I know I should know this, but what leads do I look for the “turn signal” trick in BBB in a 12-lead?  I have tried looking up the “bunny ear” and “turn signal trick” on the internet and can’t seem to figure it out.  And turning which way makes it a right or left?

jer5150's picture


The answer to your first question is:  The only lead you can use to look for this clue on a 12-lead ECG is in precordial (i.e., chest) lead V1.  You can not apply this rule to any of the other 11 leads on the electrocardiogram.  The paramedic who is historically credited with coining this term was Mike Taigman, et al.  In his textbook, Taigman cited a former student of his (Willard Crary) as the inspiration for creating this clue.  Taigman originally called it "The Turn Signal Theory" but a different author named Tim Phalen published it in his textbook as "The Turn Signal Method".  Others have referred to it as "The Turn Signal Rule", "Sign", "Clue", etc.

Using descriptors like "bunny-ears", "rabbit-ears", "peaks", or "notches" are generally unreliable because they do not always manifest themselves in all examples of BBB and most healthcare providers generally don't know how to use them correctly since they were not trained on which leads to observe them in.  The term "rabbit-ears" was first described by ICU nurses in the 1960s that worked with the late Dr. Henry J. L. Marriott.  This is the original research paper/article of the (now famous) "rabbit-ears":  Gozensky C and Thorne D. Rabbit ears: an aid in distinguishing ventricular ectopy from aberration. Heart Lung 1974 Jul-Aug; 3(4) 634-6. pmid:4495389. PubMed.  Definitely worth reading if you can find a copy online.

To answer your second question, flipping the turn signal up makes it RBBB, and flipping it down makes it LBBB which corresponds with the direction you flip the turn signal on your car's steering wheel if you want to make a Right or Left turn.

I won't do the subject any justice if I try to explain the "Turn Signal" by using written words alone since you really need to see images to get the big picture.  Instead, I'll just refer you to this document I found in a Google search.
Download the following Adobe PDF to see a visual explanation:  http://www.similima.com/ppt/ecg/12lead-ecg-blocks.pdf .  You can also go to this website to see a picture of the actual steering wheel minus its turn signal:  http://medic2010.webs.com/bundlebranchblocks.htm

Both of the references I've listed below are worthy of adding to one's medical library!  I highly recommend both of them, especially if you're a paramedic yourself.  With a little practice, you'll find yourself not even needing tricks like this to spot RBBB and LBBB in the future but they do help add your "interpretive-eye" early on when you're trying to learn the basics.

References / Sources
1.)  Taigman, M., Canan, S., Miller, C. Taigman’s Advanced Cardiology (In Plain English). Englewood Cliffs: Brady, 1995, p. 55-57
2.)  Phalen, T. The 12-lead ECG – In Acute Myocardial Infarction. St. Louis: Mosby, 1996, p. 86-87

Jason E. Roediger - Certified Cardiographic Technician (CCT)
[email protected]

Dawn's picture

To make it a little easier to follow this discussion, click on these links to view a NORMAL ECG, a LEFT BUNDLE BRANCH BLOCK, and a RIGHT BUNDLE BRANCH BLOCK.

Dawn Altman, Admin

jamie_bisson's picture

I like to make things simple....

If you remember the words "MaRRoW" and "WiLLiaM" you will be half way there.

If you see an M in V1 and a W in V6 with a QRS greater than 0.12 seconds (3 small squares) then you have a right bundle branch block.

If you see a W in V1 and an M in V6 with a QRS greater than 0.12 seconds (3 small squares) then you have a left bundle branch block.

Hope this helps.

jamie_bisson's picture

Ok, this may be a bit too simplistic, but the M and W are generally in the 1st and 6th chest lead respectively in right bundle branch block and W and M in 1st and 6th chest lead respectively in left bundle branch block. Sometimes you may see a W shape in V3 and a M in V6, which would still be a LBBB, what is important here is the width of the QRS and the general wave deflections. A lot will depend upon chest lead placement.

To be more accurate you should look for QS or rS in V1 and a RsR in V6 for a LBBB and an rSR in V1 and qRS in V6 for a RBBB.



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