OBJECTIVE The aim of this study was to elucidate determinants of coronary compliance in patients with coronary artery disease. BACKGROUND Intravascular ultrasound potentially enables in vivo evaluation of coronary artery compliance. METHODS Twenty-seven patients (mean age [+/- SD] 57 +/- 11 years, three women) undergoing coronary angioplasty were studied with intravascular ultrasound imaging. A mechanical intravascular ultrasound system (4.8F, 20 MHz) was used. A total of 58 different coronary segments (proximal to the target angiographic lesion) were studied. Of these, 35 were located in the left anterior descending, 9 in the left main, 8 in the left circumflex and 6 in the right coronary arteries. During intravascular ultrasound imaging, 22 segments (38%) appeared normal, but 36 (62%) had plaque (24 fibrotic, 3 lipidic and 9 calcified). Systolic-diastolic changes in area (delta A) and pressure (delta P) with respect to vessel area (A) were used to study normalized compliance (Normalized compliance = [delta A/A]/delta P [mm Hg-1 x 10(3)]). RESULTS Lumen area and plaque area were 12.6 +/- 5.7 and 3 +/- 3 min2, respectively. Plaque was concentric (more than two quadrants) at 10 sites, but the remaining 26 plaques were eccentric. Compliance was inversely related to age (r = -0.34, p < 0.05) but was not related to other clinical variables. Compliance was greater in the left main coronary artery (3.9 +/- 2.1 vs. 1.8 +/- 1.2 mm Hg-1, p < 0.05) and in coronary segments with normal findings on ultrasound imaging (2.9 +/- 1.9 vs. 1.6 +/- 1.1 mm Hg-1, p < 0.01). Moreover, at diseased coronary segments compliance was lower in calcified plaques than in other types of plaques (1.2 +/- 0.7 vs. 2.3 +/- 1.6 mm Hg-1, p < 0.01) but was similar in concentric and eccentric plaques (1.6 +/- 1.5 vs. 1.6 +/- 0.9 mm Hg-1). Plaque area (r = -0.38, p < 0.01) was inversely correlated with compliance. On multivariate analysis, only age and plaque area were independently related to compliance. CONCLUSIONS Intravascular ultrasound may be used to evaluate compliance in patients with coronary artery disease. Compliance is reduced with increasing age and is mainly determined by the arterial site and by the presence, size and characteristics of plaque on intravascular ultrasound imaging.