I was reading EKGs on the system and came across this one. Among the chaotic waves, what stands out?

 I was reading EKGs on the system and came across this one.  What is it?

It looks confusing, right?  Like there are just too many waves?  

Among all the noise, can you make out the essential feature(s)?  

See Ken Grauer's complete analysis below.

There are massive U-waves, which I point out with arrows here:

I went to the chart to see what the K level was; it was 2.6 mEq/L.  Such relatively mild hypokalemia does not commonly produce U waves of this size, but it certainly can.

There is no follow up ECG after correction of K.

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MY Comment by KEN GRAUER, MD (3/18/2022):

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As per Dr. Smith — the ECG in today's case manifests the "telltale" finding of massive U waves that indicates Hypokalemia until you prove otherwise. I found today's ECG interesting, in that it also manifests a number of additional interesting findings. 

• Thy rhythm is sinus tachycardia at ~110/minute (raising the question of the cause of the fast rate?).
• As per Dr. Smith — there are just "too many waves". The extra "notching" in the ST segment of the inferior leads (and to a lesser extent in other leads) is bizarre. This is not due to an extra hidden P wave — because the peak-to-peak interval between pointed deflections is not equal (as it should be if there was 2:1 block). Instead, these bizarre extra peaks appear to be artifact caused by a problem in the left foot (since artifact deflections are largest in leads II, III and aVF — and virtually absent in lead I).
• There is significantly increased QRS amplitude, consistent with LVH (ie, R≥20 in any inferior lead — and also deep enough S waves in V3,V4 to satisfy both Cornell and Peguero Criteria [See My Comment in the June 20, 2020 post of Dr. Smith's ECG Blog]).
• There is RAA (Right Atrial Abnormality) — as suggested by tall, peaked and pointed P waves in inferior leads — which together with slight right axis deviation (more negative than positive QRS in lead I) is consistent with RVH. (Alternatively, for reasons I've never been able to explain — RAA is sometimes seen with hypokalemia).
• Evidence for 3-chamber enlargement on ECG (LVH, RAA — possible RVH) suggests that there may be a cardiomyopathy.
• In addition to the huge U waves in today's case — there are diffuse ST-T wave changes (ie, flattening and depression). This finding is of course consistent with hypokalemia — but tachycardia and LVH may also be contributing to these ST-T wave changes.

We've commented many times on "the Many Faces" of Hypokalemia in Dr. Smith's ECG Blog (the May 9, 2020 post — and the May 3, 2020 post, to name just 2). By way of review — I'll add 2 PEARLS and the summarizing chart in Figure-1 below, from that May 9, 2020 post.

• If U waves are so large that they become bigger than the T waves that precede them (as is seen in multiple leads for today's tracing) — the ECG becomes much more reliable for predicting significant hypokalemia (Panels E and F in Figure-1 below).
• In my experience — Hypomagnesemia produces virtually identical ECG changes as hypokalemia. This is important — because serum Mg++ levels are not necessarily included in chem profiles unless specifically ordered. (If serum Mg++ in today's case was also low — this could be contributing to the very large U wave size).

Figure-3: Sequential development of ST-T wave changes of hypokalemia. Note increasing U wave amplitude (Full discussion in the May 9, 2020 post).