[1] Framingham Heart Dis Epidemiol Study, Framingham, MA 01702 USA
[2] Harvard Univ, Brigham & Womens Hosp, Sch Med, Div Cardiovasc Med, Boston, MA 02115 USA
[3] Boston Univ, Sch Med, Cardiol Sect, Boston, MA 02118 USA
[4] Boston Univ, Sch Med, Prevent Med Sect, Boston, MA 02118 USA