Itoh Akinobu, Ennis Daniel B, Bothe Wolfgang, Swanson Julia C, Krishnamurthy Gaurav, Nguyen Tom C, Ingels Neil B, Miller D Craig
Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA.
J Thorac Cardiovasc Surg. 2009 Nov;138(5):1090-9. doi: 10.1016/j.jtcvs.2009.03.067. Epub 2009 Sep 11.
The mitral annulus is a dynamic, saddle-shaped structure consisting of fibrous and muscular regions. Normal physiologic mechanisms of annular motion are incompletely understood, and more complete characterization is needed to provide rational basis for annuloplasty ring design and to enhance clinical outcomes.
Seventeen sheep had radiopaque markers implanted; 16 around the annulus and 2 on middle anterior and posterior leaflet edges. Four-dimensional marker coordinates were acquired with biplanar videofluoroscopy at 60 Hz. Hinge angle was quantified between fibrous and muscular annular planes, with 0 degrees defined at end diastole, to characterize its contribution to alterations in mitral septal-lateral dimension and 2-dimensional total annular area throughout the cardiac cycle.
During isovolumic contraction (pre-ejection), hinge angle abruptly increased, reaching maximum (steepest saddle shape, change 18 degrees +/- 13 degrees ) at peak left ventricular pressure. During ejection, hinge angle did not change; it then decreased during early filling (change 2 degrees +/- 2 degrees ). Septal-lateral dimension and total area paralleled hinge angle dynamics and leaflet distance (anterior to posterior marker). Pre-ejection septal-lateral reduction was 13% +/- 7% (3.3 +/- 1.5 mm) from 9% muscular dimension fall and 18 degrees +/- 13 degrees hinge angle increase.
Pre-ejection increase in hinge angle contributes substantially to septal-lateral and total area reduction, facilitating leaflet coaptation. Semirigid annuloplasty rings or partial bands may preserve hinge motion, but possible recurrent annular dilatation could result in recurrent mitral regurgitation. Long-term clinical studies are required to determine who might benefit most from preserving intrinsic hinge motion without compromising repair durability.
二尖瓣环是一个由纤维和肌肉区域组成的动态鞍形结构。目前对二尖瓣环运动的正常生理机制了解尚不完整，需要更全面的特征描述，以为瓣环成形环设计提供合理依据并改善临床结果。
对17只绵羊植入不透射线的标记物；16个围绕瓣环，2个位于前后叶中间边缘。通过双平面视频荧光透视以60Hz获取四维标记物坐标。在纤维性和肌肉性瓣环平面之间量化铰链角，舒张末期定义为0度，以表征其在整个心动周期中对二尖瓣间隔-侧壁尺寸改变和二维瓣环总面积的影响。
在等容收缩期（射血前期），铰链角突然增加，在左心室压力峰值时达到最大值（最陡的鞍形，变化18度±13度）。在射血期，铰链角不变；然后在早期充盈期减小（变化2度±2度）。间隔-侧壁尺寸和总面积与铰链角动态变化以及瓣叶距离（前后标记物之间）平行。射血前期间隔-侧壁尺寸减小13%±7%（3.3±1.5mm），其中9%是由于肌肉尺寸减小，18度±13度是铰链角增加所致。
射血前期铰链角增加对间隔-侧壁尺寸和总面积减小有很大贡献，有利于瓣叶贴合。半刚性瓣环成形环或部分带可能保留铰链运动，但可能的瓣环反复扩张可能导致二尖瓣反流复发。需要长期临床研究来确定谁最有可能从保留固有铰链运动中获益而又不影响修复耐久性。
