Flow and atherosclerosis in coronary bifurcations.

Coronary bifurcations are among the most frequent sites affected by atherosclerosis. In these regions, complex haemodynamic conditions prevail and local flow disturbances dictate the localisation and progression of atheroma. Endothelial shear stress (ESS) is the main flow-related factor affecting the distribution of atherosclerosis in a bifurcation. Plaques are more prevalent in low ESS areas, such as the lateral walls of the main vessel and side branches, while they are less common in the flow divider or carina, which is characterised by high ESS. However, the carina is not free of atheroma and is affected in up to one third of cases, but never in isolation. Lesions in the carina are likely to develop at a later stage of atherosclerosis, as result of circumferential expansion of plaques from the lateral wall. Pulsatile flow augments the local atherogenic environment by inducing low and oscillatory ESS. The geometrical configuration is also important as increased curvature and wide angles between the side branches of the bifurcation intensify flow perturbations, and highly curved segments show low ESS in the inner aspect of curvatures. Further research on the flow conditions which determine the initiation and progression of atherosclerosis in bifurcations will allow for more efficient prevention and management strategies.