Significance of hypomagnesemia in cardiovascular disease
- Buddhadeb Dawn, MD
Buddhadeb Dawn, MD
- Maureen and Marvin Dunn Professor
- University of Kansas Medical Center
- Alan S L Yu, MB, BChir
Alan S L Yu, MB, BChir
- Harry Statland and Solon Summerfield Professor of Medicine
- University of Kansas Medical Center
Mild hypomagnesemia is a common electrolyte abnormality , particularly in the elderly who may have increased urinary magnesium losses due to diuretic therapy or interstitial renal disease. Whether this abnormality should be treated or prevented with prophylactic magnesium administration is unclear. The major concern is whether mild magnesium depletion predisposes to cardiac arrhythmias [2,3]. There are conflicting data as to whether this occurs in otherwise healthy subjects. A report on over 3000 patients from the Framingham Heart Study suggests that how arrhythmia is defined is an important determinant . No association with hypomagnesemia was noted for more than 10 ventricular premature complexes (VPCs) per hour or for repetitive VPCs. There was, however, an increased risk of complex or frequent (≥30/hour) VPCs with reductions in the plasma magnesium concentration of 0.16 meq/L (0.2 mg/dL or 0.08 mmol/L) or more. The formulas to convert between these units can be found elsewhere. (See "Regulation of magnesium balance".)
Thus, attempts have been made to identify those patients who might be at risk. The data suggest that this might occur when hypomagnesemia occurs in the setting of an acute ischemic event, congestive heart failure, torsades de pointes, after cardiopulmonary bypass, or in the acutely ill patient in the intensive care unit.
The mechanisms underlying the possible association between hypomagnesemia and arrhythmias are at present unknown. Arrhythmias could be due to concurrent hypokalemia, hypomagnesemia itself, or both [2,3]. Magnesium regulates several cardiac ion channels, including the calcium channel and outward potassium currents through the delayed rectifier . Lowering the cytosolic magnesium concentration in magnesium depletion will markedly increase these outward currents, shortening the action potential and increasing susceptibility to arrhythmias.
ACUTE ISCHEMIC HEART DISEASE
Patients with acute myocardial infarction who have mild hypomagnesemia appear to have a two- to threefold increase in the frequency of ventricular arrhythmias in the first 24 hours when compared with those with normal plasma magnesium levels [6,7]. Uncontrolled studies suggest that the administration of intravenous magnesium at this time can reduce the frequency of potentially fatal ventricular arrhythmias [8,9].
A relationship has also been found between the plasma magnesium concentration and ventricular arrhythmias occurring in the second or third week after myocardial infarction. In one study, for example, the mean plasma magnesium concentration was 1.83 mg/dL (0.76 mmol/L) in patients with no abnormal rhythms, 1.68 mg/dL (0.7 mmol/L) in those with multifocal ventricular premature complexes (VPCs), and 1.55 mg/dL (0.65 mmol/L) in those with unsustained ventricular tachycardia . Thirteen patients with complex arrhythmias and hypomagnesemia received intravenous magnesium over 24 hours; a normal rhythm was restored in ten.
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