Hyperkalemia ECG Recognition

Why this matters

Most ambulances cannot measure a potassium level. Use the story instead: a dialysis patient who missed a session, a crushed leg, an ACE-inhibitor plus a potassium-sparing diuretic, or a wide, slow strip. An ACE-inhibitor is a blood-pressure drug. The strip can look like ventricular tachycardia (VT) and not be VT.

Hyperkalemia means high potassium. It is one of the reversible causes in arrest. The ECG can lag or mislead. No peaked T waves does not rule high potassium out. When the progression is there, treat the heart’s response to that potassium per protocol. Do not treat it as ordinary VT.

Clinical sequence

1. Look for that story before you name the rhythm.
2. If the progression is there, read it in order. Peaked T waves come first, then a flat P wave, then a wide QRS, then a sine wave.
3. If the tracing looks toxic, give calcium per protocol. Calcium protects the heart. It does not lower the potassium.
4. Do not treat a dialysis patient’s wide-complex “VT” with lidocaine or amiodarone first. See the wide-complex tachycardia lesson.

ECG Progression

• Tall, peaked, symmetric T waves are often the earliest clue.
• The PR gets longer. P waves flatten and then disappear.
• The QRS widens. Blocks appear. The rate slows. A sine-wave ventricular rhythm can follow, then VF, asystole, or PEA. VF means ventricular fibrillation. PEA means pulseless electrical activity.

On the paper, the T wave looks tall and peaked. That change can flatten the P wave and widen the QRS. Do not wait for a perfect textbook peaked T before you think of high potassium in the right patient.

Field treatment — not a dose list

• Calcium (gluconate or chloride, per protocol) protects the heart from high potassium. It does not lower the potassium number. Repeat it per protocol if the QRS stays wide. Watch the strip. A narrower QRS means it is working.
• Shift potassium into cells: use nebulized albuterol if your high-potassium protocol includes it. Insulin with glucose is a hospital treatment, or a written ALS protocol. Most ambulances do not mix insulin on scene.
• Stop adding potassium. You cannot provide dialysis in the field. Choose the hospital. Do not hang potassium-containing fluids in crush injury. See crush.
• Sodium bicarbonate is not a universal high-potassium drug. Follow protocol. It does not replace calcium when the QRS is a sine wave.

Arrest

Wide, slow PEA (pulseless electrical activity) in a dialysis or crush patient is high potassium until you have a better story. Do CPR, give calcium per protocol, and keep looking at the other reversible causes. Do not treat it as ordinary VT with an antiarrhythmic first. See wide-complex mimics and amiodarone and lidocaine.

Common errors

• Shocking a sine wave over and over without giving calcium.
• Calling peaked T waves a hyperacute STEMI without a territorial story. STEMI means an ST-elevation heart attack. Still transmit the 12-lead. Keep ACS in mind, and keep high potassium in mind. ACS means a heart-attack workup.
• Waiting for a hospital lab before you treat a sine-wave tracing.

Practice

Related: PEA, Albuterol, Crush Syndrome.

Sources & Further Study

Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.

• NASEMSO National Model EMS Clinical Guidelines (2022) — U.S. EMS model language; protocol still wins
• AHA 2025 Part 10: Special Circumstances of Resuscitation — hyperkalemia as a reversible cause
• LITFL Hyperkalaemia ECG library — teaching atlas for peaked T / wide QRS / sine-wave patterns (not a treatment guideline)
• Calcium for ECG toxicity; shifting agents per protocol. This site does not publish milligrams.