[The form of atherosclerotic coronary plaques: pathoanatomic concepts and new insights using intravascular ultrasound]

Abstract

In addition to the degree of vessel obstruction and to the composition of the atheroma, the geometric shape of the plaque--in particular the presence of non-diseased wall segments--is an important factor in the pathophysiology and therapy of coronary heart disease. The relevance of the plaque shape has been emphasized by pathoanatomic studies in the late 1970s. The in vivo assessment of the plaque shape using coronary angiography has major limitations: The lumen silhouette obtained by angiography does not accurately reflect the histologic extent of the plaque due to compensatory vessel enlargement, atrophy of the media, and diffuse plaque accumulation. In contrast, intravascular ultrasound (IVUS) allows direct, cross-sectional visualization of the plaque. Although this method has a small, but definite acute risk, it provides the first technique for in vivo assessment of the extent and shape of coronary plaque. In agreement with prior pathoanatomic investigations, IVUS studies have confirmed that the majority of advanced coronary plaques are located eccentrically in the vessel and that non-diseased wall segments are often present in these lesions. Using IVUS imaging, it has also been proven that in vivo relaxation of advanced coronary stenoses by vasodilatory drugs is mainly based on expansion of the non-diseased wall segment. IVUS studies have also shown that the presence of non-diseased wall segments may be important for the effect of intracoronary interventions: Balloon angioplasty of eccentric coronary lesions often causes dilatation of the non-diseased wall segments; immediate and chronic elastic recoil of these vessel segments may diminish the lumen gain from this procedure. During directional coronary atherectomy IVUS imaging of the exact location and shape of the plaque may limit subintimal tissue retrieval and thereby also reduce restenosis.