['To determine the phenotype and outcome of patients with QTc of at least 500 ms and to create a pro-QTc risk score for mortality.', 'An institution-wide computer-based QT alert system was developed and implemented at Mayo Clinic in Rochester, Minnesota. This system screens all electrocardiograms (ECGs) performed and alerts the physician if the QTc is 500 ms or greater. Between November 10, 2010, and June 30, 2011, 86,107 ECGs were performed in 52,579 patients. Clinical diagnoses, laboratory abnormalities, and medications known to influence the QT interval were collected from the medical records and summarized in a new pro-QTc score. Survival was compared with that of the 51,434 Mayo Clinic patients with a QTc less than 500 ms during the same period.', 'QT alerts were sent for 1145 patients (2%); of these, 470 (41%) had no other identifiable ECG reason for QT prolongation (eg, pacing). All-cause mortality during a mean ± SD of 224 ± 174 days of follow-up was 19% in those with QTc of 500 ms or greater compared with 5% in patients with QTc less than 500 ms (log-rank P<.001). The pro-QTc score was an age-independent predictor of mortality (pro-QTc score: hazard ratio, 1.18; 95% CI, 1.05-1.32; P=.006; age: hazard ratio, 1.02; 95% CI, 1.01-1.03; P=.004.). QT-prolonging medications accounted for 37% of the pro-QTc score.'] Does institution-wide QT alert system identify patients with a high risk of mortality?