DIAGNOSTIC METHODS MYOCARDIAL ISCHEMIA Iodine 123-phenylpentadecanoic acid myocardial scintigraphy: usefulness in the identification of myocardial ischemia

In this study, we tested the hypothesis that myocardial ischemia induced by exercise in patients is associated with diminished metabolism and/or delayed clearance of an intravenously injected fatty acid, iodine 123-labeled phenylpentadecanoic acid (IPPA). Fifteen normal volunteers and 18 patients with significant coronary heart disease (CHD) received IPPA during exercise. In the patients with CHD, radionuclide ventriculograms were also obtained during exercise. The normal volunteers had relatively uniform initial left ventricular segmental IPPA activity after exercise and uniform IPPA clearance in the interval from 4 to 20 min immediately after exercise. In contrast, the patients with CHD had increased initial left ventricular segmental IPPA activity (63%, p < .001) and delayed IPPA clearance (44%, p < .01) in segments supplied by significantly narrowed coronary arteries. Based on analysis with the mean values + 1 SD for initial IPPA activity, clearance, or both in normal volunteers, the sensitivity and specificity of exercise IPPA scintigraphy for detecting CHD were 89% and 67%, respectively; when + 2 SD differences from the mean values in the normal volunteers were considered, the sensitivity and specificity were 72% and 100%, respectively. Among the total of 27 noninfarcted left ventricular segments supplied by significantly narrowed coronary arteries in the study patients, 26 (96%) had an abnormality (mean + 1 SD) of either initial IPPA activity or clearance compared with corresponding segments in the normal volunteers and/or with other left ventricular segments in the same image that were not supplied by significantly narrowed coronary arteries. Thus, these data suggest that IPPA scintigraphy may be used in the identification of myocardial ischemia in patients with CHD by demonstrating abnormal initial left ventricular segmental IPPA activity and/or delayed clearance after exercise. Circulation 74, No. 5, 1007-1015, 1986. UNDER AEROBIC and fasting conditions, free fatty acids are the preferred substrate of normal myocardium, providing up to 90% of resting energy requirements." 2 Therefore, radiolabeled fatty acids have attracted great interest for cardiac imaging and as potential probes of myocardial metabolism. Studies by Sobel, Schelbert, and Weiss and their colleagues and others using "C-palmitate with positron tomography have shown great promise for this technique in definFrom the Departments of Internal Medicine (Cardiology Division), Pathology, and Radiology at the University of Texas Health Science Center at Dallas. Supported in part by NHLBI Ischemic SCOR grant HL-17669 and the Moss Heart Fund, Dallas. Address for correspondence: James R. Corbett, M.D., The University of Texas Health Science Center, Department of Radiology, 5323 Harry Hines Blvd., Dallas, TX 75235. Received Jan. 27, 1986; revision accepted July 17, 1986. Vol. 74, No. 5, November 1986 ing ischemic and infarcted myocardium.3-1 However, such studies require a cyclotron to produce short-lived radioisotopes as well as specialized imaging systems. Thus, these methods are expensive and not presently available for routine clinical use at most institutions. Several fatty acids, including hexadecanoic and heptadecanoic acids, have been synthesized and labeled with single photon-emitting radioisotopes. 12-18 Modifications of fatty acid chain length,19 degree of methylation,20 or incorporation of metallic heteroatoms such as tellurium21-23 have been attempted to alter myocardial uptake or metabolism. In some instances, however, interpretation of the myocardial kinetics of these agents has been hampered by poor image contrast due to release of free radioiodine by the myocardium and by hepatic ,B-oxidation. Freundlieb et al."8 have proposed correction procedures for identify1007 by gest on A ril 6, 2017 http://ciajournals.org/ D ow nladed from