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Fatty Acid Imaging with ¹²³I-15-(p-Iodophenyl)-9-R,S-Methylpentadecanoic Acid in Acute Coronary Syndrome

First Department of Internal Medicine and Department of Radiology, Yamagata University School of Medicine, Yamagata, Japan

Correspondence: For correspondence or reprints contact: Satomi Fujiwara, MD, First Department of Internal Medicine, Yamagata University School of Medicine, 2-2-2 Iida-Nishi, Yamagata 990-9585, Japan.

ABSTRACT

¹²³I-15-(p-iodophenyl)-9-R,S-methylpentadecanoic acid (9-MPA) has recently been developed as a tracer for myocardial fatty acid uptake. The aim of this study, which was performed as part of a phase III clinical trial of 9-MPA, was to test the usefulness of 9-MPA for the assessment of myocardial viability in patients with acute coronary syndrome (ACS). Methods: Fifteen patients with ACS who had undergone direct percutaneous transluminal coronary angioplasty were examined. Myocardial SPECT with 9-MPA and ^99mTc-sestamibi and low-dose dobutamine echocardiography were performed within 2 wk after onset. The 9-MPA images were obtained 10 and 60 min after tracer administration, and sestamibi imaging was begun 60 min after the injection. The left ventricle was divided into 9 segments, and 9-MPA and sestamibi uptake were scored from 0 (normal) to 3 (no activity) in each segment. Lower uptake of 9-MPA than of sestamibi was defined as a mismatch. Myocardial segments showing improvement in wall motion during low-dose dobutamine infusion (5–10 µg/kg/min) were considered viable. Results: The 9-MPA images were of high quality for all patients. Myocardial uptake of 9-MPA was lower in ischemic myocardium than in nonischemic myocardium (58.2% ± 14.2% versus 91.9% ± 6.5%, P < 0.0001). Clearance of 9-MPA from ischemic myocardium was slower than that from nonischemic myocardium (10.2% ± 11.7% versus 19.1% ± 5.9%, P < 0.01). A mismatch was seen in 10 of 15 patients, and 18 of 20 (90%) mismatched segments were defined as viable by dobutamine echocardiography. Conversely, 18 of 20 (90%) matched segments did not show any improvement in function during dobutamine stimulation (P < 0.0001). Uptake of 9-MPA in nonviable segments was lower than that in dysfunctional but viable segments (P < 0.05), and 9-MPA clearance from nonviable segments was slower than that from viable segments (P < 0.05). Conclusion: The imaging characteristics of 9-MPA for SPECT are excellent, allowing noninvasive assessment of myocardial fatty acid uptake. Myocardial imaging with 9-MPA may reveal impaired fatty acid uptake in dysfunctional but viable myocardium and thus provide useful information for clinical decision making in ACS.

Key Words: ¹²³I-15-(p-iodophenyl)-9-R,S-methylpentadecanoic acid • acute coronary syndrome • fatty acid metabolism • myocardial viability • stunned myocardium

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