 rapid transform human fibroblast cultur simian viru 40 risk system embol assess group 754 patient chronic rheumat heart diseas period 5 833 patient-year incid embol 1 5 patient-year group time higher atrial fibril sinu rhythm durat atrial fibril on-third emboli occur month two-third 12 month onset atrial fibril incid embol recurr 8 patient-year irrespect natur cardiac rhythm 66 recurr place 12 month initi embol episod mitral valvotomi elimin danger embol question reduc incid anticoagul treatment reduc incid embol recurr 