Right bundle block in a patient with acute posterior myocardial infarction

We present here a patient with the unusual combination of a newly developed right bundle branch block (RBBB) and an acute posterior myocardial infarction (MI). A dissecting MI with interventricular septal (IVS) rupture was initially thought to have caused RBBB. However, histologic examination revealed that the right bundle branch (RBB) had no ischemic involvement, but did show fibrosis, which suggests that this chronic damage of the RBB was a major contributor to the development of RBBB. This case confirms that the RBB is rarely involved by a posterior MI even in the presence of a dissecting IVS rupture.