Low Serum Magnesium and the Development of Atrial Fibrillation in the Community: The Framingham Heart Study

Study Questions:

Does a low serum magnesium concentration predispose to atrial fibrillation (AF) in the ambulatory setting?

Methods:

The serum magnesium concentration was measured in 3,530 subjects (mean age 44 years) upon entry into the Framingham Offspring Study in 1979-1983. Follow-up examinations were performed on a regular basis during a mean of 18.6 years. AF was diagnosed on the basis of outpatient electrocardiograms, hospitalizations, or Holter monitors.

Results:

The mean serum magnesium concentration was 1.87 mg/dl (range 1.15-2.46 mg/dl). Five percent of subjects developed new-onset AF during follow-up. After adjustment for age and gender, the risk of AF was significantly higher in the lowest quartile of serum magnesium (hazard ratio 1.54 compared to highest quartile). There was no risk gradient among the three highest quartiles. The risk of AF remained higher in the lowest serum magnesium quartile even after adjustment for multiple confounding variables such as serum potassium concentration, diuretic use, alcohol intake, and body mass index.

Conclusions:

A low serum magnesium concentration is associated with an approximately 50% higher risk of developing AF.

Perspective:

A low serum magnesium concentration has been shown to be a risk factor for the development of AF after open heart surgery, but this is the first study to show an association between serum magnesium and AF in an ambulatory setting. Given the fluctuations that typically occur in serum electrolyte concentrations, it is remarkable that a single measurement of serum magnesium concentration was predictive of the development of AF during up to 20 years of follow-up. Nevertheless, the study raises the intriguing question of whether magnesium supplementation might prevent AF in individuals with low serum magnesium concentrations.

Clinical Topics: Cardiac Surgery, Invasive Cardiovascular Angiography and Intervention

Keywords: Magnesium, Electrolytes, Follow-Up Studies, Diuretics, Risk Factors, Electrocardiography, Pyrrolidinones, Incidence, Potassium, Confounding Factors (Epidemiology), Body Mass Index, Outpatients, Cardiac Surgical Procedures, Coronary Artery Bypass


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