Myocardial Infarction

A myocardial infarction or "heart attack" is the sudden death of part of the heart muscle due to a blockage in the blood supply to that area of the heart. The disorder is popularly known as a heart attack. Myocardial infarction (MI) is the most common cause of death in the UK.


The usual cause is atherosclerosis of the coronary arteries. In this condition, plaques (fatty deposits) develop on the artery walls; a clot may then form over a plaque and block an artery. Men are more likely to have a heart attack than women, and smokers are at greater risk than nonsmokers. Other risk factors include increased age, an unhealthy diet, obesity, and disorders such as hypertension (high blood pressure) and diabetes mellitus.


There is a sudden, crushing pain that starts in the centre of the chest and may spread into the arms or up to the jaw. Breathlessness, restlessness, clammy skin, and nausea and/or vomiting may also occur. In some cases, the first symptom is sudden collapse and loss of consciousness.

A few people have only mild symptoms or have none at all; this type of heart attack is known as a silent myocardial infarct. The damage to the heart tissue may cause immediate heart failure (reduced pumping efficiency) or arrhythmias (irregular heartbeat).

Ventricular fibrillation is the most dangerous form of arrhythmia; it prevents the heart from pumping effectively and, if untreated, is fatal within a few minutes.


Diagnosis is made from the patient’s history, together with an ECG. Tests are also carried out to measure levels of certain enzymes, and of a protein called troponin, which are released into the blood from damaged heart muscle.


A myocardial infarction is a medical emergency. A person who suspects that he or she is having a heart attack should chew an aspirin tablet, which will help to dissolve the clot in the artery. He or she should then be taken to hospital as soon as possible. Initially, oxygen and diamorphine are given in order to relieve the pain and intravenous thrombolytic drugs may be given to dissolve the blood clot (unless there is a risk that the drugs will cause excessive bleeding).

Afterwards, patients are monitored in an intensive care or coronary care unit so that any complications, such as heart failure, arrhythmias, or rupture of a heart valve can be detected and treated as early as possible. If thrombolytic drugs have failed to restore blood flow in the affected artery, surgery may be considered.

On leaving hospital, patients may be advised to take aspirin, beta-blocker drugs to protect the heart muscle, and statin drugs to lower blood cholesterol. ACE inhibitors are also given to treat heart failure or impaired function of the left ventricle. In addition, people will undergo a rehabilitation programme to help them return to full activity and to increase awareness of risk factors.

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