Functional mitral stenosis after surgical annuloplasty for ischemic mitral regurgitation: importance of subvalvular tethering in the mechanism and dynamic deterioration during exertion

Abstract

Objective: Diastolic subvalvular mitral leaflet tethering by left ventricular remodeling that restricts leaflet opening in the presence of annular size reduction by surgery for ischemic mitral regurgitation potentially causes functional mitral stenosis in the absence of organic leaflet lesions. Exercise, known to worsen systolic tethering and ischemic mitral regurgitation, might also dynamically exacerbate such mitral stenosis by increasing tethering. This study evaluates the mechanism and response of such mitral stenosis to exercise.

Methods: We measured the diastolic mitral valve area, annular area, and peak and mean transmitral pressure gradient by echocardiography in 20 healthy individuals and 31 patients who underwent surgical annuloplasty for ischemic mitral regurgitation.

Results: Although the mitral valve area and annular area did not significantly differ in healthy individuals (4.7 +/- 0.6 cm(2) vs 5.2 +/- 0.6 cm(2), not significant), mitral valve area was significantly smaller than the annular area in patients after annuloplasty (1.6 +/- 0.2 cm(2) vs 3.3 +/- 0.5 cm(2), P < .01). The mitral valve area was less than 1.5 cm(2) only after the surgery (P < .01) and was significantly correlated with restricted leaflet opening (r(2) = 0.74, P < .001), left ventricular dilatation (r(2) = 0.17, P < .05), and New York Heart Association functional class (P < .05). Exercise stress echocardiography of 12 patients demonstrated dynamic worsening in functional mitral stenosis (mitral valve area: 2.0 +/- 0.5 cm(2) to 1.4 +/- 0.2 cm(2), P < .01; mean pressure gradient: 1.5 +/- 0.9 mm Hg to 6.0 +/- 2.2 mm Hg, P < .01).

Conclusions: Persistent subvalvular leaflet tethering in the presence of annular size reduction by surgery in ischemic mitral regurgitation frequently causes functional mitral stenosis at the leaflet tip level, which is related to heart failure symptoms and can be dynamic with significant exercise-induced worsening.

FIGURE 1

A, Potential mechanism of functional MS after surgical annuloplasty for ischemic MR. Valve tethering in ischemic MR restricts leaflet mobility even in diastole, thereby reducing leaflet opening (middle). However, MVA is not usually small enough to cause significant MS. Surgical annuloplasty to reduce annular size might further limit valve opening, which could result in significant functional MS without organic leaflet disease (right). B, Methods to quantify diastolic mitral leaflet tethering in apical long-axis view. α1 and α2 express diastolic tethering of anterior and posterior leaflets, respectively. Mitral leaflet tip opening dimension ($\ell 1$), annular dimension ($\ell 2$), and their ratios ($\ell 1∕\ell 2$) were also measured. C, Mitral leaflet opening and filling flow velocity before and after surgical annuloplasty for ischemic MR. Before surgery, leaflet opening angle a1 is restricted, leaflet opening dimension is mildly reduced, and filling flow velocity is mildly increased. After surgery, leaflet opening dimension is further reduced and increase in filling flow velocity is significant. Ao, Aorta, LA, left atrium; LV, left ventricle; MS, mitral stenosis; MR, mitral regurgitation; IMR, ischemic mitral regurgitation.

FIGURE 2

A, B, Dynamic worsening of functional MS observed by exercise stress echocardiography in a patient who underwent surgical annuloplasty for ischemic MR. During exercise, the left ventricle tended to dilate, mitral leaflet opening dimension decreased, and mitral flow velocity increased.