What is an incomplete bundle branch block?

Not true "block": Two bundles of electrical tissue carry each heartbeat from the top part of the heart to the bottom--the "right" and "left" bundle branches. When one of these doesn't conduct at all, or does so much more slowly than the other, it is a complete bundle branch block. When one conducts slightly slower than the other, it is called "incomplete" bundle block. This often is of no clinical consequence.

Slow conduction: The electrical activity in the bottom chambers of the heart take a certain range number of milliseconds to conduct (<120ms, commonly <100ms). If longer than 120, it represents a slowing in the system, called a bundle branch block. If there is an appearance of some delay in the conduction, but doesnt meet criteria (>120ms) for a full bundle branch block, it is an incomplete bundle branch block..

Mild conduction prob: The righty and left ventricles are induced to beat through electrochemical currents transmitted through the right and left bundle branches, respectively. Irbbb means part of the right bundle is not transmitting fully. It is a benign condition of no significant clinical consequence.