1. From the Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark (K.C., S.G., N.M.T., N.S.); and Department of Medicine, University of California San Francisco, San Francisco, CA (M.M.R., J.W., J.C., R.L.N., M.M.S.).