Although obstructive coronary atherosclerosis and myocardial infarction tend to be predominant topics when discussing coronary heart disease, many other clinically relevant processes affect the coronary arteries. In this chapter, we will discuss a wide array of nonobstructive atherosclerotic and nonatherosclerotic coronary heart diseases. Our discussion will begin with pathology of the coronary artery intima and media, then move to diseases that affect the entire coronary, and conclude with physical abnormalities of the coronary arteries and mechanical disruption of coronary blood flow. Most of these diseases, however, can overlap and adversely interact. For example, coronary microvascular dysfunction (CMD) contributes to angina in patients with obstructive atherosclerosis, coronary spasm can occur at both micro and macro levels, and inflammatory disease can have an impact on the entire coronary tree.
NORMAL CORONARY ANATOMY AND FUNCTION
The normal arrangement of the coronary arteries is for the left main artery and right coronary artery to arise from the ascending aorta, 1 to 2 cm above the base of their respective coronary sinuses. The left main artery divides into anterior descending and circumflex branches, which travel in the interventricular and atrioventricular grooves, respectively. The right coronary artery also travels in the atrioventricular groove on the right side of the heart, typically terminating in the posterior descending artery in the inferior interventricular groove. Each vessel gives rise to branch vessels to create a comprehensive network of epicardial conduits. Vessels branch and decrease in size, from prearterioles to arterioles to capillaries. Myocardial blood flow is regulated mostly in the coronary microcirculation, where only small changes in arteriolar diameter can result in large changes in conductance and flow as predicted by Poiseuille’s law (Fig. 35–1).1 For example, a 20% reduction in arteriolar diameter results in a more than 100% increase in resistance and reduces blood flow by more than 50%.
Regulators of coronary microvascular function. Healthy endothelium produces nitric oxide (NO) and prostacyclin (PGI2), which are anti-inflammatory and promote homeostasis. Unhealthy endothelium produces hydrogen peroxide (H2O2), which promotes inflammation, proliferation, and atherosclerosis. EET, epoxyeicosatrienoic acids. Reproduced with permission from Gutterman DD, Chabowski DS, Kadlec AO, et al: The Human Microcirculation: Regulation of Flow and Beyond. Circ Res. 2016 Jan 8;118(1):157-172.1
The coronary arteries are lined by the intima (endothelial cells and internal elastic lamina), the media (vascular smooth muscle cells), and adventitia (eg, external elastic lamina, fibroblasts, vasa vasorum) (Fig. 35–2).2 Many macrovascular diseases result from mechanical disruption of one or more of these layers, whereas microvascular diseases predominantly result from dysfunction of endothelial cells and/or vascular smooth muscle cells.
Components of the coronary circulation. The precapillary coronary tree consists of conductive, prearteriolar, and arteriolar vessels. Resistance in these vessels components is primarily responsive to flow, ...