Last updated 9/12/24
Learning Objectives
- Recognize common ECG findings of hypo and hyperkalemia
- Understand how reliable an ECG is for identifying underlying potassium electrolyte abnormalities
- Know which ECG findings warrant treatment, and apply this knowledge to modify how quickly you treat
Hypokalemia
ECG Characteristics
Expected findings with hypokalemia
- Expect to see some ECG changes above in 40% of patients with potassium of < 3.5 mmol
- Increases to 75% when potassium is < 2.5 mmol/L
Practice (7 ECGs)
Identify ECG findings that may suggest hypokalemia
What does this mean for the patient in front of me? Can I just replete the K and have the patient follow up outpatient?
The issue is that patients with significant hypokalemia (generally < 2.5 mmol/L) are at increased risk for life threatening arrhythmias likely ventricular tachycardia, torsade de pointes, and ventricular fibrillation…or so we’ve been told. If you follow the paper trail back to the referenced trials for this data, one study does not include any data, and the other does not site any paper claiming that severe hypokalemia can increase the incidence of cardiac arrhythmias.
Data seems to support an increased risk of hypokalemia and supraventricular arrhythmias, but this hasn’t demonstrated any increased risk of mortality in the average patient. Data also supports the increased risk of cardiac arrest in patients with MI, but most of our patients with hypokalemia are clearly not having an MI. So what is the real risk then?
We may overestimate a patient’s risk of malignant dysrhythmias from hypokalemia.
A 2024 multicenter cohort study of 79,599 patients in Denmark and Sweden that compared patients with eukalemia (3.5-4.4 mmol/L) to those with hypokalemia (<3.5 mmol/L) found that, after adjusting for confounders, only a heart rate > 100 was associated with increased 7-day mortality and admission to the ICU (specifically if < 3.0 mmol/L).
Hyperkalemia
Hyperkalemia decreases the resting membrane potential of cardiac myocytes, leading to slowed phase 0 of the action potential, which prolongs the PR, QRS, and QT intervals
ECG Characteristics
ECG Characteristics - Emergent
Practice (7 ECGs)
Identify ECG findings that may suggest hypokalemia
Caveats
Serum Potassium does not always correlate with “expected” ECG findings
- Unfortunately, there is no reliable progression of ECG changes for hyperkalemia
- A normal ECG does not rule out hyperK, especially in patients with ESRD who likely live at higher potassium levels. Other findings like LVH, intraventricular conduction defect, and ischemia can mask these findings as well
When should I give calcium?
- Though we often reflexively treat ECGs with isolated peaked T waves with Calcium, it is really features such as wide QRS, severe bradycardia, PR prolongation, and 2nd/3rd degree heart blocks that are truly at higher risk.
See a bizarre wide complex QRS —> Consider hyperK
- Severe hyperK can cause both ACS (ST elevations as above) and Brugada mimics (see above)
Practice (10 ECGs)
After completion
This post is for education and not medical advice.