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Are technetium-99m-labeled myocardial perfusion agents adequate for detection of myocardial viability?
1Department of Medicine, University of Virginia, Charlottesville 22908, USA.
Insights
New technetium-99m (99mTc) perfusion agents like 99mTc-sestamibi show promise for assessing myocardial viability in ischemic cardiomyopathy. These agents, when used with quantitative SPECT, can identify patients who benefit from revascularization.
Area of Science:
- Nuclear Cardiology
- Cardiovascular Imaging
- Radiopharmacology
Background:
- Assessing myocardial viability is crucial for guiding revascularization in coronary artery disease patients with reduced left ventricular function.
- Thallium-201 (201Tl) has been the standard for viability assessment, but new technetium-99m (99mTc) agents offer improved imaging properties.
- The efficacy of 99mTc-based perfusion agents for myocardial viability assessment remains under investigation.
Purpose of the Study:
- To evaluate the utility of new 99mTc-labeled perfusion agents (99mTc-sestamibi, 99mTc-tetrofosmin) for assessing myocardial viability.
- To compare the performance of 99mTc agents with Thallium-201 (201Tl) in identifying viable myocardium.
- To determine if these agents can identify patients with myocardial hibernation who would benefit from revascularization.
Main Methods:
- Utilized quantitative SPECT imaging with 99mTc-sestamibi and 99mTc-tetrofosmin.
- Conducted experimental laboratory studies to assess tracer uptake in ischemic myocardium.
- Employed ECG-gated SPECT to evaluate regional systolic thickening and assess viability in cases of attenuation.
- Administered nitrates prior to tracer injection to improve sensitivity.
Main Results:
- 99mTc-sestamibi and 99mTc-tetrofosmin show only slightly lower uptake than 201Tl in ischemic myocardium.
- These 99mTc agents remain intracellularly bound in viable myocytes under stunning and hibernation.
- ECG-gated SPECT demonstrated preserved systolic thickening indicative of viability despite decreased 99mTc counts due to attenuation.
- Nitrate administration improved sensitivity for identifying viable segments.
Conclusions:
- New 99mTc perfusion agents are effective for determining myocardial viability in patients with severe regional dysfunction and coronary artery disease.
- Quantitative SPECT with 99mTc agents can identify myocardial hibernation and predict improved function post-revascularization.
- Higher resting myocardial uptake of 99mTc agents correlates with a greater probability of improved systolic function after revascularization.
Abstract:
The noninvasive assessment of myocardial viability in patients with coronary artery disease and depressed left ventricular function has proven clinically useful for identifying those patients with ischemic cardiomyopathy who benefit most from coronary revascularization. Thallium-201 (201Tl) imaging at rest has been the radionuclide imaging technique most often utilized for distinguishing viable myocardium from scar. However, new technetium-99m (99mTc) perfusion agents such as 99mTc-sestamibi and 99mTc-tetrofosmin have emerged as alternatives to 201Tl for imaging of regional myocardial perfusion. Whether these new agents, which have better physical properties for imaging with a gamma camera than 201Tl, are valid for use in assessing myocardial viability is still uncertain. Recent clinical studies have demonstrated that these agents, when imaged using quantitative SPECT, can identify patients with myocardial hibernation who exhibit improved regional systolic function following revascularization. Experimental laboratory studies have shown that the uptake of 99mTc-sestamibi and 99mTc-tetrofosmin in ischemic myocardium is only slightly lower than the uptake of 201Tl. These 99mTc-labeled agents remain bound intracellularly in mitochondria of viable myocytes under conditions of myocardial stunning and short-term hibernation, producing severe myocardial asynergy. With respect to determination of viability, the inferior wall region is at times problematic since attenuation of 99mTc-sestamibi and 99mTc-tetrofosmin is greatest in this area. Demonstration of preserved systolic thickening on ECG-gated SPECT images is indicative of viability in the instance of decreased regional 99mTc counts due to attenuation and not scar. Administration of nitrates prior to tracer injection improves the sensitivity for identifying viable myocardial segments using rest imaging with 99mTc-sestamibi or 99mTc-tetrofosmin. Thus, it appears that the new 99mTc perfusion imaging agents can be successfully employed for the determination of myocardial viability in the setting of severe regional dysfunction and chronic coronary artery disease. The greater the myocardial uptake of these agents in the resting state, the greater the probability of improved systolic function after coronary revascularization.