Heart Attack (or Myocardial Infarction) means that part of the heart muscle suddenly loses its blood supply. Without prompt treatment, this can lead to damage to the affected part of the heart. An MI is sometimes called a heart attack or a coronary thrombosis. An MI is part of a range or disorders called 'acute coronary syndromes'.

Thrombosis - the cause in most cases

The common cause of an MI is a blood clot (thrombosis) 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 MI. (The diagram above shows four patches of atheroma as an example. However, atheroma may develop in any section of the coronary arteries.)

Treatment with 'clot busting' drugs 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.

Uncommon causes
Various other uncommon conditions can block a coronary artery and cause an MI. For example: inflammation of the coronary arteries (rare); a stab wound to the heart; a blood clot forming elsewhere in the body (for example, in a heart chamber) and travelling to a coronary artery where it gets stuck; cocaine abuse which can cause a coronary artery to go into spasm; complications from heart surgery; and some other rare heart problems. There are not dealt with further.

Severe chest pain is the usual main symptom. 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. The pain may be similar to angina, but it is usually more severe and lasts longer. (Angina usually goes off after a few minutes. MI pain usually lasts more than 15 minutes - sometimes several hours.)

A small MI occasionally happens without causing pain (a 'silent MI'). It may be truly pain-free, or sometimes the pain is mild and you may think it is just heartburn or 'wind'.

Some people collapse and die suddenly if they have a large or severe MI.

Call 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 an MI. For example, you can have quite bad chest pains with heartburn, gallbladder problems, or with pains from conditions of the muscles in the chest wall. However, tests can usually confirm MI. These are:

• A heart tracing called an ECG (electrocardiograph). There are typical changes to the normal pattern of the heart tracing if you have an MI. Patterns that occur with an MI include things called 'pathological Q waves' and 'ST elevation'. However, it is possible to have a normal ECG even if you have had an MI.

• Blood tests. A blood test that measures a chemical called troponin is the usual test that confirms an MI. This chemical is present in heart muscle cells and damage to heart muscle cells releases troponin into the bloodstream. The blood level of troponin increases within 3-12 hours from the onset of chest pain, peaks at 24-48 hours, and returns to a normal level over 5-14 days.

A rough idea as to the severity of the MI (the amount of heart muscle that is damaged) can be gauged by the degree of abnormality of the ECG and the level of troponin in the blood. Another chemical that may be measured in a blood test is called creatine kinase. This too is released from heart muscle cells during an MI.

Your heart tracing will be monitored for a few days to check on the heart rhythm.

Various blood tests will be done to check on your general wellbeing. 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 echocardiogram (an ultrasound scan of the heart) or a test called myocardial perfusion scintigraphy may be done.

Also, before discharge from hospital, you may be advised to have tests to assess the severity of atheroma in the coronary arteries. For example, an ECG taken whilst you exercise on a treadmill or bike ('exercise-ECG'). Or, angiography of the coronary arteries. In this test a dye is injected into the coronary arteries. The dye can be seen by special X-ray equipment. This shows up the structure of the arteries (like a road map) and can show the location and severity of any atheroma.

The following is a 'typical' situation and mentions the common treatments offered. Each case is different and treatments may vary depending on your situation.

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 usually given as soon as possible. This works in a different way to aspirin and adds to the action of reducing platelet stickiness.

Pain relief
A strong pain killer given by injection into a vein will 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 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: the 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 betablocker drug

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

Injections of heparin or a similar drug
These are usually given for a few days to help prevent further blood clots.

Everybody has a risk of developing atheroma which can lead to an MI. However, certain 'risk factors' increase the risk and include:

• Preventable or treatable risk factors:
  
  • smoking
  • hypertension (high blood pressure)
  • high cholesterol level
  • lack of exercise
  • a poor diet
  • obesity
  • excess alcohol
• Having diabetes. But if you have diabetes, the increased risk of heart disease is minimised by good control of the blood sugar level, and reducing blood pressure if it is high.
• Risk factors that are fixed and you cannot change:
  
  • a family history of heart disease or a stroke that occurred in a father or brother aged below 55, or in a mother or sister aged below 65
  • being male.
  • ethnic group (for example, British Asians have an increased risk).

Risk factors are discussed more fully in another leaflet called 'Preventing Heart Disease'. Briefly, if you can reduce any risk factors, it reduces your risk of having an MI (or of having a further MI if you have already had one). Some risk factors are fixed and you cannot change them. However, if you have a fixed risk factor, you may want to make extra effort to reduce preventable risk factors such as smoking or lack of exercise.