Letter to the Editor Exercise-induced left bundle branch block and propafenone administration Polychronis Dilaveris T , Andreas Synetos, George Giannopoulos, Spyros Massias, Andreas Michaelides, Christodoulos Stefanadis A’ University Department of Cardiology, University of Athens Medical School, Hippokration Hospital, Athens, Greece Received 7 November 2004; accepted 31 December 2004 Available online 17 March 2005 Propafenone, a sodium channel blocker, has been shown to be an effective and well-tolerated antiarrhythmic agent. Sodium channel blockade is probably responsible for the important QRS prolongation during exercise in patients taking propafenone [1]. Rate-dependent conduction slowing by the sinus tachycardia of exercise may be responsible for some cases of proarrhythmia caused by class IC drugs [2]. Although propafenone-induced QRS prolongation or even left bundle branch block (LBBB) have been previously reported [3,4], there is no previous data in the literature demonstrating exercise-induced LBBB due to propafenone administration. We report a case of exercise-induced LBBB due to propafenone administration. A 66-year-old man, who was effectively treated with propafenone 450 mg (257 mg/m 2 ) daily for the last 3 months because of history of paroxysmal atrial fibrillation, underwent maximal symp- tom-limited exercise testing to rule out the presence of coronary artery disease. He had no risk factors or symptoms suggestive for coronary artery disease and had a normal echocardiogram. His resting heart rate was 74 bpm and the QRS duration was 124 ms with no repolarization abnormalities. He exercised according to the BRUCE protocol for 10:21 min, achieving a work level of max. METS: 12.40. During exercise testing heart rate rose to 144 bpm, which represents 94% of the maximal age-predicted heart rate. Resting blood pressure 130/80 mm Hg rose to a maximum blood pressure of 190/ 90 mm Hg. The exercise test was stopped because of fatigue. No chest discomfort or shortness of breath was reported during or after the exercise testing. During exercise testing a gradual prolongation of the QRS duration was demonstrated which finally resulted to LBBB morphology with QRS duration of 165 ms and a leftward axis deviation (À708) at peak exercise (Fig. 1). During the recovery period after exercise, LBBB morphology dis- appeared and the prolonged QRS duration gradually returned to the pre-exercise value (Fig. 1). Although this exercise test result was considered an effect of propafenone administration, to exclude the possible confounding effects of exercise-induced myocardial ischemia on ventricular conduction and the QRS duration, a detailed work-up including stress thallium scintigraphy and coronary arte- riography was performed. Both stress thallium-201 scintig- raphy (Fig. 2) and coronary angiography were normal. The patient was advised to consult a specialized department of clinical pharmacology in order to adjust his medical treatment. Propafenone is a potent class IC antiarrhythmic agent. The electrophysiological effects of propafenone have been previously reviewed [5]: the transmembrane properties of the drug are largely responsible for the reduction in transmembrane phase 0 upstroke and for the prolongation of action potential duration. The effect of propafenone on the duration of the QRS complex is well known but not dose-dependent. Several authors have paid attention to the prolongation of the QRS after propafenone admin- istration and have reported the development of LBBB 0167-5273/$ - see front matter D 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijcard.2004.12.080 T Corresponding author. 22 Miltiadou Street, 155 61 Holargos, Athens, Greece. Tel./fax: +30 210 6531377. E-mail address: hrodil@yahoo.com (P. Dilaveris). International Journal of Cardiology 106 (2006) 279 – 281 www.elsevier.com/locate/ijcard