[1] Harvard Univ, Dept Med, Cambridge Hlth Alliance, Sch Med, Cambridge, MA 02138 USA
[2] Univ Alabama Birmingham, Dept Neurol, UAB Stn, Birmingham, AL 35294 USA
[3] Univ Texas SW Med Ctr Dallas, Div Cardiol, Dallas, TX 75390 USA
[4] Univ Iowa, Dept Internal Med, Carver Coll Med, Iowa City, IA 52242 USA
[5] Beth Israel Deaconess Med Ctr, Dept Med, Boston, MA 02215 USA