[1] Oslo Univ Hosp, Dept Cardiol, Ulleval, Norway
[2] Univ Oslo, Fac Med, Oslo, Norway
[3] Univ Eastern Finland, Fac Hlth Sci, Inst Clin Med, Kuopio, Finland
[4] Univ Oslo, Dept Informat, N-0316 Oslo, Norway
[5] Oslo Univ Hosp, Dept Cardiol, Rikshosp, N-0424 Oslo, Norway