ECG Pointers: Hyperkalemia or Toddler Squiggles?

Authors: Lloyd Tannenbaum, MD (EM Attending Physician, Geisinger Wyoming Valley, PA); Mai Saber, DO (EM Attending Physician, Hackensack University Medical Center, NJ); Rachel Bridwell, MD (EM Attending Physician, Charlotte, NC) // Reviewer: Brit Long, MD (@long_brit)

Hello and welcome back to ECG Pointers, a series designed to make you more confident in your ECG interpretations.  This week, we feature a post from Dr. Tannenbaum’s ECG Teaching Cases, a free ECG resource. Please check it out. Without further ado, let’s look at some ECGs!

Take a look at this ECG.  Before we get too far, I promise, this is an ECG from a human, not my toddler drawing squiggles on ECG paper:

Yikes.  Not good right?  Let’s take a look:

Rate: 110-115

Rhythm: Definitely not normal sinus

Axis: Bad.  Unlikely clinically relevant.

Intervals: Extremely wide QRS complexes.  No obvious P waves, no PR interval

Morphology:  Well, I doubt any of us would look at this and say, “Normal.. good to go home.”

Final read: This is a VERY VERY wide complex tachycardia.  This patient is likely in extreme distress and hopefully you are bedside right now fixing him!

But what causes this?  Does this ECG give us any clues to the underlying pathology?  Well… Yes!

Last week we talked about wide complex tachycardias leading us to two large buckets of pathology: Toxicology and Electrolytes.  We hit tox last week (don’t do 3 grams of cocaine…).  This time, we’re going to jump into the electrolyte bucket, specifically hyperkalemia.  Let’s take a look at the changes that high potassium can cause on an ECG!

***Remember, before we get started, potassium does not follow a textbook when it comes to causing changes to an ECG, so these levels are just guidelines.  There will be some dialysis patients who aren’t phased at all by a potassium of 7.6 mEq/L, but a young, fit athlete who goes into rhabdo may have severe complications from a potassium of 6.8 mEq/L.  Stay sharp out there!***

Ok, so let’s say your potassium starts to go up, what’s going to happen to your ECG?  Well, the first change you see is in the T wave.  Hyperkalemia shortens the action potential duration, which leads to the narrowing and peaking of the T wave.  A friend sent me this ECG, take a look:

Doesn’t look great, but doesn’t look terrible, right?  Here’s what I saw:

Rate: 70 ish bpm

Rhythm: Normal sinus

Axis: Normal axis (QRS complexes up in I and aVF)

Intervals: Narrow QRS complexes, normal PR interval, normal QTc

Morphology: The T waves are very sharp and peaked!

Final read: This ECG is consistent with early hyperkalemia.  The T waves are peaked.  Classically, peaked T waves show up around a potassium of 5.5 – 6 mEq/L. Take a look at this close up of V2 below to really zoom in on the T wave morphology:

Ok, let’s say you missed it and the patient’s potassium keeps going up?  Maybe he’s just sitting in the ER eating bananas.  What happens next?  The atria paralyze.  Let’s take a look at another ECG which will show you what happens as the hyperkalemia worsens:

Let’s just jump to the conclusion of this ECG.  The T waves are still sharp and peaked and we’ve lost atrial activity (no P waves).  Classically we start to lose atrial activity with a K around 6.5 – 7 mEq/L.  I’m going to zoom in on V2 again so you can keep comparing the same area on the ECG to really cement the changes in your mind:

As the potassium continues to climb, finally, notice that the QRS complex starts to stretch out wider and wider.  Take a look at this ECG below:

Classically, we see the QRS stretch out when the potassium is greater than 7 mEq/L.  Same plan with this ECG, let’s zoom in on V2 and really take a look at the morphology:

As the potassium continues to rise, now the patient is peri-arrest.  Take a look again at the first ECG at the top of this post (the one that looks like my toddler drew it).  This ECG would be concerning for severe hyperkalemia, with a potassium likely over 8.7 mEq/L.  Now, look at the zoomed in V2:

Ok, let’s wrap up by putting it all together and really engrave these changes in your memory.  The figure below is a compilation of all the changes we’ve seen V2 go through:

Looking down at this figure from top to bottom you can see how V2 changes morphology as the potassium climbs higher and higher.  Notice the prominent peaking of the T waves initially, then the loss of the p waves as the atria paralyze.  Next, notice the QRS start to stretch out, followed by the extreme widening of the QRS consistent with the “sine wave pattern.”

Finally, remember, the potassium values above are just guidelines; potassium can do wild things to an ECG.  Keep these patterns fresh in your brain, you’ll definitely see them in the ER!

For extra bonus science, Figure 2 found on page 90 of this article below maps out the effects of potassium on the ECG tracing. Warning, it may give you med school flashbacks, but it’s very well done.

Extra bonus science article:

• Gupta AA, Self M, Mueller M, Wardi G, Tainter C. Dispelling myths and misconceptions about the treatment of acute hyperkalemia. Am J Emerg Med. 2022 Feb;52:85-91. doi: 10.1016/j.ajem.2021.11.030. Epub 2021 Nov 27. PMID: 34890894.

For more amazing ECGs, please check out Dr. Tannenbaum’s ECG Teaching Cases