[Myocardial scintigraphy with iodine 123-labeled fatty acids]

Abstract

This study presents experimental and clinical data in the use of I-123 labeled aromatic and aliphatic fatty acids. I-123 p-phenylpentadecanoic acid (p-IPPA) and I-123 heptadecanoic acid (HDA) were applied for myocardial scintigraphy. The feasibility of p-IPPA and HDA for myocardial scintigraphy was substantiated in animal experiments. Clinical studies were performed in patients with coronary artery disease (CAD) and cardiomyopathy (CMP). In CAD the results of fatty acid studies were compared with those of T1-201. Myocardial scintigraphy with p-IPPA and HDA was done with the patients supine and the collimator of the gamma camera in the LAO 45 grade position. Following intravenous administration of the labeled compounds data were continuously monitored. The regional distribution of the I-123 labeled fatty acids was assessed visually and supplemented with a semiquanitative analysis to estimate regional fatty acid uptake within the myocardium. The uptake was expressed as a ratio of background corrected regional myocardial activity to background activity (V. cava superior region). In initial studies data were accumulated for 40 minutes after intravenous HDA and for 50 minutes after intravenous p-IPPA, respectively. Data interpretation could be improved by an extended data acquisition (HDA: 70 minutes; p-IPPA: 90 minutes). In earlier experiments the decline in the myocardial count rate seemed to be monoexponential. However, in studies with prolonged data acquisition the myocardial time activity curve could be better described by two exponentials. Accordingly, the time activity curve was fitted with a biexponential function and the elimination half time of the initial and second component were determined. In addition, by extrapolation of the monoexponential slope of each component to zero, the size of each component was evaluated and the relative contribution of each phase on the myocardial elimination curve was expressed by a ratio of these extrapolated values. Our data provided evidence that I-123 labeled fatty acids can be used as metabolic tracers, as their kinetic behaviour was comparable to C-11 palmitate. Furthermore, in p-IPPA studies catabolites of its metabolic degradation were identified in plasma samples. Additionally it was shown in HDA studies that pharmacological interventions and acute ischemia were effective modulators of myocardial HDA utilization. In our patients we found a slower myocardial elimination half time for p-IPPA than for HDA; also the amount of p-IPPA utilized via the initial component was smaller than for HDA.(ABSTRACT TRUNCATED AT 400 WORDS)