Attenuated Plaque at Nonculprit Lesions in Patients Enrolled in Intravascular Ultrasound Atherosclerosis Progression Trials

Objectives: We investigated attenuated plaque (hypoechoic plaque with deep ultrasonic attenuation despite absence of bright calcium) in nonculprit lesions. Background: Recent intravascular ultrasound (IVUS) studies describe acoustic shadowing behind large, echolucent, acute culprit lesion sites in the absence of bright calcium. Such "attenuated plaque" is considered a characteristic of high-risk lesions, but its prevalence in stable nonculprit lesions is incompletely known. Methods: We reviewed IVUS pullback data from nonculprit vessels in 159 patients from the ASTEROID (A Study to Evaluate the Effect of Rosuvastatin on Intravascular Ultrasound-Derived Coronary Atheroma Burden) trial. We identified attenuated plaque and compared volumetric IVUS data in the segments with and without attenuation. In addition, we described plaque morphology in segments with attenuation at baseline and follow-up. Results: Attenuated plaque was found in 17 of 159 patients (10.7%, 95% confidence interval: 6% to 17%). At baseline, there were no significant differences in clinical presentation and cardiovascular risk factors between patients with and without attenuation. Other than a greater plaque eccentricity index (p = 0.008), there were no significant differences between segments with and without attenuation. In segments with attenuated plaque, expansive remodeling was observed in 53%, and calcified plaque adjacent to the attenuation site in 70% of patients. During follow-up, attenuation remained stable, and no events occurred in the patients with attenuation. Conclusions: Attenuated plaque is present in a significant number of nonculprit segments in patients enrolled in IVUS progression trials and remains stable during follow-up. There is a relationship with mixed calcified lesions. These findings challenge the prior assumption that attenuated plaque is a finding limited to culprit lesions associated with acute clinical presentation.