Bonow R O, Dilsizian V
Cardiology Branch, National Heart, Lung, and Blood Institute, Bethesda, MD 20892.
Semin Nucl Med. 1991 Jul;21(3):230-41. doi: 10.1016/s0001-2998(05)80043-1.
Left ventricular (LV) performance is reduced in a large subset of patients with chronic coronary artery disease (CAD) and LV dysfunction on the basis of regionally ischemic or hibernating myocardium rather than irreversibly infarcted tissue. The detection of dysfunctional but viable myocardium is clinically relevant since regional and global LV function in such patients will improve after revascularization procedures; however, the identification of patients with such potentially reversible LV dysfunction is difficult. Although thallium 201 imaging may be of value in detecting viable myocardium if regions with perfusion defects during exercise demonstrate redistribution of thallium on a 3- to 4-hour resting image, thallium defects often appear persistently "fixed" within regions of severely ischemic or hibernating myocardium. It has been shown that up to 50% of regions with apparently irreversible thallium defects will improve in function after revascularization. Thus, standard exercise-redistribution thallium scintigraphy may not differentiate LV dysfunction arising from infarcted versus hibernating myocardium. The precision with which thallium imaging identifies viable myocardium can be improved greatly by additional studies once 4-hour redistribution imaging demonstrates an irreversible thallium defect. These additional studies include late (24-hour) redistribution imaging, repeat imaging after thallium reinjection, or a combination of thallium reinjection followed by late imaging. Several recent studies suggest that thallium reinjection techniques, by demonstrating thallium uptake in dysfunctional regions with apparently irreversible defects, predict improvement after revascularization with similar predictive accuracy as that achieved using metabolic imaging with positron emission tomography (PET). Studies directly comparing such thallium methods and PET, which thus far involve only small numbers of patients, suggest that the assessment of regional metabolic activity using PET and the assessment of regional thallium activity using single photon emission computed tomography provide concordant results. These findings, if confirmed by larger ongoing studies, suggest that thallium reinjection imaging is a convenient, clinically accurate, and relatively inexpensive method with which to identify viable myocardium in patients with chronic CAD and LV dysfunction.
在患有慢性冠状动脉疾病（CAD）且左心室（LV）功能不全的大部分患者中，左心室功能降低是基于局部缺血或冬眠心肌，而非不可逆梗死组织。检测功能失调但存活的心肌具有临床意义，因为此类患者在血运重建术后局部和整体左心室功能会改善；然而，识别具有这种潜在可逆性左心室功能障碍的患者却很困难。尽管如果运动期间有灌注缺损的区域在3至4小时静息图像上显示铊再分布，铊201显像在检测存活心肌方面可能有价值，但铊缺损在严重缺血或冬眠心肌区域常持续呈现“固定”状态。已表明，高达50%表面上不可逆的铊缺损区域在血运重建后功能会改善。因此，标准运动再分布铊闪烁显像可能无法区分梗死心肌与冬眠心肌引起的左心室功能障碍。一旦4小时再分布显像显示不可逆铊缺损，通过额外研究可大大提高铊显像识别存活心肌的精确度。这些额外研究包括延迟（24小时）再分布显像、铊再注射后重复显像，或铊再注射后延迟显像的联合应用。最近的几项研究表明，铊再注射技术通过显示在表面上不可逆缺损的功能失调区域摄取铊，预测血运重建后的改善情况，其预测准确性与使用正电子发射断层扫描（PET）代谢显像所达到的相似。直接比较此类铊方法和PET的研究（目前仅涉及少数患者）表明，使用PET评估局部代谢活性和使用单光子发射计算机断层扫描评估局部铊活性可提供一致结果。如果正在进行的更大规模研究证实这些发现，则表明铊再注射显像对于识别患有慢性CAD和左心室功能障碍患者的存活心肌是一种方便、临床准确且相对廉价 的方法。
