Electron Microscopic Insights Into the Vascular Biology of Atherosclerosis
Study of Coronary Endarterectomy Specimens
Coronary artery disease, typically discrete and proximal in distribution, is sometimes more diffuse in nature, in which case, it is often associated with poorer outcomes of revascularization. Does diffuse coronary artery disease represent an advanced and burned-out stage of atherosclerosis, representing a “metabolically inert graveyard” of atheromatous tissue, or is there ongoing atherosclerotic activity? To answer this question, plaques obtained during surgical coronary endarterectomy were examined using transmission and scanning electron microscopy, and the results form the basis of this study.
The various stages of atherosclerotic plaque progression are well known1 and could be clearly identified in different regions of the same plaque under electron microscopic examination. Figure 1 shows monocytes diapedesing between the endothelial lining of the coronary lumen to enter the intima. In other regions, macrophages were seen phagocytosing lipid droplets and being transformed into foam cells (Figure 2). Foam cells of smooth-muscle origin with surrounding collagen deposition could also be seen (Figure 3). The role of plaque neovascularization in recruiting macrophages into the plaque was also graphically captured; we have previously published these observations.2 Transmission electron microscopy offers some unique insights into the mechanisms of plaque calcification. The process seems to start as an encrustation around individual microvesicles of lipid, eventually coalescing to form larger clumps of calcification (Figure 4). Scanning electron microscopy of the same plaque revealed areas of endothelial erosion and plaque fissuring (Figure 5).
Coronary endarterectomy plaques show evidence of active, ongoing atherosclerotic activity and are a valuable source for studying the vascular biology of atherosclerosis.
The authors acknowledge the help of the following in carrying out the electron microscopic studies: Christian Medical College Hospital, Vellore, India; and Drs Usha Ramamoorthy and A. Rajaram, Department of Biophysics, Central Leather Research Institute, Chennai, India.
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Balakrishnan KR, Kuruvilla S. Role of inflammation in atherosclerosis: immunohistochemical and electron microscopic images of a coronary endarterectomy specimen. Circulation. 2006; 113: e41–e43.