Glasson J R, Komeda M, Daughters G T, Foppiano L E, Bolger A F, Tye T L, Ingels N B, Miller D C
Department of Cardiovascular and Thoracic Surgery, Stanford University School of Medicine, Calif 94305-5247, USA.
Circulation. 1997 Nov 4;96(9 Suppl):II-115-22; discussion II-123.
Conventional surgical thinking indicates that mitral annular (MA) size reduction plays a key role in mitral valve closure, and most MA size and shape changes are thought to occur during left ventricular (LV) systole. The influences of left atrial (LA) and LV systole on MA size and shape, however, remain debated.
Eight radiopaque markers were placed equidistantly around the MA and imaged using high-speed simultaneous biplane videofluoroscopy in seven closed-chest, sedated sheep before and during asynchronous LV pacing. Marker images were used to compute the three-dimensional coordinates of each marker every 16.7 ms throughout the cardiac cycle, allowing calculation of three-dimensional MA area, septal-lateral (SL) dimension, and commissure-commissure (CC) dimension under control and LV pacing conditions. Maximum MA area occurred in early diastole, and minimum MA area near end-diastole; maximum area reduction was 12+/-1% (P< or =.001). Interestingly, 89+/-3% of area reduction occurred before LV systole. During this "presystolic" period, SL decreased by 8+/-1% and CC by 2+/-1%; the SL/CC ratio fell from 0.73+/-0.02 to 0.69+/-0.01 (P< or =.005), indicating a less circular shape at end-diastole. With LV pacing, total MA area reduction was similar (13+/-2 versus 12+/-1%, P=NS versus control); however, all MA area reduction occurred during LV systole with minimum MA area occurring at end-systole. Presystolic shortening in both SL and CC dimensions was lost, and presystolic ellipticalization disappeared.
Changes in MA size and shape coincident with LA systole included area reduction and shape change prior to the onset of LV contraction. These presystolic changes vanished when LA systole was absent (LV pacing). Thus, LA systole plays a pivotal role in MA size reduction and shape alteration. The unexpected timing of these MA dynamics should be taken into account during mitral valve reparative procedures.
传统外科观念认为，二尖瓣环（MA）尺寸减小在二尖瓣关闭过程中起关键作用，且多数MA尺寸和形状变化被认为发生在左心室（LV）收缩期。然而，左心房（LA）和LV收缩对MA尺寸和形状的影响仍存在争议。
在7只开胸、镇静的绵羊身上，于LV非同步起搏前及起搏过程中，在MA周围等距放置8个不透射线的标记物，并使用高速同步双平面视频荧光透视成像。在整个心动周期中，每隔16.7毫秒利用标记物图像计算每个标记物的三维坐标，从而能够计算出对照及LV起搏条件下的三维MA面积、间隔-侧壁（SL）维度和瓣环-瓣环（CC）维度。MA最大面积出现在舒张早期，最小面积接近舒张末期；最大面积减小为12±1%（P≤0.001）。有趣的是，89±3%的面积减小发生在LV收缩期之前。在这个“收缩前期”，SL减小8±1%，CC减小2±1%；SL/CC比值从0.73±0.02降至0.69±0.01（P≤0.005），表明舒张末期形状更不呈圆形。LV起搏时，MA总面积减小相似（13±2%对12±1%，与对照相比P=无显著差异）；然而，所有MA面积减小均发生在LV收缩期，最小MA面积出现在收缩末期。SL和CC维度的收缩前期缩短消失，收缩前期椭圆化消失。
与LA收缩同时发生的MA尺寸和形状变化包括在LV收缩开始前的面积减小和形状改变。当不存在LA收缩时（LV起搏），这些收缩前期变化消失。因此，LA收缩在MA尺寸减小和形状改变中起关键作用。在二尖瓣修复手术中应考虑这些MA动态变化的意外时机。
