Heart Attack (Myocardial Infarction) | Symptoms and Causes

Treatment with a clot-busting medicine or an emergency procedure to restore the blood flow through the blocked blood vessel is usually done as soon as possible. This is to prevent or minimise any damage to your heart muscle. Other treatments help to ease the pain and to prevent complications. Reducing various risk factors can help to prevent a heart attack.

The heart is mainly made of special muscle (myocardium). The heart pumps blood into blood vessels (arteries) which take the blood to every part of the body. Like any other muscle, the heart muscle needs a good blood supply. The coronary arteries take blood to the heart muscle. The main coronary arteries branch off from the aorta. The aorta is the large artery which takes oxygen-rich blood from the heart chambers to the body. The main coronary arteries divide into smaller branches which take blood to all parts of the heart muscle. See separate leaflet called The Heart and Blood Vessels.

If you have a heart attack, a coronary artery or one of its smaller branches is suddenly blocked. The part of the heart muscle supplied by this artery loses its blood (and oxygen) supply if the vessel is blocked. This part of the heart muscle is at risk of dying unless the blockage is quickly removed. When a part of the heart muscle is damaged it is said to be infarcted. The term myocardial infarction (MI) means damaged heart muscle.

If a main coronary artery is blocked, a large part of the heart muscle is affected. If a smaller branch artery is blocked, a smaller amount of heart muscle is affected. After a heart attack, if part of the heart muscle has died, it is replaced by scar tissue over the following few weeks.

A heart attack and myocardial infarction (MI) are commonly used terms and they mean the same thing. However, the term MI is used less often now by doctors. This is because there is actually a range of conditions that can be caused by a sudden reduction in blood flow in a coronary artery. This range of conditions has an overall term called acute coronary syndrome (ACS).

Two main subtypes of ACS can be diagnosed by what is seen on your heart tracing (electrocardiogram, or ECG). The two main types are called ST-elevation MI (STEMI) and non-ST-elevation MI (NSTEMI). The ST elevation refers to a section on the ECG tracing.

NSTEMI can also include unstable angina. Most people with angina chest pains only have pain with a certain amount of exertion. This is called stable angina. If the pattern of your pain changes suddenly and the pains develop after minimal exertion, or while you are resting, this is called unstable angina. This is an emergency and needs immediate medical care. See separate leaflet called Angina.

In STEMI, the artery supplying an area of the heart muscle is completely blocked. However, in NSTEMI, the artery is only partly blocked, so only part of the heart muscle supplied by the affected artery is affected. Your treatment can depend upon which type you have - STEMI or NSTEMI.

This leaflet mainly discusses STEMI - which is just referred to as a heart attack from now on. Read more about acute coronary syndrome for more details on NSTEMI, unstable angina and ACS.

The most common cause of a heart attack is a blood clot that forms inside a coronary artery or one of its branches. This blocks the blood flow to a part of the heart.

Blood clots do not usually form in normal arteries. However, a clot may form if there is some atheroma within the lining of the artery. Atheroma is like fatty patches or plaques that develop within the inside lining of arteries. (This is similar to water pipes that get furred up.) Plaques of atheroma may gradually form over a number of years in one or more places in the coronary arteries. Each plaque has an outer firm shell with a soft inner fatty core.

What happens is that a crack develops in the outer shell of the atheroma plaque. This is called plaque rupture. This exposes the softer inner core of the plaque to blood. This can trigger the clotting mechanism in the blood to form a blood clot. Therefore, a build-up of atheroma is the root problem that leads to most cases of ACS. (The diagram below shows four patches of atheroma as an example. However, atheroma may develop in any section of the coronary arteries.)

Treatment with clot-busting medication or a procedure called angioplasty (see below) can break up the clot and restore blood flow through the artery. If treatment is given quickly enough this prevents damage to the heart muscle, or limits the extent of the damage.

Various other uncommon conditions can block a coronary artery - for example:

These are not dealt with further in this leaflet.

The rest of this leaflet deals only with the common cause - thrombosis over an atheroma plaque.

Heart attacks are common. Most occur in people aged over 50 years and it becomes more common with increasing age. Sometimes younger people are affected.

A heart attack is three times more common in young men than in young women. However, after the menopause, the female hormones no longer protect the heart so the risk is then the same for men and women.

A heart attack may occur in people known to have heart disease, such as people with chest pain called angina. It can also happen suddenly in people with no previous symptoms of heart disease. This is because fatty patches or plaques (atheroma) often develop without any symptoms at first.

Certain risk factors increase the risk of more atheroma forming. This can lead to ACS. See separate leaflet called Cardiovascular Disease(Atheroma).

Briefly, risk factors that can be modified and may help to prevent a heart attack include:

The most common symptom is severe chest pain, which often feels like a heavy pressure feeling on your chest. The pain may also travel up into your jaw and down your left arm or down both arms. You may also sweat, feel sick and feel faint. You may also feel short of breath. The pain may be similar to angina but it is usually more severe and lasts longer. (Angina usually goes off after a few minutes. Angina pain usually eases if you rest straightaway and take angina medication. Heart attack pain usually lasts more than 15 minutes - sometimes several hours.) Heart attack pain also doesn't usually improve if you rest or take your usual angina medication.

However, some people have only a mild discomfort in their chest. The pain can sometimes feel like indigestion or heartburn.

Occasionally, a heart attack happens without causing any pain. This is usually diagnosed when you have a heart tracing (electrocardiogram, or ECG) at a later stage.

Some people collapse and die suddenly if they have a large portion of heart muscle damaged. This is not very common.

Dial 999/112/911 for an ambulance immediately.

Then, if you have some, take one aspirin tablet (see below for the reason for this). You will normally be admitted straight to hospital.

Many people develop chest pains that are not due to a heart attack. For example, you can have quite bad chest pains with heartburn, and with gallbladder problems or with pains from conditions of the muscles in the chest wall. Therefore, tests are usually done to confirm a heart attack. These are:

A rough idea as to the severity of the heart attack (the amount of heart muscle that is damaged) can be gauged by:

Another chemical that may be measured in a blood test is called creatine kinase. This too is released from heart muscle cells during a heart attack.

Your ECG will be monitored for a few days to check on the heart rhythm. Various blood tests will be done to check on your general well-being.

Other tests may be done in some cases. This may be to clarify the diagnosis (if the diagnosis is not certain) or to diagnose complications such as heart failure if this is suspected. For example, an ultrasound scan of the heart (echocardiogram, or 'echo') or a test called a myocardial perfusion scan may be done.

Also, before discharge from hospital, you may be advised to have tests to assess the severity of the fatty patches or plaques (atheroma) in the coronary arteries - for example:

The following is a typical situation and mentions the common treatments that are usually offered. However, each case is different and treatments may vary depending on your situation.

As soon as possible after a heart attack 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 on to a patch of atheroma inside an artery that go on to form the clot.

Other antiplatelet medicines called clopidogrel or ticagrelor may be given. They work in a different way to aspirin and help reduce platelet stickiness.

See separate leaflet calledAspirin and other Antiplatelet Medicines.

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

A strong painkiller such as morphine is given by injection into a vein to ease the pain.

The part of the heart muscle starved of blood does not die immediately. If blood flow is restored within a few hours, much of the heart muscle that would have been damaged and die will survive. This is why a heart attack 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 restore blood flow back through the blocked artery:

Both the above treatments usually work well to restore blood flow and greatly improve the outlook. The most crucial factor is the speed at which one or other treatment is given after symptoms have started.

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

Some people have a raised blood sugar level when they have a heart attack, even if they do not have diabetes. If this occurs then your blood sugar (glucose) 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.

Normally you will be advised to take regular medication for the rest of your life. Many people recover well from a heart attack and have no complications. Before discharge from hospital, it is common for a doctor or nurse to advise you how to reduce any risk factors (see above). This advice aims to reduce your risk of a future heart attack as much as possible. Read more about medication after a heart attack (myocardial infarction).

This often depends on the amount of heart muscle that is damaged. In many cases, only a small part of the heart muscle is damaged and then heals as a small patch of scar tissue. The heart can usually function normally with a small patch of scar tissue. A larger heart attack is more likely to be life-threatening or cause complications.

Even before treatments became available to restore blood flow, many people made a full recovery. With the help of modern treatment, particularly if you are given treatment within a few hours to restore blood flow, a higher percentage of people now make a full recovery.

Some possible complications include the following:

The most crucial time is during the first day or so. If no complications arise and you are well after a couple of weeks then you have a good chance of making a full recovery. A main objective then is to get back into normal life and to minimise the risk of a further heart attack.

When recovering from a heart attack, it is natural to wonder if there are any dos and don'ts. In the past, well-meaning but bad advice to 'rest and take it easy from now on' caused some people to become over-anxious about their hearts. Some people gave up their jobs, hobbies and any activity that caused exertion, for fear of straining the heart.

However, quite the opposite is true for most people who recover from a heart attack. Regular exercise and getting back to normal work and life are usually advised. Much can be done to reduce the risk of a further heart attack. Read more about after a heart attack (myocardial infarction).

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Heart Attack (Myocardial Infarction) | Symptoms and Causes