Risk factors for QTc Interval Prolongation in the Ambulatory Setting

Purpose: Prolongation of the QT interval through acquired characteristics or congenital abnormalities can lead to Torsades de Pointes (TdP), a life-threatening arrhythmia. A number of clinical characteristics and medications have an association with acquired QT prolongation, with some having a higher risk than others. The objective of our study was to identify patients seen by University of North Texas Health Science Center (UNTHSC) providers at risk for QT interval prolongation and to describe the most common QT-prolonging clinical characteristics and medications in this patient population. Methods: A retrospective analysis for those aged 18 to 99 years seen by UNTHSC providers between July 1st through October 1st, 2018 was conducted. Records were obtained for: diagnoses, laboratory values, vitals, most recent medication list, and presence of completed electrocardiogram (EKG). Clinical characteristics were filtered for those with high quality evidence for clinical association with increased QT interval. Medications were classified, based on published evidence of prolonging the QT interval via CredibleMeds.com, as: ‘Known Risk of TdP’, ‘Possible Risk of TdP’, and ‘Conditional Risk of TdP’. Collected data were analyzed using descriptive statistics. Results: A total of 11,759 patients were identified for inclusion. Patients were mostly female and White with 15% of patients identifying themselves as Hispanic or Latino. The median age was 60 years, and 40% were at least 65 years of age. The median BMI was 29.44 kg/m2. Twenty-one patients had a calcium level below 8.5 mg/dL; with 28 having a potassium level below 3.5 mmol/L. Twenty-five patients had an eGFR (if African American) below 30 mL/min/1.73m2, and 35 patients had an eGFR (if non-African American) below 30 mL/min/1.73m2. A total of 1,359 patients had a documented EKG. The five most commonly prescribed medications in the ‘Known Risk of TdP’ category were escitalopram, donepezil, citalopram, ondansetron, and fluconazole. Conclusions: Our findings highlight the importance of reviewing both medications, some of which only pose a risk under certain conditions, and clinical characteristics. Future studies can aid providers in more easily identifying patients at risk for life-threatening arrhythmias.