Bundle Branch Block



P wave

Normal if the underlying rhythm is sinus


Wide; > 0.12 seconds


This block occurs in the right or left bundle branches or in both. The ventricle that is supplied by the blocked bundle is depolarized abnormally.


Regular or irregular depending on the underlying rhythm.

Left bundle branch block is more ominous than right bundle branch block because it usually is present in diseased hearts. Both may be caused by hypertension, MI, or cardiomyopathy. A bifasicular block may progress to third degree heart block.

Treatment is artificial pacing for a bifasicular block that is associated with an acute MI.