Cumulative dose of hydroxychloroquine is associated with a decrease of resting heart rate in patients with systemic lupus erythematosus: a pilot study

Introduction: The use of hydroxychloroquine (HCQ) in patients with systemic lupus erythematosus (SLE) offers a wide range of benefits. However, there are evidence in favour of cardiotoxicity, including heart conduction disturbances and congestive heart failure. Objective: To determine the effects of HCQ in the resting heart rate (RHR) of SLE patients. Patients and methods: Included were patients with non active SLE, with a sedentary lifestyle and treated with HCQ. Excluded were patients on beta blocker treatment, trained patients, pacemaker's users and patients with clinical or analytical evidence of anemia, renal disease, obstructive pulmonary disease, obesity, uncontrolled thyroid disease, fever or current infection. Standard 12-lead electrocardiogram was performed in the resting condition (supine decubitus and orthostatic position). Comparison between groups was performed using Mann-Whitney U test. A multiple linear regression was performed. A p value <0.05 was considered statistically significant. Results: 42 patients were included. Patients were divided in two groups based on the cumulative dose of HCQ (CD-HCQ), considering 365 g as cut-off. There were 24 patients with low-HCQ (<365 g) and 18 patients with high-HCQ (>365 g). Non significant differences were found in age, sex, prednisone dose or SLEDAI. The mean RHR was 73 +/- 6 beats/min in the low-HCQ and 65 +/- 7 beats/min in the high-HCQ, with a significant decrease of 11% (p = 0.003). In multiple linear regressions, there were non significant association between the decrease of RHR and prednisone dose, age, SLEDAI or TSH, but there was significant association between RHR and CD-HCQ (p = 0.024) and RHR and time of exposure to HCQ (p = 0.029). Conclusion: CD-HCQ higher than 365 g was associated with a significant decrease (11%) in RHR in non-active SLE patients, although a larger prospective study is required to allow more definitive conclusions.