New ways to scan the myocardium
Disease of the coronary arteries, the major blood vessels supplying the heart, can be detected by imaging of the myocardium, or heart muscle, using radioactive thallium chloride (Tl-201). The thallium is injected into the bloodstream and taken up into the heart cells. A special camera is used to detect the radioactive emissions given off by Tl-201, thereby showing its distribution in the heart. When blood flow in the heart is normal, the thallium will be evenly distributed. Under conditions of myocardial ischemia, or an insufficient blood supply to heart tissue, there is uneven distribution of radioactivity generated by thallium. Administering the drug dipyridamole or exercise testing results in dilation, or widening, of the coronary arteries, and causes increases in blood flow and movement of Tl-201 into the heart cells; however, coronary arteries that are narrowed will show reduced or delayed uptake of Tl-201. Dipyridamole is used in patients who cannot exercise, but should not be given to patients with a recent heart attack or refractory angina, chest pain that cannot be relieved with conventional agents. Dipyridamole causes few serious side effects, and minor side effects can be reversed. Adenosine can also be used to dilate the coronary arteries, but causes more frequent and transient serious effects than dipyridamole. Single photon emission computed tomography (SPECT) is an imaging technique that produces images of several layers of the heart tissue and appears to be sensitive in detecting a diseased coronary artery. Compounds with radioactive technetium (Tc-99m) can be used in higher doses than that of Tl-201 and produce superior images of the heart. Tc-99m sestamibi and Tc-99m teboroxime have recently been approved for use in the imaging of the heart by the Food and Drug Administration. Positron emission tomography (PET) is similar to SPECT and can detect areas of altered metabolism in the heart in addition to defects in blood flow. Innovations in techniques that provide images of the heart have helped to improve the diagnosis of coronary heart disease. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: Medical Letter on Drugs and Therapeutics
Electron-beam computed tomography, coronary artery calcium, and evaluation of patients with coronary artery disease
It may be too soon to recommend electron beam computed tomography (CT) as a diagnostic tool to identify patients with coronary artery disease. This technique detects calcium deposits in the arteries, which can be a component of plaque. A review of the medical literature on electron-beam CT revealed that although the technique can easily detect severe blockage in the coronary arteries, blockage less than 50% might be missed. And the absence of calcium deposits would not guarantee that the artery was free of plaque. Even a large plaque might be stable and not inclined to rupture.
Publication Name: Annals of Internal Medicine
Nuclear Cardiology in the UK: Do We Apply Evidence Based Medicine?
Nuclear medicine, particularly myocardial perfusion imaging, is useful to identify patients with coronary artery disease. It is helpful in identifying the correct level of treatment and therefore cost effective for the National Health Services in allocating resources.
Publication Name: Heart
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