54. van der Meer FJ, Rosendaal FR, Vandenbroucke JP, Bri t E. Bleeding complications in oral anticoagulant therapy. An anal- ysis of risk factors. Arch Intern Med. 1993;153(13):1557-1562. 55. Petersen P, Boysen G, Godtfredsen J, Andersen ED, Andersen B. Placebo-controlled, randomised trial of warfa- rin and aspirin for prevention of thromboembolic complica- tions in chronic atrial brillation. The Copenhagen AFASAK study. Lancet. 1989;1(8631):175-179. 56. The Boston Area Anticoagulation Trial for Atrial Fibrillation Investigators. The effect of low-dose warfarin on the risk of stroke in patients with nonrheumatic atrial brillation. N Engl J Med. 1990;323(22):1505-1511. 57. Connolly SJ, Laupacis A, Gent M, Roberts RS, Cairns JA, Joyner C. Canadian Atrial Fibrillation Anticoagulation (CAFA) Study. J Am Coll Cardiol. 1991;18(2):349-355. 58. Stroke Prevention in Atrial Fibrillation Study. Final results. Circulation. 1991;84(2):527-539. 59. Ezekowitz MD, Bridgers SL, James KE, et al; Veterans Affairs Stroke Prevention in Nonrheumatic Atrial Fibrillation Investigators. Warfarin in the prevention of stroke associ- ated with nonrheumatic atrial brillation. N Engl J Med. 1992;327(20):1406-1412. on Practice Guidelines; European Society of Cardiology Committee for Practice Guidelines; European Heart Rhythm Association; Heart Rhythm Society. ACC/AHA/ ESC 2006 Guidelines for the Management of Patients with Atrial Fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients With Atrial Fibrillation): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society. Circulation. 2006;114(7):e257-e354. 30. Gage BF, Waterman AD, Shannon W, Boechler M, Rich MW, Radford MJ. Validation of clinical classi cation schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. JAMA. 2001;285(22):2864-2870. 31. Albers GW, Dalen JE, Laupacis A, Manning WJ, Petersen P, Singer DE. Antithrombotic therapy in atrial brillation. 