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The noninvasive assessment of myocardial viability
1Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville 22908.
Insights
Noninvasive imaging techniques like thallium-201 (201Tl) scintigraphy help select patients with coronary artery disease for revascularization. Quantitative resting 201Tl scintigraphy is most effective for identifying viable myocardium.
Area of Science:
- Cardiology
- Nuclear Medicine
- Medical Imaging
Background:
- Coronary artery disease (CAD) with severe left ventricular dysfunction necessitates accurate assessment of myocardial viability.
- Improved patient selection for revascularization is crucial for better outcomes.
Purpose of the Study:
- To evaluate noninvasive imaging techniques for detecting myocardial viability.
- To identify the most effective method for distinguishing viable from irreversibly injured myocardium in patients with CAD.
Main Methods:
- Comparison of thallium-201 (201Tl) scintigraphy, positron emission tomography (PET), technetium-99m (99mTc) sestamibi imaging, and dobutamine echocardiography.
- Analysis of imaging findings such as tracer uptake, redistribution, and reversibility.
- Correlation of imaging results with improvement in ejection fraction and systolic function post-revascularization.
Main Results:
- Stress 201Tl scintigraphy indicates viability through normal uptake, redistribution, or reversibility.
- Higher 201Tl uptake in dysfunctional areas predicts greater ejection fraction improvement after revascularization.
- FDG uptake on PET correlates with improved systolic function; 99mTc sestamibi is useful post-myocardial infarction; dobutamine echocardiography has limitations in akinetic zones.
Conclusions:
- Quantitative resting 201Tl scintigraphy appears superior for differentiating viable from irreversibly injured myocardium.
- Accurate viability assessment guides patient selection for revascularization, optimizing treatment strategies.
Abstract:
The major objective of noninvasive imaging for detection of myocardial viability is to assist in the improved selection of patients with coronary artery disease and severe left ventricular dysfunction who would benefit most from revascularization. The techniques most commonly used to identify viable myocardium are thallium-201 (201Tl) scintigraphy, positron emission tomography (PET) using a flow tracer in combination with a metabolic tracer, technetium-99m (99mTc) sestamibi imaging, and dobutamine echocardiography. On stress 201Tl scintigraphy, asynergic regions showing normal thallium uptake, an initial defect with delayed redistribution at 3-4 h, late redistribution at 24 h, or defect reversibility after reinjection of a second dose of 201Tl at rest all suggest preserved viability. The greater the final uptake of 201Tl in areas of regional myocardial dysfunction preoperatively, the greater the improvement in ejection fraction after coronary revascularization. Demonstration of uptake of fluoro-18 deoxyglucose (FDG) in regions of diminished blood flow on PET imaging also correlates well with improved systolic function after revascularization. 99mTc sestamibi may also be useful for assessment of myocardial viability, particularly after thrombolytic therapy for acute myocardial infarction. Dobutamine echocardiography has good positive predictive value for viability determination, but absence of systolic thickening in an akinetic zone in response to intravenous infusion of the drug may still be associated with viable myocardium in 25-50% of segments. Of all the techniques cited above, quantitative resting 201Tl scintigraphy may be the best approach for distinguishing between viable and irreversibly injured myocardium.