Boston, Jan. 1 (Reuters): A controversial open heart surgery technique, designed to avoid the complications caused when a patient is hooked up to a heart-lung machine, may not be as good as conventional surgery, according to a New England Journal of Medicine study released on Wednesday.

Doctors in London found that when the newer off-pump technique was used for bypass surgery, 12 per cent of the blood vessels grafted to the heart became completely clogged after three months, compared to just 2 per cent of the grafts sewn into place when a heart-lung machine was used.

But they also found that such off-pump surgery, which has been available for less than a decade, is as safe as standard surgery and does less damage to the heart. The off-pump technique may also decrease incidents of kidney and brain damage, researchers say.

Nevertheless, “this is a shot across the bow that we need to be a little careful about how widely we apply this technique,” the lead author of the study, Natasha Khan of the Royal Brompton Hospital in London, said.

She said researchers had expected that the two types of surgery would yield similar results.

The popularity of the technique seems to have reached a plateau in the US, where, perhaps, 25-30 per cent of bypass operations are done off pump, said coauthor John Pepper of the National Heart and Lung Institute.

About 800,000 bypass operations of all types are done worldwide each year. But many patients — estimates range as high as 42 per cent — seem to have some type of brain impairment five years after the operation.

In the new study, 54 volunteers were randomly assigned to off-pump bypass surgery, where the heart was allowed to keep beating, yet held immobile with a special clamp equipped with suction cups.

Another 50 volunteers received conventional surgery, where the heart-lung machine allows doctors to completely stop the heart while they do their delicate stitching.

The new results are only the latest to suggest that off-pump heart surgery, which is more difficult than standard surgery, may not be as beneficial as its supporters had once hoped.

A study last January in the New England Journal found that off-pump operations were just as good as — but not really superior to — conventional surgery.

In an editorial in Thursday's Journal, Thomas MacGillivray and Gus Vlahakes of Massachusetts General Hospital said ”off-pump” surgery may still be a better option for some patients, particularly those with lung and liver problems, or with a diseased aorta.

However, MacGillivray and Vlahakes said, because it may be better for some patients,“cardiac surgeons should embrace off-pump surgery as an important option that must be mastered with the same technical precision as conventional coronary artery bypass graft surgery.”

”It's a technique that has to be targeted carefully,” Pepper told Reuters.