It is estimated that 1,000 Singaporeans die from sudden cardiac death (SCD) every year, about half of whom are below the age of 60.

Is sudden cardiac death the same as a heart attack?

"A sudden cardiac death, or SCD, is not a heart attack," said Dr Aaron Wong, Head and Senior Consultant at the National Heart Centre Singapore (NHCS). "A SCD can be due to many causes but is usually caused by an abnormal heart rhythm due to an abnormal 'electrical circuit' of the heart. A heart attack is caused by blockages in the heart arteries supplying blood to the heart, causing a portion of the heart muscle to be damaged. A heart attack may lead to abnormal heart rhythm, and therefore SCD, but not always."

Unlike a heart attack, which has symptoms such as chest pain and breathlessness, SCD usually has no warning signs. The only way to treat a SCD is to set the rapid heartbeat back to its normal pace by delivering an electrical shock to the heart using a device called a defibrillator.

Patients at high risk of SCD may be advised by their doctors to have an Implantable Cardiac Defibrillator (ICD) implanted. The ICD is a pocket-sized device which detects abnormal heart beats or rhythm and sends an electric current to the heart. This electric current shocks the heart and helps to reset the heart rhythm like a mini-defibrillator.

The most common cause of sudden cardiac death (SCD)

The most common cause of SCD is a sudden onset of abnormal heart rhythm. This is usually due to a fast but chaotic heart rhythm called ventricular fibrillation (VF) or tachycardia (VT). An extremely slow heart rate may cause SCD as well but usually presents with prior symptoms of giddiness or fainting episodes.

In a patient with VF (a form of cardiac arrest), the heart beats 400 to 500 beats per minute and the normal rhythmic contractions of the lower chambers of the heart stop. When this happens, blood and oxygen are not pumped to the rest of the body and within seconds, the brain becomes starved of oxygen and the person loses consciousness. Without immediate treatment, the brain will cease to function and the person can die within minutes.

See next page for the risk factors of sudden cardiac death.

Ref: N18