Sudden failure of the heart to pump blood, which is often fatal
- More common with increasing age
- More common in males
- Smoking, a high-fat diet, lack of exercise, and excess weight are risk factors
- Genetics is not a significant factor
During cardiac arrest, the heart stops pumping. As a result, the brain and other organs no longer receive oxygenated blood, without which they cannot function. Within about 3 minutes of cardiac arrest, the brain will have sustained some damage. Death is likely to occur within about 5 minutes if the pumping action of the heart is not restored by emergency treatment or if circulation is not maintained by external cardiac massage.
What are the causes?
Cardiac arrest is commonly caused by one of two types of electrical problem in the heart: ventricular fibrillation, the more common type, and asystole. During ventricular fibrillation, the ventricles (lower chambers of the heart) rapidly contract in an uncoordinated manner, preventing the heart from pumping out blood. Ventricular fibrillation may occur suddenly in people with coronary artery disease, for which lifestyle factors such as smoking and a high-fat diet increase the risk. It is also a frequent complication of a heart attack (see Myocardial infarction), usually occurring shortly after the attack. Ventricular fibrillation may also be caused by electrical injuries, drowning, and dilated cardiomyopathy, in which a disease of the heart muscle reduces its pumping efficiency.
Asystole is an electrical problem of the heart in which there is a total failure of the heart muscle to contract, leading to cardiac arrest. Asystole may be due to suffocation or to disorders or injuries that cause massive bleeding.
What are the symptoms?
Within seconds of a cardiac arrest, these symptoms usually occur:
Loss of consciousness.
Blue lips, fingers, and toes.
An affected person has no pulse and has stopped breathing.
What might be done?
If you are with a person who has had a cardiac arrest, send for medical help immediately. If you are alone with the affected person, shout for help. At the same time, you should begin resuscitation to maintain blood flow to the brain.
While continuing cardiopulmonary resuscitation, the paramedic team may conduct electrocardiography (see ECG) to establish whether the cause of cardiac arrest is asystole or ventricular fibrillation. They will then administer the appropriate treatment. Ventricular fibrillation can be treated effectively with a device called an electric defibrillator (see Cardioversion), which delivers electric shocks to the heart to restore its normal rhythm and rate. Asystole may sometimes be treated successfully by an injection of epinephrine (adrenaline) into a large vein or directly into the heart to start it pumping again.
After resuscitation, monitoring in an intensive therapy unit will determine if a heart attack has occurred and, if so, whether it was the cause of the cardiac arrest. Monitoring will also detect a recurrence of cardiac arrest. A person with ventricular fibrillation may be prescribed antiarrhythmic drugs on a long-term basis or have a miniature defibrillator surgically implanted (see Cardiac pacemaker).
What is the prognosis?
If resuscitation has been performed without delay, the chances of survival depend on the underlying cause. In a person who has ventricular fibrillation as a complication of a heart attack, a complete recovery may be possible if the normal heartbeat is restored by prompt cardioversion, particularly if the heart attack has not resulted in major damage to the heart muscle. Afterwards, the person will be carefully assessed and may have a defibrillator pacemaker implanted to prevent further episodes of ventricular fibrillation. The outlook for cardiac arrest caused by asystole depends on whether rapid, effective treatment can be given for the underlying cause and whether the normal heartbeat can be re-established. People are more likely to survive a cardiac arrest that occurs in hospital than one that takes place elsewhere because recognition of the condition and access to emergency treatment is more rapid.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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