A heart attack, also known as a myocardial infarction, is a medical emergency that occurs when a portion of the heart is deprived of oxygen because of blockage of one of the coronary arteries, which supply the heart muscle (myocardium) with blood. Lack of oxygen causes characteristic chest pain and death of myocardial tissue.

Heart attacks are more likely to occur when arteries have already been substantially narrowed by years of coronary heart disease. Plaque (composed of cholesterol-rich fatty deposits, collagen and other proteins, and excess smooth muscle cells) builds up in the arterial walls, a process known as atherosclerosis. Arterial walls thicken and narrow, inhibiting the flow of blood into the heart.

When arterial walls have been roughened by plaque deposits, it becomes much easier for blood clots to form along the surface of the plaque. If the clots grow, or if they detach from their place of origin and are carried along to a narrower section of artery, they may block a coronary artery completely, causing a heart attack. Arteries may also narrow suddenly as a result of an arterial spasm.

One-third of all heart attacks occur with no prior warning signs. In the remainder, attacks of chest pain (angina) brought about by stress or exertion occur periodically for months or years prior to a heart attack. In some cases a mild heart attack produces no symptoms—a so-called silent heart attack.

Prompt emergency medical attention is crucial: If treatment is received within a few hours of the onset of a heart attack, chances for survival are good. Improved treatment methods—including the administration of thrombolytic (clot dissolving) drugs and angioplasty (inflation of a tiny balloon at the site of the blockage to widen the artery and permit the flow of blood through the artery)—have led to a steady decrease in mortality from heart attacks.

However, the best treatment remains prevention. The process of atherosclerosis may be halted or even reversed with fairly simple measures, and the risk of heart attack can thus be reduced.

Symptoms of Heart Attack

• Chest pain or pressure, tightness, squeezing, burning, aching, or heaviness in the chest, lasting longer than 10 minutes. The pain or discomfort is usually located in the center of the chest just under the breastbone and may radiate down the arm (especially the left), up into the neck, or along the jaw line.

• Shortness of breath.

• Profuse sweating.

• Dizziness.

• Muscle weakness.

• Nausea and vomiting.

• A choking sensation.

• Anxiety, or a feeling of impending doom.

• No symptoms occur with a silent heart attack.

What Causes Heart Attack?

• Blood clots that block a coronary artery are the most common cause of heart attacks. Clots develop on plaque in a coronary artery. Pieces of a clot may also be carried along the coronary artery and cause an obstruction.

• Severely narrowed arteries due to atherosclerosis underlie the development of a heart attack.

• Cigarette smoking, high blood pressure, high blood cholesterol levels, a diet rich in saturated fat (especially animal fat), obesity, lack of exercise, and diabetes mellitus all promote atherosclerosis and thus increase the risk of heart attacks.

• A family history of early or premature heart attacks (before the age of 55 in men and 65 in women) increases the risk of heart attack.

• Men have a significantly higher risk of heart attack than premenopausal women. But the risk for postmenopausal women approaches that of men as estrogen production decreases with menopause.

• Risk increases with age: Heart attacks are most common after age 65.

• A spasm of the muscles of the arterial walls may cause a heart attack by narrowing an artery. Spasms may be triggered by smoking, extreme emotional stress, or exposure to very cold air or water.

• Abuse of cocaine or amphetamines may cause a sudden heart attack even in those with no signs of heart disease.

• Heavy exertion, such as shoveling snow or carrying heavy objects up stairs, and severe emotional stress may trigger a heart attack.

• Having had one heart attack increases the risk of future heart attacks.

Prevention of Heart Attack

• Don’t smoke. Your doctor may recommend methods for quitting, including nicotine replacement.

• Eat a diet low in fat, cholesterol, and salt.

• See your doctor regularly for blood pressure and cholesterol monitoring.

• Pursue a program of moderate, regular aerobic exercise. People over age 50 who have led a sedentary lifestyle should check with a doctor before beginning an exercise program.

  Lose weight if you are overweight.

• Your doctor may advise you to take a low dose of aspirin regularly. Aspirin reduces the tendency for the blood to clot, thereby decreasing the risk of heart attack. However, such a regimen should only be initiated under a doctor’s expressed recommendation.

Diagnosis of Heart Attack

• Patient history and physical examination are needed. Diagnosis will often be made immediately by a doctor or emergency response technician.

• An electrocardiogram (ECG) will be performed. This test measures changes in the electrical activity of the heart that result from abnormalities in the flow of blood.

• Blood tests measure the release of enzymes from damaged heart muscle into the bloodstream.

• A coronary angiography (using a tiny catheter inserted into an artery in a leg or arm and threaded up the artery to the heart) is performed to locate the arterial blockage prior to angioplasty or bypass surgery. A contrast material is then injected from the end of the catheter into the coronary arteries, and a high-speed series of x-rays is taken.

How To Treat Heart Attack

• It is advised to chew on an aspirin at the onset of the symptoms of a heart attack. It may help break up the clot.

• Emergency treatment and immediate hospitalization is necessary.

• A stopped heartbeat must be restarted immediately by cardiopulmonary resuscitation (CPR) or by a device known as an electrical defibrillator.

• Thrombolytic, or clot-dissolving, drugs such as tissue plasminogen activator (tPA), streptokinase, or urokinase may be injected immediately to dissolve arterial blockage. This technique is most effective within three hours of the onset of a heart attack.

• Painkillers such as morphine or meperidine are administered to relieve pain.

• Nitroglycerin may be given to reduce the heart’s oxygen demands and to lower blood pressure.

• Antihypertensive drugs such as beta-blockers, ACE inhibitors, or calcium channel blockers may also be administered to lower blood pressure and to reduce the heart’s oxygen demand. The effect of these drugs may be enhanced by diuretics.

• Oxygen may be administered through nasal tubes.

• Anticoagulants such as heparin, aspirin, or warfarin may be administered to reduce the risk of blood clots.

• A cholesterol-lowering drug may be started in the hospital.

• Digitalis glycosides may be prescribed in some cases to strengthen heart muscle contraction. (In the United States, digoxin is the most commonly prescribed type of digitalis.)

• Dopamine or dobutamine may be administered to increase blood flow to the heart and strengthen the heartbeat.

• Blocked arteries may be opened or widened by percutaneous transluminal coronary angioplasty (PTCA). A small balloon is inserted into an artery, guided with a catheter to the narrowed point in the coronary artery, and then inflated. This compresses the plaque, widens the passageway, and improves blood flow. A stent may be placed to help keep the artery open.

• Coronary bypass surgery may be performed to restore adequate blood flow to the heart muscle. A mammary artery or a vein from the leg is grafted onto the narrowed coronary artery to circumvent the blocked portion.

• Electronic implants such as a pacemaker or a defibrillator may be attached to the heart to maintain strong, regular contractions of the heart muscle.

• A heart transplant may be advised in severe cases when heart tissue has been badly damaged. The survival rate for heart transplant is 80 percent after one year and over 60 percent after four years.

• During recovery, follow prevention tips to reduce the risk of another heart attack.

• Contact your local chapter of the American Heart Association for information about support groups.

When To Call A Doctor

• Emergency: Call an ambulance if you experience crushing chest pain, with or without nausea, vomiting, profuse sweating, breathlessness, weakness, or intense feelings of dread.

• Emergency: Call an ambulance if chest pain from previously diagnosed angina does not subside after 10 to 15 minutes.

For more information on heart attack and heart disease, click on this link -- Johns Hopkins Health Alerts: Heart Health

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