SINGAPORE - When credit risk officer Zhao Chun began experiencing back pains about a month ago, the avid gym-goer, who is 34 years old, put it down to overexerting himself while exercising.

A visit to a general practitioner seemed to confirm this, as an electrocardiogram and X-ray did not turn up any serious issues, and the Singapore permanent resident was prescribed painkillers.

However, the pain and breathing difficulties worsened after Mr Zhao played soccer on June 25, with the back pain spreading to his chest as well.

He was admitted to Ng Teng Fong General Hospital emergency department, where he was found to have suffered a heart attack.

"It was shocking," said business development manager Ginger Jiang, 34, of her husband's diagnosis. She noted he was a non-smoker, exercised regularly and had no family history of heart attacks.

Every year, one in 10 heart attack patients here has no standard risk factors for the condition, a new study by the National University Heart Centre, Singapore (NUHCS) found.

These patients have an 80 per cent increased risk of death following a heart attack compared to those with risk factors such as smoking, diabetes, high blood pressure and high cholesterol.

They also have a 150 per cent greater chance of suffering a stroke following an attack, as well as 30 per cent increased chance of cardiogenic shock, which causes unstable blood pressure, the study found.

The study - which examined 8,680 patients who had experienced heart attacks between January 2011 and March last year - found that 746, or about 8.6 per cent of cases, had no such risk factors.

Of those without conventional risk factors, 87 died, making up 11.7 per cent of those without such factors.

In comparison, only 5.5 per cent of those with conventional risk factors died after a heart attack.

The average age of those without risk factors who died was 57, compared to 61 for those with risk factors.

"Often patients without risk factors come in and ask why me, 'why did I have a heart attack despite me taking care of my body (and) despite me being active with a good lifestyle?'," said the study's principal investigator Nicholas Chew, a senior resident at the NUHCS cardiology department.

Some possibilities are that these patients may be genetically predisposed to high-risk heart attacks, as well as have risk factors that are considered non-standard, such as fatty liver disease or blood clotting disorders, Dr Chew told reporters on Friday (July 8).

The findings contradict the common perception that significant coronary artery disease is an unlikely health concern for those without conventional risk factors, said co-investigator Loh Poay Huan, a senior consultant with the NUHCS cardiology department.

Clinicians should raise their guard when seeing patients without such risk factors but displaying symptoms suggestive of cardiovascular diseases, he said.

"The message to the general public is really to not ignore symptoms of chest pain, even in those without risk factors," said Dr Chew.

Further studies are needed to assist clinicians to identify such at-risk people, he said, adding that he expects NUHCS to begin such a study in about a year.

Though Mr Zhao is still uncertain about why he suffered a heart attack, he said he is faring well and the experience has only strengthened his resolve to live healthily. He told reporters he intends to give up alcohol as well as switch to less strenuous exercises such as swimming once he is able to resume exercising.