HARTFORD, CONNECTICUT. Magnesium (Mg) is an enormously important mineral being a cofactor in over 300 enzymatic reactions continuously taking place in the body. Magnesium is also a vital component of the skeletal structure and about 65% of the body�s magnesium stores are found in bone, another 34% is found in transcellular fluids, and the remaining 1% is found in extracellular fluids such as blood. It is thus clear that measuring magnesium in blood serum is not likely to be a very accurate measure of the body�s overall magnesium status.

There is increasing evidence that magnesium plays a crucial role in preventing and terminating cardiac arrhythmias. A group of cardiologists and pharmacologists at the Hartford Hospital reasoned that a pre-procedure infusion of magnesium might help prevent the acute development of atrial fibrillation following a radiofrequency ablation for this disorder. As a first step in proving or disproving this hypothesis, they decided to do a trial in which half the participants would have saline solution (0.9% sodium chloride) with 4 grams of magnesium sulfate (800 mg elemental magnesium) infused over a 15-minute period just prior to accessing the left atrium in a standard PVI procedure, while the other half would just have a saline solution infusion.

The trial involved 22 patients with paroxysmal or persistent afib. Samples of venous blood (for determination of extracellular Mg concentration) and buccal scrapings (scrapings from inside the cheek) were collected before the start of the procedure, 15 minutes after the completion of the infusion, at the end of the ablation procedure, and at 6 hours after the infusion. The blood samples (serum) were analyzed for extracellular magnesium concentration and the buccal scrapings were analyzed (using the EXAtest) for intracellular magnesium concentration as well as for concentrations of calcium, potassium, sodium, chloride, and phosphate. At least one study has shown that there is an excellent correlation between the magnesium (intracellular) content of buccal scrapings and that of myocytes (heart cells). The major findings are as follows:

• None of the study participants were deficient in Mg at baseline when considering blood serum values only. The average serum Mg concentration was 2.08 mg/dL versus the normal lower limit of 1.6 mg/dL.

• The majority (89%) of participants were magnesium-deficient at baseline when considering intracellular (EXAtest) values only. The average intracellular Mg concentration was 32.2 mEq/IU versus a normal lower limit of 33.9 mEq/IU. NOTE: The unit is defined as x-ray intensity (peak divided by background) divided by unit cell volume.

• There was no correlation whatsoever between serum magnesium and intracellular magnesium concentrations.

• Serum levels of Mg rose rapidly in the magnesium infusion group 15 minutes post-infusion and, although declining over the 6-hour observation period, remained considerably higher than the level in the placebo group (saline infusion only).

• Intracellular level of Mg increased rapidly in the magnesium infusion group 15 minutes post infusion and continued to rise throughout the 6-hour observation period. Somewhat surprisingly, the intracellular Mg level also increased somewhat (over baseline) in the placebo group over the 6-hour period. The Hartford researchers speculate that the ablation procedure itself, most likely the anaesthesia, facilitates the transfer of magnesium from serum to intracellular space.

• The intracellular calcium concentration increased significantly in the Mg infusion group post infusion, but gradually reverted to baseline over the 6-hour period.

• The intracellular potassium concentration increased by about 50% from baseline to the end of the PVI procedure and then began to drop off at the 6-hour mark.

The authors of the report conclude that future studies are needed to evaluate the electrophysiologic benefits of magnesium repletion and the effects of routine procedures and anaesthesia on intracellular electrolytes.

Shah, SA, et al. The impact of magnesium sulfate on serum magnesium concentrations and intracellular electrolyte concentrations among patients undergoing radio frequency catheter ablation. Connecticut Medicine, Vol. 72, May 2008, pp. 261-65

Editor�s comment: A 2006 LAF Survey (LAFS-11) found that, among a small sample of 7 afibbers who had EXAtest results, all 7 were either below or very close to the lower normal limit. The Hartford report provides important additional evidence to support the conclusion that afibbers are likely low in intracellular magnesium even though their blood serum levels may be normal. It is also of interest that replenishing magnesium via an infusion not only increases intracellular Mg concentration, but also increases intracellular potassium levels. This is all good support for our long-held conviction that lone afibbers with normal kidney function are likely to benefit from supplementing with magnesium, potassium, and taurine (facilitates the uptake of Mg and K).