Echocardiographic Diagnosis of Mitral Valve Prolapse

Transcription

1 Echocardiographic Diagnosis of Mitral Valve Prolapse Pravin M. Shah, MD, Loma Linda, California HISTORICAL PERSPECTIVE Barlow et al. 1 are generally credited with drawing attention to the correlation between the presence of mid-late systolic click and angiographic evidence of aneurysmal protrusion of the posterior leaflet of the mitral valve; they subsequently called this association billowing mitral leaflet syndrome. Crily et al. 2 coined the term mitral valve prolapse and reported the cineangiographic findings correlating timing of clicks with timing of prolapse. Shah and Gramiak, 3 in abstract form, first reported the echocardiographic recognition of mitral valve prolapse in 1970 with M mode echocardiography. Several investigators confirmed its usefulness and further refined the criteria, and M-mode echocardiography was readily embraced as a noninvasive marker to diagnose mitral valve prolapse. 4-7 This method was used in population surveys including the famous Framingham studies. 8 9 Kisslo et al. 10 first reported use of two-dimensional echocardiography using parasternal cross sections. 10 Morganroth et al. 11 subsequently used the apical views to diagnose mitral valve prolapse because the annular orifice plane can generally be well delineated from the apical cross sections. The two-dimensional echocardiography with multiple imaging planes provided improved assessment of tomographic anatomy and soon replaced them-mode approach with its limited ice-pick view for diagnosis of mitral valve prolapse. TERMINOLOGY AND DEFINITIONS The diagnosis of mitral valve prolapse is further complicated by a lack of consensus on the precise defi- From the Department of Medicine, Lorna Linda University Medical Center. JAM Soc ECHOCARDIOGR 1994;7: Reprint requests: Pravin M. Shall, MD, Professor of Medicine, Lorna Linda University Medical Center, Lorna Linda, CA Copyright 1994 by the American Society ofechocardiography /94$ / nition of mitral valve prolapse among cardiologists, cardiac surgeons, cardiac pathologists, and cardiac sonographers or echocardiographers. The clinical symptom-complex associated with mitral valve prolapse is diverse, and its pathophysiologic aspects are poorly understood. A pathoanatomic definition that could be commonly agreed on and that could be uniformly applied would be useful in achieving consistency in diagnosis and in the study of the natural history of the condition. The following definition is proposed: The mitral valve prolapse is characterized by varying portions of one or both leaflets of the mitral valve extending or protruding abnormally above the mitral annular plane. This definition recognizes that a normal hooding or bulging of the closed mitral leaflets is a consequence of disparity between the combined leaflets area and the annular orifice area. The normal mitral leaflets are relatively "redundant'' as compared with the orifice that they render competent. The posterior leaflet normally shows a scalloped appearance, usually with three distinct scallops: lateral, middle, and medial scallops. The middle scallop is the largest, and the medial is the smallest. The anterior leaflet is normally not scalloped. A transition from a normal bulging to an abnormal "billowing" or "excessive hooding" constitutes the occurrence of mitral valve prolapse. The excessive hooding resulting from increased redundancy or thickening (caused by "myxomatous" changes) of varying portions of the valve leaflets constitutes primary or myxomatous mitral valve prolapse. In advanced cases, the mitral annulus is often dilated, and more extensive development of leafletchordal redundancy and thickening are noted with pronounced billowing leaflet appearance. The valve is often incompetent but not severely so until one or more chordae rupture. When excessive hooding or valve prolapse results from hemodynamic causes without intrinsic abnormality of the leaflets, as with marked volume depletion and decreased left ventricular size or with large atrial septal defect and a small left ventricle, stretched (akinetic) ischemic papillary muscle, for example, the term secondary mitral prolapse has been used. Thus "secondary'' mitral pro-

2 Journal of the American Society of Echocardiography Volume 7 Number 3 Part l Shah 287 lapse occurs in the absence of pathologic or morphologic changes in the valve leaflets, whereas the primary mitral valve prolapse must, by definition, be associated with myxomatous thickening and redundancy. This latter condition may be idiopathic, as is more common, associated with Marfan's syndrome or Ehlers-Danlos syndrome, or, infrequently, may be a result of acute rheumatic carditis. Because the terms "primary'' mitral valve prolapse and "secondary'' mitral valve prolapse have been used differently by various authors, the following new classification and terminology is proposed. Myxomatous mitral valve prolapse may be idiopathic (often familial) or associated with connective tissue disorders (e.g., Marfan's syndrome, Ehlers-Danlos syndrome, Stiekler syndrome) or infection (e.g., rheumatic valvulitis). 'CJiemodynamic'J mitral valve prolapse may be associated with hypovolemia with a decrease in left ventricular cavity size; atrial septal defect with a large left-to-right shunt; or severe isolated right ventricular enlargement (e.g., severe tricuspid regurgitation). The hemodynamic group is associated with an alteration in geometry or marked reduction in the size of the left ventricular cavity, making the normal leafletchordal apparatus more redundant, with resulting excessive hooding. ((Flail)) mitral valve prolapse is a term reserved for chordae rupture resulting in prolapse associated with failure of leaflet margins to coapt. The causes of chordae rupture include spontaneous rupture, which commonly but not exclusively results from myxomatous change; trauma, especially blunt chest trauma, such as steering wheel injuries; and infection, a consequence of bacterial endocarditis. ECHOCARDIOGRAPHIC DIAGNOSIS Echocardiography is probably the most used and most useful technique for objective confirmation of the diagnosis of mitral valve prolapse. Practically no role exists for undertaking contrast angiography solely to make a diagnosis. Diagnostic criteria for each of the three major categories of mitral valve prolapse are proposed. Myxomatous Mitral Valve Prolapse The echocardiographic findings are best considered under two headings, namely, structural and functional. It must be emphasized that the extent and severity of the myxomatous change vary from being focal and limited to one segment of a leaflet to being generalized and involving extensive aspects of both leaflets and the chordae tendineae. Multiple tomographic planes must be viewed to diagnose a localized abnormality. Structural changes. With regard to leaflet thickening) the myxomatous change consists of an increase in the spongiosa layer and its encroachment of the fibrosa with its resulting disruption. The echocardiographic hallmark of the myxomatous change is thickening. Thus an increase in valve thickness is an important finding. Because echocardiographic image is highly gain dependent, detection of increased thickness is not easily made except when it is extensive and prominent. An assessment of thickness of a tissue at a given depth may best be made by comparing other anatomic structures at similar depth. Thus a comparison of the aortic valve cusps or posterior aortic wall with the anterior mitral leaflet as viewed in parasternal long-axis view could prove useful. Normally, anterior leaflet is less thick than the posterior aortic wall and has thickness similar to the aortic cusps. Another mark for comparison is the ventricular endocardium, which normally has thickness similar to the normal leaflet structure. Thus, at any given gain setting, an internal comparison of these structures provides a useful clue of true increase in thickness rather than a factitious one caused by an increase in gain. The mitral leaflet structure, including an increase in thickness, may be better appreciated by transesophageal echocardiography. A localized abnormality may be more readily detected by multiplane or ornniplane probe. With regard to mitral annular size) a frequent, although by no means constant, accompaniment of myxomatous mitral valve prolapse is the presence of annular dilation. Echocardiography is capable of providing accurate assessment of mitral annular size. The annular diameters in the apical four- and two-chamber views can be measured directly and the annular area calculated considering an oval geometry of the mitral annulus. Primary dilation or ectasia of the annulus in the absence of enlargement of the left ventricle or the left atrium may be seen. The annular orifice becomes markedly enlarged and patulous when significant mitral regurgitation coexists. With regard to subvalve structures) elongated redundant chordae tendineae may be visualized in association with other valvular changes. Functional changes. The diagnostic functional change is an abnormal protrusion of a variable portion of the mitral leaflet( s) posterosuperior to the annular plane into the left atrium. The earlier echocardiographic criteria used multiple apical cross sec-

3 288 Shah Journal of the American Society of Echocardiograpl1y May-June 1994 Figure 1 Effect of nonplanarity of the mitral annulus on appearance of mitral leaflet prolapse in four-chamber and long-axis views. The normal anterior mitral leaflet is displaced superior to the annular plane in the four-chamber view (A) but not in the long-axis view (B). However, the posterior leaflet and the coaptation points are not normally displaced superior to the annular plane in either cross section. Such a displacement in four-chamber view (C) and in long-axis view (D) are both abnormal and indicative of prolapse of different segments of the posterior leaflet. tions to demonstrate the abnormal protrusion with an assumption that the annulus is planar. The mitral annular size and shape during the phases of cardiac cycle were reported by Ormiston et al ; however, its planarity was not investigated. Levine et al. 14 investigated this aspect and reported that the annular outline resembled that of a saddle so that both the annular margins as visualized in the four-chamber view were more apically displaced as compared with the two annular margins as visualized in the longaxis views. This observation led to a proposition that abnormal protrusion of the leaflet( s) may only be diagnosed in the long-axis view because the true superior extent of the annular plane is obtained in that view. Suzuki et al. 15 investigated the annular shape in a larger population of normal subjects and those with mitral valve prolapse and confirmed the annulus to be nonplanar but with one important difference. The annular margin along the anterior leaflet attachment alone was displaced apically but not along the posterior leaflet attachment in the four-chamber view. It had an outline of only one half of a saddle tilted apically at the anterior leaflet attachment in the four-chamber view. The posterior leaflet attachment all along the annular margins was observed to be in a uniform plane. This observation has recently been confirmed in our laboratory with the three-dimensional transesophageal echocardiographic technique (echo computed tomography). The implications of these data on the planar shape of the annulus are schematically shown in Figure l. Thus a superior protrusion of the anterior leaflet may be observed normally in the four-chamber view (Figure la) but not in the long-axis view (Figure lb). However, superior protrusion of the posterior leaflet is abnormal as visualized in either the four-chamber view (Figure lc) or the long-axis view (Figure ld). A clinical example is shown in Figure 2. This observation is important in diagnosis because the myxomatous prolapse may be localized to a portion of one leaflet, and the tomographic nature of echocardiographic imaging may fail to detect it in any given cross section. It may be recalled that apical fourchamber view transects the posterior aspect of the anterior leaflet and anterior edge of the large middle scallop or the lateral scallop of the posterior leaflet.

4 Journal of the American Society of Echocardiography Volume 7 Number 3 Part 1 Shah 289 Figure 2 Diastolic frame in apical long-axis cross section of left ventricle (,.4l{); left atrium (LA), and aorta (AO). B, Systolic frame with the mitral leaflets in closed Pf:>.~ition. Dotted line refers to the plane of the mitral annulus. Mitral valve does not show pr~pse in this view. However, four-chamber view (C) in the same patient clearly demonstqtted prolapse localized to posterior mitral leaflet (arrow). The mitral annular diameter was 3.~ em, and estimated mitral annular area was approximately ll cm 2 No valve regurgitati9n ~as"rioted at rest; however, with Valsalva's maneuver a late systolic jet by continuous wa~e Dl!>ppler was demonstrated. An anteriorly angulated four-chamber view, the socalled five-chamber view with aorta in view, will generally provide an image of the lateral scallop of the posterior leaflet. The long-axis plane transects the anterior portion of the anterior mitral leaflet and the middle scallop of the posterior leaflet. The small medial scallop of the posterior leaflet is visualized in the two-chamber cross section. When myxomatous change is localized, its prevalence is observed in order of decreasing frequency: the middle scallop of posterior leaflet, the lateral scallop of posterior leaflet, the anterior mitral leaflet, and the medial scallop of the posterior leaflet. I emphasize that the magnitude of nonplanarity of the mitral annulus is such that the anterior leaflet protrusion in excess of l em as visualized even in the four-chamber view should be considered abnormal. To summarize, a functional change of posterior

5 290 Shah Journal of the American Society of Echocardiography May-June 1994 Figure 3 A, Appearance of severe prolapse of both leaflets with intact coaption at the tips suggests hooding and may be referred to as billowing mitral valve. B, Appearance of failure of tip coaption with posterior leaflet free margin displaced superiorly indicates flail mitral leaflet. A tip of the ruptured chordae tendineae (arrow) may be visualized, especially by transesophageal echo. leaflet protrusion is abnormal in either the fourchamber or the long-axis view and that of the anterior leaflet protrusion is always abnormal in the long-axis view and may also be abnormal in the four-chamber view when it exceeds 1 em. The abnormal protrusion or prolapse may involve predominantly the bellies of the leaflets (Figure 3A), and this appearance may be referred to as billowing mitral leaflets. Alternately, the free margin of a leaflet may protrude or prolapse (Figure 3B), and this appearance may be referred to as the flail mitral valve. The flail valve is generally a result of chordal rupture that may be visualized more readily with transesophageal echocardiography (see arrow in Figure 3B). A clinical example of billowing mitral valve in a patient with Marfan's syndrome is shown in Figure 4; an example of flail mitral valve is seen in Figure 5. Hemodynamic Mitral Valve Prolapse The hemodynamic mitral valve prolapse is characterized by excessive hooding or billowing without associated structural changes. The leaflet-chordae reveal normal thickness, and left ventricular cavity size is decreased. Associated conditions, such as atrial septal defect, pulmonary hypertension, or severe tricuspid regurgitation without left ventricular abnormality (e.g., carcinoid syndrome), may be diagnosed. Flail Mitral Valve Prolapse The appearance of flail mitral valve as schematized in Figure 3B is characteristic. However, the extent of flail leaflet is determined by the number and type of chordae ruptured. A localized flail leaflet may be visualized only in one cross section depending on the anatomic portion involved. An extensive flail leaflet may be seen in multiple views. In addition to its characteristic appearance, the flail leaflet is generally associated with an eccentric jet of mitral regurgitation. The direction of the eccentric jet is determined by location of the flail leaflet. Thus flail middle scallop of the posterior leaflet is associated with an eccentric jet directed anteriorly behind the aortic root and may extend somewhat medially based on size of the middle scallop. The flail lateral scallop is associated with a jet directed medially toward the inter atrial septum (Figure 6). The flail anterior leaflet results in the jet being directed posterolaterally, and the medial scallop flail is associated with laterally directed jet. SUMMARY AND CONCLUSIONS The present editorial, besides providing a historical review, offers a succinct definition and a new classification and terminology. It is hoped that this or a similar classification would clarify some of the confusion surrounding the diagnosis of mitral valve prolapse. The current echocardiographic criteria are reviewed. Some difficulty in the diagnosis of milder forms of prolapse is inevitable because a distinction between normal bulging and excessive hooding may be subtle in such cases. The proposed criteria using multiple echocardiographic cross sections (rather

6 Journal of the American Society of Echocardiography Volume 7 Number 3 Part l Shah 291 Figure 4 A patient with Marfan's syndrome shows thickened anterior mitral leaflet (two arrows) in an open diastolic position as seen in the apical long-axis view (A). The systolic frame in the same view (B) shows billowing of both leaflets and posteriorly displaced but intact coaptation point (arrow). A more striking billowing or hooding appearance of both leaflets was also noted in the apical four-chamber view. Arrow points to coaptation. The patient had no mitral regurgitation. Auscultation revealed multiple clicks that varied with Valsalva's maneuver. than the long-axis view alone) is more likely to provide a comprehensive visualization of several components of the leaflets and avoid errors of underdiagnosis of localized myxomatous prolapse abnormality. The criteria and discussion are based on the author's experience and interest in the diagnosis of this condition and clinical correlations with intraoperative findings. If the cardiac surgeons and the echocardiologists could agree on a common terminology and classification scheme, it could result in

7 Journal of the American Society of Echocardiography May-June Shah Figure 5 Systolic frame in a lower parasternal imaging plane demonstrated the flail posterior mitral leaflet in systole. AML, anterior mitral leaflet; PML, posterior mitral leaflet- RA R 8 APICAL FOUR CHAMBER VIEW Figure 6 Apical four-chamber view shows eccentric jet of mitral regurgitation directed toward the interatrial septum and swirling within the left atrial (LA) cavity as seen in A and shown schematically in B. MR, Mitral regurgitation; R V, right ventricle; RA, right atrium; LV, left ventricle; LA, left atrium. Small curved arrows in left atrium show a clockwise swirling in this view. At surgery, the patient had ruptured chordae to a large middle scallop of the posterior mitral leaflet. better anatomic correlations of the echocardiographic findings in this condition and potentially result in improved patient care. I thank Diane Battin, Debra Pulps, and Charlene LaBelle for technical assistance and Shari Reddall for expert secretarial assistance. REFERENCES 1. Barlow JB, Bosman CK, Pocock WA, et al. Late systolic murmur and nonejection (mid-late) systolic clicks. Br Heart J 1968;30: Criley JM, Lewis KB, Humphries JO, et al. Prolapse of the mitral valve: clinical and cine-angiocardiographic findings. Br Heart J 1966;28:

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