[1] Sahlgrens Univ Hosp, Dept Clin Physiol, SE-41345 Gothenburg, Sweden
[2] Sahlgrens Univ Hosp, Dept Cardiol, SE-41345 Gothenburg, Sweden
[3] Natl Hosp Norway, Dept Cardiol, Oslo, Norway
[4] Univ Leicester, Dept Med & Therapeut, Leicester LE1 7RH, Leics, England