Myocardial scintigraphy in coronary artery disease

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Advances in nuclear medicine physics and engineering technology have permitted the practical application of scintigraphic methods for the diagnosis and evaluation of cardiac disease. For the ambulatory patients with suspected or known coronary disease, there are now two new, valuable, noninvasive clinical tools.

Myocardial perfusion scintigraphy

Thallium-201 (T1) is an intracellular cation which behaves much like potassium following its intravenous injection. Seventy-five to 80% of the radionuclide is extracted from the coronary circulation during the first pass, where it localizes in the myocardial cell in proportion to the relative coronary blood flow. Other determinants of T1-201 distribution include the presence of scar and, likely, the integrity of the myocardial cell membrane. Myocardial regions which are relatively underperfused, scarred, or possess membrane abnormalities will demonstrate scintigraphic defects of “cold spots.” Although coronary perfusion may remain relatively normal even through grossly stenotic vessels at rest, coronary vessels with significant stenoses cannot accommodate the increased flow necessitated by the demands of stress. Injection of T1-201 during graded treadmill exercise may, therefore, demonstrate a stress-induced heterogeneity of coronary flow resulting from the presence of a stenotic vessel among other patent or less diseased vessels. The demonstration of new stress-induced perfusion scintigram defects has proven to be both more sensitive and more specific for the diagnosis of ischemic heart disease than stress-induced electrocar-diographic S-T segment depression. Further, the stress electrocardiogram is difficult to interpret in the setting of prior infarction, intraventricular conduction abnormalities, drug effect, electrolyte abnormalities, hyperventilation, or a multitude of other conditions. The . . .



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