^99mTc-glucarate imaging for the early detection of infarct in partially reperfused canine myocardium

Purpose: ^99mTc-glucarate is an imaging agent developed for the detection of acutely infarcted myocardium. The purposes of the current study were to (1) determine whether ^99mTc-glucarate can detect acute infarct in the setting of only partial minimal reperfusion, (2) study the persistence and time course of scan positivity following coronary occlusion and intravenous tracer injection, (3) assess the ability of ^99mTc- glucarate to determine infarct size, and (4) compare these data with previous results obtained using a 100% reperfusion model. Methods: Six dogs underwent left circumflex (LCx) coronary occlusion for 90 min, followed by 10% epicardial blood flow reperfusion. Fifteen mCi (555 MBq) ^99mTc-glucarate was injected intravenously 30 min later. Serial gamma camera images were acquired over 240 min. Microsphere blood flow determinations were performed at baseline, during occlusion, during tracer administration, and just before euthanasia. Ex vivo gamma camera images were obtained. Triphenyltetrazolium chloride (TTC) staining was performed to assess infarct size. Results: Qualitatively, ^99mTc-glucarate images showed a well-defined "hot spot" in all six dogs by 30 min after tracer injection (150 min following coronary occlusion), which persisted for 240 min following tracer administration. Quantitatively, there was a significant increase in the LCx/LAD (left anterior descending) counts ratio beginning 10 min after tracer administration (130 min after occlusion), and continuing to 240 min after tracer administration. Tracer retention was 12.0±0.9% for the LAD and 39.0± 4.1% for the LCx hot spot zone (p<0.05) at 240 min after ^99mTc-glucarate injection. The correlation coefficient was 0.90 for infarct size by TTC versus ^99mTc-glucarate. Conclusion: In the setting of only partial minimal coronary reperfusion following infarction, ^99mTc-glucarate myocardial uptake is delayed and less intense compared with the setting of complete reperfusion. Nevertheless, infarcts can still be reliably detected in dogs using qualitative in vivo imaging, and significant abnormalities in quantitative parameters are observed. Thus, ^99mTc-glucarate imaging may be useful for the clinical detection and relative sizing of acute myocardial infarction, even in the setting of only minimal coronary reperfusion.