bundle-branch block

n.
  1. Intraventricular block due to interruption of conduction in one of the two main branches of the bundle of His and manifested in the electrocardiogram by marked prolongation of the QRS complex.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.