Mr Sherif Nagueh
Imaging can be used to identify the presence as well as the extent of myocardial damage in patients with coronary artery disease (CAD). The presence of segmental dysfunction due to myocardial necrosis is readily examined by echocardiography. Most labs use a semiquantitative score and a 17 segment model. Left ventricular (LV) endocardial border visualization can be enhanced using intravenous contrast agents, if needed. In addition to looking at regional function at rest, the use of dobutamine echocardiography can help determine the presence of contractile reserve. In the absence of contractile reserve, there is a low likelihood of improvement in segmental function after revascularization. For global function to improve, the presence of at least 3-5 segments with a biphasic response (improvement of function at low dose with deterioration at high dose) is needed. Recent developments with 3D and myocardial strain have been applied to study cardiac function in patients with CAD. For example, the presence of reduced (less negative) longitudinal strain/strain rate and the occurrence of post-systolic deformation are characteristics of dysfunctional segments.
Cardiac magnetic resonance (CMR) is another modality that has been used for the same objectives as those outlined above for echocardiography. CMR detects and quantifies injured myocardium. It can quantify transient injury and can be used to derive the salvation index. CMR measurements of infarct size have been shown to predict outcomes in several patients groups, including those presenting with acute coronary syndromes and those with CAD and hibernating myocardium. There is growing interest in using T1 mapping to study myocardial damage, but additional studies are needed.
Both SPECT and PET have been used to diagnose myocardial ischemia and scarring, and thus to detect viability. The presence of viability using nuclear imaging techniques was shown to predict segmental and global recovery of function after revascularization. However, there is a discrepancy between observational studies and randomized clinical trials with respect to prognosis. The ESC guidelines for heart failure management published in 2012 recommend revascularization for heart failure patients with CAD and angina, but there is no clear recommendation for viability imaging in the absence of angina. The detection of myocardial denervation in the region of an MI is possible using I-123 MIBG and the extent of denervation has been shown to predict outcome, including risk of ventricular arrhythmias.
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