1 Department of Medicine, Larner College of Medicine at the University of Vermont, Burlington, Vermont.
2 Division of Cardiology, Department of Medicine, and the Cardiovascular Research Institute, University of California, San Francisco, San Francisco, California.
3 Department of Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, California.
4 Lillehei Heart Institute, Department of Medicine, University of Minnesota, Minneapolis, Minnesota.