Study population demographics and characteristics are described in Table 1. Individuals with a normal ECG without evidence of cardiac disease before or within one month following the ECG, without concurrent use of medications that interfere with QRS duration, and who did not have abnormal electrolyte values at the time of the ECG were included. Using natural language processing combined with EMR (structured database queries) to query (specific to VGER), we excluded individuals with any of the following before or within one month of the ECG: indication of heart failure, arrhythmia, cardiomyopathy, cardiac conduction defect, or myocardial ischemia/infarct based on clinical notes, unstructured text, billing codes, and labs. VGER subjects were African American as indicated by observer reported ancestry, which is highly concordant with genetic ancestry (Dumitrescu et al. 2010). African American ancestry was self-reported for Northwestern subjects (McCarty et al. 2011), which is also known to be highly concordant with genetic ancestry. All ECGs had normal Bazett’s corrected QT intervals (<450ms), heart rates (between 50–100 bpm), and QRS duration (65–120 ms).
