Myocardial fatty acid utilization at various workloads in normal volunteers: Iodine-123 phenylpentadecanoic acid and single photon emission computed tomography to investigate myocardial metabolism

Iodine-123 phenylpentadecanoic acid (IPPA) is a synthetic long chain fatty acid that is useful for the scintigraphic evaluation of myocardial perfusion and fatty acid metabolism. The current investigation was undertaken to characterize IPPA uptake and washout patterns in normal volunteers. Nineteen healthy volunteers (11 men and 8 women) underwent IPPA scintigraphic imaging using single photon emission computed tomography (SPECT). Studies were performed at rest, following submaximal exercise, and following maximal (symptom limited) exercise. Analyses of IPPA uptake, activity distribution, washout, and the true negativity of the method were performed for both pooled and sex specific data at all three cardiac workloads. This study found similar total heart IPPA uptake for men and women at each workload, and evidence for faster total heart IPPA washout for men. A consistent pattern of diminished relative IPPA activity anteriorly for women, and inferiorly for men, was shown. Submaximal exercise produced minimally increased IPPA uptake and significantly increased washout compared with rest values, whereas maximal exercise resulted in substantially increased IPPA uptake associated with markedly decreased IPPA washout. Thus, IPPA SPECT at various cardiac workloads in normal volunteers demonstrates (1) sex related differences in IPPA myocardial distribution, (2) evidence for greater IPPA turnover in men, (3) enhanced IPPA utilization during submaximal exercise, and (4) uncoupling of IPPA uptake and washout during maximal exercise, reflecting impaired myocardial fatty acid metabolism at high cardiac workloads.