Blood Flow - Blood Flow Coronary Anatomy and Blood Flow The...

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Coronary Anatomy and Blood Flow The major vessels of the coronary circulation are the left main coronary that divides into left anterior descending and circumflex branches, and the right main coronary artery. The left and right coronary arteries originate at the base of the aorta from openings called the coronary ostia located behind the aortic valve leaflets. The left and right coronary arteries and their branches lie on the surface of the heart, and therefore are sometimes referred to as the epicardial coronary vessels . These vessels distribute blood flow to different regions of the heart muscle. When the vessels are not diseased, they have a low vascular resistance relative to their more distal and smaller branches that comprise the microvascular network . As in all vascular beds, it is the small arteries and arterioles in the microcirculation that are the primary sites of vascular resistance, and therefore the primary site for regulation of blood flow. The arterioles branch into numerous capillaries that lie adjacent to the cardiac myocytes. A high capillary-to-cardiomyocyte ratio and short diffusion distances ensure adequate oxygen delivery to the myocytes and removal of metabolic waste products from the cells (e.g., CO 2 and H + ). Capillary blood flow enters venules that join together to form cardiac veins that drain into the coronary sinus located on the posterior side of the heart, which drains into the right atrium. There are also anterior cardiac veins and thesbesian veins drain directly into the cardiac chambers. Although there is considerable heterogeneity among people, the following table indicates the regions of the heart that are generally supplied by the different coronary arteries. This anatomic distribution is important because these cardiac regions are assessed by 12-lead ECGs to help localize ischemic or infarcted regions, which can be loosely correlated with specific coronary vessels; however, because of vessel heterogeneity, actual vessel involvement in ischemic conditions needs to be verified by coronary angiograms or other imaging techniques. Anatomic Region of Heart Coronary Artery (most likely associated) Inferior Right coronary Anteroseptal Left anterior descending Anteroapical Left anterior descending (distal) Blood Flow 1
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Anatomic Region of Heart Coronary Artery (most likely associated) Anterolateral Circumflex Posterior Right coronary artery The following summarizes important features of coronary blood flow: Flow is tightly coupled to oxygen demand. This is necessary because the heart has a very high basal oxygen consumption (8-10 ml O 2 /min/100g) and the highest A-VO 2 difference of a major organ (10-13 ml/100 ml). In non-diseased coronary vessels, whenever cardiac activity and oxygen consumption increases, there is an increase in coronary blood flow ( active hyperemia ) that is nearly proportionate to the increase in oxygen consumption.
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