Arrhythmia (abnormal heart rhythm) and sudden cardiac arrest (sudden cardiac death)

When something goes wrong with the ‘electric circuitry’ of the heart, it can cause the heartbeat to be irregular, fast or slow. Ventricular fibrillation, an arrhythmia (abnormal heart rhythm), which causes the lower chambers of the heart to beat too fast, is the most common cause of sudden cardiac arrest.

During ventricular fibrillation, the heart rate can be as fast as 400-500 beats per minute, compared to the normal 60-100 beats. The heart’s lower chambers, which pump blood and oxygen to the body, do not effectively pump blood out of the heart. As a result, insufficient blood is delivered to the brain and the person loses consciousness. It is a medical emergency and the victim is likely to die within minutes without treatment. Even if the victim survives, there is a high chance of brain damage leading to poor quality of life.

“An extremely slow heart rate can cause sudden cardiac death but it is usually not drastic and sudden, and presents with prior symptoms of giddiness or fainting,” says Clinical Associate Professor Ching Chi Keong, Senior Consultant, Department of Cardiology and Director, Electrophysiology and Pacing, National Heart Centre Singapore (NHCS), a member of the SingHealth group.

Other heart conditions caused by arrhythmia

Often, a life-threatening arrhythmia is linked to a heart condition such as:

  • Coronary artery disease: The Singapore study found that 81 per cent of all sudden cardiac deaths were caused by coronary artery disease (hardening and narrowing of the arteries supplying the heart).

  • Heart attack: Almost 75 per cent of all sudden cardiac arrest patients show signs of a previous heart attack (myocardial infarction).

  • Hypertrophic cardiomyopathy: An abnormal thickening of the heart muscle can cause ventricular fibrillation, especially during exertion.

  • Electrical disorders of the heart: One of these disorders is Wolff-Parkinson-White (WPW) syndrome, characterised by an extra nerve connecting the heart chambers. This can cause an ‘electrical short-circuit’ in the heart, resulting in a rapid heartbeat. Brugada syndrome and long QT syndrome are also examples of electrical disorders.

See page one to learn the difference between a sudden cardiac arrest and heart attack, and what puts you at risk of sudden cardiac arrest.

Ref: R14

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