SPECT Imaging for Detecting Coronary Artery Disease and Determining Prognosis by Noninvasive Assessment of Myocardial Perfusion and Myocardial Viability |
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Authors: | George A Beller Ruth C Heede |
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Institution: | (1) University of Virginia Health System, Box 800158, Charlottesville, VA 22908, USA |
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Abstract: | Basic knowledge of active and passive transport mechanisms for concentrating monovalent cations in myocardial cells led to
the investigation of the application of radioisotopes of potassium, thallium, rubidium, and ammonia to the in vivo noninvasive
assessment of regional myocardial perfusion and viability utilizing gamma camera or positron emission tomographic (PET) imaging
technology. Subsequently, technetium-99m (Tc-99m)-labeled isonitriles (sestamibi and tetrofosmin), which bind to mitochondrial
membranes, emerged as superior imaging agents with single photon emission tomography (SPECT) imaging. When any of these imaging
agents are injected intravenously during either exercise or pharmacologic stress, myocardial defects in tracer uptake represent
either abnormal regional flow reserve or myocardial scar reflecting of coronary artery disease (CAD). The major clinical indications
for stress SPECT or PET myocardial perfusion imaging are for detection of CAD as the cause of chest pain and risk stratification
for prognostication. Patients with normal stress myocardial perfusion scans have an excellent prognosis with <1.0% annual
rate future annual death or nonfatal infarction. The greater the extent and severity of ischemic perfusion defects (defects
seen on stress images but improve on resting images), the greater the subsequent death or infarction rate during follow-up.
Rest imaging alone is performed for determination of myocardial viability in patients with CAD and severe left ventricular
dysfunction. Myocardial segments showing >50% uptake compared to normal uptake have a better long-term outcome with revascularization
than with medical therapy with enhanced left ventricular function and improved survival. Other applications of SPECT imaging
include the evaluation of cardiac sympathetic function, assessment of myocardial metabolism in health and disease, and molecular
imaging of coronary atherosclerosis and myocardial stem cell therapy. |
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