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Right Bundle Branch Block

Sat, 11/03/2012 - 00:06 -- Dawn

This ECG is from a healthy young man in his 20's.  He was born with a ventricular septal defect (VSD) that was surgically repaired when he was a toddler.  He now has a right bundle branch block, which could be a result of the defect, or the surgery.  This is a good ECG for the Instructors' Collection because it clearly shows all the ECG characteristics of right bundle branch block:  wide QRS in a supraventricular rhythm (in this case, NSR), rSR' pattern in V1, wide or "slurred" S waves in Leads I and V6.  There is no rhythm strip below the 12 leads in this ECG, but there is no rhythm disturbance.

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ekgpress@mac.com's picture

As per Dawn - the above ECG is a nice example of complete RBBB. There are 2 additional teaching points:

  • ST-T waves are typical "secondary" changes that are expected with BBB. That is - in the 3 key leads used for diagnosis of BBB (= leads I, V1, V6) - the ST-T waves are oppositely directed to the last QRS deflection. Thus, in leads I,V6 - the last QRS deflection is negative (the wide terminal S wave) - and the ST-T waves are opposite (= upright). Also - in V1 - the last QRS deflection is the upright R' - so the ST-T wave are oppositely deflected (negative) as expected.
  • The value of looking for ST-T waves with typical RBBB and LBBB - is that IF the ST-T wave in any of the 3 key leads is not oppositely directed to the last QRS deflection in that lead - then you have a "primary" ST-T wave change, which may signal ischemia and/or infarciton in association with the BBB.

The 2nd teaching point I'd make - is that QRS morphology almost suggests LPHB (Left Posterior HemiBlock) in addition to RBBB. By far - LAHB (Left Anterior HemiBlock) is much more common than LPHB. This is because the left posterior hemifascicle is much thicker than the left anterior hemifascicle, as well as having a dual blood supply from both the right and left coronary arteries. The way to recognize this rare form of bifascicular block is to focus on lead I in a patient who has complete RBBB. IF R wave amplitude is small and the straight (unblocked) portion of the S wave in lead I is very steep - and, in addition you have predominantly positive QRS complexes in leads II, III - then the RBBB/LPHB form of bifascicular block is probably present. That's the case here.

For anyone interested - I've made a free download web page on the Basics of BBB at: https://www.kg-ekgpress.com/bundle_branch_block_pdf_file/

For a web page on the basics of axis and the hemiblocks - go to: https://www.kg-ekgpress.com/axis_basics-ecg/

 

Ken Grauer, MD  www.kg-ekgpress.com   ekgpress@mac.com 

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