機能的僧帽弁逆流に対する弁輪縫縮術 -―僧帽弁ジオメトリーに及ぼす影響

Beneficial Effects of Restrictive Annuloplasty on Subvalvular Geometry in Patients with Functional Mitral Regurgitation and Advanced Cardiomyopathy

機能性僧帽弁逆流症（functional mitral regurgitation：FMR）は，拡張型心筋症や虚血性心筋症にしばしば合併し，それらの予後を悪化させることが知られている．弁尖の器質的病変によって発生する器質的僧帽弁逆流症と異なり，FMRでは僧帽弁自体に病的所見を認めない．FMRの主たる機序は，弁輪拡大ならびに進行性の左室拡大に伴う乳頭筋付着部左室壁の外側変位による僧帽弁尖の心尖部方向への牽引（tethering）に起因する閉鎖不全という見解でおおむね一致している1～9）．このtetheringにより弁尖のcoaptation zoneの減少およびcoaptation pointの心尖部方向の変位が起こった結果，僧帽弁逆流症（MR）が生じる．

Objectives: The effects of restrictive mitral annuloplasty （RMA） on subvalvular geometry remains unknown. We evaluated changes in left ventricular （LV） function, severity of mitral regurgitation （MR） and leaflet tethering parameters after RMA and clarified their associations.

Methods: In 44 patients with clinically-relevant functional MR who underwent RMA, distances between papillary muscle （PM） tips and anterior mitral annulus （PM-tethering distance）, leaflet angles relative to lines connecting annuli, and interpapillary muscle distance （IPMD） were serially quantified.

Results: One month after surgery, LV function and MR severity improved with decreased anterior （34±5 to 30±4 mm） and posterior PM-tethering distance （37±4 to 32±4 mm）, anterior-leaflet angle （ALA）［32±8 to 22±7 degree］, and IPMD （31±6 to 25±5 mm）, while these variables remained abnormal and posterior-leaflet angle （PLA） increased （34±8 to 48±14 degree）［p＜0.01 for all］. During follow-up （66±37 months）, these effects were maintained in 33 patients without MR recurrence, whereas 11 with it showed worsened tethering with less LV function recovery. Multiple linear regression analyses identified that change in MR severity from baseline to 12-month examination independently associated with corresponding change in IPMD （parameter estimate of 0.100 with standard error of 0.039, p＝0.019） and that in posterior PM-tethering distance （parameter estimate of 0.104 with standard error of 0.045, p＝0.035）, while not with change in PLA. The IPMD change was independently associated with change in LV end-systolic dimension （parameter estimate of 0.299 with standard error of 0.110, p＝0.013）.

Conclusions: RMA procedure partially relieved leaflet tethering, evidenced by decreased tethering distances and IPMD；the latter was the main determinant of MR. These beneficial effects might be mainly attributed to post-RMA reverse LV remodeling, potentially offsetting the negative effect of augmented PLA in selected patients.