Molecular imaging identifies regions with microthromboemboli during primary angioplasty in acute coronary thrombosis

Microthromboemboli (MTE) may contribute to the no-reflow phenomenon in acute myocardial infarction (AMI) either spontaneously or after primary percutaneous transluminal coronary angioplasty (PTCA). We hypothesized that myocardial MTE in acute coronary syndromes can be identified on imaging by in vivo ^99mTc labeling of the coronary thrombus with a compound that binds to the glycoprotein IIb/IIIa present on activated platelets (DMP-444). Methods: Fifteen dogs underwent left anterior descending coronary artery (LAD) injury in to produce thrombus, whereas 5 control dogs had LAD ligation. Before recanalization, the risk area (RA) and myocardial blood flow (MBF) were measured, and in vivo thrombus labeling was performed using ^99mTc- labeled DMP-444. Nine of the 15 LAD injury dogs had occlusive thrombus on angiography and underwent PTCA. MBF measurements were repeated 30 and 60 min after recanalization, and ^99mTc autoradiography (hot spot imaging) was performed ex vivo to determine the extent and magnitude of MTE. Results: The ratio of hot spot size to RA size was higher in the 9 LAD injury dogs with thrombus compared with the 6 dogs with no thrombus (90% ± 22% vs. 42% ± 16%; P = 0.005). In control dogs, this ratio was significantly lower (29% ± 11%; P = 0.05). ^99mTc activity within the RA was higher in 8 of the 15 coronary injury dogs with AMI compared with those without AMI (1.8 ± 0.48 vs. 1.24 ± 0.22; P = 0.02). Conclusion: MTE can be detected and quantified after primary PTCA. The infarct size is proportional to the magnitude and extent of MTE, indicating that MTE may contribute to the AMI. Thus, in vivo thrombus labeling during reperfusion may provide important information in patients with AMI that may lead to better adjuvant therapy during PTCA.