MEASUREMENT BY INTRACORONARY ULTRASOUND OF IN-VIVO ARTERIAL DISTENSIBILITY WITHIN ATHEROSCLEROTIC LESIONS

Arterial distensibility is diminished by atherosclerosis. This process has not been well studied in the coronary arteries. The purpose of this study was to assess changes in coronary arterial distensibility in 4 groups of patients. Group I (n = 20) consisted of patients with normal vessels, group II (n = 40) with diseased undilated vessels, group III (n = 15) after successful percutaneous transluminal coronary angioplasty (PTCA), and Group IV (n = 20) after successful directional coronary atherectomy (DCA). Intracoronary ultrasound imaging was used to assess distensibility, plaque morphology and atherosclerotic burden (expressed as the percentage of total vessel cross-sectional area occupied by plaque: percent plaque area). Distensibility was defined as percent change in lumen area in a cardiac cycle. Group I (normal vessels) had a distensibility = 14 +/- 5%, which was significantly greater than that seen in group II (distensibility = 4 +/- 2%, p < 0.001). In undilated vessels, distensibility was related to the degree of atherosclerotic burden (r = 0.75). This relation was curvilinear with a marked decrease in distensibility when percent plaque area exceeded 30%. Distensibility in group III (after PTCA) was higher than in group II (10 +/- 3 vs 4 +/- 2%, p < 0.001) despite a larger plaque burden (percent plaque area of 56 +/- 12 vs 46 +/- 11%, p < 0.005). The distensibility in group IV (after DCA) was also higher than in group II (8 +/- 4 vs 4 +/- 2%, p < 0.001) despite a similar residual percent plaque area (49 +/- 13 vs 46 +/- 11%, p = NS). After PTCA, hard lesions had greater distensibility than soft lesions (distensibility = 11 +/- 3 vs 8 +/- 2%, p = 0.04), whereas after DCA hard lesions had less distensibility than soft lesions (distensibility = 6 +/- 4 vs 10 +/- 4%, p = 0.04). In conclusion, arterial distensibility is decreased by atherosclerosis with a marked reduction in even minimally diseased vessels. PTCA and DCA result in an increase in arterial distensibility at the site of the treated lesion. Hard lesions have greater distensibility after PTCA, suggesting greater plaque disruption in these lesions than in soft lesions. Hard lesions have less distensibility after DCA, consistent with less effective plaque cutting and removal in these lesions than in soft lesions. It is concluded that the study of arterial distensibility by intracoronary ultrasound provides insights into the mechanisms of interventional therapy and may be useful for the assessment of early atherosclerosis.