Goldfine H, Aurigemma G P, Zile M R, Gaasch W H
Department of Medicine, University of Massachusetts Medical Center, Worcester 01655, USA.
J Am Coll Cardiol. 1998 Jan;31(1):180-5. doi: 10.1016/s0735-1097(97)00453-1.
We tested the hypothesis that postoperative left ventricular (LV) systolic wall stress can be predicted from the change in LV diastolic dimension and ejection fraction (EF) after surgical correction of chronic mitral regurgitation (MR). We used a simple mathematic model to predict postoperative systolic stress from end-diastolic dimension and EF. The validity of this model was assessed using data from 21 patients undergoing mitral valve replacement (MVR) for chronic MR.
The decline in EF after MVR for chronic MR is traditionally thought to be a consequence of a postoperative increase in afterload, caused by closure of a low resistance runoff into the left atrium. However, consideration of the Laplace relation suggests that afterload does not necessarily increase after the operation.
A spherical mathematical model of the left ventricle was used to define the relations between LV end-diastolic dimension, systolic wall stress and EF. To test the validity of this model, clinical and echocardiographic data were obtained from 21 patients with chronic MR before and 10 to 14 days after MVR. These echocardiographic data were examined with reference to plots derived from the mathematical model.
Patients were categorized as those in whom end-diastolic dimension declined after the operation (group I, n = 15) and those with no reduction in end-diastolic dimension (group II, n = 6). Group I patients were subclassified into those undergoing MVR with chordal preservation (group Ia) and those undergoing MVR with chordal transection (group Ib). In groups Ib and II, there were significant reductions in EF (56 +/- 3% to 48 +/- 3% in group Ib and 50 +/- 2% to 40 +/- 3% in group II, both p < 0.05), but the changes in end-diastolic dimension and wall stress differed. In group Ib, end-diastolic dimension decreased and systolic wall stress was unchanged; in group II, end-diastolic dimension was unchanged and wall stress increased. In contrast, group Ia patients experienced a substantial reduction in end-diastolic dimension, no change in EF and a reduction in stress. The corresponding length-force-shortening coordinates closely approximate those predicted from a mathematic model relating end-diastolic dimension to EF and systolic wall stress.
Concordant echocardiographic and mathematical model results indicate that postoperative changes in systolic stress are directly related to changes in chamber size and that LV afterload may fall when chordal preservation techniques are used in combination with MVR.
我们检验了这样一个假设，即慢性二尖瓣反流（MR）手术矫正后左心室（LV）收缩期壁应力可根据LV舒张末期内径和射血分数（EF）的变化来预测。我们使用一个简单的数学模型，根据舒张末期内径和EF来预测术后收缩期应力。使用21例因慢性MR接受二尖瓣置换术（MVR）患者的数据评估该模型的有效性。
传统上认为，慢性MR患者MVR后EF下降是由于左心房低阻力血流通道关闭导致术后后负荷增加所致。然而，考虑拉普拉斯关系表明术后后负荷不一定增加。
使用左心室的球形数学模型来定义LV舒张末期内径、收缩期壁应力和EF之间的关系。为检验该模型的有效性，获取了21例慢性MR患者MVR术前及术后10至14天的临床和超声心动图数据。参照从数学模型得出的图表对这些超声心动图数据进行分析。
患者被分为术后舒张末期内径下降的患者（I组，n = 15）和舒张末期内径未降低的患者（II组，n = 6）。I组患者又被细分为保留腱索进行MVR的患者（Ia组）和横断腱索进行MVR的患者（Ib组）。在Ib组和II组中，EF均显著降低（Ib组从56±3%降至48±3%，II组从50±2%降至40±3%，均p<0.05），但舒张末期内径和壁应力的变化不同。在Ib组中，舒张末期内径减小而收缩期壁应力未改变；在II组中，舒张末期内径未改变而壁应力增加。相比之下，Ia组患者舒张末期内径大幅减小，EF无变化且应力降低。相应的长度-力-缩短坐标与根据将舒张末期内径与EF和收缩期壁应力相关联的数学模型预测的结果非常接近。
超声心动图和数学模型结果一致表明，收缩期应力的术后变化与心室大小的变化直接相关，并且当保留腱索技术与MVR联合使用时LV后负荷可能降低。
