Chronic stable angina myocardial perfusion scintigraphy
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Synonyms and Keywords: Myocardial perfusion imaging, MPI, myocardial perfusion scan, exercise myocardial perfusion imaging, stress thalium scan, nuclear stress test.
In patients with baseline ECG abnormalities, a myocardial perfusion test can be used to localize the region of ischemia. Thallium-201 and technetium-99m are the two radio-labeled agents that are frequently used for the assessment of myocardial perfusion. Myocardial uptake of thallium-201 chloride is directly proportional to the regional myocardial blood flow and is dependent on the presence of viable myocardium. In patients with known CAD, a normal thallium stress test without a perfusion defect is indicative of a benign process and associated with excellent prognosis. Patients with a normal thallium scan are at low risk for CAD and subsequent coronary angiography is indicated only if the patient has a high probabilty Duke treadmill score. Contraindications for thallium stress test include the presence of arrhythmia, acute myocarditis, severe aortic stenosis and acute MI within the past 2 days.
Stress Thallium-201 Test
- Myocardial perfusion scintigraphy with thallium-201 is frequently employed as a noninvasive test to evaluate abnormalities of myocardial perfusion in patients with established or suspected CAD.
- Thallium images may be planar or tomographic (single photon emission computed tomography i.e. SPECT). The latter are more accurate and are therefore used more frequently to assess the presence and extent of ischemic and infarcted myocardium.
Mechanism of Benefit
- Myocardial uptake of thallium-201 chloride is proportional to regional myocardial blood flow and is dependent on the presence of viable myocardium.
- During exercise, the magnitude of the increase in blood flow to the non-ischemic myocardial zones is greater than to the zones supplied by stenotic coronary arteries. Due to heterogeneous distribution of blood flow, the relative extraction of thallium by non-ischemic myocardium is greater than that by ischemic myocardium.
- During exercise thallium testing, the isotope is administered intravenously during peak exercise, and stress images are obtained immediately after discontinuation of exercise. These images reveal a decreased uptake by the ischemic myocardium, creating a perfusion defect.
- Redistribution images are obtained after 4 hours. Myocardium that was ischemic during stress but that is not ischemic at rest now extracts the isotope. Therefore, the perfusion defects during stress images are not observed in the rest images, and these reversible perfusion defects indicate the presence of viable myocardium.
- If the perfusion defects in stress images persist in the rest images, that is, if the perfusion defects are fixed, the myocardium is usually necrotic or fibrotic.
- A repeat injection of thallium and scanning 24 hours after stress can distinguish severely ischemic area from viable myocardium.
Sensitivity and Specificity
- In pooled analyses from multiple studies, the sensitivity for detecting coronary artery disease (CAD) using exercise treadmill thallium myocardium scintigraphy was approximately 84%. The specificity of excluding CAD using this test was approximately 88%. The sensitivity approaches 90% with a quantitative computer-assisted analysis of the images; during which, there is no loss of specificity.
- Considerable experience is required for the performance and interpretation of exercise thallium scintigraphy to achieve a high degree of specificity and sensitivity.
- Exercise thallium scintigraphy is less likely than exercise ECG to provide false positive test results in women.
- Exercise thalloum scintigraphy may, however, give false positive test results in patients with:
- Like the exercise ECG, thallium stress scintigraphy is less sensitive in the diagnosis of single vessel disease, particularly of circumflex coronary artery stenosis, than in multi-vessel coronary artery disease.
- Technetium-99m, a calcium analog with a higher photon energy and a shorter half life than thallium chloride, can be linked to a variety of agents.
- Technetium-99m-sestamibi is an isonitrile compound that, like thallium, is taken up by the myocardium proportional to blood flow but in contrast to thallium does not undergo redistribution.
- Technetium-99m is used as a marker of myocardial perfusion.
- Tomographic images with technetium-99m also allow images to be acquired on the first pass through the ventricle and can be used to assess the left ventricular ejection fraction.
- As a noninvasive, less expensive and readily available test at care centers, echocardiography is usually the preferable method for this purpose.
For more information on stress radionuclide myocardial perfusion imaging, click here.
For more information on comparison of exercise SPECT imaging and exercise echocardiography, click here.
For more information on techniques used to assess myocardial viability, click here.
ACC/AHA Guidelines- Nuclear Stress Testing in patients Who Are Able to Exercise (DO NOT EDIT)
Patients able to exercise
|"1. Exercise stress with nuclear MPI or echocardiography is recommended for patients with an intermediate to high pretest probability of IHD who have an uninterpretable ECG and at least moderate physical functioning or no disabling comorbidity (Level of Evidence: B)|
|"1. Exercise stress with nuclear MPI or echocardiography is reasonable for patients with an intermediatge to high pretest probability of obstructive IHD who have an interpretable ECG and at least moderate physical functioning or no disabling comorbidity (Level of Evidence: B)|
|"1. Exercise stress with nuclear MPI or echocardiography is reasonable for patients with an intermediate to high pretest probability of obstructive IHD who have an interpretable ECG and at least moderate physical functioning or no disabling comorbidity (Level of Evidence: B)|
|"2. Exercise stress with nuclear MPI is not recommended as an initial test in low-risk patients who have an interpretable ECG and at least moderate physical functioning or no disabling comorbidity.(Level of Evidence: C)|
Patients unable to exercise
|"1.Pharmacological stress with nuclear MPI or echocardiography is recommended for patients with an intermediate to high pretest probability of IHD who are incapable of at least moderate physical functioning or have disabling comorbidity (Level of Evidence: B)|
- Fihn SD, Gardin JM, Abrams J, Berra K, Blankenship JC, Dallas AP; et al. (2012). "2012 ACCF/AHA/ACP/AATS/PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease: executive summary: a report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines, and the American College of Physicians, American Association for Thoracic Surgery, Preventive Cardiovascular Nurses Association, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons". Circulation. 126 (25): 3097–137. doi:10.1161/CIR.0b013e3182776f83. PMID 23166210.