A device that doctors had hoped would be a major advance for many stroke patients appears to be doing more harm than good, according to a federally funded study released Wednesday. The “Gateway-Wingspan” system,” which was approved in 2005 in the hopes of protecting thousands of stroke survivors from another, more devastating attack, turned out to cause more strokes and deaths than simply aggressively treating patients with drugs and advice, the study found. As many as 90,000 Americans every year suffer the kind of stroke the treatment was designed to prevent.