1. Cardiology Section, San Francisco Veterans Affairs Health Care System , 4150 Clement St., San Francisco, CA 94121 , USA
2. Department of Medicine, University of California San Francisco , 505 Parnassus Ave, San Francisco, CA 94143 , USA
3. Department of Epidemiology and Biostatistics, University of California San Francisco , 550 16th St., San Francisco, CA 94158 , USA