A formal collaboration was established in 1999 between the authors, an echocardiologist (P.M.S.) and a cardiothoracic surgeon (A.A.R.), to evaluate and provide state-of-the-art surgical treatment for valvular heart disease with an emphasis on mitral valve repair. The collaborative plan consists of jointly reviewing all preoperative transthoracic echocardiographic and transesophageal echocardiographic images with an emphasis on quantification and pathologic anatomy of the mitral valve. Nearly every intraoperative transesophageal echocardiographic study was performed by the same echocardiologist (P.M.S.) before and immediately after attempted valve repair. The surgeon (A.A.R.) systematically evaluated the valve anatomy. Any discrepancies between echocardiographic and surgical anatomy were jointly reviewed. We estimate that over the 10-year period, we have jointly evaluated nearly 1,000 patients with mitral regurgitation, with 840 undergoing valve surgery. Mitral valve repair with the joint echocardiographic and surgical approach has been accomplished in >700 patients, with 97% successful outcomes. Success is defined as none or trace to mild residual mitral regurgitation. In approximately 5% of patients with residual moderate mitral regurgitation, detailed intraoperative echocardiographic analyses resulted in successful revision of repair in 75% of these patients.
The lessons learned and opinions expressed in this article are based on our collaborative experience. Our three-dimensional (3D) echocardiographic experience consisted of selected intraoperative cases of reconstructed 3D images before July 2007 and real-time 3D transesophageal echocardiographic images in all cases subsequent to that time frame. Our real-time 3D echocardiographic experience consists of >300 intraoperative studies involving mitral valve repair.
Historical Perspective
The mitral valve was the first valve identified and studied using early A-mode and M-mode echocardiography. However, the assessment of mitral regurgitation was made by cardiac auscultation and selective left ventriculography until the introduction of Doppler echocardiography. The pulsed Doppler technique was initially used to map the regurgitant jet by meticulous placement of the sample volume in different segments of the left atrium in multiple cross-sectional views. This approach was soon abandoned in favor of color flow Doppler imaging, which facilitated the visual assessment of intracardiac flow, including valvular regurgitation. This led to the quantitative assessment of mitral regurgitation, such that color Doppler echocardiography has supplanted left ventriculography in clinical practice.
The pathologic assessment of the mitral valve using echocardiography has lagged behind its functional assessment. M-mode echocardiography provided clues to a limited extent of rheumatic pathology, valve prolapse, and flail leaflet with chordal rupture. Two-dimensional (2D) echocardiography permitted the visualization of both leaflets in multiple cross-sections. This in turn led to the assessment of different pathologies, such as rheumatic, degenerative valve prolapse, infective endocarditis, and functional mitral regurgitation. A more detailed assessment of pathology followed developments in surgical techniques for mitral valve repair. Surgically relevant pathologic assessment of the mitral valve can be achieved through transthoracic and transesophageal approaches using 2D and 3D techniques.
In this report, we emphasize the current echocardiographic approach to evaluating patients with mitral regurgitation with regard to defining severity and pathologic anatomy as relevant to mitral valve surgery.
Quantitative Assessment
Unlike the quantitation of valvular stenosis, the severity of regurgitant lesions is at best semiquantitative, following a comprehensive assessment of several direct and indirect clues. The direct clues include the following.
Color Doppler “Angiography”
Color Doppler angiography (i.e., color flow images in multiple 2D cross-sections with appropriate color scale and gain settings) provides a quick visual analysis categorizing a lesion as mild, moderate, moderately severe, or severe. It is generally unnecessary and probably unwise to planimeter jet areas and/or left atrial areas in different cross-sections. The eccentric wall-hugging jets are thin, and the severity is visually gauged by the extent of penetration of the jet into the left atrial cavity.
Flow Acceleration Parameters
In controlled in vitro experiments involving flow through flat surface circular orifices, it is demonstrated that isovelocity hemispheric shells of flow velocities provide an accurate estimation of the orifice area. Proximal isovelocity surface area (PISA)–derived measures are less accurate for noncircular orifice shapes or when flow acceleration (hence PISA) occurs through orifices located at the margin so as to distort the hemispherical shape of PISA. There are few clinical conditions in which the shape, size, location, and flat surface considerations of in vitro experiments are valid. Hence, the PISA-derived quantitation of regurgitant orifice area and regurgitation flow rates must not be relied on solely for purposes of timing of surgery. These parameters, even when obtained using careful techniques, are at best semiquantitative.
Vena Contracta
In vitro studies also demonstrate a correlation between regurgitant severity and a zone of vena contracta. In clinical practice, measuring the vena contracta diameter is fraught with problems. First, its shape is often not circular, as demonstrated by real-time 3D color flow studies. Second, a small error in measurement may result in a major misinterpretation of regurgitation severity. We do not find this a clinically useful parameter.
Regurgitant Volume and Regurgitant Fraction
A combination of echocardiographic and pulsed Doppler techniques may be used to calculate regurgitant volumes and fractions. One approach is to measure inflow across the mitral orifice by placement of the sample volume at the annular level. The velocity-time integral multiplied by the annular area with its elliptical geometry is a measure of mitral inflow volume, which represents forward stroke volume plus regurgitation volume. In the absence of associated aortic regurgitation or left ventricular (LV) outflow obstruction, the forward stroke volume may be estimated from the LV outflow tract (LVOT) velocity-time integral and calculated outflow area. This approach, although providing a quantitative parameter of mitral regurgitation, is subject to a number of inaccuracies. The mitral annular area is dynamic and changes through diastole. The estimators of LVOT area are also subject to errors depending on the shape of the upper interventricular septum at the site of placement of the sample volume.
An alternate approach uses the modified Simpson approach to planimeter LV end-diastolic and end-systolic volumes to measure LV total stroke volume, which is then compared to mitral regurgitant volume. The inaccuracies of this approach are well documented in studies comparing 2D measurements of LV volumes and 3D echocardiographic quantitation of volumes.
These quantitative measurements are recommended for use in laboratories that routinely obtain them with care and technical expertise, but they are not practical for most busy clinical echocardiographic laboratories.
There are some additional indirect clues that provide useful semiquantitative assessment:
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Continuous-wave Doppler recording of mitral regurgitation jet may be visually assessed for the intensity of the jet as well as its profile. An intense mitral regurgitation jet indicates more than moderate severity. Similarly, a jet profile with early peak and rapid deceleration (the so-called v-wave cutoff sign) is consistent with severe mitral regurgitation, with equalization of LV and left atrial pressures in late systole.
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Pulsed-wave Doppler of mitral inflow showing a prominent E wave with rapid deceleration may provide a clue to severe regurgitation. This may be especially useful when the left atrial cavity is obscured by heavy mitral calcification or a mitral valve prosthesis, thus interfering with visualization of the color flow jet of mitral regurgitation. Pulsed-wave Doppler recordings of pulmonary venous flow are used to confirm more severe grades of mitral regurgitation through blunting or reversal of “S” waves.
We strongly support the consensus statement of the American Society of Echocardiography task force, which favors a comprehensive evaluation of valvular regurgitation using all available clues. We use the grading scale of 0 to 4: 1 = trace or mild, 2 = moderate, 3 = moderately severe, and 4 = severe regurgitation. Only patients with grade 3 or 4 regurgitation are potential candidates for surgical intervention. Those undergoing coronary artery bypass surgery or aortic valve surgery may be considered for mitral valve intervention for grade 2 severity of mitral regurgitation.
Quantitative Assessment
Unlike the quantitation of valvular stenosis, the severity of regurgitant lesions is at best semiquantitative, following a comprehensive assessment of several direct and indirect clues. The direct clues include the following.
Color Doppler “Angiography”
Color Doppler angiography (i.e., color flow images in multiple 2D cross-sections with appropriate color scale and gain settings) provides a quick visual analysis categorizing a lesion as mild, moderate, moderately severe, or severe. It is generally unnecessary and probably unwise to planimeter jet areas and/or left atrial areas in different cross-sections. The eccentric wall-hugging jets are thin, and the severity is visually gauged by the extent of penetration of the jet into the left atrial cavity.
Flow Acceleration Parameters
In controlled in vitro experiments involving flow through flat surface circular orifices, it is demonstrated that isovelocity hemispheric shells of flow velocities provide an accurate estimation of the orifice area. Proximal isovelocity surface area (PISA)–derived measures are less accurate for noncircular orifice shapes or when flow acceleration (hence PISA) occurs through orifices located at the margin so as to distort the hemispherical shape of PISA. There are few clinical conditions in which the shape, size, location, and flat surface considerations of in vitro experiments are valid. Hence, the PISA-derived quantitation of regurgitant orifice area and regurgitation flow rates must not be relied on solely for purposes of timing of surgery. These parameters, even when obtained using careful techniques, are at best semiquantitative.
Vena Contracta
In vitro studies also demonstrate a correlation between regurgitant severity and a zone of vena contracta. In clinical practice, measuring the vena contracta diameter is fraught with problems. First, its shape is often not circular, as demonstrated by real-time 3D color flow studies. Second, a small error in measurement may result in a major misinterpretation of regurgitation severity. We do not find this a clinically useful parameter.
Regurgitant Volume and Regurgitant Fraction
A combination of echocardiographic and pulsed Doppler techniques may be used to calculate regurgitant volumes and fractions. One approach is to measure inflow across the mitral orifice by placement of the sample volume at the annular level. The velocity-time integral multiplied by the annular area with its elliptical geometry is a measure of mitral inflow volume, which represents forward stroke volume plus regurgitation volume. In the absence of associated aortic regurgitation or left ventricular (LV) outflow obstruction, the forward stroke volume may be estimated from the LV outflow tract (LVOT) velocity-time integral and calculated outflow area. This approach, although providing a quantitative parameter of mitral regurgitation, is subject to a number of inaccuracies. The mitral annular area is dynamic and changes through diastole. The estimators of LVOT area are also subject to errors depending on the shape of the upper interventricular septum at the site of placement of the sample volume.
An alternate approach uses the modified Simpson approach to planimeter LV end-diastolic and end-systolic volumes to measure LV total stroke volume, which is then compared to mitral regurgitant volume. The inaccuracies of this approach are well documented in studies comparing 2D measurements of LV volumes and 3D echocardiographic quantitation of volumes.
These quantitative measurements are recommended for use in laboratories that routinely obtain them with care and technical expertise, but they are not practical for most busy clinical echocardiographic laboratories.
There are some additional indirect clues that provide useful semiquantitative assessment:
- •
Continuous-wave Doppler recording of mitral regurgitation jet may be visually assessed for the intensity of the jet as well as its profile. An intense mitral regurgitation jet indicates more than moderate severity. Similarly, a jet profile with early peak and rapid deceleration (the so-called v-wave cutoff sign) is consistent with severe mitral regurgitation, with equalization of LV and left atrial pressures in late systole.
- •
Pulsed-wave Doppler of mitral inflow showing a prominent E wave with rapid deceleration may provide a clue to severe regurgitation. This may be especially useful when the left atrial cavity is obscured by heavy mitral calcification or a mitral valve prosthesis, thus interfering with visualization of the color flow jet of mitral regurgitation. Pulsed-wave Doppler recordings of pulmonary venous flow are used to confirm more severe grades of mitral regurgitation through blunting or reversal of “S” waves.
We strongly support the consensus statement of the American Society of Echocardiography task force, which favors a comprehensive evaluation of valvular regurgitation using all available clues. We use the grading scale of 0 to 4: 1 = trace or mild, 2 = moderate, 3 = moderately severe, and 4 = severe regurgitation. Only patients with grade 3 or 4 regurgitation are potential candidates for surgical intervention. Those undergoing coronary artery bypass surgery or aortic valve surgery may be considered for mitral valve intervention for grade 2 severity of mitral regurgitation.
Pathologic Anatomy
In the era when mitral valve surgery for mitral regurgitation consisted primarily of prosthetic replacement, the underlying pathologic anatomy was of little relevance. As surgical trends in the past 15 years began to favor mitral valve repair as a preferred solution over valve replacement, preoperative assessment of valve anatomy and pathology developed increasing importance. In response to a surgical need to select appropriate repair techniques to address the underlying pathology, the echocardiographic approaches were developed to systematically assess valve anatomy using suitable cross-sections with 2D transthoracic echocardiography (TTE) as well as transesophageal echocardiography (TEE). The information provided by modern echocardiography on detailed valve anatomy and pathology is so critical to patient care that any echocardiographic report failing to include that information may be considered incomplete. It is no longer acceptable to refer a patient to surgery with sole assessment of regurgitation severity.
To facilitate communication between the echocardiologist and the surgeon, we use a modified Carpentier classification of leaflet terminology and of pathologic anatomy.
Mitral Valve Leaflet Terminology
Carpentier proposed leaflet terminology that is commonly used by most cardiac surgeons. The lateral scallop of the posterior leaflet is labeled P1, the middle scallop P2, and the medial scallop P3. Because the anterior leaflet is smooth and devoid of natural scallops, the leaflet segments opposing the corresponding posterior leaflet scallops are labeled A1, A2, and A3. This approach fails to account for the distribution of chordal insertions from the two papillary muscle groups. The chords arising from anterolateral papillary muscle heads are inserted into the lateral half of the valve and those from posteromedial papillary muscle heads to the medial half of both leaflets. Because P2 is the largest of the posterior leaflet scallops, it may be divided into lateral and medial halves, designated P2L and P2M. The corresponding A2 scallop is then subdivided into A2L and A2M halves. The lateral and medial commissures are in reality composed of small leaflets and may be designated CL and CM, for the lateral and medial commissural leaflets, respectively. Thus the chordae arising from anterolateral papillary muscles are attached to CL, A1, P1, A2L, and P2L, while those arising from the posteromedial papillary muscle are attached to CM, A3, P3, A2M, and P2M. In addition to anatomic relevance, there is a practical application to this approach. When artificial chords are used to reconstruct the mitral valve, it is essential to maintain correct laterality. Thus, a chord placed on P2L or A2L must be sutured to the anterolateral papillary muscle, and similarly, one placed on A2M or P2M must be attached to the posteromedial papillary muscle. A failure to maintain correct laterality may result in leaflet distortion and failed repair.
Echocardiography-Based Classification of Mitral Valve Pathology
Since the first description in 1983 by Carpentier in his classic report, termed the “French correction,” developments in echocardiography have provided newer insights into the pathologic anatomy of mitral regurgitation. TEE, introduced >20 years ago, was soon applied to intraoperative imaging. Intraoperative TEE is the one imaging modality designated as a class I indication by the joint American College of Cardiology and American Heart Association Task Force on Valvular Heart Disease in 2006. The mitral valve pathology may be classified as follows ( Table 1 ).
