[1] Univ N Carolina, Dept Med, Div Cardiol, Sch Med, Chapel Hill, NC 27599 USA
[2] Massachusetts Gen Hosp, Boston, MA USA
[3] US Dept Vet Affairs, Vet Hlth Adm Off Qual & Patient Safety, Washington, DC USA
[4] Univ North Carolina Hosp, Chapel Hill, NC USA
[5] Univ Colorado, Colorado Sch Publ Hlth, Dept Biostat & Informat, Anschutz Med Campus, Denver, CO USA