A histopathologic study of the mechanism of Evans blue staining of myocardial infarcts in rats.

In a study of the mechanism of Evans blue (EB) staining of experimental infarcts in rats, it has been reported that when the dye was injected iv before left coronary occlusion (LCO) it diffused centripetally from the periphery of the excluded vascular bed region (ExVB), i.e., the myocardial area with circulation interrupted by LCO, to its center. In the present study, we have attempted to identify the mechanism of this phenomenon. The animals were sacrificed at different times after EB injection, i.e., 10, 20, and 30 min and 1, 2.5, 4.5, 6, 16, 24 and 48 h. This phenomenon occurred from 4.5 up to 24 h after LCO and could not be ascribed to either collateral circulation or to venous backflow. We conclude that diffusion from one necrotic cell to another, beginning at the ill-perfused periphery of the ExVB (lateral and endocardial margins of the ExVB), and also at the epicardium (bathed by pericardial effusion rich in EB) is responsible for the production of the so-called "blue infarct".