Hypermagnesemia and ECG Changes

Introduction

Hypermagnesemia is a condition characterized by an abnormally high level of magnesium in the blood, typically above 2.5 mEq/L. It is relatively uncommon but can have significant effects on the cardiovascular system, including ECG (electrocardiogram) abnormalities.

Causes of Hypermagnesemia

• Renal failure – The most common cause due to the inability to excrete magnesium.
• Excessive magnesium intake – Often from antacids, laxatives, or intravenous administration.
• Endocrine disorders – Such as Addison’s disease or hypothyroidism.
• Tissue breakdown – Including rhabdomyolysis and tumor lysis syndrome.

ECG Changes in Hypermagnesemia

Magnesium plays a crucial role in cardiac electrophysiology. When magnesium levels rise significantly (>4.0 mEq/L), the following ECG changes can occur:

Early Stage (Mild Hypermagnesemia 2.5–4.0 mEq/L):

• Prolonged PR interval – Due to slowed atrioventricular (AV) conduction.
• Widened QRS complex – Magnesium affects sodium and potassium channels, slowing depolarization.

Moderate to Severe Hypermagnesemia (>4.0 mEq/L):

• Further Widening of the QRS complex – Leading to decreased heart contractility.
• Peaked T waves – Similar to hyperkalemia but often less pronounced.
• QT interval prolongation – Risk of arrhythmias.

Critical Hypermagnesemia (>7.0 mEq/L):

• Severe heart block – Including complete AV block.
• Asystole/Cardiac arrest – If left untreated, high magnesium can suppress cardiac activity entirely.

Treatment of Hypermagnesemia

• Mild cases: Discontinuation of magnesium-containing medications.
• Moderate to severe cases:
  • IV calcium gluconate – To counteract the cardiac effects.
  • Diuretics (if renal function is normal) – Such as loop diuretics to enhance excretion.
  • Dialysis – In cases of severe renal failure.

Conclusion

Hypermagnesemia is a rare but potentially life-threatening electrolyte disturbance. Its ECG manifestations progress from prolonged conduction intervals to complete heart block and cardiac arrest. Early recognition and treatment are crucial to prevent fatal outcomes.

Source recommendations

1. American Heart Association Guidelines on Electrolyte Abnormalities

1. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.105.166563
2. https://www.heart.org/en/news/2024/02/26/how-eating-disorders-can-damage-the-heart
3. https://www.ahajournals.org/doi/abs/10.1161/CIRCULATIONAHA.105.166563
4. https://www.heart.org/en/news/2024/06/19/electrolytes-can-give-the-body-a-charge-but-try-not-to-overdo-it
5. https://pubmed.ncbi.nlm.nih.gov/10966675/

2. European Society of Cardiology Guidelines on Cardiac Arrhythmias

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death
2. https://academic.oup.com/eurheartj/article/43/40/3997/6675633
3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Supraventricular-Tachycardia
4. https://pubmed.ncbi.nlm.nih.gov/36017572/
5. https://www.ahajournals.org/doi/10.1161/01.cir.0000091380.04100.84