1. University of California-Los Angeles Cardiac Arrhythmia Center, Los Angeles, California;
2. Cardiac Autonomics Group, Gail and Gerald Oppenheimer Family Center for Neurobiology of Stress, University of California-Los Angeles, Los Angeles, California;
3. Department of Cardiac Anesthesia, University of California-Los Angeles, Los Angeles, California;
4. Department of Cardiac Surgery, University of California-Los Angeles, Los Angeles, California; and
5. Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah