A heart attack (also known as a myocardial infarction) is the death of heart muscle from the sudden blockage of a coronary artery by a blood clot. Coronary arteries are blood vessels that supply the heart muscle with blood and oxygen.
Blockage of a coronary artery deprives the heart muscle of blood and oxygen,causing injury to the heart muscle. Injury to the heart muscle causes chest pain and chest pressure sensation. If blood flow is not restored to the heart muscle within 20 to 40 minutes, irreversible death of the heart muscle will begin to occur.
Muscle continues to die for six to eight hours at which time the heart attack usually is "complete". The dead heart muscle is eventually replaced by scar tissue.
Approximately one million Americans suffer a heart attack each year. Four hundred thousand of them die as a result of their heart attack.
Although chest pain or pressure is the most common symptom of a heart attack, heart attack victims may experience a variety of symptoms including:
- Pain, fullness, and/or squeezing sensation of the chest.
- Jaw pain, toothache, headache.
- Shortness of breath.
- Nausea, vomiting, and/or general epigastric (upper middle abdomen) discomfort.
- Heartburn and/or indigestion.
- Arm pain (more commonly the left arm, but may be either arm).
- Upper back pain.
- General malaise (vague feeling of illness).
No symptoms (Approximately one quarter of all heart attacks are silent, without chest pain or new symptoms. Silent heart attacks are especially common among patients with diabetes mellitus).
Even though the symptoms of a heart attack at times can be vague and mild, it is important to remember that heart attacks producing no symptoms or only mild symptoms can be just as serious and life-threatening as heart attacks that cause severe chest pain. Too often patients attribute heart attack symptoms to "indigestion", "fatigue", or "stress", and consequently delay seeking prompt medical attention.
One cannot overemphasize the importance of seeking prompt medical attention in the presence of symptoms that suggest a heart attack. Early diagnosis and treatment saves lives, and delays in reaching medical assistance can be fatal.
A delay in treatment can lead to permanently reduced function of the heart due to more extensive damage to the heart muscle. Death also may occur as a result of the sudden onset of arrhythmias such as ventricular fibrillation.
Atherosclerosis is a gradual process by which plaques (collections) of cholesterol are deposited in the walls of arteries. Cholesterol plaques cause hardening of the arterial walls and narrowing of the inner channel (lumen) of the artery. Arteries that are narrowed by atherosclerosis cannot deliver enough blood to maintain normal function of the parts of the body they supply.
For example, atherosclerosis of the arteries in the legs causes reduced blood flow to the legs. Reduced blood flow to the legs can lead to pain in the legs while walking or exercising, leg ulcers, or a delay in the healing of wounds to the legs. Atherosclerosis of the arteries that furnish blood to the brain can lead to vascular dementia (mental deterioration due to gradual death of brain tissue over many years) or stroke (sudden death of brain tissue).
In many people, atherosclerosis can remain silent (causing no symptoms or health problems) for years or decades. Atherosclerosis can begin as early as the teenage years, but symptoms or health problems usually do not arise until later in adulthood when the arterial narrowing becomes severe.
Smoking cigarettes, high blood pressure, elevated cholesterol, and diabetes mellitus can accelerate atherosclerosis and lead to the earlier onset of symptoms and complications, particularly in those people who have a family history of early atherosclerosis.
Coronary atherosclerosis (or coronary artery disease) refers to the atherosclerosis that causes hardening and narrowing of the coronary arteries.
Diseases caused by the reduced blood supply to the heart muscle from coronary atherosclerosis are called coronary heart diseases (CHD). Coronary heart diseases include heart attacks, sudden unexpected death, chest pain (angina), abnormal heart rhythms, and heart failure due to weakening of the heart muscle.
Atherosclerosis and angina pectoris
Angina pectoris (also referred to as angina) is chest pain or pressure that occurs when the blood and oxygen supply to the heart muscle cannot keep up with the needs of the muscle. When coronary arteries are narrowed by more than 50 to 70 percent, the arteries may not be able to increase the supply of blood to the heart muscle during exercise or other periods of high demand for oxygen.
An insufficient supply of oxygen to the heart muscle causes angina. Angina that occurs with exercise or exertion is calledexertional angina. In some patients, especially diabetics, the progressive decrease in blood flow to the heart may occur without any pain or with just shortness of breath or unusually early fatigue.
Exertional angina usually feels like a pressure, heaviness, squeezing, or aching across the chest. This pain may travel to the neck, jaw, arms, back, or even the teeth, and may be accompanied by shortness of breath, nausea, or a cold sweat.
Exertional angina typically lasts from one to 15 minutes and is relieved by rest or by taking nitroglycerin by placing a tablet under the tongue. Both resting and nitroglycerin decrease the heart muscle's demand for oxygen, thus relieving angina. Exertional angina may be the first warning sign of advanced coronary artery disease. Chest pains that just last a few seconds rarely are due to coronary artery disease.
Angina also can occur at rest. Angina at rest more commonly indicates that a coronary artery has narrowed to such a critical degree that the heart is not receiving enough oxygen even at rest.
Angina at rest infrequently may be due to spasm of a coronary artery (a condition called Prinzmetal's or variant angina). Unlike a heart attack, there is no permanent muscle damage with either exertional or rest angina.
Atherosclerosis and heart attack
Occasionally the surface of a cholesterol plaque in a coronary artery may rupture, and a blood clot forms on the surface of the plaque. The clot blocks the flow of blood through the artery and results in a heart attack (see picture below).
The cause of rupture that leads to the formation of a clot is largely unknown, but contributing factors may include cigarette smoking or other nicotine exposure, elevated LDL cholesterol, elevated levels of blood catecholamines (adrenaline), high blood pressure, and other mechanical and biochemical forces.
Unlike exertional or rest angina, heart muscle dies during a heart attack and loss of the muscle is permanent, unless blood flow can be promptly restored, usually within one to six hours.
While heart attacks can occur at any time, more heart attacks occur between 4:00 A.M. and 10:00 A.M. because of the higher blood levels of adrenaline released from the adrenal glands during the morning hours. Increased adrenaline, as previously discussed, may contribute to rupture of cholesterol plaques.
Approximately 50% of patients who develop heart attacks have warning symptoms such as exertional angina or rest angina prior to their heart attacks, but these symptoms may be mild and discounted.
Early treatment for a heart attack can prevent or limit damage to the heart muscle. Acting fast, at the first symptoms of a heart attack, can save your life. Medical personnel can begin diagnosis and treatment even before you get to the hospital.
Certain treatments usually are started right away if a heart attack is suspected, even before the diagnosis is confirmed.
- Oxygen therapy.
- Aspirin to thin your blood and prevent further blood clotting.
- Nitroglycerin to reduce your heart's workload and improve blood flow through the coronary arteries.
- Treatment for chest pain.
Once the diagnosis of a heart attack is confirmed or strongly suspected, doctors start treatments to try to promptly restore blood flow to the heart. The two main treatments are "clot-busting" medicines and angioplasty, a procedure used to open blocked coronary arteries.
Thrombolytic medicines, also called "clot busters," are used to dissolve blood clots that are blocking the coronary arteries. To work best, these medicines must be given within several hours of the start of heart attack symptoms. Ideally, the medicine should be given as soon as possible.
Angioplasty is a nonsurgical procedure that opens blocked or narrowed coronary arteries. This procedure also is called percutaneous (per-ku-TA-ne-us) coronary intervention, or PCI.
A thin, flexible tube with a balloon or other device on the end is threaded through a blood vessel to the narrowed or blocked coronary artery.
Once in place, the balloon is inflated to compress the plaque against the wall of the artery. This restores blood flow through the artery.
During the procedure, the doctor may put a small mesh tube called a stent in the artery. The stent helps prevent blockages in the artery in the months or years after angioplasty.
For more information, go to the Diseases and Conditions Index (DCI) Angioplastyarticle.
Other Treatments for Heart Attack
- Beta blockers. Beta blockers decrease your heart's workload. These medicines also are used to relieve chest pain and discomfort and to help prevent repeat heart attacks. Beta blockers also are used to treat arrhythmias (irregular heartbeats).
- ACE inhibitors. ACE inhibitors lower blood pressure and reduce strain on your heart. They also help slow down further weakening of the heart muscle.
- Anticoagulants. Anticoagulants, or "blood thinners," prevent blood clots from forming in your arteries. These medicines also keep existing clots from getting larger.
- Anticlotting medicines. Anticlotting medicines stop platelets from clumping together and forming unwanted blood clots. Examples of anticlotting medicines include aspirin and clopidogrel.
You also may be given medicines to relieve pain and anxiety, treat arrhythmias (which often occur during a heart attack), or lower your cholesterol (these medicines are called statins).
Coronary artery bypass grafting (CABG) also may be used to treat a heart attack. During CABG, a surgeon removes a healthy artery or vein from your body. The artery or vein is then connected, or grafted, to the blocked coronary artery.
The grafted artery or vein bypasses (that is, goes around) the blocked portion of the coronary artery. This provides a new route for blood to flow to the heart muscle.
For more information, go to the DCI Coronary Artery Bypass Grafting article.
Treatment After You Leave the Hospital
Most people spend several days in the hospital after a heart attack. When you leave the hospital, treatment doesn't stop. At home, your treatment may include daily medicines and cardiac rehabilitation (rehab). Your doctor may want you to have a flu shot and pneumococcal vaccine each year.
Your doctor also may recommend lifestyle changes, including following a heart healthy diet, being physically active, maintaining a healthy weight, and quitting smoking. Taking these steps can lower your chances of having another heart attack.
Your doctor may recommend cardiac rehab to help you recover from a heart attack and to help prevent another heart attack. Almost everyone who has had a heart attack can benefit from rehab.
Cardiac rehab is a medically supervised program that may help improve the health and well-being of people who have heart problems.
The cardiac rehab team may include doctors, nurses, exercise specialists, physical and occupational therapists, dietitians or nutritionists, and psychologists or other mental health specialists.
Rehab has two parts:
Exercise training. This part helps you learn how to exercise safely, strengthen your muscles, and improve your stamina. Your exercise plan will be based on your personal abilities, needs, and interests.
Education, counseling, and training. This part of rehab helps you understand your heart condition and find ways to reduce your risk of future heart problems. The rehab team will help you learn how to cope with the stress of adjusting to a new lifestyle and deal with your fears about the future.