Assessing the risk of drug-induced corrected QT interval prolongation in primary care

Tisdale risk score has been validated for predicting drug-induced QTc prolongation (QTP) in cardiac care. This study aims to determine whether it can guide prescribing and monitoring of QTc-prolonging medications in primary care.

A retrospective chart audit using Tisdale Risk Score was conducted. Data from 486 primary care patients from two Family Medicine Clinics, prescribed medications with known or possible risk of Torsades de Pointes (TdP) were reviewed. Eighty-five patients with pre- and post-pharmacotherapy ECGs comprised the cases. A control group of 184 patients not on QTc-prolonging medications was assessed. Patients were categorized as low, moderate, or high risk for QTP.

Psychotropics were the most frequently prescribed QTc-prolonging medications. Baseline QTc did not differ significantly between cases (428 ms) and controls (426 ms). Among cases, most were stratified as low risk (69.4%), with fewer in moderate (25.9%) and high-risk (4.7%) categories. Comparatively, 99.5% of control patients were at low risk. QTc prolongation occurred in 5/85 (5.9%) post-pharmacotherapy, with none in the high-risk category. Odds ratio for QTP in moderate-risk patients versus low-risk was 0.71 (95% CI: 0.07-6.98).

Most primary care patients were at low risk for drug-induced QTc prolongation. QTP events were low with none in the high-risk category, which limited evaluation of association between risk categories and QTc prolongation. The study highlights commonly prescribed QTc-prolonging medications in family medicine and their variable QTc effects, emphasizing the need for an outpatient-tailored risk assessment tool.