Authors: Katholi Richard E, Ervin Marcella R.
Although magnesium is mainly an intracellular cation, magnesium in the extracellular space is an important mechanism by which this cation exerts its effects on the electrical system of the heart. This is an important concept for two reasons: 1) a serum magnesium level reflects extracellular magnesium and is a sensitive indicator to determine whether magnesium is affecting cardiac rhythms, and 2) because rapid changes in serum magnesium may occur in clinical situations independent of total body magnesium resulting in important arrhythmias. Hypomagnesemia depolarizes heart cells resulting in both supraventricular and ventricular tachyarrhythmias. Keeping serum magnesium levels greater than 2 milliequivalents per liter is recommended. In contrast, hypermagnesemia hyperpolarizes heart cells suppressing atrial and ventricular arrhythmias.
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