Role of intravascular ultrasound imaging in identifying vulnerable plaques

A plaque that has a large lipid core and a thin fibrous cap may undergo rup ture. Once it ruptures, it may lead to thrombus formation and subsequent ve ssel occlusion. To identify unstable plaques before they rupture is essenti al for clinical management and patient's prognosis. Intravascular ultrasoun d (IVUS) opens a new window for the assessment of plaque morphology to iden tify vulnerable plaques and plaque rupture. We examined 144 patients with angina and ischemic ECG changes using IVUS. R uptured plaques, characterized by a plaque cavity and a tear on the thin fi brous cap, were identified in 31 patients (group A) of which 23/31 (74%) cl inically presented as unstable angina. Plaque rupture was confirmed by inje cting contrast medium filling the plaque cavity during IVUS examination. Of the patients without plaque rupture (group B, n = 108), only 19 (18%) had unstable angina. No significant differences between the 2 groups were found concerning the vessel and plaque areas (p > 0.05). The percent stenosis in group A (56.2 +/- 16.5%) was significantly lower than in group B (67.9 +/- 13.4%) (p < 0.001), Area of the plaque cavity in group A (4.1 +/- 3.2 mm(2 )) was significantly larger than the echolucent zone in group B (1.32 +/- 0 .79 mm(2)) (p < 0.001). The plaque cavity/plaque ratio in group A (38.5 +/- 17.1%)was larger than the echolucent area/plaque ratio in group B (11.2 +/ - 8.9%) (p < 0.001). The thickness of the fibrous cap in group A (0.47 +/- 0.20 mm) was significantly thinner than that (0.96 +/- 0.94 mm in group B ( p < 0.001), Conclusions: Plaques seem to be prone to rupture when the echolucent area i s larger than 1 mm(2), the echolucent areal plaque ratio greater than 20% a nd the fibrous cap thinner than 0.7 mm. IVUS has the capacity of identifyin g plaque rupture and vulnerable plaques. This may have potential influence on patients management and therapy.