At 82, if you have to go for a heart by-pass surgery, there is a higher chance you may not make it out alive.

The average risk of death from surgery for an octogenarian is five times higher compared to younger patients, doctors say.

And the rate of recovery for such patients will be longer and more painful. But this is what makes the surgery on former Malaysian prime minister Mahathir Mohamad eyebrow-raising.

UNUSUAL

What makes it even more unusual is that this is his second operation.

 Dr Lim Chong Hee, senior consultant at the department of cardiothoracic surgery and director of the heart and lung transplant programme at the National Heart Centre, said there are not many operations done on octogenarians.

 But when the symptoms cause the patient to be unable to function normally, such as in Dr Mahathir's case, doctors will operate."

 Hospital officials at Kuala Lumpur's National Heart Institute reported on Thursday that Dr Mahathir is eating, exercising and talking after his surgery on Tuesday.

 He may be the oldest person in Malaysia to have a second heart bypass operation, his daughter Marina Mahathir said. He had his first bypass in 1989 while he was still in office.

 In Singapore, one of the oldest patients to undergo heart bypass surgery was an 87-year-old man in March at the National Heart Centre (NHC), a spokesman said. It was his first bypass operation.

 An operation can take anywhere from two to six hours depending on the number of bypasses needed.

 At the NHC, about seven to eight bypass operations are carried out each year on those aged 80 and above. "Most of them were first-timers," Dr Lim said.

 In 2004, none of the eight who were aged 80 and above died from the operation.

 In 2005, all eight survived as well.

 In 2006, out of the seven octogenarians who had bypass operation, two died.

 The NHC has not looked into how many of the bypasses done at the centre were re-operations.

 But Dr Lim says there are other factors that affect the risk other man age.

"If he is in a very bad condition like in an emergency, then the operation will be at much higher risk compared to someone who may be older but in better physical condition," Dr Lim said.

MOST COMMON

 The NHC does an average of over 550 bypass operations a year and it is the most common form of heart surgery.

 At the centre, it accounts for two-thirds of their surgical procedures.

 But having a bypass does not mean that you won't have blocked arteries any more.

 Dr Lim said:"Coronary artery disease is progressive and not solved by a bypass. The cholesterol still collects and the arteries as well as the bypasses will get blocked again."

 Each bypass lasts on average five to 15 years depending on the individual.

 "Four in 10 patients who have bypass surgery have blocks again in five years, but not all will need surgery," Dr Lim said.

 Some centres in the US report that 20 to 30 per cent of patients will need a second bypass in 10 years.

 Dr Mahathir's first bypass lasted 18 years - described by daughter Marina as "really good going" on her blog - before his second operation.