Introduction we presume that the plaque vulnerability of mildly lesions will be related to its intrinsic structural features and biomechanical characteristics. However, very little is known about their relationship between structural features and plaque vulnerability and about effect of biomechanical characteristics and plaque behaviour on vulnerable plaque. It is well known that coronary angiography (CAG) cannot accurately determine lesion morphology because it only shows the silhouette of the contrast materiel passing through the stenotic lesions. In recent years, intravascular ultrasound (IVUS) has evolved as a valuable adjunct to angiography. IVUS allows precise tomographic measurement of lumen area and plaque size, distribution and, to some extent, composition. Therefore, IVUS provide us likelihood for study on structural features and biomechanics characteristics in angiographic mildly stenosis in vivo.
Materials and methods In 42 patients of angiographic intermediate coronary stenosis (diameter stenosis 40%-60%), IVUS imaging was performed and intracoronary pressure was recorded. The patients were classified as either unstable plaques group (n=30) or stable plaques group (n=12) by IVUS image. The biomechanical properties (distensibility index and stiffness) of coronary artery were calculated and the plaque behaviour during cardiac cycle was determined.
Results There was no significant difference in percent area stenosis between eccentric plaque group and concentric plaque group (53.9±8.9% vs 58.4±9.8%, p>0.05). The coronary distensibility index in unstable plaques was significantly greater than it was in stable plaques (2.1±0.3 vs 1.2±0.2 mm Hg-1, p<0.01), but stiffness β for stable plaques was significantly greater than it was for unstable plaques (8.1±1.3 vs 29.4±7.2, p<0.01). The change of plaque area during cardiac cycle (plaque distensibility) in unstable plaque group was greater than it was in stable plaque group (0.52±0.22 mm2 vs 0.24±0.19 mm2, p<0.01). Positive remodelling occurred more frequently with unstable plaques than with stable plaques (63% vs 8%, p<0.01).
Conclusion High coronary artery distensibility and high plaque distensibility during the cardiac cycle in eccentric lesions will likely increase plaque vulnerability.