It is a phenomenon - sudden death syndrome - that pops up fairly regularly in the news.

Recently, many people were shocked when they heard about the death of national triathlete Thaddeus Cheong.

He was only 17, seemingly healthy and among the top triathletes. Yet he died of heart failure after finishing a race in June.

Indeed, sudden cardiac death can strike a person in normal health.

In about one in every 20 cases, no definite cause of death can be found even after the heart has been examined by an expert.

The Singapore National Heart Centre reported an average of 87 cases a year from 2001 to 2003.

While there are usually no symptoms, some warning signs include chest pains, giddiness and loss of consciousness.

You may also be more at risk if your family members have a history of sudden cardiac death.

Causes include coronary artery disease, congenital heart diseases and genetic and other rare diseases.

According to Dr Ng Kheng Siang, a consultant cardiologist at Gleneagles Hospital, screening tests are the best way to detect coronary diseases early.

These tests include a resting electro-cardiogram (ECG), where the electrical activity of the heart is recorded, an echocardiography, where ultrasound waves are used to create images of the heart, and an exercise treadmill test, where the heart rate is monitored as you walk or run.

Death can come quickly in other situations too.

Sudden brain death results when there is severe bleeding in the brain, caused mainly by aneurysms - a permanent dilation of the arteries or veins caused by
the weakening of the vessel wall - and the existence of abnormal blood vessels between arteries and veins in the brain.

These abnormal vessels may bleed, leading to serious complications that can be life-threatening.

Warning signs include headaches, fits, weakness, numbness, visual blurring or hearing impairment. For others, however, there are no signs.

Dr Ng Puay Yong, a consultant neurosurgeon, says scans and tests that examine blood vessels can detect these problems early.

Treatments include surgery, methods to block the abnormal vessels and, in some cases, radiosurgery.

The young are not spared either. Sudden death in children occurs instantaneously or within a day of the onset of symptoms.

A rare syndrome, its estimated incidence is 1 to 1.5 per 100,000 a year.

Underlying causes include heart disease, neurological causes and metabolic disorders.

The latter, which are due to a lack of certain enzymes, result in the accumulation of toxins that damage organs such as the brain, heart and liver.

Severe infections that result in rapid deterioration in a child's health can also cause sudden death.

Dr Phuah Huan Kee, a consultant paediatrician, says that if your child has a persistent fever that hasn't gone away after more than three days, is lethargic and can't hold down food, take him or her to see a doctor immediately.

Other warning signs include loss of consciousness and seizures. Newborns should undergo metabolic screening tests, and parents should seek medical attention if their children display unusual signs such as breathing
difficulties.

"Early detection is prevention," adds Dr Phuah.