Abstract
Mitral valve disease (MVD) constitutes one of the most prevalent forms of valvular heart disease and is associated with significant cardiovascular morbidity and mortality.
Echocardiography plays an important role in the diagnosis and management of MVD. This noninvasive and accessible imaging tool allows assessment of mitral valve structure and function, which guide clinical management and decision making. Transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) provide complementary information on the anatomy of the mitral valve and the underlying etiology. Additionally, three-dimensional (3D) echocardiography has recently increased the value and scope of echocardiography.
The aim of this chapter is to provide a comprehensive review of MVD and the role of echocardiography in this context. This chapter will include a description of the anatomy of the MV and the standard TTE and TEE views of the mitral valve apparatus, including 3D echocardiography. Furthermore, this chapter will provide an overview of the common mitral valve lesions and their echocardiographic features, including mitral regurgitation, mitral stenosis, and congenital mitral valve disorders.
Keywords
mitral valve, mitral regurgitation, mitral stenosis, Doppler echocardiography, mitral valve disease
Introduction
Approximately 2.5% of the general US population suffers from significant valvular heart disease. Mitral valve disease (MVD) constitutes one of the most prevalent forms and is associated with significant cardiovascular morbidity and mortality. Furthermore, the prevalence of MVD increases exponentially with age reaching up to 10% in patients older than 75 years. Typically, MVD can be classified into mitral regurgitation (MR) and mitral stenosis (MS), which have a prevalence in the general US population of around 1.7% and 0.1%, respectively. MR can be further subdivided into primary MR (i.e., due to intrinsic mitral valve [MV] apparatus abnormalities) or secondary MR (i.e., as a consequence of other cardiac diseases, such as myocardial infarction and/or dilation). Similarly, MS can be broadly subdivided into two main groups based on the two most common etiologies of MS: rheumatic and calcific (or degenerative) MS.
Echocardiography plays an important role in the diagnosis and management of MVD. This noninvasive and relatively accessible imaging tool allows assessment of MV structure and hemodynamics, which guide clinical management and decision making. In addition to standard transthoracic echocardiography (TTE), transesophageal echocardiography (TEE) may also provide valuable and complementary information on the anatomy of the MV and the underlying etiology of anatomic abnormalities, particularly in MR. Additionally, recent technological advances, such as three-dimensional (3D) echocardiography, have increased the value and scope of echocardiography by improving its ability to define anatomy and function.
The aim of this chapter is to provide a comprehensive review of MVD and the role of echocardiography in this context. Hence, this chapter will include a description of the anatomy of the MV and the standard echocardiographic views of the MV apparatus, followed by an overview of the common MV lesions and their echocardiographic features.
Mitral Valve Anatomy
The MV apparatus is a complex structure that includes the mitral annulus, two leaflets, and associated chordae tendineae and papillary muscles (PMs; Fig. 28.1 ). The mitral annulus is a D-shaped fibromuscular ring to which the MV leaflets are anchored. It is elliptical and has a saddle shape, which is the optimal configuration for leaflet coaptation and for minimizing leaflet stress. The anteromedial portion of the mitral annulus shares a common wall with the aortic annulus and is called the intervalvular fibrosa. Because the intervalvular fibrosa is more rigid than the fibrous attachment of the posterior annulus, dilation of the mitral annulus typically occurs posteriorly (see Fig. 28.1 ).
The two leaflets of the MV are known as the anterior leaflet (which is typically the leaflet with the larger area), and the posterior leaflet. Each leaflet is also typically divided into three segments (scallops): anterolateral (A1 and P1), middle (A2 and P2), and posteromedial (A3 and P3) based on the Carpentier classification with the leaflets limited by commissures (see Fig. 28.1 ). Leaflet redundancy (i.e., larger leaflet surface area than MV annulus area) is needed to allow coaptation and avoid valve incompetence.
Chordae tendineae extend from the PMs and attach to the ventricular surface of the mitral leaflets (see Fig. 28.1 ). They serve to allow coaptation and prevent leaflet prolapse or flail. The chordae tendineae can also be divided into three types: the primary (marginal) chordae, which attach at the free edge of the leaflets and provide the support to allow for leaflet coaptation, preventing prolapse and flail; the secondary (basal) chordae attach the leaflets to the left ventricle (LV) and help optimize ventricular function; and the tertiary chordae, which attach to the base of the posterior leaflet, also provide structural support.
There are typically two PMs located within the LV, known as the anterolateral and posteromedial PMs. They are attached to the leaflets via the chordae, and play a role in the regulation of normal valve function.
Echocardiographic Views of the Mitral Valve
MVD can arise due to the disruption or malfunction of any the different components of the MV apparatus. Hence, accurate diagnosis of MV pathology requires a comprehensive and systematic assessment of the MV apparatus including the individual anatomical components, determination of the severity of the MV dysfunction using Doppler and imaging techniques, and assessment of the impact of the MV lesion on ventricular and atrial structure and function and on hemodynamics, notably pulmonary artery pressures. Frequently, this may require integration of 2D multiplanar and 3D imaging of the MV apparatus, from both TTE and TEE images.
Transthoracic Echocardiography
TTE is considered the standard of care for the primary assessment of the MV. MV anatomy can be evaluated using multiple 2D views ( Fig. 28.2A and B ): standard imaging of the MV by TTE should include parasternal long axis, basal short axis, and apical two-, three-, and four-chamber views. Nonstandard or off-axis views and subcostal images may also be needed to fully interrogate the valve with the goal of identifying each of the leaflet scallops and/or identifying localized abnormalities as may be encountered in endocarditis. Segmental MV anatomy can be identified in transthoracic views. Parasternal long-axis views show the middle segments (A2, P2) of the mitral leaflets. Short-axis views of the MV display the entire leaflets in a medial-to-lateral orientation from left to right. The apical four-chamber view display is more variable depending on the degree to which the probe is angled posteriorly or anteriorly, but typically shows A2 with variable portions of A1 and A3 and P1 or P2 near the transition from one scallop to another (see Fig. 28.2C ). The apical two-chamber view shows the MV across the coaptation line and includes a portion of the P3 and P1 scallops along with A2 (see Fig. 28.2C ). The apical long-axis view displays the A2 and P2 scallops, similar to the parasternal long-axis view (see Fig. 28.2C ). Integrating imaging and Doppler information from each of these 2D views should provide a thorough anatomic and functional evaluation of the MV.
Transesophageal Echocardiography
Although TTE is used as the primary tool to assess and quantify MVD, TEE provides complementary imaging, especially if TTE windows are technically difficult. In addition, due to the TEE transducer proximity to the left atrium, TEE is particularly suited to define MV anatomy and function with the precision needed to guide surgical decision making.
Standard TEE imaging to visualize the MV includes four mid-esophageal views ( Fig. 28.3A ) and multiple transgastric views including the short-axis view (see Fig. 28.3B ) that uniquely shows all scallops of both leaflets. Slight modifications of each of the mid-esophageal views are needed to ensure that all scallops are visualized from this window.
Like the TTE apical four-chamber view, the mid-esophageal view at 0 degrees has a display of the scallops that varies depending on the degree to which the probe is anteflexed or retroflexed, but typically shows A2 (or A1 if anteflexed, A3 if retroflexed) and P2 (or P1 if anteflexed, P3 if retroflexed near the transition from one scallop to another). The mid-esophageal view at approximately 60 degrees shows the MV across the coaptation line (the transcommissural view) and includes a portion of the P3 and P2 along with A2 floating in the middle. Manually rotating the probe (as opposed to changing the angle) can result in views that show only the anterior or posterior leaflets. The mid-esophageal view at 90 degrees displays P3 and A1 with variable portions of the A3 and A2 scallops. The mid-esophageal view at 120 degrees shows A2 and P2 (see Fig. 28.3C ). Note the impact of manual changes in the position of the probe anteflexion/retroflexion, right/left flexion, and mediolateral rotation, which can vary the scallops seen in individual views.
3D TEE can provide views that are not possible with 2D TEE, and by showing both complete leaflets simultaneously, eliminate some of the ambiguity inherent in 2D TEE imaging. Specifically, 3D TEE can display the “surgeon’s view” ( Fig. 28.4A ) in which the MV is viewed enface from the left atrial aspect. Additionally, MV clefts and the MV commissures can be better displayed with 3D compared to 2D TEE. Recent advances in 3D echo imaging and advanced analytic techniques have greatly improved image resolution and the quantitative assessment of the valve. 3D imaging can now be used to provide robust and quantitative evaluation of MV anatomy including assessment of each component of the MV (see Fig. 28.4B ). 3D has thus rapidly become part of the standard TEE evaluation of the MV.
Doppler evaluation (spectral and color [2D and 3D]) complements the anatomic characterization of the MV by providing functional information including the localization of the mitral regurgitant jets.
Mitral Regurgitation
MR is classically subdivided into two broad categories with distinct underlying mechanisms: primary MR or secondary MR. Primary MR encompasses MVD in which there is a structural abnormality of the leaflets and/or associated chords. In contrast, in secondary MR, the MV leaflets are essentially normal but the LV is dysfunctional and distorted due to ischemic or myopathic remodeling resulting in leaflet tethering and incomplete closure of the mitral leaflets. Box 28.1 summarizes common etiologies for primary and secondary MR. The differentiation between these types of MVD is necessary because management, particularly surgical decision making, is dependent on the underlying etiology of the MV dysfunction. A Carpentier classification of the mechanisms of MR that is based on leaflet mobility has also been proposed ( Table 28.1 and Fig. 28.5 ). Type I is defined by normal leaflet motion but with annular dilation, leaflet perforation, or cleft; Type II is defined by excessive leaflet motion (i.e., MV prolapse or flail) and elongated/ruptured chordae or PMs; Type IIIa is defined by diastolic and systolic restrictive leaflet motion and leaflet or chordal thickening/calcification with or without commissural fusion such as occurs with rheumatic MVD; and Type IIIb is defined by systolic restrictive leaflet motion and left ventricular dilation/aneurysm, PM displacement, and chordal tethering (secondary or functional MR). The clear distinctions among the different categories of MR can only be achieved by comprehensively assessing the anatomy and function of the MV to define underlying mechanisms.
Primary Mitral Regurgitation
Degenerative
Mitral valve prolapse spectrum
Annular calcification
Nonspecific thickening
Infectious (endocarditis with vegetation, perforation, or chordal rupture)
Inflammatory (collagen-vascular diseases)
Rheumatic
Radiation-induced
Drug-induced (e.g., anorectic drugs)
Congenital
Mitral valve cleft
Mitral valve parachute
Mitral arcade
Supravalvular mitral ring
Secondary Mitral Regurgitation
Ischemic left ventricular dysfunction
Nonischemic cardiomyopathy
Atrial fibrillation
| Type | Leaflet Motion | Lesions | Etiology |
|---|---|---|---|
| I | Normal | Annular dilation Leaflet perforation | Atrial Fibrillation Endocarditis Dilated cardiomyopathy |
| II | Excessive | Elongated/ruptured chordae Elongated/ruptured papillary muscle | Degenerative valve disease Endocarditis Trauma Ischemic cardiomyopathy |
| IIIa | Restrictive (diastole and systole) | Leaflet thickening/retraction Leaflet calcification Chordal thickening/retraction/fusion Commissural fusion | Rheumatic heart disease Carcinoid heart disease Calcific mitral valve Radiotherapy Inflammatory disease |
| IIIb | Restrictive (systole) | Left ventricle dilation/aneurism Papillary muscle displacement Chordae/leaflet tethering | Ischemic cardiomyopathy Dilated cardiomyopathy |
Primary Mitral Regurgitation
The most common cause of primary MR in developed countries is MV prolapse or flail (Carpentier type II). Prolapse is defined as leaflet billowing by more than 2 mm above the annular “plane” during systole ( Fig. 28.6 ). This assessment is typically made in the parasternal long-axis view, which displays the highest points of the saddle-shaped annulus. The diagnosis of prolapse should not be made exclusively from the apical four-chamber view, which shows lower (more apical) points on the annulus. MV prolapse spans a spectrum from minimum prolapse of the leaflets into the left atrium to diffuse leaflet thickening and redundancy. Flail leaflet is part of the MV prolapse spectrum and is defined as occurring when the leaflet becomes everted and loses its normal convex shape with the leaflet tip seen within the left atrium ( Fig. 28.7 ). Flail leaflet is caused by disruption of the primary (marginal) chordae such that effective coaptation is no longer present.
Clinically important MV prolapse/flail typically presents as two types ( Fig. 28.8 ): Barlow disease and fibroelastic deficiency. Barlow disease is an infiltrative disease characterized by excessive myxomatous tissue associated with mucopolysaccharide accumulation that can affect one or both leaflets, and chordae. In Barlow disease, there is thickening of the leaflets leading to redundant valvular tissue (see Fig. 28.8A and B ; 
) and frequently elongated or ruptured chordae. Patients with Barlow disease are usually diagnosed in young adulthood and typically present with bileaflet and multisegmental prolapse with or without flail scallops (see Fig. 28.8A and B ; 
). In contrast, in fibroelastic deficiency, which is the most common form of degenerative MR in the MV prolapse spectrum, the loss of mechanical valve integrity due to abnormal connective tissue structure and function is the most common finding. Patients with fibroelastic deficiency are usually identified in their 60s and typically present with localized and unisegmental prolapse or flail (see Fig. 28.8C and D ; 
). However, clear distinction between these two entities is difficult because it has been suggested that they constitute the different ends of a disease spectrum with some valves not demonstrating the typical appearance of Barlow disease but having myxoid infiltration on histopathological exam.
Infective endocarditis with leaflet vegetation and fenestration (Carpentier Type I) is an important cause of primary MR associated with significant morbidity and mortality. The mechanism of MR with infective endocarditis is initially an inflammation of the valve leaflets causing a valvulitis, which is seen as nonspecific thickening on echocardiography, although in many cases, thickening is not evident. Valvulitis results in inefficient or incomplete coaptation of the leaflets and MR. Subsequently, as the inflammatory response progresses, valve tissue is destroyed and vegetation forms on the valve leaflets. The destruction of valve tissue, often signaled by the development of vegetation, may also result in MR ( Fig. 28.9 ; 
). In some cases, an aneurysm or perforation of the leaflets or chordal rupture can develop (see Fig. 28.9 ; 
). The role of echocardiography in endocarditis is also discussed in Chapter 40 .
Secondary Mitral Regurgitation
The mechanism of secondary MR is mainly a consequence of abnormal leaflet tethering forces due to LV or annular distortion and dysfunction rather than valvular abnormalities (Carpentier Type IIIB). Hence the mitral leaflets appear “normal” in secondary MR. Altered LV geometry results in PM displacement, which in turn is associated with increased leaflet tethering, resulting in the apical displacement of the coaptation zone and incompetence of the MV ( Fig. 28.10 ). Tethering of the mitral leaflets is central to the pathophysiology of secondary MR and predominates even if there is large heterogeneity in the manifestation of the secondary MR. The displacement of the PM alters the force and direction of the tension exerted on the chordae preventing complete coaptation between apically displaced leaflets. Coaptation is further impeded by reduced closing forces as a result of LV systolic dysfunction. Hence, secondary MR is characterized by a significantly tented valve with restricted closure of the valve leading to incomplete mitral leaflet closure ( Figs. 28.10 and 28.11 ; 
). Annular dilation contributes to incomplete mitral leaflet closure and, less commonly, may be the sole cause of secondary MR (Carpentier Type I, see Fig. 28.5 ). In secondary MR, MV dysfunction should be understood and interpreted in relation to LV geometry and function and not as intrinsic MV abnormalities.
