HEART DISEASE
CARDIAC ANATOMY AND PHYSIOLOGY OF HEART
HEART TISSUE
Coronary Arteries ;
The coronary arteries originate in the sinus of Valsalva located in the wall of the aorta near the aortic valve.The right coronary originates from the area near the right aortic leaflet, the left coronary from the area near the left aortic leaflet. When the aortic valve is open during systole, the origins of the coronary arteries are located behind the aortic leaflets within the wall; when the aortic valve is closed during diastole, the openings of the coronaries are clearly exposed, allowing them to be easily perfused.5 he coronary arteries therefore receive the majority of their blood flow during diastole, unlike the other arteries of the body that are perfused during systole.
The left coronary artery begins as the left main (LM) and then branches into the left anterior descending (LAD) and the circumflex (CX) (Fig. 13.3). he LAD may have further divisions, known as diagonal branches, that come off of the primary LAD. he LAD and its diagonal branches primarily supply the anterior and apical surfaces of the LV, as well as portions of the interventricular septum. he circumflex may also have branches, known as marginal branches. he circumflex and its marginal branches supply the lateral and part of the inferior surfaces of the LV and portions of the left atrium (LA). he right coronary artery (RCA) supplies the RA, most of the RV, part of the inferior wall of the LV, portions of the interventricular septum, and the conduction system. he posterior descending artery (PDA) is most commonly a branch of the RCA and perfuses the posterior heart. If the RCA does not perfuse the posterior heart, the CX will supply this area. When the PDA comes from the RCA, the anatomy is referred to as being right dominant; if the PDA comes from the circumflex, the anatomy is referred to as being left dominant. For physical therapists, there is no clinical importance to whether the anatomy of the myocardium is either left or right dominant.
The inner diameter (i.e., the opening) of the arteries through which the blood flows is the lumen. he size of the lumen is critical for adequate blood flow. A significant narrowing of the lumen, such as that which occurs with a fixed atherosclerotic lesion of CAD, will decrease the available blood supply to the myocardium. Lumen size may also be altered by the smooth muscle within the walls of the arteries, because smooth muscle regulates vasomotor tone of the coronary arteries. Vasodilation will increase lumen diameter as a result of relaxation of smooth muscle, and vasoconstriction will decrease lumenal diameter as a result of smooth muscle contraction. he responsiveness of arterial smooth muscle is also influenced by the integrity of the endothelium, the lining of the coronary artery that is in direct contact with the lumen. The endothelium has a number of normal functions and “plays the central role in controlling the biology of the vessel wall.”10, p. 1,265 Some of these important functions are anti-inflammatory actions, antithrombotic activity, and its influence on vasodilation. Endothelial cells release endothelial-derived relaxing factor (EDRF), which facilitates vascular smooth muscle relaxation. Nitric oxide (NO) is the most prevalent EDRF. An injury to endothelium can result in impaired NO release and a decrease in vasodilation.11 NO release is influenced by many factors, including acetylcholine, norepinephrine, serotonin, adenosine diphosphate, bradykinin, and histamine.The etiology of the clinical condition known as coronary spasm, in which smooth muscle contraction within the walls of the artery results in narrowing of the coronary artery, is not clearly understood. Coronary spasm occurs in arteries that have endothelial injury (e.g., atherosclerosis), as well as in those arteries that appear to be normal but exhibit hyperreactivity to a variety of vasoconstrictor stimuli, such as serotonin and ergonovine, and loss of EDRF.
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