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What is a heart attack (myocardial infarction)?

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 pressure. If blood flow is not restored within 20 to 40 minutes, irreversible death of the heart muscle will begin to occur. Muscle continues to die for 6-8 hours at which time the heart attack usually is "complete." The dead heart muscle is replaced by scar tissue.

The heart is a muscular pump located in the chest. Its job is to pump blood around the body via the circulatory system of blood vessels. The heart consists of 4 chambers: right atrium and right ventricle, and left atrium and left ventricle. Blood is depleted of oxygen after circulating through the body. This blood returns into the right atrium. From there the blood flows into the right ventricle, which pumps the blood out to the lungs for oxygenation. The oxygen-rich blood then returns to the left

atrium. From there it flows into the left ventricle and is pumped out at high pressure into the arteries. The high pressure is generated by powerful contraction of the heart muscle.This raises the pressure of the blood and enables it to flow through the extensive network of arteries to every part of the body and return to the heart. For this pumping action, the heart has to be strong. The heart is nourished by the blood supplied directly to the heart muscle through the coronary arteries. The strength of the heart muscle depends very much on this blood supply. The coronary arteries are usually strong, elastic, and quite flexible. The inner lining of the arteries is normally smooth. This allows the blood to flow smoothly without clotting.

Heart attack is caused by sudden loss of blood and oxygen to heart. The most common condition that predisposes a person to heart attack is coronary heart disease, or coronary artery disease, due to atherosclerosis, or fatty build up of plaque on the inner lining of coronary arteries. The plaque and resulting blood clots block the artery partially or completely, reducing the amount of blood that can flow through the artery to the heart. This cuts off the oxygen supply to part of the heart muscle. If the blood supply is cut off long enough, that part of the heart muscle dies. This is a heart attack. If a large enough part of the heart muscle is affected, a dangerous rhythm disorder called ventricular fibrillation may occur. If this happens, the heart may stop. This is called cardiac arrest, and most people who have cardiac arrest die.

The heart is a complex, highly specialized, muscular organ in the chest that maintains the circulation of blood throughout the body. Heart attack, or acute myocardial infarction, is the death of heart tissue caused by a complete blockage in one of the arteries that supply blood to the heart (coronary arteries), resulting in an interruption in the blood supply to the heart. When heart tissue is deprived of blood-borne oxygen for longer than 30 minutes (called ischemia), it begins to die.

A heart attack is almost always preceded by a condition called coronary heart disease. Over the years, fatty deposits or plaques build up inside one or both of the coronary arteries (in a process called atherosclerosis). This constant silting narrows the artery and can cause angina (chest pain or discomfort), which typically occurs during activity or emotion. When a blood clot forms at a narrowed point and blocks the passage of blood altogether, this is called coronary thrombosis or coronary occlusion. A heart attack can 'stun' the heart and interrupt its rhythm and ability to pump. Instead of beating normally, the rhythm can be chaotic (ventricular fibrillation) or stop the heart altogether, causing cardiac arrest. A cardiac arrest can follow on from the symptoms of a heart attack or strike suddenly. Typically, the person falls unconscious, has no pulse and usually stops breathing. This is an extreme medical emergency. Without immediate help, the person will die. Ambulance officers or hospital staff will need to use a special device called a defibrillator, which passes an electric jolt through the heart which may start it beating again. In the absence of such specialised equipment, cardiopulmonary resuscitation (CPR) is crucial. This combines mouth-to-mouth resuscitation and heart massage. CPR can keep the person alive until an ambulance arrives.

In most cases, blockage occurs as a result of coronary heart disease (CHD), also called atherosclerosis, a condition in which plaques (deposits of cholesterol and fatty material) build up in the arteries and partially or completely block blood flow. When the surface of a plaque tears or ruptures, a blood clot (thrombus) can form and completely block the flow of blood in the artery. Ischemia causes electrical instability within the chambers of the heart, preventing the heart from adequately pump blood throughout the body (called ventricular fibrillation). Permanent brain damage and death can occur when the brain is deprived of blood flow for longer than 5 minutes.

More information on heart attack (myocardial infarction)

What's a heart attack (myocardial infarction)? - A heart attack (myocardial infarction) is the death of heart muscle from the sudden blockage of a coronary artery by a blood clot.
What're the signs and symptoms of a heart attack? - Symptoms of a heart attack include pain and pressure in the chest, which often spread to the shoulder, arm, and neck.
What're the women's heart attack symptoms? - A woman's heart attack has more varied symptoms than a man's. Women are more likely to have nausea and pain high in the abdomen.
What're the warning signs of a heart attack? - Warning signs of a heart attack include uncomfortable pressure, fullness, squeezing, or pain in the center of the chest, cold sweat or paleness.
What causes a heart attack? - Heart attack is caused by a lack of blood supply to the heart for an extended time period. The most common cause of heart attack is atherosclerosis.
What're the complications of a heart attack? - Complications of a heart attack include ventricular tachycardia, ventricular fibrillation, cardiogenic shock, arrhythmias, heart failure.
What're the risk factors for heart attack? - Heart attack risk factors can be devided into two groups: Inherited (or genetic) risk factors and acquired risk factors.
How is a heart attack diagnosed? - The most important factor in diagnosing and treating a heart attack is prompt medical attention. For a complete diagnosis, the medical history is vital.
What're the treatments for heart attack? - The goal of treatment for heart attack is to quickly open the blocked artery and restore blood flow to the heart muscle, a process called reperfusion.
What drugs are used to cure heart attack? - Medications used to treat heart attacks include blood vessel dilators, clot busters, beta blockers, antiarrhythmic drugs, pain relievers.
What surgeries treat heart attacks? - Surgeries to treat heart attacks include coronary angioplasty, coronary artery bypass surgery, transmyocardial revascularization, and atherectomy.
Aspirin and heart attacks - Aspirin is taken daily following a heart attack to reduce the risk of another heart attack. Aspirin reduces heart attacks and improve survival in the patients.
How to survive a heart attack? - In wilderness first aid, a possible heart attack justifies medical evacuation by the fastest available means. Heart attacks are survivable.
How to prevent a heart attack? - Heart attack can be prevented with a healthy liestyle. Daily aspirin therapy or other medical treatment help prevent heart disease and heart attack.
How to recover after a heart attack? - Following discharge from the hospital, patients continue their recovery at home. Lowering cholesterol can reduce the risk for another heart attack.
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All information is intended for reference only. Please consult your physician for accurate medical advices and treatment. Copyright 2005,, all rights reserved. Last update: July 18, 2005