Nonrheumatic Etiologies of Mitral Stenosis: Situations That Mimic Mitral Stenosis

Mitral Annular Calcification

Rheumatic mitral stenosis (MS) is, by far, the most common cause of left ventricular (LV) inflow obstruction. Less common cause are listed in Box 92.1 . Among these, a heavily calcified mitral annulus is the most often encountered. Calcium deposits in the mitral annulus are extremely common, mainly in older persons or “prematurely” in patients with chronic renal disease on long-term dialysis. ^, Mitral annulus calcium (MAC) is commonly asymptomatic and an incidental finding. Despite the frequency with which such deposits are encountered, hemodynamic consequences are relatively uncommon. Large deposits, however, may produce mild or moderate degrees of mitral regurgitation (MR) and uncommonly severe MR. ^, The valvular MR results from splinting of the physiologic contraction of the mitral annulus during systole and by stiffening of the leaflets. MS caused by severe MAC is much less common. The mechanisms by which MAC contributes to degenerative mitral stenosis (DMS) include (1) reduced normal annular dilatation during diastole, (2) impaired mobility of the anterior mitral leaflet because the leaflet’s hinge point is displaced toward its free margin because of calcium, and (3) large posterior mitral annular deposits narrowing the annulus. ^{, , ,} This is especially true in patients with valvular aortic stenosis (AS) because of calcium extending from the aortic annulus into the base of the anterior mitral leaflet. Elevated LV pressure (as is the case in significant AS) increases mitral annular stress and, if present, may lead to trauma and annular micro cracks. These sites of annular damage are thought to undergo further degenerative calcification, leading to MAC.

Gross pathologic differences exist between rheumatic mitral stenosis (RMS) and MS associated with MAC ( Boxes 92.2 and 92.3 ). Likewise, the echocardiographic appearance of the mitral apparatus can distinguish these entities. The echocardiographic features of MS caused by MAC can be seen in Fig. 92.1 and Video 92.1A, Video 92.1B, Video 92.1C, Video 92.1D and are summarized as follows: Calcification is prominent in the basal portion of both mitral leaflets with sparing of the free edges of the leaflets. This is precisely the opposite of the pattern seen in RMS where the tips or free edges are the thickest portion of the leaflets. In addition, unlike RMS, in which the mitral leaflets move in tandem (“parallel”) because of commissural fusion, the leaflets in MAC have qualitatively normal (“antiparallel”) diastolic motion, although the amplitude of leaflet motion is reduced. These features are best imaged in the parasternal long-axis and apical four-chamber views. Last, in rheumatic MS, there is commissural fusion best imaged in the short-axis view. Commissural fusion is absent in MS because of MAC. This feature has important clinical relevance, because these patients do not benefit from percutaneous balloon mitral valvotomy, which derives its benefit from splitting the fused commissure(s).

Video 92.1. The echocardiographic features of mitral stenosis caused by mitral annular calcification. A–D, Calcification is prominent in the basal portion of both mitral leaflets with sparing of the free edges of the leaflets.

There are no standardized echocardiographic criteria to grade the severity of MAC. The classic echocardiographic techniques used for rheumatic MS (mitral valve [MV] area planimetry, pressure halftime, proximal isovelocity surface area, and continuity equation) lack validation for DMS. The limiting orifice of mitral inflow in DMS is typically located at the base of the mitral leaflets. Thus, planimetry at the level of the leaflet tips does not represent the true stenotic orifice. Moreover, severe calcification and blooming artifacts may interfere with visualizing the limiting orifice. Three-dimensional (3D) echocardiography, with transthoracic (TTE) or transesophageal echocardiography (TEE), may overcome these limitations be cause of its ability to obtain an en face view of the mitral orifice. 3D-echocardiography can also be helpful in demonstrating the absence of commissural fusion.

The treatment of calcific MS has been challenging for several reasons, including the unavailability of medical therapies to prevent progression and the lack of role for balloon mitral valvuloplasty or surgical commissurotomy. In addition, surgical MV replacement is limited by technical difficulties and complications related to trying to remove heavy MAC, placing sutures, and seating prosthetic valves, especially in older adult high-risk patients with comorbidities. Recent innovations in transcatheter interventional procedures for MV disease has been aimed predominantly at MR. Nevertheless, procedures such as transcatheter MV replacement may provide an option for these patients. Initial results have been promising.