Myocardial Infarction

Myocardial Infarction


Myocardial infarction (MI) is usually caused by a blood clot that stops blood flow in a heart (coronary) artery. Call for an ambulance immediately if you develop severe chest pain. Treatment with a 'clot busting' drug or an emergency procedure to restore blood flow through the blocked artery are usually done as soon as possible to prevent damage to heart muscle. Other treatments help to ease the pain and prevent complications. Reducing risk factors can help to prevent an MI.

What is a myocardial infarction?
Myocardial infarction (MI) 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'.

If you have an MI, 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. This part of the heart muscle is at risk of dying unless the blockage is quickly undone. (The word 'infarction' means death of some tissue due to a blocked artery which stops blood from getting past.)

If one of the main coronary arteries 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. In people who survive an MI, the part of the heart muscle that dies ('infarcts') is replaced by scar tissue over the next few weeks.

What causes myocardial infarction?
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 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.

Who has a myocardial infarction?
MI is common. About 180,000 people in the UK are admitted to hospital each year with an MI. Most MIs occur in people over 50, and become more common with increasing age. Sometimes younger people are affected. An MI is three times more common in men than women. An MI may occur in people known to have heart disease such as angina. It can also happen 'out of the blue' in people with no previous symptoms of heart disease. (Atheroma often develops without any symptoms at first.).

What are the symptoms of a myocardial infarction?
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.)

•Aspirin - to reduce the 'stickiness' of platelets in the blood which helps to prevent blood clots forming. If you are not be able to take aspirin then an alternative anti-platelet drug such as clopidogrel may be advised.
•A beta-blocker - to slow the heart rate, and to reduce the chance of abnormal heart rhythms developing.
•An ACE inhibitor (angiotensin converting enzyme inhibitor). ACE inhibitors have a number of actions including having a protective effect on the heart.
•A statin drug to lower the cholesterol level in your blood. This helps to prevent the build-up of atheroma.
Also, you will normally be advised to take the antiplatelet drug clopidogrel in addition to aspirin. However, this is usually only advised for a certain number of weeks or months, depending on the type and severity of the MI.




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).

Coronary heart disease is heart disease due to an abnormality of the coronary arteries that supply blood and oxygen to the heart, such as a build up of atheroma.

Source:
http://www.patient.co.uk/health/Myocardial-Infarction-(Heart-Attack).htm