Duke Clinical Research Institute, Durham, North Carolina, USA; Division of Cardiology, Duke University School of Medicine, Durham, North Carolina, USA. Electronic address: stephen.greene@duke.edu. Duke Clinical Research Institute, Durham, North Carolina, USA; Division of Cardiology, Duke University School of Medicine, Durham, North Carolina, USA. Duke Clinical Research Institute, Durham, North Carolina, USA; Department of Biomedical Engineering, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Gdansk, Poland. Division of Cardiology, Stony Brook University, Stony Brook, New York, USA. Department of Cardiology, Kaiser Permanente San Francisco Medical Center, San Francisco, California, USA; Division of Research, Kaiser Permanente Northern California, Oakland, California, USA. Duke Clinical Research Institute, Durham, North Carolina, USA. Brigham and Women's Hospital Heart & Vascular Center and Harvard Medical School, Boston, Massachusetts, USA. Department of Medicine, University of Mississippi Medical Center, Jackson, Mississippi, USA.