how wide is your differential

I expected last week’s lead placement imbroglio to be a tough EKG, this one proved harder than I anticipated.


As always, first things first, what’s the Rate?  It’s immediately recognizable as being fast, easily less than 2 big boxes wide, likely in the 180 range.  Another useful trick with EKG’s this fast is to count the complexes and multiply by 6.  The EKG records 10 seconds of information (and if you can’t remember that bit of trivia at the bottom of every EKG it will say 4 x 2.5 seconds, meaning that each of the 4 sections of the EKG is 2.5 seconds long).  In this case there’s 29 complexes, multiply that by 6 and you’ll get a number just under 180 so our estimation was actually pretty accurate.

On to rhythm.  Just having the rate of 180 narrows the differential.  A sinus rate of 180 in an adult (much less an octogenarian!) would be very unusual.  It appears to be very regular which make Afib much less likely (though 2:1 flutter is still very possible).  SVT is still possible.  A frequent next step to evaluate a tachycardia would be asking is it narrow or wide.  Zooming in on the chest leads in V1 and V2 is what I think led a lot of people astray on this EKG:


Indeed the QRS is about 3 little boxes wide and so does meet criteria for a wide complex tachycardia.  A rate of 180 is certainly reasonable for V tach; that’s not what this EKG shows however.  Remember there are many causes of wide complex QRS.  If you look at V1 you can see there’s a millimeter of STE; what is a commonly encountered non-acute cause of mild elevation of the J point in the setting of a wide complex QRS?  Left bundle branch block.  If the (85 y.o.) patient has a baseline wide complex QRS then EVERY time they are tachycardic they, by definition, will have a wide complex tachycardia.  That doesn’t mean they need to be shocked out of V tach every single time their heart rate blips over 100 because maybe they didn’t drink enough prune juice that day.

You’ll notice that even in the V1 and V2 leads where it looks particularly wide that the tracing is still coming back to baseline between the complexes.  This is more apparent in the rhythm strip in II and V5:


That isn’t V tach.  So we’re back to SVT or A flutter.  There are certainly times (and this EKG is one of them) where it’s going to be very difficult to definitively discriminate between these two;  we do a lot of trials of adenosine that will fix the former or unequivocally demonstrate the latter.  In this case adenosine revealed the flutter waves (apologies, I don’t have that strip).  Atrial flutter would likely be a lot more likely than SVT in an 85 y.o. in any case.  In retrospect a person can argue that there’s flutter waves in the lead II rhythm strip as well as in III (the best lead to usually see flutter waves):


Completing our review of the EKG, the patient does have some lateral (probably rate-related) STD in V5 and V6.

The take-home on this EKG is that baseline LBBB will cause a wide complex tachycardia any time a patient is tachycardic; don’t just jump to V tach because it’s wide.


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