1. Veterans Affairs Medical Center, Georgetown University School of Medicine and George Washington University School of Medicine, Washington, DC, USA.
2. Veterans Affairs Palo Alto Health Care System and Stanford University, California, USA.
3. Veterans Affairs Medical Center and George Washington University, Washington, DC, USA.
4. Veterans Affairs Medical Center, Washington, DC, USA.
5. Boston University Medical School and Asklepeion General Hospital, Division of Cardiology, Piraeus, Greece.
6. Veterans Affairs Medical Center and Georgetown University Medical Center, Washington, DC, USA.