TRANSIENT DISAPPEARANCE OF COMPLETE RIGHT BUNDLE-BRANCH BLOCK DURING EXERCISE IN A PATIENT WITH OLD INFERIOR WALL MYOCARDIAL-INFARCTION

To date, there has been no report of temporary disappearance of right bundle branch block (RBBB) during exercise. A patient with old inferop osterior myocardial infarction is described in whom complete RBBB disa ppeared transiently during treadmill exercise testing. No chest pain o r significant ST-T changes occurred during and after the exercise peri ods. Any of the following mechanisms could have been involved: (1) the patient's complete RBBB might have been bradycardia-dependent, (2) an exercise-induced increase of sympathetic tone might have produced a t emporary improvement of the conduction disturbances, or (3) the exerci se might have elicited conduction disturbances in the main left bundle branch, which could have concealed a conduction delay in the main tru nk of the right bundle branch.