INTRAVASCULAR ULTRASOUND EVIDENCE FOR IMPORTANCE OF PLAQUE DISTRIBUTION IN THE DETERMINATION OF REGIONAL VESSEL WALL COMPLIANCE

Regional vessel wall distensibility was determined by measuring lumina l area and pressure, using intravascular ultrasound (Sonicath; Boston- Scientific, Watertown, MA, USA; 3.5Fr, 30MHz) in 45 left coronary site s from 40 patients. Luminal area in diastole (A) and in systole was me asured at the diseased sites. With the ratio of luminal area changes ( dA) to coronary pressure changes (dP) during a cardiac cycle, the tota l distensibility index was calculated by the formula: {(dA/ A)/dP} x 1 0(3). At sites with non-circumferential disease, perimeters in diastol e (L) and in systole were measured at the normal and diseased portions , and the changes in perimeters (dL) during a cardiac cycle were calcu lated. The regional distensibility index was obtained by the formula: {(dL/L)/dP} x 10(3). In 22 sites with circumferential disease, the tot al distensibility index was 1.03 +/- 0.61/mmHg, significantly lower th an that for 23 sites with non-circumferential disease (1.45 +/- 0.89/m mHg; P < 0.05). In non-circumferential disease, the regional distensib ility index at the diseased portion was significantly lower (0.33 +/- 0.47/mmHg) than that at the normal portion (1.11 +/- 0.75/mmHg; P < 0. 01). Coronary sites with residual non-circumferential disease after an gioplasty also exhibited heterogeneity of regional distensibility (0.7 3 +/- 0.76 at disease sites versus 1.58 +/- 0.95/mmHg at normal sites, n = 10, P < 0.05). These results indicate that heterogeneous regional wall distensibility exists at sites with non-circumferential disease where the total vessel distensibility is preserved by the presence of compliant normal portion. This heterogeneity of regional wall distensi bility may represent a biomechanical factor that explains the mechanis m of plaque rupture that occurs mainly at the shoulder of the noncircu mferential disease.