Heart attacks result from blood vessel disease in the heart. Coronary heart disease (CHD), sometimes referred to as coronary artery disease (CAD), are more general names for heart attack (and angina).
A heart attack, or myocardial infarction, occurs when the blood supply to part of the heart muscle itself (the myocardium) is severely reduced or stopped. This occurs when one of the coronary arteries (the arteries that supply blood to the heart muscle) is blocked by an obstruction, often plaque due to atherosclerosis. A heart attack also can be caused by a blood clot lodged in a coronary artery. Such an event is sometimes called a coronary thrombosis or coronary occlusion.
If the blood supply is cut off drastically or for a long time, muscle cells suffer irreversible injury and die. Disability or death can result, depending on how much heart muscle is damaged.
Sometimes a coronary artery temporarily contracts or goes into spasm. When this happens the artery narrows and blood flow to part of the heart muscle decreases or even stops. What causes a spasm is unclear, but it can occur in normal blood vessels as well as vessels partially blocked by atherosclerosis. If a spasm is severe, a heart attack may result.
A heart attack isn't the only result of coronary artery disease. Chest pain called angina pectoris also can occur. Angina is a symptom of a condition called myocardial ischemia, which occurs when the heart muscle (myocardium) doesn't get as much blood (hence as much oxygen) as it needs for a given level of work. Lack of blood supply is called ischemia.
Angina pectoris can occur when blood circulation to the heart is sufficient for normal needs but inadequate when the heart's needs increase, such as during physical exertion or emotional excitement. Running to catch a bus, for example, could trigger an attack of angina while walking to a bus stop might not. Some people, such as those with a coronary artery spasm, may have angina when they're resting. Angina can be a warning sign that someone is at risk of heart attack.
Some people have ischemia without pain. As many as three to four million Americans may have ischemic episodes without knowing it. These people have silent ischemia. They may have a heart attack’’ with no prior warning. In addition, people with angina also may have undiagnosed episodes of silent ischemia. Various tests, such as an exercise test or a 24-hour portable monitor of the electrocardiogram (Holter monitor), are used to diagnose silent ischemia.
Collateral circulation involves small arteries that connect two larger coronary arteries or different segments of the same artery. They provide an alternate route for blood flow to the heart muscle. Everyone has collateral vessels, at least in microscopic form. These vessels aren't open under normal conditions but grow and enlarge in some people with coronary heart disease. When a collateral vessel enlarges, it lets blood flow from an open artery to either an adjacent artery or further downstream on the same artery. Myocardial ischemia stimulates collateral vessels, so they can form a kind of "detour" around a blockage, providing alternate routes of blood flow.
Research has shown that while everyone has collateral vessels, they don't open and become available in all people. Some people have available collaterals; others don't. People who have open collateral vessels are lucky, because collateral vessels help protect heart muscle from tissue death if the normal blood supply is cut off.
Angina pectoris can be treated with drugs that affect 1) the supply of blood to the heart muscle or 2) the heart's demand for oxygen. Some drugs, called coronary vasodilators, cause blood vessels to relax. When this happens the opening inside the vessels (the lumen) gets bigger. Then blood flow improves, allowing more oxygen and nutrients to reach the heart muscle. Nitroglycerin is the drug most often used. It relaxes the veins (reducing the amount of blood returning to the heart and thus lessening the work of pumping) and the coronary arteries (increasing the blood supply to the heart).
Alternatively, the heart's demand for oxygen also can be modified. For example, a drug can be prescribed to reduce blood pressure and thus reduce the heart's workload and need for oxygen. Drugs that slow the heart rate achieve a similar effect.
Invasive techniques that improve the blood supply to the heart also may be used. One technique is percutaneous transluminal coronary angioplasty (PTCA), also known as angioplasty or balloon angioplasty. Another procedure is coronary artery bypass graft surgery.
Before performing either of these procedures, a doctor must find the blocked part of the coronary arteries. This is done using coronary arteriography, which is done during a procedure called cardiac catheterization. In this procedure a doctor guides a thin plastic tube (a Catheter) through an artery in the arm or leg and into the coronary arteries. Then the doctor injects a liquid dye visible in X-rays through the catheter. High-speed X-ray movies record the course of the liquid as it flows through the arteries. Doctors can identify obstructions in the arteries by tracing the liquid's flow.
Some newer diagnostic procedures are available to evaluate how well the heart works. These tests may be done before or after a heart attack. Some of these tests are still relatively experimental and are limited to larger medical centers.
PTCA is a procedure designed to dilate (widen or expand) narrowed coronary arteries. In it a doctor inserts a catheter into an artery in an arm or leg and guides it to an obstructed coronary artery. Then a second catheter with a balloon tip is passed inside the first, and the balloon tip is inflated at the arterial blockage. This compresses the plaque, enlarging the inner diameter of the blood vessel so blood can flow more easily. Then the balloon is deflated and the catheters are withdrawn.
In about 25 percent of the people who've had PTCA, the dilated part of the coronary artery renarrows. This usually occurs within the first six months. Then a doctor must decide whether to repeat the operation or if open-heart surgery is a better choice.
In coronary artery bypass graft surgery, surgeons take a blood vessel from another part of the body (usually the leg or from inside the chest wall) and construct a detour around the blocked part of a coronary artery. One end of the vessel is attached above the blockage; the other, to the coronary artery just beyond the blocked area. This restores blood supply to the heart muscle.
People with angina should also modify their controllable risk factors. This means they must not smoke, and should control their blood pressure and make sure their diet doesn't contribute to atherosclerosis or obesity.
These tests involve injecting substances called radionuclides into the bloodstream. Computer-generated pictures can then find them in the heart. These tests show how well the heart muscle is supplied with blood, how well the heart's chambers are functioning, or identify a part of the heart damaged by heart attack.
This test uses powerful magnets to look inside the body. Computer-generated pictures can image the heart muscle, identify damage from a heart attack, diagnose certain congenital heart defects and evaluate disease of larger blood vessels such as the aorta.
This modified form of imaging records pictures of the heart and its blood vessels by computer.
Sometimes the first indications of a heart attack come as warning signals.
The actual diagnosis of a heart attack must be made by a physician who has studied the results of several tests. Besides reviewing a patient's complete medical history and giving a physical examination, a doctor will use an electrocardiogram (EKG) to discover any abnormalities caused by damage to the heart. Sometimes a blood test is used to detect abnormal levels of certain enzymes in the bloodstream.
When a heart attack occurs, it's critical to recognize the signals and respond immediately. About half of all heart attack victims wait two hours or longer before deciding to get help. This reduces their chance of survival, because most heart attack victims who die do so within two hours of when the signals begin. Time is critical. Anyone experiencing the warning signals of a heart attack should be taken immediately to the nearest hospital with 24-hour emergency cardiac care. People who become unconscious before reaching the emergency room may receive emergency cardiopulmonary resuscitation (CPR).
Most communities have an emergency cardiac care system that can quickly respond to an emergency. This prompt care for heart attack victims dramatically reduces damage to the heart. In fact, 80 percent of heart attack survivors can return to work within three months. Prompt care for heart attack victims isn't the only reason so many people recover so quickly, but it's an important one.
The importance of time cannot be overemphasized. When a coronary artery gets blocked, the heart muscle doesn't die instantaneously - damage increases the longer an artery remains blocked. If a victim gets to an emergency room fast enough, a form of reperfusion therapy (called thrombolysis) sometimes can be performed. lt involves injecting a thrombolytic (clot-dissolving) agent, such as streptokinase, urokinase or tPA (tissue plasminogen activator), to dissolve a clot in a coronary artery and restore some blood flow. These drugs must be used within a few (usually 1-3) hours of a heart attack for best effect. The sooner a drug is used, the more effective it's likely to be.
In the weeks following a heart attack, either PTCA or coronary artery bypass surgery may be performed to improve the blood supply to the heart muscle. Once part of the heart muscle dies, its function can't be restored. Function may be restored to areas with decreased blood flow, however.
Many scientific studies show that certain characteristics increase the risk of coronary heart disease. These are called risk factors. The four major modifiable risk factors are high blood pressure, high blood cholesterol, cigarette smoke and physical inactivity. Other contributing risk factors are diabetes mellitus and obesity.
The American Heart Association strongly urges Americans to control their modifiable risk factors. Also, people with angina should take episodes of chest pain seriously and see their doctor before their atherosclerosis leads to a heart attack.