Assessment of vulnerable plaques causing acute coronary syndrome using integrated backscatter intravascular ultrasound.

OBJECTIVES: This study aims to define tissue characteristics of vulnerable plaques before acute coronary syndrome (ACS) by use of integrated backscatter intravascular ultrasound (IB-IVUS). BACKGROUND: Tissue characterization of coronary plaques is possible with the use of IB-IVUS. METHODS: The subjects were 140 patients with angina pectoris, and we selected 160 coronary lesions without significant stenosis for evaluation. Ultrasound signals were obtained by an IVUS system using a 40-MHz catheter. RESULTS: At the follow-up (30 +/- 7 months), 12 plaques caused ACS after the initial IVUS examination. Ten of the 12 plaques had IVUS parameters recorded at baseline. These 10 plaques were classified as vulnerable plaques (VP), and the other plaques were classified as stable plaques (SP; n = 143). There was no significant difference of vessel area, lumen area, and plaque area between VP and SP. However, plaque burden (60 +/- 9% vs. 52 +/- 9%; p = 0.014), eccentricity (0.70 +/- 0.10 vs. 0.55 +/- 0.17; p = 0.013), remodeling index (1.30 +/- 0.08 vs. 1.16 +/- 0.16; p = 0.006) and percentage lipid area (72 +/- 10% vs. 50 +/- 16%; p < 0.0001) were greater in VP than in SP. Percentage fibrous area (23 +/- 6% vs. 47 +/- 14%; p < 0.0001) was smaller in VP than in SP. The sensitivities, specificities, and positive predictive values of percentage fibrous area (90%, 96%, and 69%, respectively) and percentage lipid area (80%, 90%, and 42%, respectively) for classifying VP were evaluated. CONCLUSIONS: Tissue characteristics of VP before ACS were different from those of SP. This suggests that VP and SP as classified by IB-IVUS are useful in predicting ACS.