Evaluation of left ventricular torsion by two dimensional tissue tracking system

背景：二维组织追踪（2DTT）技术可以利用模式匹配的方法追踪局部心肌组织。2DTT能够在临床上分别评价心内膜（Endo）和心外膜（Epi）中的左心室（LV）扭转。我们的目的是使用2DTT描述特发性扩张型心肌病（DCM）患者左室扭转对低剂量多巴酚丁胺（Dob）输注的反应。方法：10例DCM患者。我们使用配有2DTT软件的Hitachi EUB-7500超声机在静息和Dob输注期间（5，10μg/kg/min）采集LV基底和心尖短轴视图。在每个基底和心尖视图中，在Endo和Epi手动放置8个点。系统在整个心动周期中自动跟踪这些点的移动。通过定制软件确定每帧中的旋转中心，并计算和平均每个点的旋转角度。左室扭转定义为基底和心尖旋转角之间的净差。采用双平面Simpson方程计算左室舒张末期容积和左室收缩末期容积（ESV）。结果：10例患者中有7例在10μg/kg/min Dob输注后ESV下降超过10%（应答者）。在应答者中，在10μg/kg/min Dob输注时，心尖Endo和Epi旋转均增加（Endo：1.2±1.1至3.6±1.8°，Epi：0.8±0.7至2.3±1.2，p<0.01），然而，基底旋转角度在整个研究中保持不变。因此，在输注Dob后，左心室Endo和Epi的扭转增加（Endo：3.1±1.7至5.7±1.6°，Epi：2.4±1.0至4.6±1.7，p<0.05）。结论：收缩力刺激可使左室旋转增加，尤其是心尖部，反映DCM心肌收缩储备功能。

Background: The Two-Dimensional Tissue Tracking (2DTT) technique can trace regional myocardial tissue using pattern matching method. The 2DTT has a capability to clinically evaluate the left ventricular (LV) torsion in endocardium (Endo) and epicardium (Epi) separately. Our objective was to characterize the response of LV torsion to low-dose dobutamine (Dob)infusion using 2DTT in idiopathic dilated cardiomyopathy (DCM). Methods: Ten patients with DCM were studied. We acquired LV basal and apical short-axis views both at rest and during Dob infusion (5, 10μg/kg/min) using Hitachi EUB-7500 ultrasound machine equipped with 2DTT software. Eight points were manually placed both at Endo and Epi equally in each basal and apical view. The movements of these points were automatically tracked by the system throughout a cardiac cycle. The center of rotation in each frame was determined by customized software, and rotation angle of each point was calculated and averaged. The LV torsion was defined as net-difference between basal and apical rotation angle. LV end-diastolic volume and LV end-systolic volume (ESV)were assessed by the biplane Simpson's equation. Results: Seven of 10 patients showed more than 10% reduction in ESV after 10μg/kg/min Dob infusion(responder). In responders, both apical Endo and Epi rotation increased at 10μg/kg/min Dob infusion (Endo: 1.2±1.1 to 3.6±1.8°, Epi: 0.8±0.7 to 2.3±1.2, p<0.01, respectively), however, basal rotation angles unchanged throughout of study. Consequently, the LV torsion in Endo and Epi increased after Dob infusion (Endo: 3.1±1.7 to 5.7±1.6°, Epi: 2.4±1.0 to 4.6±1.7, p<0.05, respectively).On the other hand, in patients with poor LV response to Dob infusion, basal and apical rotation angles unchanged during Dob infusion. Conclusions: The augmentation of LV rotation was observed especially in apex by inotropic stimulation, which may reflect myocardial contractile reserve in DCM.