The association between intravascular ultrasound-derived echo-attenuation and quantitative flow ratio in intermediate coronary lesions

Background: The clinical relevance of moderate coronary stenosis is determined by its morphological characteristics and physiological significance. We investigated the relationship between high-risk plaque characteristics detected by intravascular ultrasound and functional significance assessed with quantitative flow ratio (QFR) in intermediate coronary lesions. Methods: QFR was retrospectively analyzed in 352 intermediate lesions from 330 patients undergoing intravascular ultrasound examination. The functional significance was defined as QFR 50.8. High-risk plaque morphologies including plaque rupture, echo-lucent, echo-attenuation, and spotty calcification were identified, and attenuation indices including maximum angle, attenuation length, and superficial attenuation were determined. Clinically relevant echo-attenuation was defined as an attenuation with a minimum lumen area 54.0 mm(2) and plaque burden >= 70%. Results: The prevalence of echo-attenuation was higher (63.0% vs. 37.6%, P=0.001) and attenuation length was longer (12.8 +/- 10.3 vs. 8.0 +/- 5.8 mm, P=0.015) in lesions with QFR 50.8 compared to those with QFR >0.8, associated with a higher rate of clinically relevant echo-attenuation (35.2% vs. 10.4%, P<0.001). On multivariable analysis, the presence of echo-attenuation was an independent predictor of QFR 50.8 [odds ratio (OR) 3.162, 95% confidence interval (CI): 1.263-7.917, P=0.014], whereas attenuation length was weakly correlated with QFR value (beta=-0.185, B=-0.002, 95% CI: -0.004 to -0.001, P=0.001). Receiver operating characteristic curve analysis revealed that the best cutoff of QFR in predicting clinically relevant echo-attenuation was 0.82 [area under the curve (AUC) =0.696, 95% CI: 0.616-0.775, P<0.001]. Conclusions: The presence of intravascular ultrasound-derived echo-attenuation confers an increased risk of QFR-defined functional significance in intermediate coronary lesions.