Bundle Branch Block | Reference Guide

EKG Features

Rate: The underlying rate
Rhythm: Regular
P Wave: Normal
PR Interval: Normal (0.12-0.20 sec)
QRS: Wide (>0.12 sec)

A bundle branch block is a partial or total interruption of the heart’s electrical impulse in either the right or left branch of the electrical pathway. This interruption, or block, causes the electrical signals for one of the ventricles to detour, so that one of the ventricles contracts slightly later than the other ventricle. As a result, cardiac output can drop. This condition can be congenital or caused by heart disease.
External Source: http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/Conduction-Disorders_UCM_302046_Article.jsp
American Heart Association