Intravascular Ultrasonic Evidence for Importance of Plaque Distribution (Eccentric vs Circumferential) in Determining Distensibility of the Left Anterior Descending Artery

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Although previous studies have shown that coronary atherosclerosis is accompanied by impaired vessel wall compliance, few data exist regarding the regional vessel distensibility that may be important in order to gain an insight into the mechanism of atherosclerotic plaque rupture. Therefore, we analyzed 45 coronary sites of the proximal left anterior descending artery from 40 patients. Using intravascular ultrasound, luminal area in diastole (A) and in systole was measured at the diseased sites. With the ratio of luminal area changes (dA) to coronary pressure changes (dP) during a cardiac cycle, the total distensibility index was obtained by the formula: [(dA/A)/dP] × 103. At the sites with noncircumferential disease perimeters in diastole (L) and in systole were measured at the normal and narrowed portions. Using the changes in perimeters (dL) during a cardiac cycle, the regional distensibility index was obtained by the formula: [(dL/L)/dP] × 103. In 22 sites with circumferential disease, the total distensibility index was 1.03 ± 0.61/mm Hg (mean ± SD), and significantly lower than that from 23 sites with noncircumferential disease that showed 1.45 ± 0.89/mm Hg (p <0.05). In noncircumferential disease, the regional distensibility index at narrowed portions was significantly lower, 0.33 ± 0.47/mm Hg, than that at normal portion, 1.11 ± 0.75/mm Hg (p <0.01), suggesting the heterogenous distribution of regional wall distensibility in noncircumferential lesions. These results indicate that the heterogeneous regional wall distensibility exists at the sites with noncircumferential disease where the total vessel distensibility is preserved by the presence of the compliant normal portion.To examine the heterogeneity of coronary distensibility at the sites with noncircumferential atherosclerotic disease, regional wall distensibility was determined by intravascular ultrasound. The regional distensibility index at the diseased portion was significantly lower than that at normal portions, suggesting the presence of the heterogeneous regional wall distensibility in noncircumferential disease; this may explain in part the plaque disarrangement that mainly occurs at the shoulder of the disease sites in noncircumferential disease.