1/30/2012 1 CHEUNG AT HOW TO APPLY 2-D AND 3-D TEE FOR MITRAL VALVE SURGERY: WHAT THE ANESTHESIOLOGIST NEEDS TO KNOW Albert T. Cheung, M.D. Department of Anesthesiology and Critical Care University of Pennsylvania Philadelphia, PA Transesophageal echocardiography (TEE) was recommended for all adult patients undergoing cardiac valve operations in the American Society of Anesthesiologists Practice Guidelines for Perioperative Transesophageal Echocardiography (1) and was assigned a Class I recommendation (useful and effective) for surgical repair of valvular lesions in the American Heart Association Guideline for the Clinical Application of Echocardiography (2). The utility of intraoperative TEE in mitral valve operations is to confirm and refine the preoperative diagnosis, detect new or unsuspected pathology and to assess the results of the surgical repair. To effectively utilize intraoperative TEE for these purposes, the intraoperative TEE examination should be directed to provide the surgeon with the following information: a) b) c) d) e) f) Mechanism and severity of mitral regurgitation. Precise anatomic location of valve pathology. Mitral annular size and shape. Likelihood of a successful repair. Risk of systolic anterior motion (SAM). Presence and severity of residual mitral regurgitation, mitral stenosis, or left ventricular outflow tract obstruction after repair. Determining the Mechanism and Severity of Mitral Regurgitation Doppler echocardiography is the primary technique for quantifying the severity of mitral regurgitation by detecting retrograde blood flow across the mitral valve into the left atrium during systole. Using Doppler color flow imaging, mitral regurgitation appears as jets of regurgitant blood flow originating from the mitral valve that extend into the left atrium during systole. Regurgitant jet area, jet length, jet width, and jet duration during systole provide information on the severity of mitral regurgitation (3). The width of the regurgitant jet at its narrowest point at the site of the regurgitant orifice in the long-axis view is called the vena contracta and provides an estimate of the width of the regurgitant orifice together with an estimate of the severity of mitral regurgitation. The severity of mitral regurgitation is graded as mild, moderate, or severe. Mild mitral regurgitation does not produce significant circulatory pathology, is not associated with cardiac chamber remodeling, and has a benign clinical course. In contrast, severe mitral regurgitation is associated with significant circulatory pathology, cardiac chamber remodeling, morbidity and mortality. A scale of 1 to 4 is used to quantify the severity of mitral regurgitation with 1 being mild and 4 being severe (Table 1). Severe mitral 1/30/2012 2 CHEUNG AT regurgitation is considered an indication for surgical valve repair or replacement (4). Trace mitral regurgitation refers to regurgitation at the limits of detection by color Doppler flow imaging and is usually physiologic and not clinically significant. Associated echocardiographic findings indicating the physiologic sequelae of mitral regurgitation such as left atrial dilation, eccentric left ventricular hypertrophy, and systolic reversal of pulmonary vein flow velocity are useful also for verifying the clinical significance of mitral regurgitation. When assessing the severity of mitral regurgitation using Doppler echocardiography, it is also important to take into consideration the hemodynamic condition of the patient because the severity of mitral regurgitation can vary depending upon the state of ventricular contractility, preload, or afterload. Underestimating the severity of mitral regurgitation from the intraoperative TEE Doppler examination is especially problematic in patients with functional or ischemic mitral regurgitation that may only become manifest with exercise or decompensated heart failure. Table 1. From . J Am Soc Echocardiogr 2003;16:777-802 The pathophysiologic mechanism of mitral regurgitation can be discerned by combining information from the 2-dimensional together with the Doppler echocardiographic examination. For example, a prolapsing or flail segment of the mitral valve leaflet detected by 2-dimensional imaging should be accompanied by an eccentric jet of mitral regurgitation directed away from the defect on imaging by Doppler echocardiography. Mitral regurgitation caused by endocarditis may be associated with leaflet destruction, perforation, or vegetations. Rheumatic disease causing mitral regurgitation may be characterized by leaflet thickening, restricted leaflet motion, and mitral stenosis. 1/30/2012 3 CHEUNG AT Myxomatous mitral disease is associated with excessive leaflet tissue, leaflet prolapse, and annular dilation. Ischemic or functional mitral regurgitation is associated with left ventricular dilation, decreased left ventricular ejection fraction, mitral annular enlargement and apical tethering of the mitral valve leaflets. Congenital cleft anterior mitral valve leaflet causing mitral regurgitation is associated with endocardial cushion defects. Echocardiographic clues to the pathology and location of defects causing mitral regurgitation can be provided by the regurgitant jet direction and location of the origin of the jet along the mitral valve commissure. A classification system based on leaflet motion devised by Carpentier is often used to characterize the mechanism of mitral regurgitation (Figure 1). In this classification, type 1 lesions have normal leaflet motion with mitral regurgitation caused by annular dilation or leaflet perforation. Type II lesions are characterized by excessive leaflet motion with mitral regurgitation caused by leaflet prolapse or flail (ruptured chordae). In type III lesions, mitral regurgitation is caused by leaflet restriction such as fibrosis in rheumatic heart disease or by leaflet tethering in cardiomyopathy. Type I lesions typically cause a central mitral regurgitant jet, type II lesions cause an eccentric jet directed away from the diseased leaflet segment, and type III lesions cause a regurgitant jet overlying the tethered leaflet. Figure 1. From: J Thorac Cardiovasc Surg 1983; 86:323-37 Anatomic Localization of Valve Pathology The mitral valve is a complex structure that can be described in terms of a valve apparatus consisting of two valve leaflets, the valve annulus, chordae tendinae, papillary 1/30/2012 4 CHEUNG AT muscles, and the left ventricle (Figure 2). Pathology affecting each of these components of the mitral valve apparatus can contribute to mitral regurgitation. The anterior mitral valve leaflet is attached to the mitral valve annulus between the right and left fibrous trigones that is in direct continuity with most of the left and part of the noncoronary aortic valve cusps. The ventricular side of the anterior mitral valve leaflet forms part of the left ventricular outflow tract in systole. The posterior mitral valve leaflet is attached to the remaining one-half to two-thirds of the annulus that is primarily muscular with little fibrous tissue. The crescent-shaped posterior leaflet is divided into three scallops separated by clefts. The scallops of the posterior leaflet can be designated as the P1 (anterolateral), P2 (middle), and P3 (posterolateral) scallops. The left atrial surface of the leading edges of the anterior and posterior mitral valve leaflets coapt in systole along the mitral valve commissure. The chordae tendinae span the left ventricular surface of the mitral valve leaflets and the papillary muscles or ventricular endocardium. Chordae from the posteriormedial half of both the anterior and posterior leaflets attach to the posteriomedial papillary muscle. Chordae from the anterolateral half of both the anterior and posterior leaflets attach to the anterolateral papillary muscle. Primary chordae attach to the leading edge of the leaflets and secondary chordae attach to the body of the leaflets. Precise anatomic localization of mitral valve pathology can be performed by deconstruction of a set of cross sectional images through the mitral valve apparatus obtained using multiplane TEE (5-6). Although it is possible to describe the anatomic location of defects to the surgeon based on multiplane 2-dimensional imaging, displaying or specifying the location of defects on a 3-dimensional image may provide a more accurate way of conveying the information. In 3-D TEE imaging of the mitral valve, a 3dimensional volume set is obtained with the ultrasound transducer positioned behind the left atrium and the ultrasound beam directed through the mitral valve towards the left ventricular apex. When obtaining the 3-D volume set of the mitral valve, the transducer and imaging sector should be adjusted to include the entire mitral valve annulus (7). The 3-D TEE image of the mitral valve can then be displayed to the surgeon en face with the aortic valve positioned on top, the anterolateral commissure on the left, and the posteriormedial commissure on the right (Figure 3). The 3-D TEE volume set can then be rotated or tilted on the screen to provide a detailed visualization of the anatomic pathology. Modern TEE instruments can also perform 3-D color Doppler flow imaging that can then be superimposed on the anatomic structures to provide enhanced structural and functional relationships of the pathology. However, the limited field of view when 3D Doppler imaging is performed requires precise knowledge of the anatomic location of the defects in order to properly capture and display the pathology in 3-D. 1/30/2012 5 CHEUNG AT Figure 2. From Chen FY and Cohn LH. Mitral Valve Repair in Cardiac Surgery in the Adult. 1/30/2012 6 CHEUNG AT Figure 3. From Chen FY and Cohn LH. Mitral Valve Repair in Cardiac Surgery in the Adult. Mitral Valve Annular Size and Shape Mitral valve repair performed for either degenerative or ischemic mitral regurgitation both involve prosthetic ring annuloplasty to remodel the mitral valve annulus. For this reason, information pertaining to the size and shape of the mitral valve annulus in relation to the size of the anterior mitral valve leaflet is important to the surgeon for determining the size and model of prosthetic ring to implant. Dimensions of the mitral valve annulus are measured in mid-systole at the time of maximum mitral leaflet coaptation. 2-D TEE can be used to provide two orthogonal dimensions of the mitral valve annulus, the septallateral diameter and the commissure-to-commissure or transverse diameter. The septallateral diameter is obtained from the TEE mid-esophageal long-axis view at a multiplane angle between 120-160 degrees from the mid-point of the attachment of the A2 segment of the anterior mitral valve leaflet on the anterior annulus to the mid-point of the attachment of the P2 segment of the posterior mitral valve leaflet on the posterior annulus. The transverse diameter is obtained from the TEE mid-esophageal mitral commissural view at a multiplane angle between 60-70 degrees. 2-D TEE measurements 1/30/2012 7 CHEUNG AT of mitral annular circumference or area cannot be performed directly and require geometrical assumptions. The application of 3-D TEE enables the direct measurement of mitral annular diameter, circumference, area, and height without geometric assumptions, but requires off-line analysis to create a 3-D model to generate the measurements (8). Assessing the Likelihood of a Successful Mitral Valve Repair The success and durability of mitral valve repair is excellent for degenerative mitral regurgitation as a consequence of isolated lesions involving the posterior mitral valve leaflet such as a prolapsed or flail of the P2 segment. The likelihood of a successful and durable repair decrease as the complexity and extent of valve pathology increases. For this reason, the intraoperative TEE examination is important for determining the extent of valve pathology by characterizing: a) disease affecting the anterior mitral valve leaflet, b) regurgitation at the commissures, c) number and location of ruptured chords, d) presence of leaflet calcification, e) evidence of leaflet fibrosis or thickening, f) presence and location of annular calcification, and g) severity of leaflet tethering in ischemic or functional mitral regurgitation. The extent and severity of disease may require specialized techniques for repair or prohibit mitral valve repair altogether. Determining the Risk of Systolic Anterior Motion (SAM) Systolic anterior motion (SAM) is a condition where the anterior leaflet of the mitral valve obstructs the left ventricular outflow tract in systole causing both LVOT obstruction and mitral regurgitation. SAM is a recognized complication of mitral valve repair. Echocardiographic features that predict the likelihood of SAM include myxomatous disease, a large anterior mitral valve leaflet in relation to the posterior mitral valve leaflet, and a mitral valve coaptation point displaced toward the interventricular septum (9). Identification of risk factors for SAM by TEE enables the surgeon to adjust the mitral valve repair to decrease the risk of SAM by selecting a larger annuloplasty ring, reducing the height of the posterior mitral valve leaflet, or even adding an Alfieri stitch (edge-to-edge) to the repair. Assessing the Success or Complications of the Repair Intraoperative TEE assessment of the mitral valve repair is important for assessing the success of the repair and to detect complications of the repair. The severity of residual mitral regurgitation predicts the durability of the repair. In the presence of more than trace mitral regurgitation, intraoperative TEE is performed to characterize the location of the regurgitant jets to direct surgical revision of the repair. For this purpose, 3D TEE is useful for displaying to the surgeon the precise location of the site of residual regurgitant jets. TEE detection of SAM after repair is important for guiding medical therapy or in severe cases, surgical revision (10). Other complications may include mitral stenosis that can be assessed with Doppler echocardiography or injury to the circumflex coronary artery that can be detected by noting the presence of new left ventricular segmental wall motion abnormalities. 1/30/2012 8 CHEUNG AT REFERENCES 1. Practice guidelines for perioperative transesophageal echocardiography. An updated report by the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists Task Force on Transesophageal Echocardiography. Anesthesiology 2010; 112(5):1084-96 2. Cheitlin MD. Armstrong WF. Aurigemma GP., et al. ACC/AHA/ASE 2003 guideline update for the clinical application of echocardiography: summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. 108;2003:1146-62. 3. Zoghbi WA, et al. Recommendation for the evaluation of the severity of native regurgitation with two-dimensional and Doppler Echocardiography. 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Maslow AD, Gegan MM. Hearing JM, et al. Echocardiographic predictors or left ventricular outflow tract obstruction and systolic anterior motion of the mitral valve after mitral valve reconstruction for myxomatous valve disease. J Am Coll Cardiol 1999;34:2096-104 10. Brown ML, Abel MD, Click RL, et al. Systolic anterior motion after mitral valve repair: Is surgical intervention necessary? J Thorac Cardiovasc Surg 2007;133:136-43
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