Hyperkalemia ECG changes: peaked T waves to sine wave
Hyperkalemia makes the T wave tall and peaked, then lengthens the PR interval, removes the P wave and widens the QRS. See the sequence and the nursing actions.
- First sign: tall, peaked T waves.
- Then: longer PR interval, lost P wave, wide QRS.
- Last: sine wave, ventricular fibrillation or asystole.
- IV calcium gluconate protects the heart. Insulin with glucose moves potassium into the cells.
Hyperkalemia first makes the T wave tall, narrow and peaked. As potassium climbs, the PR interval lengthens, the P wave disappears and the QRS widens until it merges into a sine wave, which leads to ventricular fibrillation or asystole.
Sources checked 6 October 2026.
The ECG changes in order
The Merck Manual describes the progression in three stages.
| Serum potassium | ECG change |
|---|---|
| Above 5.5 mmol/L | Tall, symmetric, peaked T waves appear first. The PR interval lengthens and the QT interval shortens. |
| Above 6.5 mmol/L | The QRS widens. The P wave disappears. Nodal and escape ventricular arrhythmias occur. |
| Higher still | The QRS degenerates into a sine wave. Ventricular fibrillation or asystole follows. |
Which potassium level counts as high
Many nursing references give the normal range as 3.5 to 5.0 mmol/L, and so does our potassium and the ECG lesson. The Merck Manual defines hyperkalemia as a level above 5.5 mmol/L. Laboratories differ a little, so use the range printed on the report and the one your course teaches.
The unit makes no difference here. For potassium, 1 mEq/L equals 1 mmol/L.
Who is at risk
- Clients with chronic kidney disease or acute kidney injury.
- Clients taking ACE inhibitors or potassium-sparing diuretics.
- Clients with advanced heart failure or a urinary obstruction.
- Clients with metabolic acidosis, such as diabetic ketoacidosis.
Hyperkalemia usually causes no symptoms until an arrhythmia develops. Muscle weakness can occur.
Rule out a false high result
A hemolysed blood sample is the most common cause of a falsely high potassium. A tourniquet left on too long or repeated fist clenching during the draw can do it too. Suspect a false result when the client has no risk factors and a normal ECG, and expect a repeat sample.
What the nurse does
- Get a 12-lead ECG and put the client on a cardiac monitor.
- Stop every source of potassium: supplements, potassium in IV fluids and salt substitutes.
- Report the result and the ECG to the provider at once.
- Review the medication list for drugs that raise potassium.
Emergency treatment the nurse should expect
These are the Merck Manual's treatments for moderate or severe hyperkalemia. The provider prescribes them. Your facility's protocol sets the doses.
| Treatment | What it does | What to know |
|---|---|---|
| IV calcium gluconate | Protects the heart | 10 to 20 mL of a 10% solution over 5 to 10 minutes. It works within minutes and lasts only 20 to 30 minutes. |
| IV regular insulin with glucose | Moves potassium into the cells | 5 to 10 units of insulin, followed at once by 50 mL of 50% glucose. The effect peaks at about one hour. Watch for hypoglycemia. |
| Inhaled salbutamol (albuterol) | Moves potassium into the cells | 10 to 20 mg inhaled over 10 minutes. |
| Hemodialysis | Removes potassium from the body | Started promptly when emergency treatment does not work. |
For mild hyperkalemia, a potassium binder such as sodium polystyrene sulfonate, patiromer or sodium zirconium cyclosilicate may be used.
High and low potassium compared
| Finding | Hyperkalemia | Hypokalemia |
|---|---|---|
| T wave | Tall and peaked | Flat or small |
| Other changes | Longer PR interval, lost P wave, wide QRS | Sagging ST segment, U wave after the T wave |
| End stage | Sine wave, then ventricular fibrillation or asystole | Ventricular fibrillation |
See hypokalemia ECG changes for the low side, and potassium and the ECG for why potassium moves the T wave at all.
These changes are easier to remember once you have watched them happen. Medibara's lesson on potassium and the ECG is a short video that shows the trace as potassium rises: the T wave peaks, the P wave fades and the QRS spreads wide. It ends with what the nurse does. You can play it in the demo on the Medibara home page. In the app, questions in your exam's format follow the lesson, and Ask Cappy explains any rationale you are unsure of. Start learning on Medibara.