4. Bundle Branch and Fascicular Blocks
Published Online: 1 NOV 2012
Copyright © 2013 John Wiley & Sons, Ltd.
Bennett's Cardiac Arrhythmias: Practical Notes on Interpretation and Treatment, Eighth Edition
How to Cite
Bennett, D. H. (2013) Bundle Branch and Fascicular Blocks, in Bennett's Cardiac Arrhythmias: Practical Notes on Interpretation and Treatment, Eighth Edition, John Wiley & Sons, Ltd, Oxford. doi: 10.1002/9781118432389.ch4
- Published Online: 1 NOV 2012
- Published Print: 14 JAN 2013
Print ISBN: 9780470674932
Online ISBN: 9781118432389
- Bundle branch;
- Fascicular blocks;
- Left anterior and posterior fascicular blocks;
- Left bundle branch block;
- Right bundle branch block
Right and left bundle branch block, and block in the left anterior and posterior fascicles of the left bundle branch, are commonly encountered.
Complete bundle branch block prolongs QRS duration to 0.12 s or greater. With right bundle branch block, there will be a secondary R wave in lead V1, resulting in an M-shaped complex. With left bundle branch block, there is no M-shaped complex in V1; there will be a notched complex in left ventricular leads.
Diagnosis of fascicular block requires an understanding of the hexaxial reference system. With left axis deviation, lead I is predominantly positive and both leads II and III are predominantly negative. The criteria for left anterior fascicular block are left axis deviation together with a small initial r wave in leads II and aVF: inferior infarction also leads to left axis deviation but there will be a Q rather than r wave in these leads.