Bundle branch block

In this condition there is abnormal conduction through the right or left bundle branches and a consequent delay in the depolarisation of part of the ventricular muscle. When the heart is in sinus rhythm, ventricular conduction along a slower, abnormal pathway results in a QRS complex of greater than 0.12 sec but with a constant PR interval.

A block of both bundles is equivalent to third degree, or complete, heart block.

Thus three types of bundle branch block may occur:

• bundle branch block involving both branches
• a right bundle branch block
• a left bundle branch block

Right bundle branch block: (1)

• principle indicator is "M" in V1 and V2.
• also, S wave: prominent in V6, slurred in I.

Left bundle branch block: (2)

• principle indicator is "M" in V5 and V6.
• also, tall and very broad in I and aVL.

Reference

1. Tusscher KH, Panfilov AV. Modelling of the ventricular conduction system. Prog Biophys Mol Biol. 2008 Jan-Apr;96(1-3):152-70
2. Pérez-Riera AR et al. Left bundle branch block: Epidemiology, etiology, anatomic features, electrovectorcardiography, and classification proposal. Ann Noninvasive Electrocardiol. 2019 Mar;24(2):e12572