EKG Project

2 Easy Steps to Determine a Left or Right Bundle Branch Block

Even though we can look at EKG strips and see some abnormalities, we still need tools to measure those abnormalities. You can purchase some of them from the links in this post and if you’re curious, you can see my full disclosure here.

I have spent way too much time being confused by bundle branch blocks. My old telemetry teacher gave me this nifty handout (that I still don’t fully understand) to use to help interpret them and I definitely have googled the bunny ear method and there is also the blinker method. I don’t know. So let’s really look at these things. Why is it even important to know whether a person has a left or right bundle?

***Of note*** Most telemetry monitoring occurs using Lead II as our main lead (this is the one that we see on the screen). HOWEVER, this is not the best lead for determining  which type of bundle branch block you’re dealing with. We need to use V1 or V6. Does a five-lead system even monitor that? Why yes. The V Lead (if it is positioned correctly) lies on the Right side of the sternum at the fourth intercostal space which is exactly where V1 is placed for a 12-lead. Sweet! This will be helpful.

Ok. So remember. Look at V1 (or V6 if you have a 12-lead) for bundle branch blocks.

Step 1:

Grab your calipers and measure your strip.  Is your QRS > 0.12?

No.  –> Well then that patient does not have a bundle branch block.

Yes –> Bundle branch block! Let’s figure out what type.

Step 2:

Look at V1.

Does the wave point mostly up or mostly down?

Up –> This is a Right bundle branch block

Down –> This is a Left bundle branch block

BUT you must be looking in V1!

Further clarification:

If you really want to be precise and you have V6

Right BBB –> you will have a ‘fat S wave’

Left BBB –> you will have a really wide ‘R wave’

Maybe that wasn’t as confusing as I thought it was. I think I usually forget that I need to be looking at V1 and try to figure it out in Lead II. Does it really even matter if a patient has a left or right bundle. Well let’s see…

Right Bundle Branch Block (RBBB)

The right side of the bundle branches is smaller than the left side and can more easily be compromised by a lesion. One of the largest contributors to RBBB is age and if you have a RBBB it is typically benign. Sometimes RBBB are rate dependent. As the  heart rate approaches 150 bpm you might see a very fast rhythm with wide complexes (that your monitor will read as V-tach but you’ll look closely and say…”Well, from the morphology and rate, that may be a rate dependent RBBB” and everyone will look at you in awe).

Other causes include:

  • Coronary artery disease
  • Hypertension
  • Acute anteroseptal MI
  • Acute pulmonary embolism
  • Right Ventricular failure or hypertrophy

The RBBB messes with the conduction system so the Right Ventricle is depolarized last.

Look here:IMG_0548

The little LV and RV indicate which side of the heart is being depolarized.


Left Bundle Branch Block (LBBB)

Ok…This one is a little more serious. Why? The LBBB consists of a thicker bundle of fibers and two additional fascicles that come off of it. So…there’s a bit more that can go wrong with it. Since my expertise is limited on this subject, I’ll try to make this fairly simple. IMG_0549

You can see from this picture how the heart gets depolarized when the conduction system is altered by a LBBB.

The biggest contributing factors to LBBB include:

  • Coronary artery disease
  • Hypertension
  • MIs
  • Valvular heart disease

What is so significant about a LBBB? If a patient has a LBBB it may be more difficult to diagnose an MI so there is an addition set of criteria to remember if your patient has a LBBB and you start noticing some ST segment changes.

Let me introduce you to Sgarbossa. Ms. Paula McDermott from Porter Adventist Hospital introduced me to him. He’s a pirate sailing high on the waves of the EKG…just kidding. I don’t really know who Sgarbossa is but the Sgarbossa criteria help us identify a STEMI in a patient with a LBBB.

The aim of this game is to stay lower than 3 points. How do you get points, you ask?

  1. ST elevation in >/= 1 mm in a lead with upward QRS complex –> You get 5 points!
  2. ST depression >/= 1 mm in lead V1, V2, or V3 –> You get 3 points!
  3. ST elevation >/= 5 mm in a lead with downward QRS complex –>  You get 2 points!

So…if your patient has 3 points or more, they will be most likely heading to the cath lab for some interventions.


Hopefully you were able to learn a little something from all this. I’ve had to review it a few times to understand this much. I was first introduced to this material by the ICU educator, Lee, at my previous employer and then Paula expounded on it in her 12-lead class. I must say I don’t feel too bad about having so much trouble understanding this (and you shouldn’t either) because one of the smartest and best cardiac nurses I knew told me she had taken Paula’s 12-lead class a few times to really understand it. All in all, if this helps you understand how to determine a LBBB from a RBBB, that’s great!

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