EKG

separating the Highs and the Lows

Trust.  So many things in life are about trust.  Who do we rely on and what assumptions do we base those assessments upon.  How much stock do you put in what a given person tells you?  I read an article once that said that people evaluate 3 things when they’re deciding how much credence to give to a statement.  The most important thing is how a thing is said, in other words, ‘It’s not what you say, it’s how you say it.’  The next, for better (or often for worse) is Do you look like a person who should be giving the advice that you’re giving.  (So residents, my advice to you is Wear Your Whitecoat.).  The third thing (and only when you get to 3rd) is the actual content of the statement.

This concept is going to apply to this week’s (and next week’s) EKG.

20180212_
60’s y.o. woman with weakness like when her potassium was low

Let’s start with the vignette.  I think I ask at least 95% of patients if they’ve felt their current symptoms before.  When they say yes and can give an explanation you’re generally well on your way to a diagnosis.  Generally.  So let’s see if Hypokalemia makes sense for the above EKG.

Rate appears to be in the low 40’s or high 30’s.  It’s a little irregular.  If you count the T wave that just makes it into the frame on the left side of the EKG as a beat then there’s 7 complexes, multiply by 6 and you get 42.  If you don’t count that one then you get less.

Looking at the rhythm, I see one definite P wave.

20180212_a.jpg

That’s the only definite one, and noticeably this is the shortest R-R interval.  Also of interest is that the QRS which follows it is identical to the other QRS’s.  That may imply that the P wave just happens to fall in a location with a normal PR interval and that the beat doesn’t actually transmit.  Given that the RR interval is the shortest I would argue that the P wave does transmit the QRS and that all the QRS’s are equally either supraventricular or junctional in origin.

There may be one non-conducting P wave earlier in the EKG.

20180212_b

This is probably mostly a junctional escape rhythm (the P wave beat aside).  I would expect a ventricular rhythm to have a wider QRS in the beats lacking the P wave.  For the most part the R-R interval is about 8 big boxes without a ton of variability.  A Fib with complete heart block would look pretty similar depending on how much irregularity you’re looking for.  In any case there’s a pretty significant block present.

QRS is up in I and down in aVF so Left Axis.  Going along with the L axis, the QRS is mildly widened, probably about 2.5 little boxes.  T waves are very symmetric, fairly prominent and mildly peaked.

So we have basically absent P waves, a slightly wide QRS, and peaked T waves.  That sounds kind of like the opposite of the patient’s assessment of hypokalemia.  Indeed her potassium was nearly 9, clearly she’d simply reversed “High” and “Low” in her mind, hyperkalemia is her actual problem.  For those of you who wanted to float a pacer right away, full marks for a proper EM resident mindset, but always ask yourself if any weird bradycardia could be hyperkalemia and so be fixable a little less invasively.

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