History of Present Illness: A woman in her mid 70’s with a history of HTN on unknown meds is sent to the ER for low potassium.  She denies any symptoms

Vital Signs & Physical Exam: Vital signs are normal.   Physical exam is normal with clear lungs, no splinting and no murmur.  She is short and thin

An ECG is done:

Computer Read: NSR at 69 with short PR, low QRS voltage, 

What is the most likely cause of ECG findings in this patient?

  • A) ACS
  • B) Hypokalemia
  • C) PE
  • D) Drug effect
  • E) None of the above

SCROLL DOWN FOR ANSWERS & 1-MINUTE CONSULT

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ANSWER:

  • A) ACS
  • B) Hypokalemia
  • C) PE
  • D) Drug effect
  • E) None of the above – CORRECT – K was 6.3 and Cr 1.9 and bicarb 17

My Read: There is ST depression in the inferior and lateral leads with maybe a touch of ST elevation in V1-V2, thought that might be normal (would be nice to compare to a prior ECG).  I was handed this ECG from triage and was initially worried about ischemia due to the ST depression in multiple leads.

CASE CONCLUSION: After being handed the ECG I then read the triage not and it said patient had no symptoms but was sent in for low potassium from blood drawn yesterday at the PCP office.  I then went to see the patient.  I had a little confirmation bias and overconfidence, knowing hypokalemia could cause ST depression.  I actually ordered potassium before the labs came back with a potassium of 6.2.  I had forgotten that hyperkalemia can also cause ST depression.  Looking at the morphology of the ST depression and T wave a second time I realized they are both more consistent with hyperkalemia and not the typical scooped out ST depression of hypokalemia.  Fortunately the nurses had not give the potassium and I was able to cancel it.  She was on HCTZ which is famous for dropping K but was also on losartan and spironolactone, both of which can increase K.  Here creatinine had risen from 0.8 to 1.5 as well, likely contributing

Case lessons:

  1. Thought it may be safer to treat electrolyte issues suggested by the ECG without lab confirmation, especially if the patient has been fainting or is symptomatic or ECG changes are severe, consider waiting for labs if the patient has been asymptomatic.  Venous blood gas can give quicker results.
  2. ST depression and QT prolongation can both be caused by either high or low potassium.  With high potassium the ST depression is usually flat and the QT prolongation is due to a long ST segment.  With hypokalemia the ST depression is usually scoopy and the QT prolongation is due to a U wave to TU fusion.  These look different so pay attention and do as I say not as I did.