Abstract: Objective Hydroxychloroquine (HCQ) is one of the most used drugs in patients with systemic lupus erythematosus (SLE). In these patients, where heart involvement is common, cardiac HCQ toxicity may lead to fatal outcomes. The aim of this work is to study the influence of cumulative HCQ (cHCQ) in a selected group of patients with SLE and its association with electrocardiographic (EKG) abnormalities. Methods Single-center retrospective, observational study in which data were collected from the medical records of consecutive patients with a diagnosis of SLE who started treatment with HCQ and who had a 12-lead EKG before starting treatment and during follow-up. EKG abnormalities were grouped as conduction or structural abnormalities. The association of cHCQ with the occurrence of EKG disturbances was analyzed together with other demographic and clinical variables through univariate and multivariate logistic regression models. Results 105 patients were selected with median cHCQ of 913 g. The sample was classified into two groups, above or below 913 g. Significantly, more conduction disturbances were observed in the group above the median (OR: 2.89; 95%CI: 1.01?8.23). In the multivariate analysis, the OR per 100 g of cHCQ dose was 1.06 (95%CI: 0.99?1.14). Age was the only variable associated with conduction disturbances. There were no significant differences in the development of structural abnormalities and a tendency for more high-grade atrioventricular block was shown. Conclusion Our study suggests an association between the cHCQ and the development of EKG conduction disturbances that disappears after multivariate adjustment. No increased number of structural abnormalities was observed

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