitral annular dimensions and identification of calcification. In cases when mitral regurgitation is suspected to be underestimated by echocardiography, CMR may be helpful in determining regurgitation severity [32]. In a study comparing echocardiography and cardiovascular magnetic resonance imaging (CMR) in severe mitral regurgitation, PISA-derived effective regurgitant orifice area, PISA-derived regurgitant volume, LV end-diastolic volume, and the presence of a flail leaflet were the best predictors of CMR-derived regurgitant volume [33].
Structural parameters — Structural abnormalities associated with mitral regurgitation supplement the quantitation of regurgitation and include left atrial size, LV size, and appearance of the mitral apparatus.
●Mild mitral regurgitation is usually associated with normal or near-normal left atrial size, LV size, and intact mitral apparatus.
●Moderate mitral regurgitation is frequently associated with some degree of left atrial enlargement, normal or mildly dilated LV, and varying degrees of mitral apparatus abnormalities.
●Severe chronic mitral regurgitation is usually associated with moderate to severe left atrial enlargement, some degree of LV dilatation, and often associated with flail mitral leaflet, ruptured papillary muscle, or malcoaptation of the mitral leaflets. Ultimately, reduced LV systolic function will occur if severe mitral regurgitation is left untreated. Frequently after mitral valve intervention, LV systolic function will be lower due to removal of a low pressure "pop-off" valve (the left atrium).
Color flow Doppler — The features of severe mitral regurgitation seen by color flow Doppler imaging arise from the high energy transfer of a volume of blood into the left atrium, producing the characteristic "jet" in the left atrium (movie 17 and movie 18 and movie 19 and movie 20 and image 7) [34]. Color flow Doppler is usually considered a qualitative or semi-quantitative parameter.
●In current practice, it is common to judge a small jet occupying less than 20 percent of the left atrial area as mild, a middle-sized jet as moderate, and a large jet (more than 40 percent and extending into the pulmonary veins) as severe mitral regurgitation. However, these jets are very sensitive to instrument settings, and the size of a color jet may be misleading; thus, reliance on these size judgments alone is imprudent [35].
●On the ventricular side of the valve, proximal flow acceleration (proximal isovelocity surface area or PISA) is seen as a concentric series of hemispheric shells of alternating colors, each shell denoting an isovelocity of aliasing [35]. The diameter of the ring closest to the regurgitant orifice is measured and, in severe mitral regurgitation, usually approaches 1 cm. (See 'Quantitative parameters of mitral regurgitation' below.)
●After the color jet crosses the valve defect, the width of the jet increases. In the parasternal long-axis view, the narrowest portion of the regurgitant jet across the valve is defined as the vena contracta. Mild mitral regurgitation is usually associated with a vena contracta less than 0.3 cm, while severe mitral regurgitation is usually associated with a vena contracta of 0.7 cm or more [36,37].
●As the jet of severe mitral regurgitation enters the left atrium, it becomes eccentric and hugs the wall of the chamber (entrainment or Coanda effect). Once entrained on the wall, the jet may completely circle the chamber. The jet also tends to penetrate the atrial appendage and one or more of the pulmonary veins. The color flow pattern in the receiving chamber is agitated and multidirectional, and spontaneous contrast is absent. During most of the jet's passage around the atrium, it is broad and aliased. It must be emphasized that any aliased (mosaic) wall hugging jet, however small in apparent area, should be considered to potentially represent severe mitral regurgitation. Generally, milder degrees of mitral regurgitation are associated with central jets that lose their mosaic pattern before reaching the atrial wall.
●Some researchers have found the jet area in the left atrium on TEE to be a useful guide to mitral regurgitation severity [34]. However, since the entire left atrium cannot be seen at one time, the measurement of total jet size is problematic. Furthermore, careful study of most jets with appropriate frame rates reveals that they are not central jets but entrained wall jets, which do not lend themselves to "jet area measurement." We do not endorse this method.
Pulsed and continuous wave Doppler of mitral inflow — Spectral Doppler (pulsed and continuous wave) recognition of severe mitral regurgitation also has many diagnostic features. In severe mitral regurgitation, the early diastolic mitral inflow pulsed-wave Doppler signal wave (E wave), obtained at the tips of the mitral leaflets, is almost always increased to greater than 1.4 m/sec (figure 6A-B) [38].
In addition to increased peak transmitral inflow E wave velocity, the pattern is strongly E-wave dominant with a small A-wave (E/A ratio greater than 2.0). This pattern is identical to the restrictive inflow pattern and has a similar origin, in that filling pressures may be elevated in both situations. Finding an A-wave dominant pattern of mitral inflow makes severe mitral regurgitation very unlikely.
Several features of the continuous wave Doppler systolic patterns of regurgitant mitral flow support the presence of severe mitral regurgitation. Because density of the continuous wave jet is proportional to the number of red blood cells reflecting sound, severe mitral regurgitation usually has a dense continuous wave jet. However, it is important to note that jet density is gain dependent. In addition, eccentric jets can be less dense even though the regurgitation is severe [26]. If the flow signal can be aligned parallel to the beam, the jet will appear uniformly dense throughout its duration, have a well-defined envelope, and may, in its late phases, show evidence of a "v-wave cut-off sign." This sign results from a rapid decrease in ventriculoatrial gradient as the large volume of regurgitant blood abruptly raises pressure in the left atrium (waveform 5).
In severe decompensated mitral regurgitation, the tricuspid regurgitation peak velocity is often increased as the result of pulmonary hypertension.
Quantitative parameters of mitral regurgitation — Using the PISA method and various volumetric methods, quantitative measures including regurgitant volume, regurgitant fraction, and effective regurgitation orifice area (EROA) can be calculated [26].
Color flow imaging displays the convergence signal known as PISA as a hemispheric shell with surface velocity equal to the chosen aliasing velocity (Va) [39]. At a given aliasing velocity, the radius (r) of PISA increases with increasing regurgitant volume. The EROA can be calculated by dividing the flow rate through the regurgitant orifice (which is estimated as the product of the surface area of the hemisphere [2πr2] and Va) by the peak velocity of the regurgitant jet (PkVreg):
EROA = (2πr2 * Va)/PkVreg
PISA has been extensively studied as a moderately accurate means of quantifying severity of mitral regurgitation [35]. Limitations of PISA include reduced accuracy for eccentric jets and, compared with central jets, difficulty in identifying the regurgitant orifice and inaccurate estimation of the convergence shape [40]. Performed correctly, these parameters are considered most accurate because they are objective. However, measurements must be performed carefully by experienced sonographers. For example, the PISA signal must not impinge on a chamber wall in order to retain accuracy [39].
●Mild mitral regurgitation is associated with regurgitant volume, regurgitant fraction, and EROA of less than 30 mL/beat, less than 30 percent, and less than 0.2 cm, respectively.
●Moderate mitral regurgitation is associated with regurgitant volume, regurgitant fraction, and EROA of 30 to 59 mL/beat, 30 to 49 percent, and 0.2 to 0.39 cm, respectively.
●Severe mitral regurgitation is associated with regurgitant volume, regurgitant fraction, and EROA of at least 60 mL/beat, at least 50 percent, and at least 0.4 cm, respectively. However, if the LV chamber size is normal, a diagnosis of severe mitral regurgitation should be questioned and reconsidered.
Doppler of pulmonary veins — Doppler interrogation of the pulmonary veins has produced insights into hemodynamics. In mitral regurgitation, this evaluation is a standard part of the examination and usually includes pulse Doppler of the left and right upper pulmonary veins from the apical four-chamber view. Normal pulmonary venous flow is antegrade during both ventricular systole and diastole (ventricular systolic component dominates), with slight retrograde flow during atrial systole. In hemodynamically severe mitral regurgitation, the flow in one or more pulmonary veins (depending upon the direction of the jet) will show systolic flow reversal (image 8) and is the analog of the V wave seen in the left atrial pressure tracing and on a pulmonary artery wedge pressure tracing. After mitral valve intervention, normalization of pulmonary vein flow (an indication of normal left atrial pressure) is a key sign that mitral regurgitation has been reduced to mild [41]. (See "Hemodynamics of valvular disorders as measured by cardiac catheterization".)
Index of severity — An echocardiographic index of mitral regurgitation severity has been developed and is based on six variables, each scored on a scale of 0 to 3 and then averaged [42]:
●Color Doppler regurgitant jet width and penetration
●Color Doppler proximal isovelocity surface area diameter
●Continuous wave Doppler characteristics of the regurgitant jet
●Tricuspid regurgitant jet-derived pulmonary artery pressure by continuous wave Doppler
●Pulse wave Doppler pulmonary venous flow pattern
●Left atrial size by 2D echocardiography
In the report presenting this index, all patients with mild mitral regurgitation had an index ≤1.7 and all patients with severe mitral regurgitation (regurgitant fraction greater than 40 percent) had a value of at least 1.8. A value of at least 2.2 identified patients with severe mitral regurgitation with a sensitivity, specificity, and positive predictive value of 90, 88, and 79 percent, respectively.
A ratio of time velocity integral of mitral inflow (continuous wave Doppler) to the time velocity integral of the LV outflow (pulse wave Doppler) has been proposed to discriminate severe from nonsevere regurgitation and has excellent interobserver agreement and very good correlation with ASE-recommended parameters [43].
MITRAL VALVE LESIONS CAUSING MITRAL REGURGITATION — The major causes of mitral regurgitation are mitral valve prolapse, flail mitral valve, endocarditis, functional mitral regurgitation from cardiomyopathy, ischemic heart disease with papillary muscle displacement (previously known as papillary muscle dysfunction), and rheumatic heart disease. (See "Clinical manifestations and diagnosis of chronic mitral regurgitation" and "Acute mitral regurgitation in adults".)
Mitral valve prolapse — Echocardiographic diagnosis of mitral valve prolapse is discussed in detail separately (see "Definition and diagnosis of mitral valve prolapse"). Briefly, leaflet displacement ≥2 mm above the plane of the mitral annulus in long axis 2D echocardiographic views is the accepted criterion for a positive diagnosis of mitral valve prolapse [44]. It is important to note that mitral regurgitation limited to late systole is rarely severe because it is not holosystolic and regurgitant volume is limited.
Flail mitral valve — In most cases of flail mitral valve leaflet, the leaflet is only partially flail. One of the most common causes for a flail mitral valve is ruptured chordae tendineae, often associated with mitral valve prolapse, endocarditis, or trauma (movie 21 and movie 20). A less common cause is partial rupture of a papillary muscle in the setting of an acute myocardial infarction. (See "Role of echocardiography in acute myocardial infarction".)
Two-dimensional transthoracic echocardiography (TTE) and transesophageal echocardiography are the best methods for detecting a flail leaflet. Using the TTE parasternal long axis and apical four chamber views, extension of a portion of the valve into the left atrium in systole, with a portion of the chordae attached at the tip of the valve, is readily seen (movie 21 and movie 20) [45,46].
Other findings of flail mitral leaflet include noncoaptation of the two leaflets. If the etiology is papillary muscle rupture, the ruptured papillary muscle can occasionally be visualized.
Endocarditis of the mitral valve — For establishing a diagnosis of endocarditis, the first target of the echocardiography examination is the identification, characterization, and localization of valvular vegetations. The process integrates circumstantial findings and epiphenomena (eg, endocarditis is a destructive process resulting in pathologic regurgitation) to reach a reasonable conclusion that a given set of echocardiographic observations has identified the pathologic hallmark of endocarditis, the vegetation (movie 22 and image 9). Once a vegetation has been identified, a series of criteria can be applied to judge prognosis. The use of echocardiography in the evaluation of endocarditis is described in detail elsewhere. (See "Role of echocardiography in infective endocarditis".)
Functional mitral regurgitation — Primary myocardial disease or dilated cardiomyopathy (DCM) is universally associated with some degree of mitral regurgitation (usually mild to moderate) through the agency of spherical LV remodeling, which distorts the alignment of the mitral apparatus, dilates the annulus, and decreases the area of valve apposition. Severe mitral regurgitation can occur in DCM but is less common. The response of mitral regurgitation severity to treatment has been used to guide therapy [47,48].
Ischemic heart disease — Ischemia as a cause of mitral regurgitation is suggested by the presence of regurgitation in a patient with coronary artery disease, frequently with a previous inferior myocardial infarction or a dilated LV (movie 23 and movie 24 and movie 25). On 2D echocardiography, there is shortening of the mitral valve apparatus, resulting in failure of the leaflets to close properly or completely; the leaflets often do not reach the level of the mitral annulus [49,50]. Patients with ischemic heart disease may also have mitral regurgitation from annular dilatation (functional mitral regurgitation). A 3D echocardiographic study suggested that it may be possible to differentiate ischemic mitral regurgitation from functional mitral regurgitation in DCM [51]. The pattern of mitral valve deformation was asymmetric in the ischemic mitral regurgitation and symmetric in functional mitral regurgitation; in addition, the LV chamber and mitral annulus were less enlarged in ischemic MR. In this review, we have not used the term "papillary muscle dysfunction" because we believe it to be anachronistic and uninformative. (See "Management and prognosis of chronic secondary mitral regurgitation".)
Rheumatic mitral regurgitation — Rheumatic mitral regurgitation is often associated with some degree of mitral stenosis, and the valve area is usually sufficiently reduced to alter its echocardiographic appearance and sufficiently narrowed to separate it readily from normal even when stenosis is minimal. The scarring associated with the rheumatic process usually results in characteristic alterations of valve motion (see 'Mitral stenosis' above) on the M-mode echocardiogram.
On 2D imaging, failure of coaptation can also be seen during systole on a short axis image; its extent is proportional to the severity of regurgitation. Rheumatic mitral regurgitation is the only form of insufficiency to have been quantitated by failure of coaptation (image 10) [52].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Cardiac valve disease".)
SUMMARY AND RECOMMENDATIONS
●Echocardiography is the primary diagnostic modality for evaluation of mitral valve structure and function. (See 'Normal mitral valve' above.)
●Mitral valve obstruction is caused chiefly by rheumatic mitral stenosis. Less common causes include left atrial myxoma and other tumors, severe mitral annular calcification, left-sided carcinoid heart disease, and congenital disorders. (See "Clinical manifestations and diagnosis of rheumatic mitral stenosis" and "Carcinoid heart disease".)
●In the presence of characteristic valvular and subvalvular structural changes, severe mitral stenosis is associated with a mean transmitral gradient greater than 10 mmHg, pulmonary artery systolic pressure greater than 50 mmHg, and a mitral valve area less than 1.0 cm2. (See 'Doppler echocardiography' above.)
●In patients with rheumatic mitral stenosis who are potential candidates for percutaneous mitral balloon valvotomy, echocardiography enables evaluation of the likelihood of procedural success. (See 'Echocardiography in balloon valvuloplasty' above.)
●Echocardiography enables quantification of the severity of mitral regurgitation and identification of causes including mitral valve prolapse, flail mitral leaflet, endocarditis, ischemic heart disease, functional regurgitation caused by a cardiomyopathy, and rheumatic mitral disease. (See 'Abnormalities associated with mitral regurgitation' above and 'Mitral valve lesions causing mitral regurgitation' above.)
1 : Ultrasound cardiogram in mitral valve disease
2 : Ultrasoundcardiography in mitral valve stenosis.
3 : Transesophageal echocardiography in the evaluation of mitral regurgitation. The twenty-four signs of severe mitral regurgitation.
4 : Normal left atrial function determined by 2-dimensional echocardiography.
5 : Three-dimensional reconstruction of cardiac structures from transesophageal echocardiography.
6 : Real-time 3-dimensional echocardiographic quantification of left ventricular volumes: multicenter study for validation with magnetic resonance imaging and investigation of sources of error.
7 : EAE/ASE recommendations for image acquisition and display using three-dimensional echocardiography.
8 : Analysis of procedural effects of percutaneous edge-to-edge mitral valve repair by 2D and 3D echocardiography.
9 : Discordance between echocardiography and MRI in the assessment of mitral regurgitation severity: a prospective multicenter trial.
10 : Prospective comparison of valve regurgitation quantitation by cardiac magnetic resonance imaging and transthoracic echocardiography.
11 : Are Echocardiography and CMR Really Discordant in Mitral Regurgitation?
12 : 2014 AHA/ACC guideline 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.
13 : Two-dimensional echocardiographic assessment of mitral stenosis.
14 : Determination of mitral valve area by cross-sectional echocardiography.
15 : Noninvasive assessment of pressure drop in mitral stenosis by Doppler ultrasound.
16 : Noninvasive assessment of atrioventricular pressure half-time by Doppler ultrasound.
17 : Exercise echocardiography in combined mild mitral valve stenosis and regurgitation.
18 : Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice.
19 : Dobutamine stress echocardiography for noninvasive assessment and risk stratification of patients with rheumatic mitral stenosis.
20 : Real-time three-dimensional echocardiography for rheumatic mitral valve stenosis evaluation: an accurate and novel approach.
21 : Improved assessment of mitral valve stenosis by volumetric real-time three-dimensional echocardiography.
22 : Prediction of successful outcome in 130 patients undergoing percutaneous balloon mitral valvotomy.
23 : Percutaneous balloon dilatation of the mitral valve: an analysis of echocardiographic variables related to outcome and the mechanism of dilatation.
24 : Percutaneous balloon mitral valvotomy with the Inoue single-balloon catheter: commissural morphology as a determinant of outcome.
25 : Clinical and echocardiographic comparison of patients with the carcinoid syndrome with and without carcinoid heart disease.
26 : Recommendations for Noninvasive Evaluation of Native Valvular Regurgitation: A Report from the American Society of Echocardiography Developed in Collaboration with the Society for Cardiovascular Magnetic Resonance.
27 : Cardiac valve surgery--the "French correction".
28 : Noninvasive evaluation of pulmonary artery systolic pressures during dynamic exercise by saline-enhanced Doppler echocardiography.
29 : 2017 AHA/ACC Focused Update of the 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines.
30 : 2017 ESC/EACTS Guidelines for the management of valvular heart disease.
31 : Exercise pulmonary hypertension in asymptomatic degenerative mitral regurgitation.
32 : ACC/AATS/AHA/ASE/ASNC/HRS/SCAI/SCCT/SCMR/STS 2017 Appropriate Use Criteria for Multimodality Imaging in Valvular Heart Disease: A Report of the American College of Cardiology Appropriate Use Criteria Task Force, American Association for Thoracic Surgery, American Heart Association, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons.
33 : A Comparative Assessment of Echocardiographic Parameters for Determining Primary Mitral Regurgitation Severity Using Magnetic Resonance Imaging as a Reference Standard.
34 : Color Doppler assessment of mitral regurgitation with orthogonal planes.
35 : Regurgitant volume estimation in patients with mitral regurgitation: initial studies using color Doppler "proximal isovelocity surface area" method.
36 : Multiplane transesophageal echocardiographic assessment of mitral regurgitation by Doppler color flow mapping of the vena contracta.
37 : Assessment of mitral regurgitation severity by Doppler color flow mapping of the vena contracta.
38 : Peak mitral inflow velocity predicts mitral regurgitation severity.
39 : Recommendations for evaluation of the severity of native valvular regurgitation with two-dimensional and Doppler echocardiography.
40 : Current status of flow convergence for clinical applications: is it a leaning tower of "PISA"?
41 : Guidelines for the Evaluation of Valvular Regurgitation After Percutaneous Valve Repair or Replacement: A Report from the American Society of Echocardiography Developed in Collaboration with the Society for Cardiovascular Angiography and Interventions, Japanese Society of Echocardiography, and Society for Cardiovascular Magnetic Resonance.
42 : The Mitral Regurgitation Index: an echocardiographic guide to severity.
43 : Usefulness of the Mitral Regurgitation Severity Index to Assess the Severity of Chronic Mitral Regurgitation.
44 : 2008 Focused update incorporated into the 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 Revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease): endorsed by the Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons.
45 : Reliability of M-mode, two-dimensional and Doppler echocardiography in diagnosing a flail mitral valve leaflet.
46 : The role of cross-sectional echocardiography in the diagnosis of flail mitral leaflet.
47 : Functional mitral regurgitation predicts 1-year mortality in elderly patients with systolic chronic heart failure.
48 : Long-term outcome of patients with heart failure and dynamic functional mitral regurgitation.
49 : [Two-dimensional echocardiographic findings of patients with papillary muscle dysfunction].
50 : Incomplete mitral leaflet closure in patients with papillary muscle dysfunction.
51 : Geometric differences of the mitral apparatus between ischemic and dilated cardiomyopathy with significant mitral regurgitation: real-time three-dimensional echocardiography study.
52 : Cross-sectional echocardiographic detection of rheumatic mitral regurgitation.
