Prophylactic (hydroxy)chloroquine in COVID-19 Potential relevance for cardiac arrhythmia risk

(Hydroxy)chloroquine ((H)CQ) is being investigated as a treatment for COVID-19, but studies have so far demonstrated either no or a small benefit. However, these studies have been mostly performed in patients admitted to the hospital and hence likely already (severely) affected. Another suggested approach uses prophylactic (H)CQ treatment aimed at preventing either severe acute respiratory syndrome coronavirus 2 infection or the development of disease. A substantial number of clinical trials are planned or underway aimed at assessing the prophylactic benefit of (H)CQ. However, (H)CQ may lead to QT prolongation and potentially induce life-threatening ar-rhythmias. This may be of particular relevance to patients with pre-existing cardiovascular disease and those taking other QT -prolonging drugs. In addition, it is known that a certain percentage of the population carries genetic variant(s) that reduces their repo-larization reserve, predisposing them to (H)CQ-induced QT prolon-gation, and this may be more relevant to female patients who already have a longer QT interval to start with. This review provides an overview of the current evidence on (H)CQ therapy in patients with COVID-19 and discusses different strategies for prophylactic (H)CQ therapy (ie, preinfection, postexposure, and postinfection). In particular, the potential cardiac effects, including QT prolonga-tion and arrhythmias, will be addressed. Based on these insights, recommendations will be presented as to which preventive mea-sures should be taken when giving (H)CQ prophylactically, including electrocardiographic monitoring.