[1] Massachusetts Gen Hosp, Dept Internal Med, Boston, MA 02114 USA
[2] Univ Massachusetts, Sch Med, Dept Populat & Quantitat Hlth Sci, Worcester, MA USA
[3] Univ Massachusetts, Sch Med, Dept Med & Quantitat Hlth Sci, Div Cardiovasc Med, Worcester, MA USA
[4] Massachusetts Gen Hosp, Cardiac Arrhythmia Serv, Simches Res Bldg,185 Cambridge St 3-188, Boston, MA 02114 USA
[5] Massachusetts Gen Hosp, Cardiovasc Res Ctr, Simches Res Bldg,185 Cambridge St 3-188, Boston, MA 02114 USA