Missing P Wave on Electrocardiogram in Hypermagnesemia
Article ID: CJ-20-0460
Details
Article ID: CJ-20-0460
A 94-year-old Japanese man who had chronic kidney disease and hypertension presented with a 3-day history of diarrhea and fatigue. He was taking antihypertensive drugs and magnesium oxide (MgO) at 700 mg/day as a laxative; 6 days earlier, his dosage of MgO had been increased to 1,500 mg/day for constipation. On admission, his blood pressure was 102/60 mmHg; pulse rate, 44 beats/min. Laboratory examination revealed the following: creatinine, 3.64 mg/dL; potassium, 4.8 mEq/L; magnesium, 4.6 mg/dL. Electrocardiography (ECG) showed the absence of P waves and junctional rhythm (Figure A). Left bundle branch block was also observed and had been seen 3 months prior. We terminated MgO and administered extracellular fluid for 3 days. The diarrhea and fatigue improved. At 7 days after admission, the creatinine level decreased to 1.49 mg/dL and Mg to 2.4 mg/dL. His pulse rate elevated and P waves reappeared on ECG (Figure B).
ECG recordings showing (A) absence of P waves and junctional rhythm with left bundle branch block and (B) P waves with left bundle branch block after treatment.
Electrolyte imbalance causes varying abnormal ECG findings. In hypermagnesemia, these findings include sinus bradycardia, PR interval prolongation, prolonged QT interval, and atrioventricular block and have been reported when the serum Mg concentration is >7 mg/dL.1,2 In the present case, there was an absence of P waves on ECG at a lower concentration of Mg. Activation and opening of the calcium channel is related to depolarization of the sinus node. In hypermagnesemia, Mg acts as a calcium channel blocker,3 which might have led to the sinus dysfunction in this case.
The author declares no conflicts of interest. No funding was received for this study.
The Ethics Committee of Kobe City Medical Center General Hospital does not require ethical approval for case reports.
