Exercise-induced left bundle branch block with chest pain related to antimalarial prophylaxis with chloroquine

Left bundle branch block (LBBB) during exercise can be associated with chest pain. Though this association is mostly correlated with an underlying coronary artery disease, painful LBBB has been described in patients with normal coronary arteries. We report a case of exercise-induced LBBB with typical angina pectoris related to antimalarial prophylaxis with chloroquine in a 66-year old woman with normal coronary arteries, which was reversed after treatment discontinuation. The effect of chloroquine on the electrophysiological properties of nodal cardiac tissue is responsible for this rate-dependent LBBB. Precautions for future antimalarial prophylaxis are also discussed.