Background: Hydroxychloroquine is used as an antimalarial and immunomodulator, however it can induce QT prolongation that could potentially lead to fatal arrhythmia. We investigated changes in QT interval in long-term hydroxychloroquine users, and identified possible risk factors associated with significant QTc prolongation.

Methods: We retrospectively enrolled 3603 patients who received long-term hydroxychloroquine treatment from 2009 to 2019, of whom 167 had electrocardiography (ECG) results before and during hydroxychloroquine therapy. Baseline characteristics, laboratory data, comorbidities, concurrent medications, and related clinical outcomes were reviewed.

Results: Overall, 225 patients (6.2%) died within the study period, with 50 patients (1.4%) continuously receiving hydroxychloroquine treatment until death. Three patients had fatal ventricular arrhythmia. No significant change in corrected QT interval (QTc) was noted before and during hydroxychloroquine treatment (451.1 ± 39.9 ms vs. 456.0 ± 37.3ms, P = 0.140) in the ECG cohort. Multivariable logistic regression showed that diabetes mellitus [odds ratio (OR): 9.55, 95% confidence interval (CI): 2.02-45.22; P = 0.005] and use of additional QT-prolonging drugs (OR: 2.89, 95% CI: 1.40-5.94; P = 0.004) were independent risk factors for significant QTc prolongation. Multiple linear regression, with the number of QT-prolonging drugs and comorbidities including diabetes mellitus, hypertension, and atrial fibrillation as explanatory variables, predicted QTc response (adjusted R² = 0.385) in the long-term hydroxychloroquine users.

Conclusions: In the long-term users of hydroxychloroquine, those with diabetes mellitus and concurrent use of additional QT-prolonging drugs were at a higher risk of significant QTc prolongation. Baseline QTc interval, concurrent medications, and comorbidities predicted QTc response.