Hyperkalemia ECG changes (progressive with rising serum K⁺)

Mild hyperkalemia (≈ 5.5–6.5 mmol/L)

• Tall, narrow, peaked T waves (“tented” T)

• Shortened QT interval

• ST segment may appear flattened or absent

Moderate hyperkalemia (≈ 6.5–7.5 mmol/L)

• Progressive PR prolongation

• P wave flattening → low amplitude P

• Widening of QRS complex

• Bradycardia may appear

Severe hyperkalemia (≥ 7.5 mmol/L)

• Disappearance of P waves

• Markedly wide QRS

• Sine-wave pattern (fusion of QRS and T)

• Ventricular arrhythmias: VT, VF

• Asystole / cardiac arrest

Key electrophysiologic concept

• Hyperkalemia reduces resting membrane potential → slows atrial, AV nodal, and ventricular conduction

• Atrial myocardium is affected earlier than ventricular myocardium (early P-wave loss)

Clinical pearls

• ECG changes may not correlate perfectly with serum K⁺ level

• Rapidly rising potassium is more dangerous than chronic elevation

• Any ECG change = medical emergency → treat immediately, do not wait for lab confirmation

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