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Heart Attack (Myocardial Infarction)

A heart attack, or myocardial infarction (MI), is permanent damage to the heart muscle. "Myo" means muscle, "cardial" refers to the heart and "infarction" means death of tissue due to lack of blood supply.

What Happens During a Heart Attack?

The heart muscle requires a constant supply of oxygen-rich blood to nourish it. The coronary arteries provide the heart with this critical blood supply. If you have coronary artery disease, those arteries become narrow and blood cannot flow as well as it should. Fatty matter, calcium, proteins and inflammatory cells build up within the arteries to form plaques of different sizes. The plaque deposits are hard on the outside and soft and mushy on the inside.

When the plaque's hard, outer shell cracks (plaque rupture), platelets (disc-shaped particles in the blood that aid clotting) come to the area, and blood clots form around the plaque. If a blood clot totally blocks the artery, the heart muscle becomes "starved" for oxygen. Within a short time, death of heart muscle cells occurs, causing permanent damage. This is called a myocardial infarction (MI), or heart attack.

While it is unusual, a heart attack can also be caused by a spasm of a coronary artery. During coronary spasm, the coronary arteries restrict or spasm on and off, reducing blood supply to the heart muscle (ischemia). It may occur at rest and can even occur in people without significant coronary artery disease.

Each coronary artery supplies blood to a region of heart muscle. The amount of damage to the heart muscle depends on the size of the area supplied by the blocked artery and the time between injury and treatment.

Healing of the heart muscle begins soon after a heart attack and takes about eight weeks. Just like a skin wound, the heart's wound heals and a scar will form in the damaged area. But, the new scar tissue does not contract or pump as well as healthy heart muscle tissue. So, the heart's pumping ability is lessened after a heart attack. The amount of lost pumping ability depends on the size and location of the scar.

What Are the Symptoms of a Heart Attack?

Symptoms of a heart attack include:

  • Discomfort, pressure, heaviness, or pain in the chest, arm or below the breastbone
  • Discomfort radiating to the back, jaw, throat or arm
  • Fullness, indigestion or choking feeling (may feel like heartburn)
  • Sweating, nausea, vomiting or

  • How Is a Heart Attack Diagnosed?

    Once the emergency care team arrives, they will ask you about your symptoms and begin to evaluate you. The diagnosis of the heart attack is based on your symptoms, ECG and the results of your blood tests. The goal of treatment is to treat you quickly and limit heart muscle damage.

    Tests You Take

    ECG. The ECG (also known as EKG or electrocardiogram) can tell how much damage has occurred to your heart muscle and where it has occurred. In addition, your heart rate and rhythm can be monitored.

    Blood tests. Blood may be drawn to measure levels of cardiac enzymes in the blood that indicate heart muscle damage. These enzymes are normally found inside the cells of your heart and are needed for their function. When your heart muscle cells are injured, their contents -- including the enzymes -- are released into your bloodstream. By measuring the levels of these enzymes, the doctor can determine the size of the heart attack and approximately when the heart attack started. Troponin levels will also be measured. Troponins are proteins found inside of heart cells that are released when they are damaged by ischemia. Troponins can detect very small heart attacks as well as those that occurred more than a day after symptoms ensued.

    Echocardiography. Echocardiography is an imaging test that can be used during and after a heart attack to learn how the heart is pumping and what areas are not pumping normally. The "echo" can also tell if any structures of the heart (valves, septum, etc.) have been injured during the heart attack.

    Cardiac catheterization. Cardiac catheterization, also called cardiac cath, may be used during the first hours of a heart attack if medications are not relieving the ischemia or symptoms. The cardiac cath can be used to directly visualize the blocked artery and help your doctor determine which procedure is needed to treat the blockage.

    Types of heart attack

    Heart attacks can be classified by a measurement that is known as the ST segment. The ST segment is an electrical measurement that is recorded by an ECG. It corresponds to the level of damage that has been inflicted on the heart. The higher the ST segment, the greater the amount of damage that is likely to have occurred.

    There are three main types of heart attack:

  • ST segment elevation myocardial infarction (STEMI)
  • Non-ST segment elevation myocardial infarction (NSTEMI)
  • unstable angina
  • The three types are described in more detail below.

    ST segment elevation myocardial infarction (STEMI)

    ST segment elevation myocardial infarction (STEMI) is the most serious type of heart attack. In this type of heart attack, a prolonged interruption to the blood supply, resulting from a total blockage of the coronary artery, causes extensive damage to a large area of the heart. A STEMI is what most people think of when they hear the term heart attack.

    Non-ST segment elevation myocardial infarction (NSTEMI)

    Non-ST segment elevation myocardial infarction (NSTEMI) is less serious than a STEMI. This is because the supply of blood to the heart is only partially blocked, rather than completely blocked. As a result, a smaller section of the heart is damaged. However, NSTEMI is still regarded as a serious medical emergency.

    Unstable angina

    Unstable angina is the least serious type of heart attack although, like NSTEMI, it is still regarded as a medical emergency. In unstable angina, the blood supply to the heart is still seriously restricted, but the extent of the damage is much less severe than in cases of STEMI and NSTEMI.

    How Is a Heart Attack Treated?

    Once heart attack is diagnosed, treatment begins immediately -- possibly in the ambulance or emergency room. Medications and surgical procedures are used to treat a heart attack.

    What Medications Are Used to Treat a Heart Attack?

    The goals of medication therapy are to break up or prevent blood clots, prevent platelets from gathering and sticking to the plaque, stabilize the plaque and prevent further ischemia.

    These medications must be given as soon as possible (within one to two hours from the start of your heart attack) to decrease the amount of heart damage. The longer the delay in starting these drugs, the more damage can occur and the less benefit they can provide.

    Medications for this purpose may include:

  • Aspirin to prevent blood clotting that may worsen the heart attack.
  • Antiplatelet to prevent blood clotting.
  • Thrombolytic therapy ("clot busters") to dissolve any blood clots those are present in the heart's arteries.
  • Any combination of the above

  • Other drugs, given during or after a heart attack, lessen your heart's work, improve the functioning of the heart, widen or dilate your blood vessels, decrease your pain and guard against any life-threatening heart rhythms.

    What is the treatment for myocardial infarction?

    The following is a typical situation and mentions the common treatments offered. Each case is different and treatments may vary depending on your situation. Treatments for STEMI and NSTEMI can also differ.

    Aspirin and other antiplatelet drugs

    As soon as possible after an MI is suspected you will be given a dose of aspirin. Aspirin reduces the 'stickiness' of platelets. Platelets are tiny particles in the blood that trigger the blood to clot. It is the platelets that become stuck onto a patch of atheroma inside an artery that go on to form the clot (thrombosis) of an MI.

    Another antiplatelet drug called clopidogrel is also given. This works in a different way to aspirin and adds to the action of reducing platelet stickiness.

    Injections of heparin or a similar drug

    These are usually given for a few days to help prevent further blood clots forming.

    Pain relief

    A strong pain killer given by injection into a vein is given to ease the pain.

    Treatment to restore blood flow in the blocked coronary artery

    The part of the heart muscle starved of blood does not die (infarct) immediately. If blood flow is restored within a few hours, much of the heart muscle that would have been damaged will survive. This is why an MI is a medical emergency, and treatment is given urgently. The quicker the blood flow is restored, the better the outlook.

    There are two treatments that can be done to restore blood flow back through the blocked artery:

  • Emergency angioplasty is, ideally, the best treatment if it is available and can be done within a few hours of symptoms starting. In this procedure a tiny wire with a balloon at the end is put into a large artery in the groin or arm. It is then passed up to the heart and into the blocked section of a coronary artery using special X-ray guidance. The balloon is blown up inside the blocked part of the artery to open it wide again. A stent may be left in the widened section of the artery. A stent is like a wire mesh tube which gives support to the artery and helps to keep the artery widened. See separate leaflet called 'Angioplasty' for details.
  • An injection of a 'clot busting' drug is an alternative to emergency angioplasty. In reality, this is the more common treatment as it can be given easily and quickly in most situations. Some ambulance crews are trained to give this treatment. Note: a common 'clot buster' drug used in the UK is called streptokinase. If you are given this drug you should not be given it again if you have another MI in the future. This is because antibodies develop to it and it will not work so well a second time. An alternative 'clot buster' drug should be given if you have another MI in the future.
  • Both the above treatments usually work well to restore blood flow and greatly improve the outlook. The most crucial factor is the quickness in which one or other treatment is given after symptoms have developed.

    A beta-blocker drug

    Beta-blocker drugs block the action of certain hormones such as adrenaline. These hormones increase the rate and force of the heartbeat. Beta-blocker drugs have some protective effect on the heart muscle and they also help to prevent abnormal heart rhythms from developing.

    Beta-blocker drugs will also help to prevent having either another myocardial infarction.


    Some people have a raised blood sugar level when they have a myocardial infarction, even if they do not have diabetes. If this occurs, then your blood sugar levels may need to be controlled with insulin. If you have diabetes then it is also likely that you will need to be treated with insulin to control your blood glucose levels when you are in hospital.


    You may be given oxygen which works to reduce the risk of damage to your heart muscle


    Cardiopulmonary resuscitation (CPR)

    Cardiopulmonary resuscitation (CPR) is a first aid technique that can be used if you think that someone's heart has stopped beating as the result of a heart attack (cardiac arrest).

    Someone may have had a cardiac arrest if:

  • they appear to not be breathing
  • they are not moving
  • they do not respond to any stimulation, such as being touched or spoken to

  • CPR consists of combining two techniques:

  • chest compressions
  • rescue breathing

  • Chest compression

    To carry out a chest compression, place the heel of your hand at the centre of the person's chest, in between their nipples. Place your other hand on top of your first hand and interlock your fingers. Using your body weight (not just your arms), press straight down (4-5cm) onto their chest.

    Rescue breathing

    To carry out rescue breathing, tilt the person's head back and lift their chin up to open their airways. Pinch their nostrils closed and breathe into their mouth for one second. If their chest rises, give another breath. If their chest does not rise, tilt their head back and lift their chin again, before giving the second breath.

    If you have received training in how to give CPR and you feel confident about performing the manoeuvre:

  • give 30 chest compressions
  • followed by two rescue breaths
  • before repeating the cycle
  • Aim to do the chest compressions at a rate of 100 compressions a minute.

    If you have not been trained in CPR, do not attempt to perform rescue breathing because it is possible to damage the person's airways if it is not performed correctly. Instead, focus on giving 100 chest compressions a minute.

    The above advice only applies to adults.

    What Other Treatment Options Are There?

    During or shortly after a heart attack, you may go to the cardiac catheterization laboratory for direct evaluation of the status of your heart, arteries and the amount of heart damage. In some cases, procedures (such as angioplasty or stents) are used to open up your narrowed or blocked arteries. These procedures may be combined with thrombolytic therapy (drug treatments) to open up the narrowed arteries, as well as to break up any clots that are blocking them.

    If necessary, bypass surgery may be performed to restore the heart muscle's supply of blood.

    Treatments (medications, open heart surgery and interventional procedures, like angioplasty) do not cure coronary artery disease. Having had a heart attack or treatment does not mean you will never have another heart attack; it can happen again. But, there are several steps you can take to prevent further attacks.

    How Are Subsequent Heart Attacks Prevented?

    The goal after your heart attack is to keep your heart healthy and reduce your risks of having another heart attack. Your best bet to ward off future attacks are to take your medications, change your lifestyle, and see you doctor for regular heart checkups.

    Why Do I Need to Take Medicine After a Heart Attack?

    Medications are prescribed after a heart attack to:

  • Prevent future blood clots.
  • Lessen the work of your heart and improve your heart's performance and recovery.
  • Lower cholesterol.
  • Other medications may be prescribed if needed. These include medications to treat irregular heartbeats, lower blood pressure, control angina and treat heart failure.

    It is important to know the names of your medications, what they are used for and how often and at what times you need to take them. Your doctor or nurse should review your medications with you. Keep a list of your medications and bring them to each of your doctor visits. If you have questions about your medications, ask your doctor or pharmacist.

    What Lifestyle Changes Will I Need to Make?

    There is no cure for coronary artery disease. In order to prevent the progression of this disease, you must follow your doctor's advice and make necessary lifestyle changes. You can stop smoking, lower your blood cholesterol, control your diabetes and high blood pressure, follow an exercise plan, lose weight, and control stress.