Biomechanics of plaque rupture: progress, problems, and new frontiers

Plaque rupture has become identified as a critical step in the evolution of arterial plaques, especially as clinically significant events occur in critical arteries. It has become common in the past dozen years or so to consider which plaques are vulnerable, even though not yet ruptured. Thrombotic events have remained significant, but in a context where they are seen as being triggered often by plaque rupture. Weaving together considerations from structural mechanics, fluid mechanics, plaque morphology, epidemiological pathology, micromechanical measurements of arterial wall tissues, and emerging information on the complex roles of the matrix metalloproteinases, this critical review draws attention to the relative paucity of data (i) on the mechanical behavior of small test portions of arterial tissues and (ii) on the relation of plaque locations to local vessel curvature and curvature flexure. This is especially important in the epicardial arteries, where combination of biplane angiograms and intravascular ultrasound (both becoming increasingly available in digital recordings) offer opportunities for clinical investigation, allied to biomechanics, to an extent previously not possible. Improved imaging and local tissue property assessments provide related opportunities for the carotid bifurcation. The discussion includes a proposal for developing an assessment scale for plaque vulnerability.