Exercise-induced left bundle branch block: an infrequent phenomenon: Report of two cases

Figure 2 Resting electrocardiogram depicting normal sinus rhythm at a rate of 85 bpm with normal conduction (A), during exercise tolerance testing normal conduction till a frequency of 129 bpm (left panel) and at a heart rate of 141 bpm (right panel) a left bundle branch block occurred which recovered at a frequency of 96 bpm (not shown) (B), on repeat exercise tolerance tests, under β-blocker therapy, exercise-induced left bundle branch block occurred at a heart rate of 129 bpm (C) and disappeared at a frequency of 100 bpm (D). Black arrows indicate the transition from normal to abnormal conduction and vice versa.