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Ann Thorac Surg 1998;65:1025-1031
© 1998 The Society of Thoracic Surgeons
a Cardiac Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA
b Cardiac Surgical Unit Units, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA
Accepted for publication October 31, 1997.
Address reprint requests to Dr Foster, Cardiology Consultants, PC, 520 Medical Center Dr, Suite 100, Medford, OR 97504
| Abstract |
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Methods. Fifty patients with mitral regurgitation underwent intraoperative transesophageal echocardiography for the evaluation of mitral pathology and potential repair. Mitral regurgitant defects were localized using a systematic strategy and a simple nomenclature that divides each mitral valve into six sections (three sections per leaflet) and each prosthetic sewing ring into six sections (60 radial degrees = one section).
Results. Thirty-nine patients with native mitral valves were studied, for a total of 234 sections evaluated. Eighty-seven of these sections contained regurgitant defects by transesophageal echocardiography (mean number of regurgitant defects per valve, 2.2; range, 1 through 6). There was agreement between the transesophageal echocardiographic and surgical localizations in 96% (224/234; p < 0.0001) of the sections. Eleven patients with prosthetic mitral valves were studied, for a total of 66 sections evaluated. Twenty-three of these sections contained paravalvular leaks by transesophageal echocardiography (mean number of leaks per prosthesis, 2.1; range, 1 through 6). There was agreement between the transesophageal echocardiographic and surgical localizations in 88% (58/66; p < 0.001) of the sections.
Conclusions. This transesophageal echocardiographic strategy provides a systematic method to accurately localize mitral regurgitant lesions and has the potential to improve the preoperative assessment of patients with significant mitral regurgitation.
| Introduction |
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The imaging capabilities of transesophageal echocardiography make it ideally suited to assess mitral anatomy and pathology [410]. This approach should allow regurgitant defects to be reproducibly located so that they can be followed throughout the course of the disease. Modern multiplane transducers image through 180 degrees of rotation while the transducer tip remains in a fixed position, thus allowing precise image alignment with the potential for accurate localization of pathologic defects.
Despite these capabilities, routine transesophageal echocardiographic evaluation of the mitral valve remains challenging for several reasons. First, a systematic examination using standardized views is needed. Second, surgical and transesophageal echocardiographic descriptions of mitral anatomy and associated abnormalities often differ substantially. The surgeon views the mitral valve from the left atrium with the heart rotated to allow optimal exposure, whereas transesophageal images are obtained from multiple planes and perspectives. The surgeon also views the mitral valve in a nonphysiologic state because the heart has been decompressed during cardiopulmonary bypass, whereas transesophageal echocardiography images the mitral valve in its normal dynamic and physiologic state prior to cardiopulmonary bypass. Third, the currently used nomenclature for the anatomic description of the mitral valve is neither standardized nor universally accepted [11].
The purpose of this study was to develop a nomenclature and a strategy to systematically localize mitral regurgitant defects in both native and prosthetic valves using multiplane transesophageal echocardiography and to test the accuracy of this approach by comparison with the available reference standard of the surgical findings.
| Material and methods |
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Mapping of native valve pathology
To assist in the localization of native mitral regurgitant defects, a reference diagram of the mitral valve was developed, similar to one proposed by Kumar and associates [11]. The reference view was chosen to reflect the anatomic perspective of looking from the left ventricular apex toward the base of the heart (Fig 1A). On this diagram, the mitral leaflets were each divided into three sections labeled in relation to their proximity to adjacent anatomic landmarks (aortic root, left atrial appendage, and papillary muscles): A1 through A3 for the anterior leaflet and P1 through P3 for the posterior leaflet. A1 and P1 represent the anterolateral sections; A2 and P2, the middle sections; and A3 and P3, the posteromedial sections.
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Mapping of prosthetic valve pathology
Using an approach similar to that just described, a second diagram was devised to describe the anatomic relationships of prosthetic mitral valves (Fig 2A). Again, the diagram could be horizontally flipped and then rotated to provide the corresponding surgical view (Fig 2B). In the surgical view, the circumference of the sewing ring was then overlaid with a clock face and oriented in such a way that the aorta was located at the 12 oclock position.
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To perform a comprehensive examination of the mitral valve, it is essential to understand how transesophageal probe maneuvers change the imaging plane with respect to the mitral valve. Our typical examination begins with an assessment of the valve in three horizontal planes (Fig 3A). In the standard midesophageal four-chamber view (typically at a transducer angle of 0 degrees), the middle portions of both leaflets (A2 and P2) are visualized. From this position, flexion, withdrawal, or both of the transducer tip allow visualization of the aortic root and the anterolateral portions of the mitral leaflets (A1 and P1). Similarly, retroflexion, advancement, or both of the transducer tip allow visualization of the posteromedial portions of the leaflets (A3 and P3).
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Using the strategy outline here, each leaflet section was examined for the presence of prolapse or ruptured chordae tendineae and the site of mitral regurgitation. If other regurgitant defects were present (eg, fenestrations), their location was identified in this manner as well. An example of focal P1 prolapse is shown in Figure 4.
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The videotape for each study was reviewed off line and independently by one of three trained echocardiographers blinded to the surgical results. The locations of all regurgitant defects were then plotted on the reference diagrams already described (see Fig 1A, 2A). The regurgitant defect locations determined by transesophageal echocardiography and at operation were then compared.
Statistical methods
The transesophageal echocardiographic and surgical examinations of all native and prosthetic mitral valves were compared on a section by section basis. The total number of sections in which there was agreement between the transesophageal echocardiographic and surgical findings was compared with the total number of mitral valve sections evaluated in the study population using Fishers test, and a p value of less than 0.05 was considered significant.
| Results |
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| Comment |
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An improved understanding of the underlying pathophysiology of mitral regurgitation has led to advances in surgical therapies [12, 13]. Specifically, in selected patients, surgical repair has become the treatment of choice [14]. Indeed, valve repair is a particularly attractive option, as it avoids the morbidity associated with both valvular prostheses and long-term anticoagulation [14]. The mitral pathology most amenable to surgical repair involves disease localized to the posterior leaflet or to a focal portion of the anterior leaflet. Conversely, repair is less often successful when there is extensive disease of the anterior leaflet or when there is incomplete closure of the mitral valve, and in such cases, valve replacement is often required [1, 15, 16].
Advances in echocardiographic technology have improved the detail in which the mitral leaflets can be examined in real time. Although monoplane and biplane transesophageal echocardiographic transducers can visualize select portions of the mitral leaflets, limited imaging planes make a thorough assessment of the entire valve technically demanding. Accordingly, considerable expertise is necessary to obtain adequate information regarding the exact site of mitral leaflet pathology when such transducers are used. With the newer multiplane imaging probes, the entire mitral valve can be visualized with relatively little instrument manipulation, allowing adequate imaging in almost any given anatomic or physiologic variation.
Advances in both surgical techniques and imaging technology have necessitated the development of a systematic transesophageal echocardiographic approach for the evaluation of mitral regurgitation. To be clinically useful, valvular abnormalities must be accurately identified and their location defined relative to fixed anatomic landmarks. Several prior studies [4, 6, 810, 1722] have demonstrated the ability of transesophageal echocardiography to evaluate the mitral valve and identify its pathology. Fehske and colleagues [9] described the mitral pathologic findings in a group of patients in whom a complete examination of the leaflets was facilitated by the use of multiplane transesophageal echocardiography. Similarly, Stewart and co-workers [10] presented the advantages of multiplane transesophageal echocardiography in the complete examination of the mitral leaflets.
Although these studies describe the mitral pathologic findings, they provide little information as to how one should systematically evaluate the valve. A natural instinct for the echocardiographer is to concentrate on conspicuous pathologic findings; however, the presence of leaflet sections with minor disease and the absence of pathologic findings are equally important, thus necessitating a complete and systematic examination. The current study proposes such a systematic strategy using multiplane transesophageal echocardiography and validates its efficacy against a reference standard.
The distribution of defects of native mitral leaflets observed in this study was a function of the patients referred for mitral valve procedures. In our series, 70% of the lesions were localized to the posterior leaflet, a finding similar to that in a series of mitral valve repair for mitral regurgitation caused by degenerative disease [16]. In the current study, there were a small number of disagreements between the transesophageal echocardiographic and surgical findings in the native valve group. The majority of these disagreements were a consequence of localization of pathology to adjacent mitral valve sections and for the most part occurred when regurgitant lesions straddled the schematically defined sections.
Similarly, in the prosthetic valve group, six of the eight disagreements were due to localization of paravalvular leaks to adjacent sections, ie, within 30 degrees between the two methods. Most of these disagreements also resulted from regurgitant jets that straddled two or more of the schematically defined sections. Of the two remaining cases of disagreement, one was an eccentrically directed paravalvular regurgitant jet that appeared echocardiographically to be a wide leak, but at operation was found to be a localized defect without extension. The surgical finding in this instance showed a focal defect with no extension. The other case was a paravalvular leak that was identified and localized preoperatively by transesophageal echocardiography but that the surgeon was unable to find once cardiopulmonary bypass was established; this paravalvular leak was still present on the postoperative transesophageal examination.
This last case exemplifies the challenge surgeons have in trying to assess mitral defects in a nonphysiologic state. When the left ventricle is decompressed, the surrounding anatomy becomes distorted, making paravalvular leaks difficult to detect or localize. For native mitral valves, the surgeon is generally limited to assessment of the left atrial surface of the leaflets while the heart is decompressed, and this again leads to distortion of the mitral anatomy. Although insufflation of the left ventricle is a helpful technique in the evaluation of valvular and paravalvular competence, it remains a crude substitute for the true dynamic physiologic state. In contrast to the surgical setting, transesophageal echocardiography is able to evaluate the mitral valve in a normal dynamic physiologic situation without distortion of the surrounding cardiac structures. Thus, transesophageal echocardiographic findings more clearly reflect true valvular function.
One last advantage of the strategy described in this study is that it provides a standardized nomenclature to localize mitral valve pathology and that this has the potential to improve communication between the surgeon and the echocardiographer. Moreover, this method should prove useful in defining the pathologic features of the mitral leaflets during preoperative transesophageal echocardiographic evaluation. This knowledge should allow decisions regarding mitral repair versus replacement to be made outside the operating room setting.
The current study was limited in its ability to evaluate and compare prospectively the transesophageal echocardiographic and surgical findings without the introduction of bias. To limit this bias, the transesophageal echocardiographic studies were independently reviewed off line before comparison with the surgical findings as outlined in the detailed surgical report. Nonetheless, bias may still have been introduced during the performance of the intraoperative transesophageal echocardiogram, at which time cursory echocardiographic findings were relayed to the surgeon that could potentially have influenced the reporting of mitral pathology.
A promising approach to localizing mitral pathology is through three-dimensional echocardiographic reconstruction of regurgitant defects and their associated color Doppler jets, but at present, this procedure is both time-consuming and incapable of giving "on-line" information [23]. The approach used in the current study provides a rapid and accurate method for the general echocardiographer to use until the time that on-line three-dimensional mitral valve reconstruction becomes available for surgical decision making.
In conclusion, this transesophageal echocardiographic strategy provides a systematic method to accurately localize native and prosthetic mitral regurgitant lesions. By accurately localizing these defects, this strategy has the potential to improve the preoperative assessment, communication, and decisions about patients with significant mitral regurgitation.
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