Sensitivity and specificity calculations
Sensitivity and specificity were first calculated for the custom alert (Table A.5 in the supplementary appendix). Of all custom alerts, 161 (31%) had a risk score of < 10 points. A score of < 10 indicates low risk for QTc-prolongation, and a custom alert will not fire. This cutoff led to a sensitivity of 81%, a specificity of 35%, a PPV of 32% and an NPV of 84% to predict QTc prolongation.
When factoring in the additional points from manual chart review for patients with QTc prolongation on previous ECG readings, sensitivity was improved by 6%, but the specificity remained the same. The PPV and NPV increased to 33% and 88%, respectively. Nevertheless, this component is not readily available from the chart and the risk score will be unable to automatically include it in the final calculation.
Five out of 100 patients had a follow up ECG that was prolonged per our definition; yet their baseline ECG was more prolonged. This was reflected in 24 risk scores which varied between 8.5 and 18.75 points (median 14.5). We eliminated these scores and recalculated sensitivity and specificity results, however, there was minimal to no change to the values.
In addition to the custom alert sensitivity and specificity calculations, we performed a calculation on the existing DDI warnings (Table A.6 in the supplementary appendix). We found a sensitivity of 54%, a specificity of 65%, a PPV of 42% and an NPV of 75%. The alerts that generated were the alerts that actually triggered for these patients. Alerts not generated refer to those which were filtered at that time, but were archived and identified by the investigators.