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Sudden cardiac death

Sudden cardiac death, sometimes called SCD, is the sudden and unexpected death of a person due to sudden cardiac arrest.

The most common cause of sudden cardiac death in older adults is coronary artery disease and blocked arteries. In under-35s, sudden cardiac death is more likely to be due to inherited heart conditions.

How is sudden cardiac arrest different from a heart attack?

Sudden cardiac arrest is not a heart attack (myocardial infarction) but can occur during a heart attack. Heart attacks occur when there is a blockage in one or more of the arteries to the heart, preventing the heart from receiving enough oxygen-rich blood. If the oxygen in the blood cannot reach the heart muscle, the heart becomes damaged.

In contrast, sudden cardiac arrest occurs when the electrical system to the heart malfunctions and suddenly becomes irregular. The heart beats dangerously fast. The ventricles may flutter or quiver ( ventricular fibrillation), and blood is not delivered to the body. In the first few minutes, the greatest concern is that blood flow to the brain will be reduced so drastically that a person will lose consciousness. Death follows unless emergency treatment is begun immediately.

Emergency treatment includes cardiopulmonary resuscitation ( CPR) and defibrillation. CPR is a manual technique using repetitive pressing to the chest and breathing into the person's airways that keeps enough oxygen and blood flowing to the brain until the normal heart rhythm is restored with an electric shock to the chest, a procedure called defibrillation. Ambulance personnel use portable defibrillators.

What are the symptoms of sudden cardiac arrest?

Some people may experience a racing heartbeat or feel dizzy, alerting them that a potentially dangerous heart rhythm problem has started. In more than half of the cases, however, sudden cardiac arrest occurs without prior symptoms.

What causes sudden cardiac death?

Most sudden cardiac deaths are caused by abnormal heart rhythms called arrhythmias. The most common life-threatening arrhythmia is ventricular fibrillation, which is an erratic, disorganised firing of impulses from the ventricles (the heart's lower chambers). When this occurs, the heart is unable to pump blood and death will occur within minutes, if left untreated.

What are the risk factors of sudden cardiac arrest?

There are many factors that can increase a person's risk of sudden cardiac arrest and SCD, including the following:

  • Previous heart attack with a large area of the heart damaged (75% of SCD cases are linked to a previous heart attack).
  • A person's risk of SCD is higher during the first six months after a heart attack.
  • Coronary artery disease (80% of SCD cases are linked with this disease).
  • Risk factors for coronary artery disease include smoking, family history of cardiovascular disease and high cholesterol.

Other risk factors include:

  • Ejection fraction of less than 40%, combined with ventricular tachycardia.
  • Prior episode of sudden cardiac arrest.
  • Family history of sudden cardiac arrest or SCD.
  • Personal or family history of certain abnormal heart rhythms, including long or short QT syndrome, Wolff-Parkinson-White syndrome, extremely low heart rates or heart block.
  • Ventricular tachycardia or ventricular fibrillation after a heart attack.
  • History of congenital heart defects or blood vessel abnormalities.
  • History of syncope (fainting episodes of unknown cause).
  • Heart failure: a condition in which the heart's pumping power is weaker than normal. Patients with heart failure are six to nine times more likely than the general population to experience ventricular arrhythmias that can lead to sudden cardiac arrest.
  • Dilated cardiomyopathy (cause of SCD in about 10% of the cases): a decrease in the heart's ability to pump.
  • Hypertrophic cardiomyopathy: a thickened heart muscle that especially affects the ventricles.
  • Significant changes in blood levels of potassium and magnesium (from using diuretics, for example), even if there is no underlying heart disease.
  • Obesity.
  • Diabetes.
  • Recreational drug abuse.
  • Taking drugs that are ‘pro-arrhythmic’ may increase the risk for life-threatening arrhythmias.
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