Researchers are reporting encouraging results for a new generation of pacemakers — miniature, wireless ones that can be implanted through a leg vein without surgery. In a study of 725 patients, one of these devices, made by Medtronic, was successfully implanted 99 percent of the time, with a low rate of complications compared to traditional pacemakers. Leaders of the company-sponsored study discussed the research Monday at an American Heart Association conference in Orlando. Results also were published online by the New England Journal of Medicine. Two months ago, the journal published a study of a similar device made by St. Jude Medical.