Development and Validation of a Risk Score to Predict QT Interval Prolongation in Hospitalized Patients

Abstract

Background— Identifying hospitalized patients at risk for QT interval prolongation could lead to interventions to reduce the risk of torsades de pointes. Our objective was to develop and validate a risk score for QT prolongation in hospitalized patients. Methods and Results— In this study, in a single tertiary care institution, consecutive patients (n=900) admitted to cardiac care units comprised the risk score development group. The score was then applied to 300 additional patients in a validation group. Corrected QT (QT_c) interval prolongation (defined as QT_c>500 ms or an increase of >60 ms from baseline) occurred in 274 (30.4%) and 90 (30.0%) patients in the development group and validation group, respectively. Independent predictors of QT_c prolongation included the following: female (odds ratio, 1.5; 95% confidence interval, 1.1–2.0), diagnosis of myocardial infarction (2.4 [1.6–3.9]), sepsis (2.7 [1.5–4.8]), left ventricular dysfunction (2.7 [1.6–5.0]), administration of a QT-prolonging drug (2.8 [2.0–4.0]), ≥2 QT-prolonging drugs (2.6 [1.9–5.6]), or loop diuretic (1.4 [1.0–2.0]), age >68 years (1.3 [1.0–1.9]), serum K⁺ 450 ms (2.3; confidence interval [1.6–3.2]). Risk scores were developed by assigning points based on log odds ratios. Low-, moderate-, and high-risk ranges of 0 to 6, 7 to 10, and 11 to 21 points, respectively, best predicted QT_c prolongation (C statistic=0.823). A high-risk score ≥11 was associated with sensitivity=0.74, specificity=0.77, positive predictive value=0.79, and negative predictive value=0.76. In the validation group, the incidences of QT_c prolongation were 15% (low risk); 37% (moderate risk); and 73% (high risk). Conclusions— A risk score using easily obtainable clinical variables predicts patients at highest risk for QT_c interval prolongation and may be useful in guiding monitoring and treatment decisions.