Collateral circulation and diabetes.

The article by Abaci et al 1 in this issue of Circulation draws our attention to a very important and novel observation that patients with diabetes mellitus (DM) have a lesser ability to develop collateral blood vessels in the presence of coronary artery disease. This is somewhat surprising, because DM is known to stimulate angiogenesis, at least in the retina of the eye, and is, because of capillary leakiness, a major cause of blindness. This article by Abaci et al is a good example for drawing attention to the recently appreciated fact that not all vascular growth should be called angiogenesis. The functionally more important collateral vessels of the heart are not the product of angiogenesis but rather of “arteriogenesis.”