Comparison of two treatment durations (6 days and 14 days) of a low molecular weight heparin with a 6-day treatment of unfractionated heparin in the initial management of unstable angina or non Q wave myocardial infarction: FRAXIS (Fraxiparine in Acute Ischaemic Syndrome) - The FRAXIS Study Group (Eur Heart J, 1999)