Boston ? A common method used in heart bypass surgery spares patients pain and problems upfront but seems to raise their risk of dying or suffering a heart attack over the next three years, a worrisome new study finds.

The results could have a big impact — about 450,000 bypass operations are done each year in the United States and 70 percent of them use the method at issue.

It involves the way doctors remove a leg vein that is cut up and moved to the chest to create detours around clogged heart arteries.

For decades, this was done with a long incision — sometimes groin to toe. That was painful, left a big scar and often led to infections and longer time in the hospital.

About 13 years ago, doctors started trying a new way: making small “porthole” cuts and using a tiny scope and tools to tunnel along the vein and pull it out through the small openings. This quickly became popular as part of a big push toward less invasive surgery.