Multiple: Coronary Artery Disease
Multiple: Coronary Artery Disease
Coronary artery disease, or CAD, is a condition in which a fatty substance called plaque builds up inside the walls of the arteries that supply the heart. The plaque begins to form when the inner layer of tissue in the artery is damaged by smoking, diabetes, high blood pressure, personality factors, or some other cause. When the deposit of plaque grows large enough to narrow or block the flow of blood through the artery, the heart muscle becomes starved for oxygen, producing angina, difficulty breathing, or a full-blown heart attack.
The buildup of plaque that leads to coronary artery disease can start as early as childhood. Arteries in the human body are blood vessels that carry blood away from the heart, in contrast to veins, which carry blood toward the heart. Arteries have three layers of tissue: an outer layer made of connective tissue, a middle layer made of smooth muscle, and a thin inner layer of cells that serve as a lining to the artery. This inner layer smoothes the flow of blood, which allows the heart to pump the blood further. The coronary arteries branch off from the base of the aorta, the large trunk artery at the top of the heart. They are the only source of blood supply to the heart muscle itself, which is why a blockage in these arteries is such a critical situation.
If the thin inner layer of a coronary artery is damaged, the body tries to heal it by covering it with a layer of plaque. Over time, the plaque deposit can become thicker, to the point where blood no longer flows smoothly through that part of the artery and the heart muscle becomes ischemic. Ischemia is a condition in which a portion of heart muscle (or any other tissue) is not receiving enough blood because of the blockage of an artery that ordinarily supplies it with blood. Ischemia in the heart can lead to angina—a type of chest pain that feels like squeezing or pressure and can move from the chest area to the arms, neck, jaw, or back.
The plaque deposits within the damaged artery can also rupture or crack open. Blood cells called platelets move to the ruptured area and form blood clots that block the artery. The loss of the blood supply following the closure of the artery leads to the death of heart tissue. The
CAD is the leading cause of death in the United States for both men and women. According to the American Heart Association, nearly fifteen million adults have some form of coronary artery disease. CAD usually develops in adults over thirty, and is common in adults over sixty. Coronary artery disease accounts for 650,000 deaths in the United States each year—25 percent of deaths among adults over the age of thirty-five.
Risk factors for coronary artery disease include:
- Age. The risk of coronary artery disease rises for men after age forty-five and for women after age fifty-five.
- Sex. Men are at greater risk of CAD throughout life; however, the risk for women rises after menopause.
- Family history of CAD. A person's risk of CAD is higher if their father or brother was diagnosed with CAD before age fifty-five, or a mother or sister diagnosed before age sixty-five.
- High blood pressure and high blood cholesterol levels.
- Race. African Americans, particularly African American women, and Native Americans have higher rates of CAD than either Caucasians or Hispanics.
- Lifestyle. People who smoke and drink heavily are at increased risk of CAD. Women who smoke a pack of cigarettes per day are six times as likely to have a heart attack as nonsmoking women; male smokers are three times as likely to develop CAD as nonsmokers.
- Sleep apnea.
- Physical inactivity.
- High levels of emotional stress.
- Personality. People who are aggressive, impatient, and highly competitive are more likely to develop CAD than those who are relatively calm and relaxed.
Coronary artery disease is caused by a slow buildup—over years or decades—of plaque along the inner wall of a coronary artery. The plaque can block the flow of blood through the artery either by becoming thick enough to narrow the artery, or by rupturing and leading to the formation of a blood clot that blocks the artery.
Coronary artery disease can progress (get worse) for years without producing any noticeable symptoms. When symptoms do appear they typically take three forms:
- Angina or chest pain. Doctors distinguish two types of angina: stable angina, which occurs during exercise, after a heavy meal, or at other predictable times; and unstable angina, which varies in severity, timing, or frequency. Unstable angina is often an early warning of a heart attack, and requires emergency medical evaluation and treatment.
- Shortness of breath.
- A heart attack.
Some patients with CAD also experience lightheadedness or dizziness, an irregular heartbeat, or a racing heartbeat.
For some people, a heart attack is the first symptom of CAD. They will be taken to a hospital emergency room, where they will be asked to describe their symptoms. In addition to taking the patient's personal and
family history of risk factors for CAD, the doctor will also take the patient's temperature, blood pressure, and pulse. Listening to the patient's lungs and heartbeat through a stethoscope can help to rule out pneumonia or other diseases that might cause chest pain or difficulty breathing.
The next step is diagnostic tests to rule out a heart attack, which include:
- Electrocardiogram (ECG or EKG). An ECG or EKG measures the heart's electrical activity. Injured heart muscle makes unusual patterns or tracings on the paper printout produced by the ECG machine. If only a small amount of the heart muscle has been affected, however, the ECG may not show any abnormal patterns.
- Blood tests. These are done to confirm the diagnosis of a heart attack or to make sure that the electrocardiogram did not miss a small heart attack. Injured heart muscle leaks small amounts of special enzymes into the bloodstream.
- Chest x ray. A chest x ray may be done to see whether the patient's lungs are normal.
- Coronary angiography. Coronary angiography is a type of x-ray study in which the doctor threads a long thin tube called a catheter into the heart through an artery in the arm or upper thigh. A dye that will show up on x ray is injected into the bloodstream through the catheter. This test allows the doctor to find the location of the blockage in the coronary artery. It is also the only test that allows a heart specialist to determine the best treatment for the blockage.
If the patient is having angina but does not appear to be having a heart attack, he or she will be asked to take a stress test. In a stress test, the patient walks on a treadmill or pedals a stationary bicycle while hooked up to an ECG machine, which measures the electrical tracings of the heart before, during, and after exercise. Another type of stress test is a radionuclide stress test, in which a radioactive tracer element is injected into a vein while a special camera records the amount of the trace element that reaches various parts of the heart.
CAD can be treated with a combination of lifestyle changes, medications, and possibly surgery. Lifestyle changes include quitting smoking, losing
weight if needed, getting enough exercise, and coping more effectively with stress.
The doctor may prescribe one or more types of medications to treat CAD. These medications may prevent or delay the need for surgery:
- Drugs to lower blood cholesterol levels. These may include niacin, fibrates, and a group of drugs known as statins.
- Aspirin and other drugs that prevent blood clots from forming.
- Nitroglycerin. This drug relieves the pain of angina by opening (dilating) the coronary arteries and by reducing the heart muscle's need for oxygen.
- Beta blockers. These drugs slow down the heart rate, lowering blood pressure and reducing the heart's need for oxygen.
- ACE inhibitors. Drugs in this group dilate the coronary arteries and lower blood pressure.
- Calcium channel blockers. These drugs also dilate the coronary arteries to increase the flow of blood to heart muscle.
In some cases the patient's doctor may recommend surgery in order to prevent a fatal heart attack. The two operations that are most commonly performed are coronary artery bypass surgery and coronary angioplasty. In bypass surgery, the surgeon takes a piece of a healthy artery from another part of the patient's body and sews it in place to go around a blocked coronary artery to restore normal blood flow to the heart. In a coronary angioplasty, the surgeon inserts a catheter with a special balloon tip into the coronary artery. When the catheter is in the proper position, the balloon is expanded, which reopens the blocked artery. The surgeon will then insert a stent, which is a tube made of metal mesh, to keep the artery open. Some stents also contain a slow-release medication.
The prognosis of CAD depends on the patient's age and the number of risk factors in their family history, personal medical history, and lifestyle. The factors that doctors take into account in evaluating an individual patient's prognosis include the number of coronary arteries that are damaged; the patient's capacity for physical exercise or activity; a history of previous heart attacks or bypass surgery; and the severity of the patient's present symptoms—particularly unstable angina or a heart attack.
People who are at risk of CAD or been diagnosed with it can lower their risk of a heart attack by:
- Quitting smoking or not starting in the first place.
- Getting regular medical checkups. This precaution is important because risk factors for CAD like high blood pressure, high cholesterol levels, and diabetes have no symptoms in their early stages.
- Avoiding using cocaine and drinking large quantities of alcohol.
- Keeping one's weight at a healthy level and getting regular exercise.
- Controlling blood pressure.
- Learning how to manage emotional stress.
- Eating a low-fat diet rich in fruits and vegetables.
Coronary artery disease is expected to be a growing problem in the developed countries over the next several decades because of the aging of the general population, the increase in obesity and the rates of obesity-related diseases like diabetes, and the high rates of smoking in many countries. In terms of prevention and treatment, new drugs to treat heart attacks are currently being studied as well as the effectiveness of using bone marrow or stem cells to help repair injured heart tissue. Some researchers are also looking at some genes on chromosome 17 as a possible risk factor in CAD.
SEE ALSO Alcoholism; Diabetes; Heart attack; Heart failure; Hypercholesterolemia; Hypertension; Sleep apnea; Smoking
WORDS TO KNOW
Angina : Chest pain caused by an inadequate supply of oxygenated blood to the heart muscle.
Atherosclerosis : Stiffening or hardening of the arteries caused by the formation of plaques within the arteries.
Cholesterol : A fatty substance produced naturally by the body that is found in the membranes of all body cells and is carried by the blood.
Ischemia : Loss of blood supply to a tissue or organ resulting from the blockage of a blood vessel.
Myocardial infarction : The medical term for a heart attack.
Plaque : A deposit of cholesterol and dead white cells along the inside wall of an artery.
Platelet : A small flat disk-shaped body in human blood that helps to form blood clots by sticking to other platelets and to damaged tissue at the site of an injury.
Stem cell : A type of unspecialized cell that can reproduce itself and differentiate into different types of specialized cells. Stem cells act as a repair system for the body.
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