One of the scariest parts of bypass surgery -- having your heart stopped and going on a heart-lung machine while doctors fix your clogged arteries -- is safe even in the elderly and doesn't cause mental decline as many people have feared, two landmark studies show.

Bypass surgery is one of the most common operations now, but there is great debate about the best way to do it.

Usually, doctors stop the heart to make it easier to connect new blood vessels to make detours around blocked ones. Some patients complain later of "pumphead" -- mental decline thought to be from the heart-lung machines used to pump their blood.

Surgeons started doing "off-pump" bypasses on beating hearts, and nearly one quarter of bypasses are done that way now. But results on the blood vessels seemed not as good.

Dr. Andre Lamy of McMaster University in Hamilton, Ontario, led a study of 4,752 people in 19 countries randomly assigned to have bypasses with or without the use of heart pumps. After one year there were no big differences in the rates of death, heart attack, stroke or kidney failure in the two groups. Slightly more people who had bypasses without a heart-lung machine needed a follow-up procedure to open clogged arteries. Mental sharpness and quality of life also was similar in the two groups.

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The two methods proved equally good even in people 75 or older, a group most worried about going on a heart-lung machine. The second study tested the two bypass methods in 2,539 of these elderly patients in Germany. Again, the methods proved equally safe and effective a year later.

The studies were published online Monday by the New England Journal of Medicine. --AP