A 75 year old woman complained of very atypical chest pain, lasting days, worse with movement and palpation.
Here is her ECG (ECG-1):
|There is diffuse ST depression, very worrisome for ischemia.
The patient had a negative initial troponin, which was puzzling to the providers.
The patient was admitted and serial troponins were all below the level of detection.
She underwent a stress sestamibi that was completely normal.
She had another ECG the next day (ECG-2):
|Slightly slower sinus rhythm.
Now there is now only minimal, nonspecific, ST depression.
What do you think happened?
I was consulted on this ECG and I asked: “What is the K?”
The answer was 3.2 mEq/L, and I said “Well, that probably does not explain it.”
But the 2nd ECG normalized after K replacement to 3.9 mEq/L. And there is no other explanation.
A potassium of 3.2 mEq/L is usually not low enough to cause ECG abnormalities.
When there is a normal QRS (that is, no LBBB, LVH, WPW, RVH, LBBB, RBBB, pathologic Q-waves of old MI), then there are only 4 etiologies of ST depression that I know of:
4. Baseline, pre-existing (but it does not look like ECG-1 when it is benign, pre-existing STD)
The STD on ECG-1 almost certainly due to hypokalemia, and resolved with treatment of low K.
When do you need to admit a patient for hypokalemia?
That is really unknown. My rule of thumb is:
1. any K less than 2.8 (even though you are replacing it, because total body stores are very low) OR
2. any ECG abnormalities that are due to hypoK.