Greater than 930K SNPs from the Illumina 1M BeadChip were tested for an association with PR interval, QRS duration, QTc interval, and heart rate using linear regression assuming an additive genetic model. Tests of association were performed unadjusted and adjusted for age, sex, PR/QT drug usage (for PR and QT interval only), and principal components (PCs; two to four PCs depending on the trait) using PLINK (Purcell et al. 2007). All results were plotted using Synthesis View, Haploview, or Locus Zoom (Barrett et al. 2005; Pendergrass et al. 2010; Pruim et al. 2010). Power calculations were performed using QUANTO (Gauderman & Morrison 2006) assuming genetic effect sizes based on the original published GWAS. The fixation index FST, a measure of population differentiation, was calculated using the Weir and Cockerham algorithm (Weir & Cockerham 1984). We calculated FST between European descent populations and our African American study population using the Platform for the Analysis, Translation, and Organization of large-scale data (PLATO) (Grady et al. 2010). Pair-wise linkage disequilibrium was calculated (r2) around the SCN5A/SCN10A and NOS1AP regions using the SeattleSNPs Genome Variation Server (gvs.gs.washington.edu/).
