17.4: Coronary Circulation
- Page ID
- 63480
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- Describe how atherosclerosis impacts blood flow in coronary arteries and can cause a heart attack
You will recall that the heart is a remarkable pump composed largely of cardiac muscle cells that are incredibly active throughout life. Like all other cells, a cardiomyocyte requires a reliable supply of oxygen and nutrients, and a way to remove wastes, so it needs a dedicated, complex, and extensive coronary circulation. And because of the critical and nearly ceaseless activity of the heart throughout life, this need for a blood supply is even greater than for a typical cell. However, coronary circulation is not continuous; rather, it cycles, reaching a peak when the heart muscle is relaxed and nearly ceasing while it is contracting.
Coronary Arteries
Coronary arteries supply blood to the myocardium and other components of the heart. Immediately after the aorta emerges from the left ventricle it gives rise to the right and left coronary arteries.
The left coronary artery distributes blood to the left side of the heart, the left atrium and ventricle, and the interventricular septum. It runs posterior to the pulmonary trunk and almost immediately branches into two vessels: the circumflex and anterior interventricular arteries. The circumflex artery follows the coronary sulcus to the left and eventually fuses with the small branches of the right coronary artery. The larger anterior interventricular artery, also known as the left anterior descending artery (LAD), follows the anterior interventricular sulcus toward the apex of the heart. Along the way it gives rise to numerous smaller branches that interconnect with the branches of the posterior interventricular artery, forming anastomoses. An anastomosis is an area where vessels unite to form interconnections that normally allow blood to circulate to a region even if there may be partial blockage in another branch. The anastomoses in the heart are very small. Therefore, this ability is somewhat restricted in the heart so a coronary artery blockage often results in death of the cells (myocardial infarction) supplied by the particular vessel.
The right coronary artery proceeds along the coronary sulcus and distributes blood to the right atrium, portions of both ventricles, and the cardiac conducting system. On the posterior surface of the heart, the right coronary artery abruptly dips inferiorly and becomes the posterior interventricular artery, also known as the posterior descending artery. It runs along the posterior portion of the interventricular sulcus toward the apex of the heart, giving rise to branches that supply the posterior aspects of the interventricular septum and portions of both ventricles. Figure \(\PageIndex{1}\) presents the major vessels of coronary circulation from both the anterior and posterior views.
Heart: Coronary Artery Disease
Coronary artery disease is the leading cause of death worldwide. It occurs when the buildup of plaque—a fatty material including cholesterol, connective tissue, white blood cells, and some smooth muscle cells—within the walls of the arteries obstructs the flow of blood and decreases the flexibility or compliance of the vessels. This condition is called atherosclerosis, a hardening of the arteries in which the accumulation of plaque increasingly narrows the diameter of the blood vessel. As the coronary blood vessels become occluded, the flow of blood to the tissues will be restricted, a condition called ischemia that causes the cells to receive insufficient amounts of oxygen, called hypoxia. Figure \(\PageIndex{2}\) shows the blockage of coronary arteries highlighted by the injection of dye. Some individuals with coronary artery disease report pain radiating from the chest called angina pectoris, but others remain asymptomatic. If untreated, coronary artery disease can lead to MI or a heart attack.
The disease progresses slowly and often begins in children and can be seen as fatty “streaks” in the vessels. It then gradually progresses throughout life. Well-documented risk factors include smoking, family history, hypertension, obesity, diabetes, high alcohol consumption, lack of exercise, stress, and hyperlipidemia or high circulating levels of lipids in the blood. Treatments may include medication, changes to diet and exercise, angioplasty with a balloon catheter, insertion of a stent, or coronary bypass procedure.
Angioplasty is a procedure in which the occlusion is mechanically widened with a balloon (Figure \(\PageIndex{3}\)). A specialized catheter with an expandable tip is inserted into a superficial vessel, normally in the leg, and then directed to the site of the occlusion. At this point, the balloon is inflated to compress the plaque material and to open the vessel to increase blood flow. Then, the balloon is deflated and retracted. A stent consisting of a specialized mesh is typically inserted at the site of occlusion to reinforce the weakened and damaged walls.
Coronary bypass surgery may also be performed. This surgical procedure grafts a replacement vessel obtained from another, less vital portion of the body to bypass the occluded area. This procedure is clearly effective in treating patients experiencing a MI, but overall does not increase longevity. Nor does it seem advisable in patients with stable although diminished cardiac capacity since frequently loss of mental acuity occurs following the procedure. Long-term changes to behavior, emphasizing diet and exercise plus a medicine regime tailored to lower blood pressure, lower cholesterol and lipids, and reduce clotting are equally as effective.
Heart: Myocardial Infarction
Myocardial infarction (MI) is the formal term for what is commonly referred to as a heart attack. It normally results from a lack of blood flow (ischemia) and oxygen (hypoxia) to a region of the heart, resulting in death of the cardiac muscle cells. An MI often occurs when a coronary artery is blocked by the buildup of atherosclerotic plaque consisting of lipids, cholesterol and fatty acids, and white blood cells, primarily macrophages. It can also occur when a portion of an unstable atherosclerotic plaque travels through the coronary arterial system and lodges in one of the smaller vessels. The resulting blockage restricts the flow of blood and oxygen to the myocardium and causes death of the tissue (Figure \(\PageIndex{4}\)). MIs may be triggered by excessive exercise, in which the partially occluded artery is no longer able to pass sufficient quantities of blood, or severe stress, which may induce spasm of the smooth muscle in the walls of the vessel.
In the case of acute MI, there is often sudden pain beneath the sternum (retrosternal pain) called angina pectoris, often radiating down the left arm in males but not in female patients. Until this anomaly between the sexes was discovered, many female patients suffering MIs were misdiagnosed and sent home. According to the American Heart Association, the symptoms of a heart attack are:
| Symptoms in Women | Symptoms in Men |
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Many of the symptoms are shared with other medical conditions, including anxiety attacks and simple indigestion, so differential diagnosis is critical. It is estimated that between 22 and 64 percent of MIs present without any symptoms.
An MI can be confirmed by examining the patient’s ECG. In addition, echocardiography or cardiac magnetic resonance imaging may be employed. Common blood tests indicating an MI include elevated levels of creatine kinase MB (an enzyme that catalyzes the conversion of creatine to phosphocreatine, consuming ATP) and cardiac troponin (the regulatory protein for muscle contraction), both of which are released by damaged cardiac muscle cells.
Important risk factors for MI include cardiovascular disease, age, smoking, high blood levels of the low-density lipoprotein (LDL, often referred to as “bad” cholesterol), low levels of high-density lipoprotein (HDL, or “good” cholesterol), hypertension, diabetes mellitus, obesity, lack of physical exercise, chronic kidney disease, excessive alcohol consumption, and use of illegal drugs.
Coronary Veins
Coronary veins drain the heart and generally parallel the large surface arteries (see Figure \(\PageIndex{1}\)). The great cardiac vein can be seen initially on the anterior surface of the heart following the interventricular sulcus running parallel to the anterior interventricular artery. Upon reaching the coronary sulcus it runs between the left atrium and left ventricle with the circumflex artery. The middle cardiac vein parallels and drains the areas supplied by the posterior interventricular artery. The small cardiac vein originates on the lateral side of the right ventricle then parallels the right coronary artery in the coronary sulcus. It drains the blood from the posterior surfaces of the right atrium and ventricle. All three of these coronary veins merge with the coronary sinus - a large, thin-walled vein on the posterior surface of the heart lying within the atrioventricular sulcus and emptying directly into the right atrium. The anterior cardiac veins drain the anterior surface of the right ventricle but, unlike these other cardiac veins, it bypasses the coronary sinus and drains directly into the right atrium.
Concept Review
The right and left coronary arteries are the first to branch off the aorta and arise from two of the three sinuses located near the base of the aorta and are generally located in the sulci. Cardiac veins parallel the small cardiac arteries and generally drain into the coronary sinus. Coronary artery disease is caused by the build up of plaque in the walls of coronary arteries that causes ischemia and hypoxia in downstream tissues.
Review Questions
Query \(\PageIndex{1}\)
Critical Thinking Questions
Query \(\PageIndex{2}\)
Glossary
Query \(\PageIndex{3}\)
- Contributors and Attributions
OpenStax Anatomy & Physiology (CC BY 4.0). Access for free at https://openstax.org/books/anatomy-and-physiology