TABLE 8.1 Causes of Mitral Regurgitation
Type 1 lesions are defined by normal leaflet motion.
Most type 1 lesions are a result of annular dilation typically with central MR.
Less common mechanisms of type 1 MR include MV clefts, aneurysms, perforation, or destruction, commonly as a result of endocarditis.
In type 2 lesions, there is excessive mitral leaflet motion and the MR jet is typically directed away from the diseased leaflet.
Billowing (or scalloping) refers to a situation where part of a mitral leaflet projects above the annulus in systole, but the coaptation point remains below the mitral annulus (Fig. 8.4).
Prolapse is used to describe the excursion of a leaflet tip above the level of the mitral annulus during systole, causing regurgitation.
Flail is where a leaflet edge is flowing freely into the LA in systole, as a result of one or more ruptured chordae tendineae. The distinction between severe prolapse and flail is sometimes difficult to make because the ruptured chordae may not be visible by echocardiogram. Also, this distinction is often unimportant clinically, since the surgical treatment of both is the same.
Type 3 lesions refer to restricted leaflet motion and the MR jet is typically directed toward the diseased leaflet. When both leaflets are equally affected, the jet may be central.
In type 3a, the restriction is in both systole and diastole, and the leaflet problem is usually “structural” (most often rheumatic). When structural restriction is present, MR often coexists with some degree of mitral stenosis.
In type 3b, the restriction is only in systole and leaflet motion is normal in diastole. Here the problem is “functional” and the valve structure is normal, but proper coaptation is prevented by systolic tethering of the mitral leaflets due to left ventricular (LV) dilation and/or papillary muscles displacement. Coronary artery disease is often the etiology of type 3b MR, which is also commonly referred to as ischemic MR. An ischemic (i.e., stiff) papillary muscle may also temporarily restrict leaflet motion, causing failure of coaptation.
intraoperative imaging of structural MV disease is probably one of the most useful. Not surprisingly, the body of literature devoted to 3D echo of the MV has outpaced that of all other cardiac structures.
Begin the examination in the ME four-chamber view at 0° of transducer rotation, with the MV in the center of the screen. The anterior mitral leaflet is medial, adjacent to the aortic valve and the posterior leaflet is lateral. Slight withdrawal (10) or anteflexion (7) of the probe brings the left ventricular outflow tract (LVOT) into the plane of the scan, which demonstrates the anterior segments of the valve (A1/A2, P1/P2). Conversely, with slight insertion (10) or retroflexion (7) of the probe, the LVOT disappears from the scanning plane, allowing the examination of the posterior segments of the valve (A2/A3, P2/P3). The entire MV can therefore be seen at 0° of transducer rotation, by gently anteflexing or retroflexing the probe. A note of caution: Because of anatomic variations, the authors do not believe that the average echocardiographer can consistently discriminate between P1 and P2, or between P2 and P3 using only 0° views.
Obtain an ME mitral commissural view by rotating the imaging array to obtain the best possible cut through the commissures. This is usually achieved between 60° and 90° (11). This cross-section typically demonstrates P1 laterally, P3 medially, and variable amounts of anterior leaflet in the middle. The apparent double orifice stems from the semicircular coaptation between the leaflets of the MV. The presence and severity of disease at the level of the commissures can be evaluated here. Finally, the annular diameter (lateral-medial diameter) should also be measured to determine the contribution of annular dilation as a mechanism of MR.
Next, the ME two-chamber view is obtained by rotating the transducer forward to approximately 80 to 100°. In addition, by turning the shaft of the probe leftward and rightward, three reproducible crosssections can be obtained, allowing further identification of the valve segments (7,10).
Then, the ME long-axis view is obtained by rotating the transducer to approximately 130 to 150°. This provides a cut through the center of each MV leaflet, which allows reliable identification of A2 and P2 (11). As this view cuts across the saddle-shaped annular plane at its most superior aspect, it is a preferred view for assessing MV prolapse because it avoids the false positives which occur while using the ME fourchamber view. The second annular diameter (anterior-posterior diameter) should be measured in this view again to determine the contribution of annular dilation as a mechanism of MR.
at the time of atriotomy. Thus, advanced analysis of the causative lesions must be undertaken. The devicespecific utility of these measurements for various repairs and devices is beyond the scope of this chapter, but the measurements can be obtained from the 2D or 3D datasets described previously. Most rely on measurements performed on an ME LAX view (again, either in 2D or the idealized 3D reconstruction).