Predictive Validity of a QT_c Interval Prolongation Risk Score in the Intensive Care Unit

Background: Torsade de pointes is a form of polymorphic ventricular tachycardia associated with heart rate-corrected QT (QT_c ) interval prolongation. With approximately 24-61% of critically ill patients experiencing QT_c interval prolongation, a predictive tool to identify high-risk patients could assist in the monitoring and management in the intensive care unit (ICU). The Tisdale et al. Risk Score (TRS) is a predictive tool that was developed and validated in a cardiac critical care unit.

Objectives: The objective of this study was to evaluate the predictive validity (sensitivity and specificity) and likelihood ratios of the TRS in a medical ICU.

Methods: This was a longitudinal, retrospective, cohort study of consecutive patients who met the inclusion criteria from October 2017 to June 2018 with a sample size of 264 patients. The sample size was derived based on the number of TRS covariates and an exploratory variable. Baseline characteristics and risk factors were documented from electronic health records. The first occurrence of QT_c interval prolongation, defined as a QT_c interval > 500 ms or an increase ≥ 60 ms above baseline, was the primary endpoint.

Main results: The sensitivity and specificity of the TRS for low-risk patients against the moderate-risk and high-risk patients were 97% (95% CI 91-99%) and 16% (95% CI 11-23%), respectively. These results corresponded to a positive likelihood ratio of 1.15 (95% CI 1.07-1.24) and a negative likelihood ratio of 0.20 (95% CI 0.06-0.65).

Conclusions: In conclusion, the TRS showed a high sensitivity, making it useful in identifying patients at risk of developing QT_c interval prolongation. Furthermore, patients categorized as low risk by the tool can be considered as having minimal risk of developing QT_c interval prolongation. Given the tool's low specificity, it does not reliably identify all patients at low risk of QT_c interval prolongation.