1 Section for Cardiac Electrophysiology, Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland.
2 Section for Cardiac Electrophysiology, Division of Cardiology, Department of Medicine, University of Mississippi School of Medicine, Jackson.
3 Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland.
4 Section for Cardiac Electrophysiology, Division of Cardiology, Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia.