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heart attack (myocardial infarction)





A heart attack, also known as myocardial infarction or coronary thrombosis, occurs when the supply of blood and oxygen to an area of heart muscle is blocked, usually by a clot in a coronary artery. Often, this blockage leads to arrhythmias (irregular heartbeat or rhythm) that cause a severe decrease in the pumping function of the heart and may bring about sudden death. If the blockage is not treated within a few hours, the affected heart muscle will die and be replaced by scar tissue.

A heart attack is a life-threatening event. Everyone should know the warning signs of a heart attack and how to get emergency help. Many people suffer permanent damage to their hearts or die because they do not get help immediately.

Each year, more than a million persons in the U.S. have a heart attack and about half (515,000) of them die. About one-half of those who die do so within 1 hour of the start of symptoms and before reaching the hospital.

Emergency personnel can often stop arrhythmias with emergency CPR (cardiopulmonary resuscitation), defibrillation (electrical shock), and prompt advanced cardiac life support procedures. If care is sought soon enough, blood flow in the blocked artery can be restored in time to prevent permanent damage to the heart. Yet, most people do not seek medical care for 2 hours or more after symptoms begin. Many people wait 12 hours or longer.

A heart attack is an emergency. Prompt treatment of a heart attack can help prevent or limit lasting damage to the heart and can prevent sudden death.





What causes a heart attack?

Most heart attacks are caused by a blood clot that blocks one of the coronary arteries (the blood vessels that bring blood and oxygen to the heart muscle). When blood cannot reach part of your heart, that area starves for oxygen. If the blockage continues long enough, cells in the affected area die.

Coronary artery disease (CAD) is the most common underlying cause of a heart attack. CAD is the hardening and narrowing of the coronary arteries by the buildup of plaque in the inside walls (atherosclerosis). Over time, plaque buildup in the coronary arteries can:
  • Narrow the arteries so that less blood flows to the heart muscle
  • Completely block the arteries and the flow of blood
  • Cause blood clots to form and block the arteries.
heart, with cross sections of arteries

A less common cause of heart attacks is a severe spasm (tightening) of the coronary artery that cuts off blood flow to the heart. These spasms can occur in persons with or without CAD. Artery spasm can sometimes be caused by:
  • Taking certain drugs, such as cocaine
  • Emotional stress
  • Exposure to cold
  • Cigarette smoking.

What makes a heart attack more likely?

Certain factors make it more likely that you will develop CAD and have a heart attack. These are called risk factors. Risk factors you cannot change include:
  • Your age
    • Men: over age 45
    • Women: over age 55
  • Having a family history of early heart disease
    • Heart disease diagnosed in father or brother before age 55
    • Heart disease diagnosed in mother or sister before age 65
  • Having a personal history of CAD
    • Angina
    • A previous heart attack
    • A surgical procedure (angioplasty, heart bypass) to increase blood flow to your heart.

Risk factors that you can change include:

Signs and symptoms of a heart attack

The warning signs and symptoms of a heart attack can include:
  • Chest discomfort. Most heart attacks involve discomfort in the center of the chest that lasts for more than a few minutes, or goes away and comes back. The discomfort can feel like uncomfortable pressure, squeezing, fullness, or pain. Heart attack pain can sometimes feel like indigestion or heartburn.

  • Discomfort in other areas of the upper body. Can include pain, discomfort, or numbness in one or both arms, the back, neck, jaw, or stomach.

  • Shortness of breath. Often comes along with chest discomfort. But it also can occur before chest discomfort.
  • Other symptoms. May include breaking out in a cold sweat, having nausea and vomiting, or feeling light-headed or dizzy.
Signs and symptoms vary from person to person. In fact, if you have a second heart attack, your symptoms may not be the same as for the first heart attack. Some people have no symptoms. This is called a "silent" heart attack.

The symptoms of angina can be similar to those of a heart attack. If you have angina and notice a change or a worsening of your symptoms, talk with your doctor right away.


How is a heart attack diagnosed?

Diagnosis (and treatment) of a heart attack can begin when emergency medical personnel arrive.

At the hospital emergency room, doctors will work fast to find out if you are having or have had a heart attack. They will consider your symptoms, medical and family history, and test results. Initial tests will be quickly followed by treatment if you are having a heart attack.


Tests used include:
  • Electrocardiogram (ECG or EKG). This test is used to measure the rate and regularity of your heartbeat. A 12-lead EKG is used in diagnosing a heart attack.

  • Blood tests. When cells in the heart die, they release enzymes into the blood. They are called markers or biomarkers. Measuring the amount of these markers in the blood can show how much damage was done to your heart. These tests are often repeated at intervals to check for changes. The specific blood tests are:

    • Troponin test. This test checks the troponin levels in the blood. It is considered the most accurate blood test to see if a heart attack has occurred and how much damage was done to the heart.
    • CK or CK-MB test. These tests check for the amount of the different forms of creatine kinase in the blood.
    • Myoglobin test. This test checks for the presence of myoglobin in the blood. Myoglobin is released when the heart or other muscle is injured.

  • Nuclear heart scan. This test uses radioactive tracers (technetium or thallium) to outline heart chambers and major blood vessels leading to and from the heart. A nuclear heart scan shows any damage to your heart muscle.

  • Cardiac catheterization. A thin flexible tube (catheter) is passed through an artery in the groin or arm to reach the coronary arteries. Your doctor can determine pressure and blood flow in the heart's chambers, collect blood samples from the heart, and examine the arteries of the heart by X-ray.

  • Coronary angiography. This test is usually performed along with cardiac catheterization. A dye that can be seen using X-ray is injected through the catheter into the coronary arteries. Your doctor can see the flow of blood through the heart and see where there are blockages.

Treatment

A heart attack is a medical emergency. Delaying treatment can mean lasting damage to your heart or even death. The sooner treatment begins, the better your chances of recovering. Your treatment may begin in the ambulance or in the emergency room and continue in a special area called a coronary care unit or CCU.


In the hospital

If you are having a heart attack, doctors will:
  • Work quickly to restore blood flow to the heart
  • Continuously monitor your vital signs to detect and treat complications
Restoring blood flow to the heart is vital to prevent or limit damage to the heart muscle and to prevent another heart attack. The main treatments are the use of thrombolytic ("clot-busting") drugs and procedures such as angioplasty.
  • Thrombolytic drugs ("clot-busters") are used to dissolve blood clots that are blocking blood flow to the heart. When given soon after a heart attack begins, these drugs can limit or prevent permanent damage to the heart. To be most effective, they need to be given within 1 hour after of the start of heart attack symptoms.

  • Angioplasty procedures are used to open blocked or narrowed coronary arteries. A stent, which is a tiny metal mesh tube, may be placed in the artery to help keep it open.

  • Coronary artery bypass surgery uses arteries or veins from other areas in your body to bypass your blocked coronary arteries.
The CCU is specially equipped with monitors that continuously measure your vital signs. Those that can show signs of complications include:
  • EKG, which detects any heart rhythm (arrhythmia) or functional problems
  • Blood pressure
  • Pulse oximetry, which measures the amount of oxygen in the blood and provides an early warning sign of a low level of oxygen in the blood.
Medications used in treating heart attacks include:
  • Beta blockers to decrease the workload on your heart by slowing your heart rate. This makes your heart beat with less force and lowers your blood pressure. Some beta blockers are also used to relieve angina (chest pain) and in heart attack patients to help prevent additional heart attacks. They are also used to correct irregular heartbeat.

  • Angiotensin-converting enzyme (ACE) inhibitors to lower blood pressure and reduce the strain on your heart. They are used in some patients after a heart attack to increase survival rate and help slow down further weakening of the heart.

  • Nitrates, such as nitroglycerin, to relax blood vessels and stop chest pain.

  • Anticoagulants to thin the blood and prevent clots from forming in your arteries.

  • Antiplatelet medications (such as aspirin and clopidigrel) to stop platelets from clumping together to form clots. These medications are given to people who have had a heart attack, have angina, or who experience angina after angioplasty.

  • Glycoprotein IIb-IIIa inhibitors, which are potent antiplatelet medicines given intravenously to prevent clots from forming in your arteries.

  • Medicines to relieve pain and anxiety.

  • Medicines to treat arrhythmias (irregular heart rhythms), which often occur during a heart attack.

  • Oxygen therapy.
The length of your hospital stay after a heart attack depends on your condition and response to treatment. Most people spend several days in the hospital after a heart attack. While in the hospital, your heart will be monitored, and you will receive needed medications. You will probably have further testing, and you will be treated for any complications that arise.

While you are still in the hospital or after you go home after your heart attack, your doctor may order other tests, such as:
  • Echocardiogram. In this test, ultrasound is used to make an image of your heart that can be seen on a video monitor. It shows how well the heart is filling with blood and pumping it to the rest of the body.

  • Exercise stress test. This test shows how well your heart pumps at higher workloads when it needs more oxygen. EKG and blood pressure readings are taken before, during, and after exercise to see how your heart responds to exercise. The first EKG and blood pressure reading are done to get a baseline. Readings are then taken while you walk on an exercise treadmill or pedal a stationary bicycle. The test continues until you reach a heart rate set by your doctor. The exercise part is stopped if chest pain or a very sharp rise in blood pressure occurs. Monitoring continues for 10 to 15 minutes after exercise or until your heart rate returns to baseline.

Cardiac rehabilitation (Rehab)

Your doctor may prescribe cardiac rehabilitation (rehab) to help you recover from a heart attack and help prevent another heart attack. Almost everyone who has survived a heart attack can benefit from rehab.

The cardiac rehab team may include:
  • Doctors
  • Your family doctor
  • A heart specialist
  • A surgeon
  • Nurses
  • Exercise specialists
  • Physical therapists and occupational therapists
  • Dietitians
  • Psychologists or other behavior therapists.
Rehab has two parts:
  • Exercise training to help you learn how to exercise safely, strengthen your muscles, and improve your stamina. Your exercise plan will be based on your individual ability, needs, and interests.

  • Education, counseling, and training to help you understand your heart condition and find ways to reduce your risk of future heart problems. The cardiac rehab team will help you learn how to cope with the stress of adjusting to a new lifestyle and to deal with your fears about the future.

After you leave the hospital

After a heart attack, your treatment may include cardiac rehab in the first weeks or months, checkups and tests, lifestyle changes, and medications. You will need to see your doctor for checkups and tests to see how your heart is doing. Your doctor will most likely recommend lifestyle changes, such as quitting smoking, losing weight, changing your diet, or increasing your physical activity.

After a heart attack, most people take daily medications. These may include:
  • Aspirin
  • Medicines that lower your cholesterol or your blood pressure
  • Other medicines to help reduce your heart's workload.

Related categories

   • HEART TOPICS
   • HEALTH AND DISEASE

Source: U.S. National Heart, Lung and Blood Institute