Some hospitals pay thousands of dollars more than others for big-ticket medical devices such as defibrillators and hip replacements, and a portion of the higher costs could be passed on to the federal Medicare program, a new government report says.   Among 31 hospitals surveyed by investigators for the Government Accountability Office, one paid $8,723 more than another for an identical model of an implantable cardioverter defibrillator, which typically costs the hospitals between $16,445 and $19,007. In another finding, prices paid for the same drug-eluting stents, used to prop open diseased blood vessels, varied by as much as $828 from their typical cost of $1,700 to $1,800.   Such price variations often result from confidential negotiations between hospitals and devices makers, hospital officials say. They could affect Medicare spending because the program sets hospital payments based in part on the costs the hospitals incur, the report says.   Because hospitals depend on doctors for patient referrals and revenue, they often bow to the demands of physicians who may prefer, for instance, a defibrillator made by a particular manufacturer to one from another, regardless of price. The GAO report highlighted that problem, and said contracts between manufacturers and hospitals often forbid disclosure of prices even to doctors, making it harder to steer doctors to less expensive options. In some cases, the report said, hospitals bound by such contracts resorted to using color-coded stickers to help doctors distinguish between cheaper or more expensive devices on stock shelves. (WSJ)