Risk factors for QTc interval prolongation

Purpose: Prolongation of the QTc interval may result in Torsade de Pointes, a ventricular arrhythmia. Numerous risk factors for QTc interval prolongation have been described, including the use of certain drugs. In clinical practice, there is much debate about the management of the risks involved. In this study, we quantified the effect of these risk factors on the length of the QTc interval. Methods: We analyzed all ECGs that were taken during routine practice between January 2013 and October 2016 in the Spaarne Gasthuis, a general teaching hospital in the Netherlands. We collected laboratory values in the week before the ECG recording and the drugs prescribed. For the identification of risk factors, we used multilevel linear regression analysis to correct for multiple ECG recordings per patient. Results: We included 133,359 ECGs in our study, taken in 40,037 patients. Patients using one QT-prolonging drug had a 11.08 ms (95% CI 10.63–11.52; p < 0.001) longer QTc interval. Patients using two QT-prolonging drugs had a 3.04 ms (95% CI 2.06–4.02; p < 0.001) increase in the QTc interval compared to patients using one QT-prolonging drug. Women had a longer QTc interval compared to men (16.30 ms 95% CI 14.59–18.01; p < 0.001). The QTc interval increased with increasing age, but the difference between men and women diminished. Other independent risk factors that significantly prolonged the QTc interval with at least 10 ms were hypokalemia, hypocalcemia, and the use of loop diuretics. Conclusion: We identified and quantified various risk factors for QTc interval prolongation.

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