The relationship between attenuated plaque identified by intravascular ultrasound and no-reflow after stenting in acute myocardial infarction: the HORIZONS-AMI (Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction) trial.

OBJECTIVES: The aim of this study was to understand the impact of attenuated plaque on distal embolization during stent implantation in patients with acute myocardial infarction (AMI).

BACKGROUND: Attenuated plaques identified by grayscale intravascular ultrasound (IVUS) might predict transient deterioration in coronary flow and/or no-reflow during percutaneous coronary intervention (PCI).

METHODS: We analyzed clinical, angiographic, and IVUS data from 364 patients (n = 364 infarct-related arteries) enrolled in the randomized HORIZONS-AMI (Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction) trial. No-reflow was final Thrombolysis In Myocardial Infarction (TIMI) flow grade ≤2 in the absence of mechanical obstruction. Attenuated plaque was hypoechoic or mixed atheroma with ultrasound attenuation without calcification. A mean attenuation score was created by measuring the angle of attenuation each 1 mm, scoring the angle as 1 to 4 (corresponding to <90°, 90° to 180°, 180° to 270°, or 270° to 360°, respectively), summing the scores, and normalizing for analysis length.

RESULTS: Overall, 284 (78.0%) patients had attenuated plaques; no-reflow occurred in 37 (10.2%). Patients with no-reflow had a higher mean attenuation score (median [interquartile range] 2.2 [0.0 to 2.8] vs. 1.3 [0.7 to 1.8], p < 0.001), lower baseline left ventricular ejection fraction (52.8% [43.2% to 61.5%] vs. 61.4% [52.2% to 68.1%], p = 0.002), and more baseline angiographic thrombus (89.2% vs. 74.1%, p = 0.043) with no differences in post-PCI stent expansion versus patients without no-reflow. Multivariate analysis indicated that mean attenuation score was the strongest predictor of no-reflow. The mean attenuation score that best predicted no-reflow was ≥2 points (90° to 180°, sensitivity of 81.5%, and specificity of 80.5%).

CONCLUSIONS: Attenuated plaque was present in three-quarters of patients with AMI. The amount of attenuated plaque strongly correlated with no-reflow; the larger the attenuated plaque, the greater the likelihood of no-reflow. (Dual Arm Factorial Randomized Trial in Patients w/ST Segment Elevation AMI to Compare the Results of Using Anticoagulation With Either Unfractionated Heparin + Routine GP IIb/IIIa Inhibition or Bivalirudin + Bail-out GP IIb/IIIa Inhibition; and Primary Angioplasty with stent implantation with Either a Slow Rate-release Paclitaxel-eluting Stent [TAXUS™] or Uncoated Bare Metal Stent [EXPRESS2™]; NCT00433966).