1 Section of Cardiac Electrophysiology, Division of Cardiology, University of California-San Francisco, San Francisco, California, USA.
2 Electrophysiology Section, Division of Cardiovascular Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
3 Section of Cardiac Electrophysiology, Division of Cardiology, University of California-San Francisco, San Francisco, California, USA. Electronic address: melvin.scheinman@ucsf.edu.