ECG Changes in Electrolyte Abnormalities

Electrolyte imbalances can profoundly affect the cardiac conduction system, leading to distinct patterns on an ECG. These changes are often the first clinical sign of life-threatening disturbances.

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1. Potassium

Potassium is the most critical electrolyte regarding ECG changes because of its role in repolarization.

Hyperkalemia

As levels rise, the ECG typically progresses through these stages:

• Mild: Tall, “peaked” T-waves (narrow base, symmetrical).
• Moderate: P-wave flattens and eventually disappears; PR interval prolongs.
• Severe: QRS widens, merging with the T-wave to form a “sine wave” pattern. This is a precursor to ventricular fibrillation or asystole.

Hypokalemia

• Flattened T-waves and ST-segment depression.
• Prominent U-waves (seen after the T-wave, best in V2–V3).
• Prolonged QU interval (often mistaken for a long QT).
• Increased risk of tachyarrhythmias like Torsades de Pointes.

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2. Calcium

Calcium primarily affects the duration of the ST segment rather than the morphology of the waves themselves.

Hypercalcemia

• Shortened QT interval.
• The ST segment is nearly absent; the T-wave begins almost immediately after the QRS complex.
• In severe cases, J-waves may occasionally appear. Though Osborn described the wave named after him in hypothermia, there is also a view that all J waves can be called Osborn waves.

Hypocalcemia

• Prolonged QT interval (specifically due to a lengthened ST segment).
• The T-wave itself remains normal in shape, but it is “pushed” further away from the QRS.
• Can predispose a patient to Torsades de Pointes.

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3. Magnesium

Magnesium abnormalities often coexist with potassium and calcium issues as it is the cofactor for the enzyme transporting those ions in the kidney.

• Hypomagnesemia: Commonly presents with a prolonged QT interval and flattened T-waves. Its most famous complication is Torsades de Pointes (polymorphic ventricular tachycardia).
• Hypermagnesemia: Rare (usually seen in renal failure). It causes bradycardia, PR prolongation, and QRS widening.

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