Left Ventricular Torsional Hysteresis: A Global Parameter for Diastolic Function

描述(由申请人提供)： 左心室(LV)舒张期功能障碍以心肌机械特性异常为特征，包括舒张性受损、LV充盈受损、心肌松弛缓慢或延迟。舒张期功能障碍是一个日益普遍的临床问题，也是充血性心力衰竭的一个主要原因。诊断舒张期功能障碍仍然是困难和有争议的。传统的超声心动图技术在提供舒张期功能的全面评估方面能力有限。具有组织标记的三维磁共振成像(MRI)提供了一种与几何无关的左心室扭转/扭转的测量方法，它确定了心肌的缩短和松弛。在这里，我们引入了一个新的概念，称为扭转滞后，它提供了一个全面的左心室舒张期功能的全球评估。在收缩过程中，心肌束的收缩及其与细胞外基质的相互作用导致扭转势能的储存。等容松弛和舒张期早期的扭转反冲释放了收缩时变形的基质中储存的势能，因此也依赖于收缩功能。我们发现，与单纯二尖瓣反流的高顺应性LV患者和正常对照组相比，有舒张期功能障碍和收缩功能保留的高血压患者的扭转滞后(定义为扭转体积环内的面积)增加。此外，我们还发现，在二尖瓣关闭不全的犬模型中，在二尖瓣关闭不全伴收缩功能障碍的进行性二尖瓣反流中，扭转滞后不会改变；在二尖瓣关闭不全且收缩功能保留的人类二尖瓣成形术中，扭转滞后不会改变。因此，我们假设，从带有标记的三维MRI计算的扭转滞后提供了一种舒张期功能的测量，反映了心肌的粘弹性特性，而不受负荷的影响。我们建议在正常受试者和可疑的舒张期功能障碍患者中测试这一假说。

DESCRIPTION (provided by applicant): Left ventricular (LV) diastolic dysfunction is characterized by abnormal myocardial mechanical properties that include impaired diastolic distensibility, impaired LV filling, and slow or delayed myocardial relaxation. Diastolic dysfunction is an increasingly prevalent clinical problem that is a major cause of congestive heart failure. Diagnosing diastolic dysfunction remains difficult and controversial. Conventional echocardiographic techniques are limited in their ability to provide a global assessment of diastolic function. 3D magnetic resonance imaging (MRI) with tissue tagging provides a geometry independent measure of LV torsion/twist, which determines shortening and relaxation of the myocardium. Here we introduce a novel concept called 'Torsional Hysteresis' that provides a comprehensive global assessment of LV diastolic function. Contraction of myocardial bundles and their interaction with extracellular matrix during systole results in storage of torsional potential energy. Torsional recoil during isovolumic relaxation and early diastole releases the potential energy stored in the deformed matrix during systole and thus is also dependent on systolic function. We have found that the torsion hysteresis defined as the area within torsion- volume loop is increased in patients with hypertension with diastolic dysfunction and preserved systolic function compared to patients with highly compliant LV of isolated mitral regurgitation and normal controls. Moreover, we have found that torsional hysteresis is not altered in progressive mitral regurgitation with progressive systolic dysfunction in a canine model of mitral regurgitation or in mitral valve repair in humans with isolated mitral regurgitation and preserved systolic function. Thus, we hypothesize that torsional hysteresis calculated from a 3-dimensional MRI with tagging provides a measure of diastolic function that reflects the viscoelastic properties of the myocardium independent of load. We propose to test this hypothesis in normal subjects and in patients with suspected diastolic dysfunction.