What’s new with hyperkalemia: EKG changes

Today I did a lecture for the fellows on hyperkalemia. It is interesting that nearly none of the content I use to teach the residents and students is used in a lecture for the fellows. Same subject complete rewrite.

I plan on doing four posts on hyperkalemia from this lecture:

  1. EKG changes
  2. Dialysis patients and hyperkalema
  3. Digoxen toxicity and hyperkalemia
  4. Renal adaptation to ACEi and aldo antagonists in CKD

The lecture started off with the case I blogged about last week with the scary EKG and the potassium of 9.9.

I focused on a well done study (Full Text) by Drs Montague, Ouellette and Buller from Yale. They looked at 90 patients with a potassium grreater than 6 and an EKG done within an hour of the potassium. They excluded hemolyzed specimens and patients with cardiac pacing or other conditions which would mask EKG changes.

They graded all the EKGs according to a prospective criteria and recorded the cardiologists assessment.
The average patient was 73 years old (20-93) and half had acute kidney injury (55%) and half had chronic kidney disease (47%). They did not comment on the degree of overlap between those groups. Half the patients had diabetes (55%). Only 31% were on ACEi and 30% on loop diuretics.

The reading cardiologist documented peaked T waves in only 3 of 90 patients with hyperkalemia. The investigators were able to find peaked T waves in only 29. QRS widening was found in only 6 patients. Of the 52 patients who could have been classified as having “Strict Criteria” (you needed a second EKG after resolution of the hyperkalemia and not everyone in the cohort had a second EKG) only 16 actually met strict criteria.
The authors found EKG criteria to be insensitive predictors of hyperkalemia:

  • Sensitivity of strict criteria: 18%
  • Sensitivity of any EKG change 52%

Interestingly, they found that acidosis decreased the likelihood of finding peaked T-waves.

When they looked at arrhythmias as an outcome, EKG changes continued to be a poor clinical guide. They were not sensitive: only one of the patients who subsequently developed an arrhythmia or cardiac arrest had previously met the strict criteria for EKG changes and only 7 had any T-wave findings at all. This is important because it emphasizes the fact that you can not be reassured by a normal EKG in a patient with hyperkalemia.

The study was unable to look at specificity because all of the patients had hyperkalemia. An earlier study by Wrenn, Slovis and Slovis was able to look at sensitivity and specificity because they did have patients without hyperkalemia in their cohort. They retrospectively reviewed the EKGs of 220 patients with either renal failure (n=133) or hyperkalemia (n=87):

  • Sensitivity: 39%
  • Specificity: 85%

When they restricted the cohort to patients with a potassium over 6.5 the sensitivity rose to 58%.

Take home message: a normal EKG should not rule out hyperkalemia and should not decerase your concearn for impending arrhythmia.

Here is the lecture this post is based on:

6 Replies to “What’s new with hyperkalemia: EKG changes”

  1. i have this question about urine osmolality.
    In my hospital it is calculated by multiplying the last two digits of urine specific gravitiy by 33. But i have no found any source of these formula. Is the specific gravity a good substitute? Is there a formula?

  2. I am not aware of a formula and it is not a good substitute. Patients how have received contrast have very high specific gravities due to the density of the contrast. This does not affect the osmolality of the urine. Spec Grav is not a substitute.

  3. Is there a criteria for amplitude of T wave to be considered to be peaked T's? I haven't found any source for this. Seems to be subjective.

  4. In the article cited above the average 7 wave amplitude of an EKG marked as having peaked Ts was 7mm vs 3.5 for the EKGs not marked as having peaked Ts. Not a criteria but a guide. That was in lead V4.

  5. Is it so that in hyper-K it is more about narrow based, symmetrical TW… the normal height of TW in precordial leads is <15mm (and in limb leads <5mm)… my impression is it is more about the appearance of the TW… however in young, tall subjects

  6. Isn't it more about narrow based, tall symmetrical T waves in hyper-K? Technically normal TW are <15mm tall in precordial leads and <5mm in limb leads… but not uncommonly you can see less than 15mm TW that are peaked and narrow in the sting of hyper-K…

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