Heart conduction disorders related to antimalarials toxicity: an analysis of electrocardiograms in 85 patients treated with hydroxychloroquine for connective tissue diseases.

OBJECTIVE The antimalarial agents chloroquine (CQ) and hydroxychloroquine (HCQ) are used in long-term treatment of connective tissue diseases (CTDs). A high incidence of heart conduction disorders, including bundle-branch block and incomplete or complete atrioventricular block, has been observed among patients treated with CQ. Since no data were available for HCQ, we studied electrocardiograms (ECGs) in 85 unselected patients with CTD treated with HCQ as the sole antimalarial. METHODS Eighty-five unselected out-patients treated with HCQ for a minimum of 1 yr, and without established cardiac diseases had standard 12-lead ECGs. RESULTS Two incomplete right bundle-branch blocks and one left bundle-branch block were observed. No atrioventricular block was observed. The mean PR interval was 137 +/- 20 ms (range 99-188). The mean QTc interval was 410 ms (range 349-464). The mean heart rate was 73 beats/min (range 53-102). CONCLUSION PR interval, QTc interval and heart rate were not different from normal values. The rate of heart conduction disorders was similar to what is expected in the general population, and contrasted with prior results in CQ-treated patients. Our results add further evidence on the safety of HCQ compared with CQ.