About 6 per cent of patients who have coronary bypass surgery could suffer a stroke directly afterwards. Of these, 5 per cent die, and nearly half suffer deterioration in their intellectual functions.

These strokes are "common and serious", conclude the researchers who made the discovery and it could mean that more than 48,000 people a year around the world suffer a stroke directly after major heart surgery.

The findings were based on the records of 2108 patients who had bypass surgery at one of 24 US hospitals. Of these, 129 patients or 6.1 per cent of the total suffered a stroke, the Multicenter Study of Perioperative Ischemia Research Group discovered.

Eight died from brain injuries caused by the stroke, 55 had nonfatal attacks, two had heart attacks, one went into a stupor, 55 suffered deterioration of their intellectual functions and eight had seizures.

It might be possible to predict the higher risk groups beforehand, the researchers suggest. Those who suffered a stroke in their study tended to be elderly, suffered atherosclerosis (narrowing of the blood vessels), had a history of neurological disease, had high blood pressure or were heavy drinkers.

Because of the prolonged care that stroke sufferers needed afterwards, surgeons might wish to consider the risks more carefully and suggest other, and less traumatic, treatments, the researchers recommend.