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Updated 05 May 2010

Heart attack

A heart attack is the death of heart muscle due to the complete blockage of a diseased coronary artery due to a blood clot.

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Summary

 

  • A heart attack is the death of heart muscle due to the complete blockage of a diseased coronary artery due to a blood clot.
  • Coronary artery disease (CAD) is by far the commonest cause.
  • Several factors increase the likelihood of a heart attack, the most important of which are family history of heart disease, hypercholesterolaemia, diabetes, smoking, obesity and uncontrolled hypertension.
  • Before a heart attack occurs, there may be warning signs in the form of angina.
  • The description given by the patient together plus the clinical examination are usually highly suggestive. An ECG will show signs of either an early, evolving heart attack, or of an already established heart attack.
  • Trials monitoring the outcome of hospitalised heart-attack patients have shown a mortality rate of up to 10% within the first 30 days after an attack.
  • Those patients with known risk factors, must have them controlled to prevent another heart attack and disease progression.

 

Alternative names

Myocardial infarction; acute myocardial infarct

What is a heart attack?

A heart attack is the death of heart muscle due to the complete blockage of a diseased coronary artery due to a blood clot.

What causes it?

Coronary artery disease (CAD) is by far the commonest cause.

Coronary arteries become narrowed, usually as a result of fatty cholesterol deposits (plaque) in the arterial wall, which bulge inwards and partly obstruct the flow of blood. The tip of this bulging cholesterol plaque can become eroded. The body attempts to seal this tip off by depositing blood platelets, forming a clot. As this clot increases in size, the artery becomes critically narrowed, or even totally blocked.

When the blood flow to the heart muscle is obstructed in this way, chest pain (angina) occurs. If the blood flow is totally cut off, the heart muscle actually dies, and this is called a heart attack, or acute myocardial infarct (AMI).

Associated risk factors

Several factors increase the likelihood of AMI, the most important of which are:

  • Family history of heart disease
  • Hypercholesterolaemia
  • Diabetes
  • Smoking
  • Obesity
  • Uncontrolled hypertension

It is impossible to eliminate family history, but all of the other factors can be controlled to minimise the risk of AMI. The more abnormal the blood pressure, weight, blood sugar, cholesterol and smoking habits, the higher the risk of AMI.

Symptoms and signs

Before an AMI occurs, there may be warning signs in the form of angina. This is central chest discomfort or pain, usually of a crushing, heavy nature, which is brought on by exertion, and is relieved by rest or sublingual nitrates.

This pain is usually due to a partly-obstructed coronary artery. If this anginal pain is not relieved by the usual measures, the pain may signal that the artery has reached critical or total occlusion, and that the patient is having an AMI.

Important exceptions to note:

  • Diabetics seldom experience classical angina, which is often the warning of an impending AMI. Their symptoms may be quite vague, or they may have no warning symptoms at all, until the AMI actually occurs.
  • Women may have only vague warning symptoms, e.g. fatigue.
  • The most common warning sign of an impending heart attack is no symptoms at all, until the AMI happens. 

The symptoms of a heart attack include the following:

  • Chest pain that is crushing or squeezing, or a feeling of a heavy weight on the chest, a tight band around the chest or a dull ache in the middle of the chest
  • Shortness of breath
  • Nausea or vomiting
  • Pain which radiates from the chest to the neck, jaw, or one or both arms
  • Dizziness or light-headedness
  • Increased perspiration
  • Fast or irregular pulse
  • Sudden urge to have a bowel action

How is it diagnosed?

The description given by the patient plus the clinical examination are usually highly suggestive.

An ECG will show signs of either an early, evolving AMI, or of an already established AMI. Rhythm abnormalities will also be shown.

A blood test for Trop T and other cardiac enzymes are also conclusive, as these enzymes are only released into the blood in significant amounts when heart-muscle cells die.

How is it treated?

The first priority is to keep the patient alive by ensuring adequate oxygenation (an oxygen mask or breathing tube may be used) and by relieving the patient’s pain (for this, morphine may be required).

If there is a life-threatening rhythm disturbance, such as severe ventricular tachycardia or ventricular fibrillation, this must be corrected immediately, e.g. with defibrillation (shock).

Once the diagnosis of AMI is confirmed, a cardiologist (when available) takes over the case for further management. This may involve admission to a special coronary care unit for a few days until the patient can be discharged.

If the patient remains unstable, or has continued pain despite treatment, the cardiologist may decide to do an urgent angiogram to examine the coronary arteries for blockages. If these are identified, corrective measures must be taken.

Some patients may have their blockages opened up by balloon angioplasty, in which a tiny balloon is placed inside the narrowed artery and inflated to push the walls open again. After this, a stent (an expandable metal mesh tube) may be inserted at the site to make sure that the artery remains open.

Not all patients are good candidates for stents. They may then be referred for bypass surgery instead.

While awaiting surgery, some unstable patients will need to have an intra-aortic balloon pump inserted. This is a computer-controlled heart-assist pump, which is used to temporarily improve blood flow through the coronary arteries. This helps to avoid a full-blown AMI, or to limit the extent of an "ongoing AMI" while waiting for surgery.

Once the acute episode has been managed and/or the patient has been stented or had surgery, the post-AMI period focuses on rehabilitation. This will include getting the patient well again, back home and back to work. The emphasis during this phase is on the reduction of risk factors (see above) and changes in lifestyle to minimise the risks of a repeat infarct, which carries a significantly higher mortality rate.

What is the outcome?

Trials monitoring the outcome of hospitalised AMI patients have shown a mortality rate of up to 10% within the first 30 days after an AMI. Arrhythmias and widespread multi-vessel disease are relevant factors here. The sooner the patient is able to receive appropriate hospital care, the better the outcome.

Survivors of an AMI face a substantial risk of further cardiovascular events, including an increase in mortality. In the first six years following an AMI, men have a four to five times greater risk of developing angina, heart failure, stroke or having a repeat MI. For women, the outlook is somewhat worse.

Patients who have a second AMI have an increased risk of complications and mortality, especially if the new AMI affects a different part of the heart, thus creating two dead areas of heart muscle. Patients, whose second AMI kills off another area of the left ventricle (main pumping chamber) wall, also have a worse prognosis.

Strict control over the known risk factors is thus crucial, after AMI, to prevent a recurrence.

Prevention

Those patients with known risk factors (see above) must obviously have them controlled in order to prevent another AMI and disease progression.

However, bearing in mind that many patients have no warning signs, such as angina, it makes sense for everybody to modify lifestyle factors to minimise the risk of AMI and sudden cardiac death. The following lifestyle modifications have proven beneficial:

  • Stop smoking. The more cigarettes you smoke, the higher the risk of heart disease.
  • Maintain a normal body weight and body-mass index (BMI).
  • Avoid foods that contain saturated fat and cholesterol. Limit fat to 30% of your daily energy intake by balancing occasional high-fat foods with low-fat choices, such as fruit, vegetables, legumes and grain products.
  • Control high blood pressure. Even small elevations in blood pressure above 140/90mmHg can double the risk of cardiovascular disease.
  • Exercise. Focus on aerobic activities such as brisk walking, swimming, jogging or cycling. Gradually work up to exercising 30 to 45 minutes at least three times a week.
  • Control cholesterol levels. Medication may be needed to achieve target levels, especially when other risk factors are present.

 

When to see a doctor

If you are experiencing symptoms of a heart attack, call the nearest emergency services immediately. Emergency treatment can prevent damage to the heart muscle and death.

A chest pain that occurs with exertion, stress or after eating a large meal, and which goes away with rest, may be a heart attack or angina (pain caused when the heart muscle receives inadequate oxygen). Such pain is a warning sign of ischaemic heart disease (blockages of blood vessels in the heart, which limits the oxygen supply).

Anyone with pain should be treated for angina and should call the nearest emergency services immediately for urgent medical attention.

Reviewed by Dr A.G. Hall (B.Soc.Sc.(SW), MB,Ch.B)
Last updated: May 2007 

 
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