Intraoperative examination of the mitral valve (MV) for repair planning is considered a category I indication for transesophageal echocardiography (TEE).1 During MV repair surgery, TEE is performed before and after cardiopulmonary bypass (CPB) to quantify MV dysfunction, assess its suitability for repair, and comment on the adequacy of repair. Assessment includes, but is not limited to, analysis of the prerepair functional anatomy, identification of the predictors of both short- and long-term failure of surgical repair, and immediate postrepair interrogation.2–7 Although the anatomical assessment is qualitative and is based on evaluation of the structural integrity of MV apparatus, the functional assessment generally relies on Doppler-derived, flow-dependent variables that are contextual in nature.8–10
When interrogated with 2-dimensional (2D) echocardiography, the complex 3-dimensional (3D) shape and orientation of MV require interpolation and mental reconstruction. Furthermore, assumptions of shape and spatial limitations inherent in 2D imaging preclude its use in accurate quantitative MV analysis.6,11,12 Three-dimensional echocardiography promises to overcome many of these pitfalls and to bring new opportunities and challenges to the perioperative assessment of the MV.13–18 The enhanced spatial orientation provided by 3D imaging obviates the need for a mental reconstruction of a 3D model based on multiple thin 2D slices.19,20 There is also an emerging interest in the quantitative aspect of 3D data. Before improvements in computational processing power, technological impediments hindered the feasibility of MV quantitative analyses with 3D data in real time, limiting the analyses of 3D data to time-consuming, off-line research techniques. With advancements in technology, it is now feasible to perform complex geometric analyses. Also, the quantitative analyses of 3D data have progressed from a static end-systolic frame to a dynamic analysis encompassing the entire duration of the cardiac cycle.9,11–14,18,21–23
The diagnosis of MV dysfunction is contingent upon investigating the complex interplay of the components of MV apparatus (leaflets, annulus, chordae tendineae, papillary muscles). Quantitative 2D imaging alone cannot comprehensively assess complex 3D intracardiac structures.10,11,22,24 An objective approach to the structural analysis of the MV apparatus helps to differentiate the appropriate uses of various annuloplasty devices on the basis of geometric distortions.4,18,25 The ability to dynamically analyze cardiac structures under physiologic conditions differentiates echocardiographic analysis from surgical analysis during CPB on a static, arrested heart.26 Geometric changes in the MV apparatus after repair also determine the imposed leaflet stress and, in turn, possibly predict durability of repair.3,27,28 Hence, the intraoperative assessment of MV is evolving from a qualitative and subjective methodology to a more precise and quantitative approach. Quantitative aspects of echocardiography also have been extended to quantification of regurgitation, linear dimensions, and geometric analyses of stress patterns before and after repair.18,21,25,29–32
Although the cinematic display of dynamic cardiac anatomy with depth perception qualitatively enhances spatial orientation, the real value of 3D imaging is in multiplanar reformatting (MPR) of the volumetric data. These MPR-derived slices offer optimal orthogonal 2D views from the 3D data, allowing geometric analysis of irregularly shaped structures that are difficult to interrogate with 2D imaging. In the future, use of percutaneous approaches to mitral repair may require a greater level of precision during intraoperative assessment. It is expected that intraoperative echocardiographers may be asked to provide quantitative information regarding MV geometric distortions before and after repair and objectively comment on the quality of repair. Therefore, anesthesiologists should appreciate and orient themselves to the quantitative approach to intraoperative analysis of MV.
Certain methods of quantification of the MV geometry have yet to be clinically validated and are considered research interests only. In this review, we examine the relevant literature and draw upon our own experiences. We present the most practical parameters of quantitative 2D and 3D intraoperative MV analysis in the context of repair (Table 1). We first review the surgical anatomy of the MV from an echocardiographic perspective. We will then describe a methodical and stepwise approach to intraoperative assessment of MV, with a focus on repair for regurgitant MVs. We then discuss in detail the indices of remodeling with particular reference to leaflets and annulus. Finally, we describe the quantitative assessment of a repaired MV.
MV ANATOMY AND FUNCTIONAL GEOMETRY
The MV consists of anterior and posterior leaflets surrounded by a saddle-shaped annulus and anchored by chordae tendineae, which insert into the papillary muscles and the surrounding left ventricle (LV) (Figs. 1 and 2; Supplemental Digital Content, Video 1, http://links.lww.com/AA/B99).33
The nonplanar shape of the annulus serves to reduce mechanical stress on valve leaflets.31 The annulus has 2 peaks at the aortic insertion and the posterior left ventricular wall, and 2 troughs in the vicinity of the medial and lateral commissures (Fig. 3). Peak leaflet stress decreases as annular height (AH) increases relative to anteroposterior (AP) diameter, previously known as anterior–posterior commissural width (CW), with leaflet stress attenuated most when the AH/CW ratio (i.e., AHCW ratio) exceeds 0.20.34,35
The annulus undergoes complex conformational changes during the cardiac cycle as the result of atrial and ventricular contraction and intracardiac blood pressures22,34,36,37 (Supplemental Digital Content, Video 2, http://links.lww.com/AA/B100). Mitral annular area is largest at end-diastole (averages 5–6 cm2/m2) and reaches the smallest value in midsystole (decreasing by roughly 25%) because of ventricular contraction.38 The change in size is attributable to both the folding and increasing elliptical shape of the annulus, which reduces the distance between 2 high points and increases the AH. Although the degree of nonplanarity varies, the annulus remains nonplanar throughout the cardiac cycle.32,34,38 It also undergoes translational motion along the LV major axis due to rotation and basal–apical motion of the LV base toward the apex (Fig. 4).34
There are a few anatomical points of differentiation between the anterior and posterior leaflet of the MV. The length of the anterior leaflet is greater than the posterior leaflet, whereas the posterior leaflet has a longer attachment along the annulus, occupying two thirds of the annular circumference. Although the anterior leaflet is continuous, the posterior mitral leaflet has indentations that delineate 3 different scallops. The 2 leaflets merge at the commissures, thus forming a line of closure between the leaflets that ends at the commissures33,38 (Fig. 1).
MV closure during systole is not merely a reaction to changing intracardiac pressures but also involves a dynamic interaction of anatomic and physiologic factors (preload, afterload, and contractility) to achieve maximal coaptation and prevent regurgitation. For example, redundancy in the scallops of the posterior leaflets allows the leaflets to accommodate the curved line of coaptation.33 The zone of leaflet coaptation roughly spans 1 cm across, allowing for sufficient overlap to prevent regurgitation despite annular dilation and the tethering forces of the chordae.38–41 Dynamic leaflet billowing toward the left atrium during ventricular contraction also helps reduce stress.31,39 Normal leaflet tips, however, do not prolapse beyond the plane of the mitral annulus, as imaged in midesophageal views.
INTRAOPERATIVE MV ANALYSIS
Intraoperative TEE examination is performed to quantify the dysfunction before repair and ensure the greatest extent possible “normal” function of the MV after repair. Carpentier’s classification of MV regurgitation divides it into 3 broad categories42,43 (Fig. 5; Supplemental Digital Content, Videos 3–5, http://links.lww.com/AA/B101, http://links.lww.com/AA/B102, http://links.lww.com/AA/B103). Regardless of the type, the primary goal of surgical MV repair performed for regurgitant MVs is to restore systolic competence without diastolic restriction.42 The conventional prerepair surgical “valve analysis” is limited in that it is performed after institution of CPB on an arrested and retracted heart.40,44,45 Functional integrity of MV is assessed with a crude “leak test” while the patient is still on CPB and the annuloplasty ring-sizing protocols are based on subjective preferences.44,46 Increased objectivity and reproducibility in ring sizing may improve overall quality and durability of repair procedures.
Intraoperative pre-CPB TEE has the advantage of being able to clearly delineate cardiac valvular anatomy and function with a physiologic perspective (preload, afterload, and contractility).14 Three-dimensional analyses, in particular, help identify significant annular enlargements, irrespective of mitral regurgitation (MR) etiology. However, in functional MR, it is possible to have substantial annular remodeling with no or mild MR due to relatively preserved annular function.47 The dynamic echocardiographic visualization of MV anatomy under both real-time and hemodynamically altered physiological stresses complements surgical analysis and assists repair planning vis-à-vis ring sizing, selection, and adequacy of eventual ring deployment.10,21,24,37,48,49
The intraoperative analysis of MV function should commence with the quantification of MR and diagnosis of the responsible mechanism and pathogenesis. This should be followed by measurements of mitral annular dimensions (to assist ring sizing) and indices of MV and left ventricular (LV) remodeling. Predictors of immediate repair failure should be identified before initiation of CPB. Finally, the success of the surgical valve repair should be established echocardiographically after separation from CPB. Due to time constraints of the pre- and post-CPB period, the challenge is to perform this examination in a methodical, time-efficient, and objective manner4,7,14,44,49,50 (Table 2).
QUANTIFICATION OF REGURGITATION
The incidence of asymptomatic MR increases with age, and a significant number of patients presenting for coronary artery bypass graft surgery have some degree of MR.44,51 Additionally, as the result of the dynamic nature of intraoperative circumstances, the severity of MR can vary (Table 3). Regurgitation associated with structural abnormalities of the MV is not significantly affected by induction of general anesthesia48,49,52–57(Table 3). Functional MR (i.e., MR in the absence of structural abnormality) is known to improve with general anesthesia compared with its preoperative severity.14,49 Underestimation of functional MR severity under general anesthesia is multifactorial (preload, afterload, and contractility). Although there is improvement with a pharmacologic simulation of awake-state hemodynamics, underestimation of MR under general anesthesia is not entirely eliminated.49,52 This is particularly challenging in functional MR cases, where there may be significant discordance between the pre- and intraoperative assessment of MR severity.49,58
A comprehensive 2D qualitative echocardiographic examination forms the basis of the subsequent quantitative assessment of MV anatomy and MR severity7 (Tables 4 and 5). Quantification of MR should always be performed in the context of the hemodynamic circumstances (heart rate, blood pressure, and filling pressures).7,58–60 Because different techniques have specific advantages and limitations, a diagnosis made by one should be corroborated using the other7,59,61,62 (Tables 4 and 5).
Intraoperative 3D imaging enhances MR assessment by improved visualization of MV anatomy and diagnosis of the mechanism of regurgitation.10,21,32,61,63 Real-time 3D TEE is particularly accurate when used to identify pathologic leaflets.13,20 An additional advantage is that image acquisition can be completed in a short period of time. Improved spatial imaging with 3D also has helped in identifying subtle structural differences in MVs of patients with structural and functional MR.17,60 The use of 3D echocardiography allows visualization of multiple components of the MR jet (flow convergence, contraction, and jet expansion) and the dynamic anatomy of the MV61,62,64,65 (Fig. 6; Supplemental Digital Content, Video 6, http://links.lww.com/AA/B104). During systole, the annulus can be observed enlarging and becoming more planar. Geometric changes proportional to the global LV systolic function can be visualized and translated to quantitative values.66 The angle subtended at the commissural diameter between the anterior and posterior high points of the MA, otherwise known as the “nonplanarity angle” (NPA; decreasing angle denotes increasing saddle-shape), is one such measure.61 The maintenance of the saddle shape throughout the cardiac cycle provides evidence to suggest that there is an association between annular saddle shape and valve competency.58 However, perhaps the most interesting method of viewing the MR jet is the use of adjustable planes (also known as “multiplanar reformatting,” or MPR). Based on an R-wave gated volumetric acquisition, orthogonal views of the MV with the overlaid color-flow Doppler representation are simultaneously displayed. In any one of the selected planes, the image can be viewed from multiple perspectives and then rotated to display an optimal midesophageal long-axis view with all the components of regurgitation (flow isovelocity shells of convergence, vena contracta, jet expansion) identified (Supplemental Digital Content, Video 3, http://links.lww.com/AA/B101). Therefore, 3D technology may be used to improve the accuracy of quantitative MR severity grading, because it may be difficult to obtain an exact orthogonal view of the regurgitant jet consistently13,67,68 (Table 6).
Despite its promise, there are significant limitations of 3D technology for its routine clinical use. Quantification of MR with 3D is time consuming and requires R-wave−gated reconstruction and the use of complex software and postacquisition processing. Although it is possible to incorporate color-flow Doppler with single-beat, full-volume 3D acquisition with TTE and TEE, it leads to significant deterioration in spatial and temporal resolution.17
MECHANISM OF REGURGITATION
The echocardiographer should be able to precisely delineate the anatomical abnormality, as well as its location and severity (Fig. 2). With 3D data, it is possible to generate left atrial (LA) dynamic en-face surgical views of the MV to facilitate diagnosis64,65,69 (Fig. 2; Supplemental Digital Content, Video 2, http://links.lww.com/AA/B100). En-face views from the LV perspective also can be simultaneously displayed to assess MR etiology in light of Carpentier’s classification, which is a universally accepted nomenclature of classification of MV dysfunction58,64,69,70 (Supplemental Digital Content, Video 7, http://links.lww.com/AA/B105). An attempt should be made to classify the mechanism of MR based on this schema during the pre-CPB TEE examination. In degenerative MV disease, excessive leaflet motion can result in billowing (leaflet body but not the tip prolapses into LA beyond the annular plane), prolapse (coaptation point above the level of mitral annulus), or flail (undersurface of leaflet exposed to left atrium as a result of chordal rupture or elongation)71–74 (Fig. 7; Supplemental Digital Content, Video 8, http://links.lww.com/AA/B106).
Degenerative MV Disease
Barlow disease is the most common MV disorder (affecting almost 3% of general population), followed by fibroelastic deficiency.69 The population of patients diagnosed with Barlow’s valve is typically younger. The characteristics of the pathology may include leaflet thickening with excessive tissue (usually >3 mm when measured with M-mode echocardiography) as well as dilated and calcified annuli (Fig. 8; Supplemental Digital Content, Video 9, http://links.lww.com/AA/B107). Echocardiographic examination of Barlow’s valve should confirm the presence of moderate-to-severe MR, indicate Carpentier type II valve dysfunction, identify the scallops involved, and delineate primary (excess leaflet tissue, chordal and leaflet thickening, chordal elongation and rupture) and secondary (calcification, annular dilation) lesions.69 Elongated chords with multiple prolapsing segments also are seen in almost 30% patients with Barlow disease.5 Regurgitation attributable to chordal elongation occurs mid-late systole, whereas chordal rupture leads to holosystolic MR. Chordal lengths may be measured in the transgastric long-axis view of the LV.
The population of patients diagnosed with fibroelastic deficiency are typically older, with a short history of MR.10,70,75 On echocardiographic assessment, regurgitation is holosystolic and the leaflets are thin and transparent, with isolated P2 prolapse or flail, although any segment of either leaflet may be involved (Fig. 8). Most patients with fibroelastic deficiency who present for surgery have a chordal rupture. Unlike what is typical of Barlow’s disease, billowing of the leaflets and annular calcification are not seen in fibroelastic deficiency and annular dilation is less severe. The differentiation between Barlow disease and fibroelastic deficiency is largely qualitative. It is not possible to differentiate the 2 MV diseases on one aspect such as leaflet thickness alone. Clinical assessment should factor in the many aforementioned differentiating qualities.69 However, the etiology of degenerative MV disease may be ascertained using parameters of MV geometry obtained by real-time 3D echocardiographic images, with the strongest predictors being the billowing height and volume.76,77 However, not all patients can be clearly categorized echocardiographically or surgically, because the valve may share features of both types. Some valves seen to be suggestive of Barlow’s disease may well turn up with myxoid infiltration on histological examination.69
Display of MV apparatus in 3D with color-flow Doppler has been shown to be useful in accurate diagnosis of valve pathology.78 It provides the exact location of mitral pathology and its extent, the degree of involvement of the commissures, and severity of leaflet involvement. The direction of MR jet, for example, away from the prolapsed leaflet and toward the restricted leaflet, can also help to identify the mechanism of valve dysfunction. Compared with 2D imaging, 3D MV models (static and dynamic) allow quantification of leaflet lengths, areas, and prolapse height with a higher degree of accuracy and reproducibility21 (Fig. 9). The ability of 3D TEE to identify the exact valve pathology, for example, Barlow’s disease (Fig. 8; Supplemental Digital Content, Videos 9 and 10, http://links.lww.com/AA/B107, http://links.lww.com/AA/B108) responsible for the mechanism of MR, also can predict the complexity of MV repair.9,25 A more advanced prolapse is significantly correlated with the complexity of the surgical technique required. In one study, a larger number of prolapsed segments and a larger annular diameter correlated with a larger number of chordae used for repair. In the same study, patients with 5 or more prolapsed segments also were more likely to undergo quadrangular rather than triangular resection.9 Quantitative data, such as chordal lengths, papillary muscle dysfunction, and the extent of billowing, could potentially refine the surgical approach to repair.
Ischemic MV Disease
Although the terms “ischemic mitral regurgitation” and “functional mitral regurgitation” are used interchangeably, they refer to 2 distinct disease states along a “clinical continuum.”2 Ischemic MR is a subset of functional MR that represents malcoaptation of leaflets in a locally dysfunctional LV. It specifically refers to MR that results from regional contractile dysfunction and diastolic expansion secondary to coronary artery disease. Functional MR, however, usually occurs in the setting of severe LV dilation secondary to systolic dysfunction, regardless of the etiology.
Ischemic MR may be acute, insidious, or incidental. Whereas acute ischemic MR typically is secondary to papillary muscle rupture, insidious ischemic MR may appear with a normal subvalvular apparatus, despite regurgitation.2 An imbalance on the closing and tethering forces acting on the MV apparatus results in inadequate coaptation and MR.3,10 Compared with functional MR, ischemic MR is associated with more asymmetric remodeling, commonly leading to isolated posteromedial papillary muscle shortening.2 Acute ischemia can lead to MR as the result of annular dilation, papillary muscle rupture, or leaflet tethering11,42 (Fig. 10; Supplemental Digital Content, Video 11, http://links.lww.com/AA/B109).
With the use of 3D echocardiography, the MV apparatus can be visualized from multiple perspectives to improve visualization and assessment of its components.6,9,12,14,25 Significant MR can present as the result of posterior leaflet clefts, despite normal-appearing apparatus. In this context, presence of commissural involvement and posterior leaflet grooves (<50% indentation) and clefts (>50% indentation) must be differentiated from ischemic tethering79 (Fig. 11; Supplemental Digital Content, Video 12, http://links.lww.com/AA/B110). It is also possible to have simultaneous restriction and excessive motion in the same valve. Improved spatial orientation of the MV apparatus can help delineate the “dominant” lesion accurately in such cases of complex valve dysfunction11,15,30 (Supplemental Digital Content, Video 13, http://links.lww.com/AA/B111). With the use of 3D imaging, the type of abnormality, specific affected scallop/s, and bileaflet and commissural involvement can be identified with precision.
INDICES OF REMODELING
Remodeling of the mitral apparatus in response to chronic volume overload caused by regurgitation has ventricular, valvular, and annular components.2
Adaptive remodeling of the LV and papillary muscles consists of focal or global LV dilation, which serves to increase stroke volume, compensating for reduced contractility.29,30,34 Enlargement of the LV in the absence of geometric distortion at the base of the papillary muscles does not usually result in significant MR.15,30,34 However, the closure of the MV is a complex interplay of closing and tethering forces.29,31,34,35 Tipping of the balance in favor of tethering forces results in ischemic MR.29,34,80
LV dilation can occur in the absence of coronary artery disease, such as in chronic aortic insufficiency or idiopathic dilated cardiomyopathy. Echocardiographically, LV end-diastolic and end-systolic diameters should be measured, and the systolic function and wall motion abnormalities should be noted. The presence and severity of LV dilation can provide useful information regarding the significance and chronicity of volume overload along with insight into whether the ventricle has irreversibly remodeled.81,82 In addition, increased LV diastolic pressure, increased systolic wall stress, and an ejection fraction <50% are all factors that may hinder ease of surgical correction.30 Therefore, information on LV size, shape, and functional depression should be factored into surgical decision-making, because repair in these circumstances is not contraindicated but associated with unpredictable outcomes.29
Mitral leaflets respond with tissue growth leading to increased leaflet areas and coaptation surface resulting in reduced MR.3,34,38 This process occurs more often in ischemic and rheumatic regurgitation rather than degenerative regurgitation. Tethering forces transmitted through the papillary muscles and the chords increase with LV remodeling, resulting in impaired coaptation of the leaflets.29,34,36,38 Leaflet tethering eventually results in an increase in the size of the regurgitant orifice area.34,80,83 Consequently, the coaptation point shifts apically below the plane of the mitral annulus and takes on a characteristic tented appearance40,84,85 (Fig. 10; left panel; Supplemental Digital Content, Video 14, http://links.lww.com/AA/B112). The degree of the leaflet tethering can be echocardiographically appreciated as a surrogate marker of the significance and chronicity of MR,31,36,38,40 and apical displacement of the coaptation point has been suggested as an index of remodeling of the subvalvular mitral apparatus.33,40,83 Remodeling of LV leads to traction on the basal chords at the point of attachment on the leaflet leading to the characteristic “sea gull” sign41,86,87 (Fig. 12). Tethering of the leaflets also leads to malcoaptation of leaflets as well as in the interscallop regions, leading to MR.88 The degree of apical displacement, or “tenting height,” also has been shown to vary with the severity of myocardial damage.14,39,40 Tenting height is the distance between the mitral annular plane and the point of coaptation during systole (Fig. 13). It is measured routinely in the midesophageal 4-chamber or long-axis view during a standardized 2D TEE examination. A tenting height of >0.6 cm and a tenting area of >1.0 cm2 should be considered abnormal.89 Both are directly related to the severity of MR and the degree of LV remodeling. Because of the spatial limitations of 2D, 3D-derived tenting volume is thought to better describe the sum of tethering forces acting on the leaflets.86
Depending on the LV walls affected, tethering force on the leaflets can be symmetric or asymmetric. Disproportionate tethering on one leaflet is sometimes echocardiographically seen as “pseudoprolapse” of the other leaflet21,39,42 (Supplemental Digital Content, Video 15, http://links.lww.com/AA/B113). Asymmetric leaflet tethering (Supplemental Digital Content, Video 16, http://links.lww.com/AA/B114) usually results in an eccentric MR jet directed toward the tethered leaflet, but a shift towards symmetric displacement can then centrally direct the jet.7,14,39 Symmetric, compared with asymmetric, tethering (Supplemental Digital Content, Video 17, http://links.lww.com/AA/B115) is associated with more dilation and flattening of the mitral annulus and larger tenting height and area.40,44,46 Symmetric leaflet tethering is associated with more LV dilation and global remodeling than asymmetric pattern.90 Tenting height, area, and volume are global measures and do not provide information regarding specific leaflet involvement, which is better estimated with measuring leaflet angles.
Although surgical annuloplasty for MR halts the annular dilation component of MV remodeling, it does not improve leaflet tethering.21,44 The disappointingly high recurrence of MR after annuloplasty also has been attributed to the irreversible nature of leaflet tethering, which is not addressed by annuloplasty. Therefore, type III lesions are most likely to have recurrent MR after annuloplasty. The presence of significant leaflet tethering implies irreversible remodeling, with less likelihood of a favorable response to MV repair alone. Hence, the echocardiographic appreciation of these structural alterations can possibly identify patients unsuitable for repair. Measurement of tenting height based on 2D images is limited, in that it is a single plane measure of a 3D structure, whereas leaflet tethering can be asymmetric.7,49 Tethering indices based on 3D data, such as tenting area and volume, have also been described which take into account the entire surface of the leaflets and are therefore presumably more accurate24 (Fig. 14). The MV tenting area as derived by 3D TEE is a strong determinant of mitral regurgitation severity in ischemic cardiomyopathy patients,91 whereas tenting volume has been found to correlate strongly with the severity of functional mitral regurgitation due to dilated cardiomyopathy.86
Remodeling of the LV also leads to changes in the mitral annulus and its dynamic relationship with the leaflets and the coaptation point.14,49–51 Here we will refer to the standard, echocardiographically described nomenclature of the MV and annulus.
Mitral Annular Size
The annulus responds to chronic MR and LV volume overload by dilation.44,49,53,92 Static geometric analysis of 3D data has shown the annular dilation to be primarily in the AP axis with relatively preserved anterolateral to posteromedial (AL–PM) axis37,49,66 (Fig. 3). However, dynamic analyses of 3D geometry have shown dilation and reduced changes in multiple annular axes during the cardiac cycle in patients with MR compared with controls.14,49,50,52,93 Along with dilation, the annulus also assumes a more circular and flatter configuration. The annular dynamics are also preferentially affected in specific disease states, for example, a greater dilation of AL–PM dimension in myxomatous disease.92,94
As the result of differences in body surface areas, indexed values of the mitral annular area should be reported. An indexed value of 5 cm2/m2 should be considered normal for average sized adults.20,59,93 With 2D echo, annular dimensions should be made in the AP (midesophageal long-axis view) and AL–PM (midesophageal transcommissural view) axes at end-systole and end-diastole. With 3D data, MPR can be used to extract exact orthogonal sections of the mitral annulus to make accurate linear measures and planimetry of the annulus (Fig. 15). This introduces an element of objectivity in valve sizing in addition to traditional “ring-sizers” alone. Severely enlarged MA is also considered a predictor of repair failure due to irreversibility of remodeling. Before the availability of commercial automated dynamic analyses, “dynamic” data were extrapolated from analyses of multiple static frames.7,32,60,94
Mitral Annular Shape
The degree of the saddle shape of the mitral annulus was initially described as annular height to commissural width (AHCW) or anterior to posterior horn ratio7,58,59,62 (Fig. 3). An AHCW ratio of 20% or more, that is, more saddle shaped, has been associated with reduced leaflet stress across species20,59,61,63 (Fig. 16). MV repair techniques are also geared to restore or augment the saddle shape with possible favorable effects on durability of repair.17,32,60,61 Progressive annular dilation and flattening has been proposed as a mechanism for increased chordal tension and rupture in myxomatous disease of the MV.59,61,62,64 Therefore, loss of nonplanarity in the mitral annulus is not the end point but a stage in the pathogenesis of chordal rupture.
The AHCW ratio has been measured radiologically and echocardiographically. Calculation of the AHCW ratio is performed with fluoroscopic annular tracking requiring significant off-line calculations and geometric reconstructions on specialized software.61,63–66 Echocardiographically, nonplanarity can be described as AH, AHCW ratio, or the NPA (Fig. 16). An NPA of >140° should be considered as significant loss of the saddle shape of the annulus.17,58,61,74 Intraoperatively measured NPA has shown a favorable correlation with geometrically derived AHCW ratio, that is, decreasing NPA is associated with a greater AHCW ratio and vice versa.61,64,69,72 The NPA is an automatically derived measure during the annular geometric analysis with the commercially available MVA 2.0 program, part of the Image Arena software (TomTec®, Munich, Germany). The AH is also an automatically derived parameter during the MV quantification workflow within Q Lab (Philips Medical Systems, Andover, MA) (Fig. 16). The TomTec-derived NPA has been shown to represent annular folding in multiple studies.64–66,69,71 In Q Lab, the angle is derived from the coaptation point of the leaflets and not the commissural diameter; hence, it is not a true representation of the planarity of the annulus. The NPA also increases in patients with chronic MR and can be used to differentiate the geometric effects of annuloplasty rings on mitral annulus.58,70,73,74
Mitral Annular Disjunction
The term mitral annular disjunction refers to separation of the LA wall–MV junction and the LV attachment. With progressive mitral annular dilation, the posterior mitral annulus gets stretched, resulting in separation of the posterior leaflet–LA junction and LV inlet externally.69,71,72,75 This condition can be appreciated with magnetic resonance as well as echocardiographically as a separation between these structures69–71,95 (Fig. 17; Supplemental Digital Content, Video 18, http://links.lww.com/AA/B116). Disjunction of the annulus can be found in most patients with complex myxomatous prolapse.70,73,96 The disjunction can have a limited effect on only portions of the posterior mitral annulus or the entire structure. This is often corrected by detaching most of the posterior leaflet from the mitral annulus, which is then repaired with multiple horizontal mattress sutures. The sutures are passed through the ventricular endocardium and the displaced annulus. The prolapsing segment, usually P2, is then resected along with the chordae tendineae attached to the ventricular surface of the remaining posterior leaflet. Next, the posterior leaflet is trimmed and reattached while the prolapsing segments are corrected with expanded polytetrafluoroethylene sutures. Lastly, an annuloplasty ring is used to reduce the area of the mitral annulus.70 The severity of annular disjunction has also been suggested to relate to the severity of the MV prolapse and the incidence of arrhythmias.71,75,97,98 Although there are no long-term data, intraoperative identification and surgical correction of mitral annular disjunction seem to prolong the durability of repair.70,95,99
PREDICTORS OF REPAIR FAILURE
Because of variations in surgical expertise, disease patterns, and patient population, predictors of repair failure at one institution may not be generalizable to other centers. Typically, the mitral repair option is reserved for degenerative diseases, ischemic or functional MR, and not for stenotic MV disease due to excessive fibrous growth. However, experienced surgeons have demonstrated the reparability of rheumatic mitral stenosis, which is otherwise considered an indication of primary valve replacement.100 Therefore, whether a regurgitant MV will be repaired or replaced is determined by a multitude of clinical and echocardiographic factors. Almost 70% of cases of MR are the result of degenerative MV disease and are considered the most suitable for MV repair.99,101 In degenerative disease, severe mitral annular dilation (>5 cm), severe mitral annular calcification, and bileaflet disease with multiple scallop involvement have been shown to predict unsuitability for MV repair in the hands of experienced surgeons.99,102 Other reports have shown younger age and relatively longer posterior and chordal lengths as favorable predictors of repair and anterior mitral annular calcification as unfavorable predictor of repair.100,103
MV repair for ischemic MR is associated with recurrence of MR in almost 30% of the cases.101,104 It is believed that continued remodeling of the LV after the annuloplasty results in progressive leaflet tethering, eventually resulting in recurrence.102,103 Preoperative presence of a complex jet, lateral wall motion abnormality, and increased tenting height have shown to be predictors of recurrence of MR after surgical annuloplasty.103,105 A tenting height of ≥11 mm has been associated with recurrence of clinically significant MR after annuloplasty for ischemic MR.104,106 In a TEE-based study, a mitral annular diameter ≥3.7 cm in midesophageal 4-chamber view, tenting area ≥1.6 cm2 in midesophageal long-axis view, and MR grade of >3.5 were associated with recurrence of MR in >50% cases.103,107 Identification of ischemic MR patients unsuitable for MV repair can potentially affect surgical decision making and outcome.
Echocardiography also can be used to quantitatively predict the susceptibility for developing dynamic left ventricular outflow tract (LVOT) obstruction as a result of systolic anterior motion (SAM) of anterior mitral leaflet. Dynamic LVOT may be precipitated in patients with susceptible anatomy (small LV, narrow LVOT, long anterior leaflet, and anterior coaptation point) with at-risk physiology (tachycardia, low systemic vascular resistance, and hyperdynamic LV)105,108,109 (Fig. 18).
IMMEDIATE POSTREPAIR ASSESSMENT
Immediate postrepair assessment of the MV is performed to exclude significant regurgitation, stenosis, or dynamic LVOT obstruction due to SAM of redundant leaflets. The principles of echocardiographic interrogation are the same as those for the native and prosthetic valves.106 It is challenging in that a critical decision has to be made in a time-limited fashion. A repaired MV should be interrogated from multiple midesophageal and transgastric windows (2D and 3D) to ensure normal function.
A combination of 2D and 3D en-face views of MV from the LA and LV perspective should be obtained to ensure the mechanical stability of the prosthetic device and normal leaflet motion. On the basis of direct visualization, the type of device (full, partial, flat, or saddle shaped) should be recorded. The presence and extent of SAM (Fig. 19; Supplemental Digital Content, Video 19, http://links.lww.com/AA/B117) in the midesophageal long-axis view should also be excluded. Echocardiographic examination for SAM includes the following criteria: 2D evidence of the anterior leaflet in LVOT, color-flow Doppler evidence of turbulence with an anteriorly directed eccentric MR jet in LVOT, early closure of the aortic valve on M-mode, and an LVOT velocity >2 m/s (Fig. 19; Supplemental Digital Content, Video 19, http://links.lww.com/AA/B117). In challenging cases, 3D imaging of the LVOT can conclusively demonstrate complete or partial LVOT obstruction by the motion of the anterior mitral leaflet over the LVOT.106,107 Postrepair 3D imaging of the LVOT has been used to conclusively demonstrate partial obstruction of LVOT, which appeared to be a complete obstruction on 2D imaging.110
A successful MV repair should not have more than mild MR immediately after separation from CPB.108,111 Guidelines for assessment of MR of native valves are applied to postrepair MVs as well.106,112,113 Visual quantitative assessment of MR jet with color-flow Doppler is the most common method used in the immediate post-CPB period.106,114 As the result of changes in MV geometry after repair, quantitative methods, for example, vena contracta and effective regurgitant orifice area calculation, are more difficult and time consuming.111,115 The use of 3D echocardiography enables the echocardiographer to obtain orthogonal views with presumably greater accuracy in quantitative calculations.116 The absence of significant stenosis or regurgitation on color-flow Doppler indicates immediate success of repair, whereas quantitative information with 3D imaging provides information on structural integrity of the valve, which could be indicative of long-term durability as opposed to immediate adequacy.
Regardless of the repair technique, MV repair with annuloplasty results in immediate reduction in MV area.112,113,117 Doppler assessment of transvalvular flow is the mainstay of calculation of MV area after repair. Before Doppler interrogation, a comprehensive structural and color-flow Doppler examination of the repaired MV should be performed.114,118 As the result of varying hemodynamics and LA/LV compliance immediately after CPB, there is controversy regarding the use of the pressure half-time method to calculate the MVA of a repaired MV.115,119 Three-dimensional planimetry has shown promise in delineating the anatomical orifice area of the MV, accounting for the curvilinear shape of the coaptation line.118 Given the limitations of each of these methods, it important not to base the decision to repair on a single parameter. Values must be interpreted in the context of the clinical circumstances; for example, gradients should be qualified with transvalvular flow (cardiac output) and pressure half-time with the LV end-diastolic pressure.
Mitral Annular Geometry
Various annuloplasty rings can be differentiated on the basis of quantification of geometric distortions of the mitral annulus.120 Assessment of the repaired MV with 3D echocardiography also has shown that different surgical techniques can variably affect mitral inflow geometry and the accuracy of Doppler-derived gradients.46,115,121–124
A quantitative approach to the MV provides an opportunity to objectify intraoperative assessment and bring this hitherto research interest into clinical relevance.122 The volumetric nature of 3D data now allows for accurate linear 2D measures without assumptions of geometry. Parameters described in this review article are being increasingly used to objectify our pre- and postrepair MV analysis. Increasing automation in the future could further simplify the workflow, enhancing the clinical feasibility of quantification-based analysis. With these tools and added knowledge and expertise of MV anatomy and function, anesthesiologists should anticipate being a part of perioperative decision making and should be recognized as perioperative echocardiologists.124
Name: Feroze Mahmood, MD.
Contribution: This author helped topic research and manuscript preparation.
Attestation: Feroze Mahmood attests to the validity of data collection and manuscript authorship.
Name: Robina Matyal, MD.
Contribution: This author helped topic research and manuscript preparation.
Attestation: Robina Matyal attests to the validity of data collection and manuscript authorship.
This manuscript was handled by: Martin J. London, MD.
The authors thank Khurram Owais, MD, and Angela Wang, BA, for their help with copyediting and illustrations.
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