1. School of Medicine, University College Dublin , Dublin , Ireland
2. Department of Cardiovascular Medicine, Mayo Clinic , 200 First St. SW, Rochester, MN 55905 , USA
3. Department of Medicine, Mayo Clinic , 200 First St. SW, Rochester, MN 55905 , USA
4. Division of Biomedical Statistics and Informatics, Mayo Clinic , 200 First St. SW, Rochester, MN 55905 , USA