Hyperkalaemia is defined as a serum potassium level of > 5.2 mmol/L. ECG changes generally do not manifest until there is a moderate degree of hyperkalaemia (≥ 6.0 mmol/L). The earliest manifestation of hyperkalaemia is an increase in T wave amplitude.

ECG features of hyperkalaemia
  • Peaked T waves
  • P wave widening/flattening, PR prolongation
  • Bradyarrhythmias: sinus bradycardia, high-grade AV block with slow junctional and ventricular escape rhythms, slow AF
  • Conduction blocks (bundle branch block, fascicular blocks)
  • QRS widening with bizarre QRS morphology

With worsening hyperkalaemia… (> 9.0 mmol/L):

  • Development of sine wave appearance (pre-terminal rhythm)
  • Ventricular fibrillation
  • PEA with bizarre, wide complex rhythm
  • Asystole

Note: Serum potassium level may not correlate closely with ECG changes. Patients with a relatively normal ECG can suffer sudden hyperkalaemia cardiac arrest. In any patient who has suffered a bradycardia PEA arrest, suspect and treat for hyperkalaemia.

Click to expand: ECG changes of hyperkalaemia

An easy way to remember the usual order of ECG changes seen is by following the ECG trace logically – effects begin on the T wave and move forwards to the P wave / PR interval, and subsequently to the QRS complex with QRS widening and conduction blocks.

The push-pull effect
  • Hypokalaemia creates the illusion that the T wave is “pushed down”, with resultant T-wave flattening/inversion, ST depression, and prominent U waves
  • In hyperkalaemia, the T wave is “pulled upwards”, creating tall “tented” T waves, and stretching the remainder of the ECG to cause P wave flattening, PR prolongation, and QRS widening


Potassium is vital for regulating the normal electrical activity of the heart. Increased extracellular potassium reduces myocardial excitability, with depression of both pacemaking and conducting tissues.

Progressively worsening hyperkalaemia leads to suppression of impulse generation by the SA node and reduced conduction by the AV node and His-Purkinje system, resulting in bradycardia and conduction blocks and ultimately cardiac arrest.

Degree of hyperkalaemiaPotassium level (mmol/L)
Mild5.3 – 6.0
Moderate6.0 – 6.9
Severe≥ 7.0
Classification of severity of hyperkalaemia

Handy Tips

Suspect hyperkalaemia in any patient with a new bradyarrhythmia or AV block, especially patients with renal failure, on haemodialysis, or taking any combination of ACE inhibitors, potassium-sparing diuretics and potassium supplements.

For an excellent review of the management of hyperkalaemia, check out this podcast by Scott Weingart.

ECG Examples
Example 1
ECG Hyperkalemia serum potassium 9.3

This ECG displays many of the features of hyperkalaemia:

  • Prolonged PR interval.
  • Broad, bizarre QRS complexes — these merge with both the preceding P wave and subsequent T wave.
  • Peaked T waves.

This patient had a serum K+ of 9.3

Example 2
ECG Hyperkalaemia peaked T waves serum potassium 7.0


  • Tall, symmetrically peaked T waves.

This patient had a serum K+ of 7.0.

Example 3
ECG Hyperkalemia prolonged PR bizarre QRS complexes


  • Long PR segment.
  • Wide, bizarre QRS.

Example 4
ECG Hyperkalemia junctional bradycardia potassium 8


  • Slow junctional rhythm.
  • Intraventricular conduction delay.
  • Peaked T waves.

Example 5
ECG Hyperkalemia broad QRS


  • Broad complex rhythm with atypical LBBB morphology.
  • Left axis deviation.
  • Absent P waves.

Example 6
ECG Hyperkalemia sine wave serum potassium 9.9


  • Sine wave appearance with severe hyperkalaemia (K+ 9.9 mEq/L).

Example 7
ECG Hyperkalemia rhabdomyolysis


  • Huge peaked T waves.
  • Sine wave appearance.

This patient had severe hyperkalaemia (K+ 9.0 mEq/L) secondary to rhabdomyolysis.

Advanced Reading



LITFL Further Reading



MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |


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