Noninvasive radionuclide procedures for diagnosis and management of myocardial ischemia

Abstract Three noninvasive radionuclide techniques are of value in diagnosis and management of patients with myocardial ischemia.201Thallium is an analogue of potassium that is distributed in myocardial tissue in proportion to regional blood flow following intravenous administration. Studies obtained using this agent during rest and exercise identify regions of myocardial fibrosis and ischemia and provide a functional assessment of regional blood flow. Improvement in the distribution of regional myocardial perfusion has been documented following coronary artery bypass grafting, and the procedure may have practical importance in the postoperative assessment of patients.99mTechnetium pyrophosphate is a radiopharmaceutical that localizes in acutely infarcted myocardial tissue and is of particular benefit in the diagnosis of postoperative myocardial infarction. Documentation of acute myocardial infarction by this method is indicated in patients in whom the diagnosis cannot be confirmed by electrocardiograms or other clinical modalities. Radionuclide angiocardiography is a third radionuclide technique that holds great promise in the management of patients with myocardial ischemia. A single bolus injection of tracer with rapid recording of precordial counts using a computerized gamma camera provides measurement of individual chamber transit times and mean volumes, cardiac output, and ventricular volumes and ejection fraction. The study provides serial measurements of cardiac function and permits evaluation of the cardiac response to acute exercise stress. Patients with myocardial ischemia acutely dilate the left ventricle in response to increased cardiac work load, and the magnitude of dilatation appears to be related to the magnitude of ischemia. Successful myocardial revascularization reverses the abnormal response to exercise, and greatly improved left ventricular function can be documented during exercise following coronary artery bypass grafting.