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Bundle Branch Block Determination III - Complete Bundle Branch Block .

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Step 4

Analyze the terminal portion of the QRS complex. Starting at the “J” point go one small box back into the QRS (moving to the left).

  • If the energy is below the isoelectric line, this is a left BBB.
  • If the energy of the depolarization is above the isoelectric line, this is a right BBB.
  • some people refer to a turn signal: down is left, up is right
bbb ecg image step4

Authors and Reviewers

Authored by Thomas O'Brien
Medically reviewed by Dr. Jonathan Keroes, MD, Cardiology
Last Update: 11/8/2020

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