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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
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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.
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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
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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.
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Figure 2. From Chen FY and Cohn LH. Mitral Valve Repair in Cardiac Surgery in the
Adult.
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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
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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.
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