Myocardial metabolism of I-123-BMIPP during low-flow ischaemia in an experimental model: comparison with myocardial blood flow and F-18-FDG

Risk stratification of coronary artery disease may provide a basis for sele ction of treatment to prevent myocardial events and to assist functional re covery. lodine-123 (p-iodophenyl)-3-R,S-methylpentadecanoic acid (I-123-BMI PP) is a radioiodinated fatty acid analogue for single-photon emission tomo graphic (SPET) imaging, and several reports have demonstrated that the abno rmal uptake of I-123-BMIPP is associated with wall motion abnormality and s evere coronary artery stenosis. Clarification of the contribution of fatty acids to myocardial metabolism would be highly valuable in recognising this critical condition. In this study, we investigated the myocardial uptake o f I-123-BMIPP under low-flow ischaemia, and compared it with the uptake of fluorine-18 fluorodeoxyglucose (F-18-FDG). Using open chest dogs, the flow of the left anterior descending coronary artery was controlled using a pneu matic occluder in order to maintain a 30%-40% reduction of Doppler flow. I- 123-BMIPP and 18F-FDG were injected into the left atrium after 90 min of is chaemia (protocols 1 and 3). Canine hearts were excised after 120 min of is chaemia for the measurement of radioactivity. In protocol 2, I-123-BMIPP al one was injected and hearts were excised 8 min after the injection. A time- course biopsy study was also performed at the same time (protocol 3). Wall thickening was evaluated using a wall tracker module. The uptake of F-18-FD G increased significantly in the ischaemic region (232%+/- 135% vs non-isch aemic. P <0.05 in protocol 1) even on mild reduction of myocardial blood fl ow (MBF). The increased uptake of F-18-FDG did not correlate well with the severity of MBF. On the other hand, I-123-BMIPP uptake decreased gradually (78.9%+/- 23.6%, P <0.05 in protocol 1, and 85.9%+/- 24.3% in protocol 2) i n the ischaemic region, specifically in the endocardium (64.0%+/- 28.9%, P <0.05 in protocol 1. and 75.1%+/- 28.8%, P<0.05 in protocol 2), and correla ted strongly with MBF (r=0.93 in protocol 1 and r=0.97 in protocol 2) as a logarithmic function. This indicated that the abnormal uptake of I-123-BMIP P was associated not only with wall motion abnormality but also with the se verity of MBF In the biopsy study (protocol 3), the radioactivity of either I-123-BMIPP or F-18-FDG correlated well with the MBF at the time of tracer injection and was similar to post-mortem analysis. It is concluded that F- 18-FDG is a valid tool for identifying ischaemic myocardium even in its ear liest stages. On the other hand, I-123-BMIPP might be used to detect modera tely to severely ischaemic myocardium such as hibernation, suggesting the p otential value of I-123-BMIPP in the risk stratification of patients with s evere coronary artery disease who require revascularisation without delay.