If you would like to learn about the causes and treatment of myocardial infarction (heart attack), you will find the following information of help.
Myocardial infarction (MI) is usually caused by a blood clot in a heart (coronary) artery. Phone for medical help immediately if you develop severe chest pain. A 'clot busting' drug should be given as soon as possible to prevent damage to heart muscle. Also, 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 it's 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.
Understanding the heart and coronary arteries
The heart is mainly made of special muscle. The heart pumps blood into arteries (blood vessels) 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.
What happens when you have a myocardial infarction?
Myocardial Infarction
If you have an MI, a coronary artery or one of it's smaller branches is suddenly blocked. The part of the heart muscle supplied by this artery loses it's 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.)
'Clot busting' drugs (see below) can break up the clot and undo the blockage. If 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.
The rest of this page only deals with the common cause - thrombosis over an atheroma plaque.
Who has a myocardial infarction?
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.)
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'.
Collapse and sudden death may occur with a large or severe MI.
What should I do if I suspect I am having a myocardial infarction?
Call an ambulance or doctor immediately. The earlier the treatment, the better the chance of a good outcome. The following describes a typical course of events that then occurs.
- You will be given a dose of aspirin immediately to reduce the 'stickiness' of the blood. It helps to prevent further blood clotting.
- You will normally be admitted to hospital.
- A strong pain killer given by injection will ease the pain.
- Heart monitoring (ECG) and blood tests are done to confirm an MI, and to rule out other causes of chest pains.
- You will usually be given an injection of a 'clot busting' drug. This dissolves the blood clot. The sooner this is given, the better. 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.
- Injections of heparin are usually given for a few days to help prevent further blood clots.
- Your heart is monitored for a few days to check on the heart rhythm.
- Various tests may be done to look for complications.
- You will be advised to take regular medication from now on. Medication after an MI is discussed more fully in another page. Briefly, the following four drugs are commonly prescribed to prevent a further MI, and to help prevent complications.
- 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) - especially if you have any heart failure (see below).
- A statin drug to lower the cholesterol level. This helps to prevent the build-up of atheroma.
Many people recover well from an MI 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 below). This advice aims to reduce your risk of a future MI as much as possible. An exercise test may also be done. Briefly, this helps to tell how badly the coronary arteries are narrowed with atheroma, and whether more complex tests of the heart need to be done.
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 well a second time. An alternative 'clot buster' drug should be given if you have another MI in the future.
Emergency angioplasty is used in some cases as an alternative to a 'clot busting' drug in some hospitals. 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 then blown up inside the blocked part of the artery to open it wide again. See separate page called Angioplasty for more details.
How serious is a 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 (infarcts or dies) which heals as a small patch of scar tissue. The heart can usually function normally with a small patch of scar tissue. A larger MI is more likely to be life-threatening or cause complications.
Even before 'clot busting' drugs became available, many people made a full recovery as many MIs are small. With the help of modern treatment, particularly if you are given a 'clot busting' drug quickly, a higher percentage of people now make a full recovery.
Some possible complications that may occur after an MI include the following.
- Heart failure. If a large area of the heart muscle is damaged, then the pumping ability of the heart may be reduced. Less blood than usual is then pumped around the body, especially when extra blood is needed when you exercise. Symptoms such as breathlessness, tiredness, and swollen ankles may develop. Mild heart failure can often be treated with medication. Severe heart failure can be serious and life-threatening.
- Abnormal heart rhythms may occur if the electrical activity of the heart is affected. The main risk of this happening is within the first few hours after an MI. Sudden, chaotic, fast heart beats may occur. This is called ventricular fibrillation and is the common cause of 'cardiac arrest'. This needs immediate treatment with an electrical shock given by a defibrillator. Otherwise, collapse and sudden death is likely.
- A further MI may occur sometime in the future. This is more likely if the coronary arteries are badly affected with atheroma, or further build up of atheroma continues. If the risk of this is thought to be high then surgery may be advised to bypass or widen severely narrowed coronary arteries.
The most crucial time is during the first day or so. If no complications arise, and you are well after a couple 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 MI.
After having a myocardial infarction
After recovering from an MI, 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 an MI. Regular exercise and getting back to normal work and life is usually advised. Much can be done to reduce the risk of a further MI. This is discussed more fully in another page called 'After a Myocardial Infarction'.
Can myocardial infarction be prevented?
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 page 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.
Further sources of information and help
British Heart Foundation
14 Fitzhardinge Street, London, W1H 4DH
Heart Information Line: 0845 070 8070 (Mon-Fri 9am-5pm)
Web: www.bhf.org.uk
Heart Information Line: 0845 070 8070 (Mon-Fri 9am-5pm)
Web: www.bhf.org.uk
©EMIS and PIP 2006 Updated: February 2006 PRODIGY Validated
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