Myocardial Infarction

Loss of blood supply to part of the heart muscle due to a blockage in a coronary artery, commonly known as heart attack

  • More common with increasing age
  • More common in males until the age of 60, then equal incidence
  • Sometimes runs in families
  • Smoking, a high-fat diet, lack of exercise, and excess weight are risk factors

Heart attack or “coronary” are common terms for the disorder myocardial infarction. The term means death of part of the heart muscle following a blockage in its blood supply. Myocardial infarction is one of the major causes of death in developed countries such as the UK. However, the mortality rates have fallen significantly since the early 1980s due to recent improvements in treatment and an increasing awareness that following a healthier lifestyle helps to prevent heart attacks.

What are the causes?

Myocardial infarction is usually a result of coronary artery disease. In this condition, the coronary arteries, which supply the heart muscle with fresh oxygenated blood, become narrowed. This narrowing is usually due to atherosclerosis, in which droplets of fatty substances, such as cholesterol, build up on the inside of the artery wall. These substances form deposits called atheroma, which then become covered with a fibrous layer that may rupture or become roughened. Blood cells called platelets can stick to the rough or damaged area and trigger the formation of a blood clot. Once formed, the clot may completely block blood flow through the artery, leading to a heart attack.

If you have a family history of coronary artery disease (CAD), you are at increased risk of having a heart attack, especially if one or more members of your family developed CAD or had a heart attack under the age of 60. The risk of having a heart attack is also increased if you have raised blood pressure (see Hypertension) or diabetes mellitus.

What are the symptoms?

The symptoms of a heart attack usually develop suddenly and may include:

  • Severe, heavy, crushing pain in the centre of the chest that may spread up to the neck and into the arms, especially the left arm.

  • Pallor and sweating.

  • Shortness of breath.

  • Nausea and, sometimes, vomiting.

  • Anxiety, sometimes accompanied by a fear of dying.

  • Restlessness.

If you develop these symptoms, you should assume that you are having a heart attack and require urgent medical attention. Do not delay calling an ambulance to “see how things go” because this delay may be fatal. A well-equipped emergency ambulance is the most appropriate means of transportation to hospital because life-saving treatment may be required on the journey. While waiting for the ambulance, you should chew an aspirin tablet (300 mg) if possible. Aspirin reduces the stickiness of the blood to prevent further clotting.

Sometimes, a myocardial infarction may cause a different pattern of symptoms. If you have been suffering from the chest pain of angina, your pain may have been getting steadily worse and may have been occurring at rest as well as on exertion. An episode of angina that does not respond to your usual treatment or one that lasts longer than 10–15 minutes may be a myocardial infarction and needs immediate emergency hospital treatment.

About 1 in 5 people does not have chest pain in a heart attack. However, there may be other symptoms, such as breathlessness, faintness, sweating, and pale skin. This pattern of symptoms is known as a “silent infarction”. This type of heart attack is more common in elderly people and those with diabetes.

Are there complications?

In the first few hours and days after a heart attack, the main risks are the development of heart rhythm problems, which may be life-threatening and lead to cardiac arrest. Although the risk of cardiac arrest is greatest close to the time of a heart attack, there is an increased long-term risk of heart rhythm problems, particularly if the heart attack causes a large amount of damage to the heart muscle. Depending on the extent and site of the damaged muscle, other problems may develop. For example, in the weeks or months after the attack, the pumping action of the heart muscle may be too weak, leading to a condition called heart failure (see Acute heart failure, and Chronic heart failure). Less common complications include damage to one of the heart valves (see Mitral incompetence); development of a ventriculoseptal defect (a hole in the septum between the heart’s two lower chambers); or inflammation of the membrane covering the heart’s surface (see Pericarditis).These conditions may also lead to the development of heart failure.

How is it diagnosed?

In many cases, the diagnosis is obvious. An ECG, which is a tracing of the electrical activity of the heart, often shows changes that confirm myocardial infarction. The ECG can be valuable in assessing which part and how much of the heart muscle has been damaged and will establish whether the heart rhythm is still normal. To confirm the diagnosis, blood samples may be taken to measure the levels of particular chemicals that leak into the blood from damaged heart muscle.

What is the treatment?

The immediate aims of treatment for myocardial infarction are to relieve pain and restore the blood supply to the heart muscle to minimize the amount of damage and prevent further complications. These aims are best achieved by immediate admission to an intensive therapy unit, where your heart rhythm and vital clinical signs can be monitored continuously. If you have severe chest pain, you will probably be given an injection of a powerful painkilling drug, such as morphine.

Within the first 6 hours of the attack, you may also be given a “clot-busting” thrombolytic drug to dissolve the blood clot blocking the coronary artery. Alternatively, you may have immediate coronary angioplasty, usually with the insertion of a stent (a tubular scaffold device) to reopen and widen the blocked artery. The sooner blood flow to the heart can be restored, the greater the chance of a full recovery.

While you are in the coronary care unit, your heartbeat is monitored, and treatment is given if arrhythmias or symptoms of heart failure develop. If your progress is satisfactory, you will be allowed out of bed briefly after 24–48 hours. Soon afterwards, you should begin a rehabilitation programme, during which you are encouraged to spend gradually longer periods out of bed.

Once you have recovered, the condition of your coronary arteries and heart muscle is assessed. Tests such as echocardiography and exercise electrocardiography (see Exercise testing) are used to help to decide on further treatment. For example, if the heart’s pumping action is impaired, you may be prescribed an ACE inhibitor and/or a diuretic drug. If a coronary artery is narrowed or blocked, you may need angioplasty and stenting or bypass surgery at a later stage (see Coronary artery bypass graft). If tests reveal a persistent slow or abnormal heart rhythm, you may need to have a pacemaker fitted (see Cardiac pacemaker).

Certain drugs taken long-term can reduce the risk of another heart attack. You may be prescribed a beta-blocker drug, an ACE inhibitor, and aspirin. You will also be advised to adopt a low-fat diet and, in most cases, to take a statin (see Lipid-lowering drugs) to lower your blood cholesterol level. Statins reduce the risk of a further heart attack even if your cholesterol level is not elevated. You will also be advised to eat oily fish 2–4 times a week or will be prescribed a highly purified omega-3 supplement to reduce the level of other lipids in your blood.

What can I do?

It is important to follow your doctor’s advice about how soon to return to normal activities. It is natural to feel worried about your health, and many people feel mild depression. It is important to avoid becoming disabled by the fear of having another heart attack. After a heart attack, you are likely to be invited to attend a cardiac rehabilitation course. This is a structure programme, led by a multidisciplinary team of healthcare professionals, that provides education, a graded exercise regimen, and psychological and social support. Such a programme can help you to return to as normal a life as possible and to maintain a healthy level of physical activity and lifestyle changes that will help reduce your long-term risk of further heart problems.

What is the prognosis?

If you have not had a previous myocardial infarction, you are treated quickly, and there are no complications, the outlook is good. After 2 weeks, the risk of another heart attack is considerably reduced, and you have a good chance of living for another 10 years at least. The outlook is better if you stop smoking, reduce alcohol intake, exercise regularly, and follow a healthy diet.

If you have had a previous heart attack or suffered a significant amount of heart muscle damage, the outlook depends on the amount of heart muscle that was damaged and whether you have additional complications. However, many people who have surgery or angioplasty live for 10 years or more.

Treatment: Coronary Angioplasty and Stenting

Self-help: Life After a Heart Attack

Treatment: Coronary Artery Bypass Graft

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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