A widely used new blood thinner that is routinely given to heart patients after angioplasty appears in rare cases to trigger a deadly blood disease. The drug, called Plavix, prevents blood clots and has been taken by more than 3 million people worldwide since its introudction two years ago. For the first time , doctors have linked to medcine to thrombotic thrombocytopenic purpura, or TTP, a dangerous form of anemia. A report to be published in the New England Journal of Medicine describes 11 cases among Plavix users.