Permanent right bundle-branch block heralded by intermittent block and ventricular extrasystoles. A 13-year observation.

A patient is described in whom the occurrence of frequent ventricular extrasystoles of right ventricular origin and intermittent right bundle-branch block caused by interpolation of these extrasystoles heralded the slow development of permanent right bundle-branch block over a period of observation of 13 years. Such a clinical course suggested gradual progression of an organic lesion in the intraventricular conducting system. The differential diagnosis of intermittent bundle-branch block and aberrant intraventricular conduction, and possible mechanisms of ectopic impulse formation in the presence of bundle-branch block are discussed.