Fatty acid imaging with 123I-15-(p-iodophenyl)-9-R,S-methylpentadecanoic acid in acute coronary syndrome.

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). 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 microg/kg/ min) were considered viable. 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). 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.