WARSAW, POLAND. Although the mechanism underlying initiation of afib is still somewhat controversial, there is a growing consensus that slowed conduction velocity and dispersion of atrial refractoriness is involved. This, in turn, may result in multiple re-entry waves and AF. Potassium (K) and magnesium (Mg) play an important role in these mechanisms and guidelines for the management of AF usually recommend that serum levels of K and Mg be measured in AF patients and corrective action taken if electrolyte imbalances are found. (NOTE: Serum levels of K and Mg are not very predictive of the actual intracellular level in myocytes; however, it serum levels are abnormally low, intracellular levels will likely be very low).

Polish researchers report a study involving 115 patients (71 men and 44 women with an average age of 60 years) admitted to hospital with a first episode of afib that had lasted less than 20 hours. Electrolyte levels were checked in all patients upon admission and 16% were found to have a magnesium level below 0.7 mmol/L (1.7 mg/dL), while 3% had a potassium level below 3.5 mmol/L. The researchers observed that the patients with low electrolyte levels were significantly more likely to be on diuretics (hydrochlorothiazide) than were those with normal levels (40% vs. 18%).

The 22 patients with low K and/or Mg levels were given an intravenous infusion consisting of 1000 mL of 10% glucose to which 10 IU of rapid-action insulin, 80 mEq of potassium chloride (3100 mg elemental K), and 8000 mg of magnesium sulfate (1600 mg elemental Mg) had been added. The infusion was maintained for up to 20 hours independent of whether the patient converted to normal sinus rhythm (NSR) or not. Twenty hours after initiation of therapy 86% of patients had regained NSR. A separate group of 31 patients with normal K and Mg levels were also given the infusion. In this case only 39% converted to NSR within the 20-hour trial period.

It is estimated that about 50% of patients with new onset afib convert spontaneously within 24 hours. Thus, the administration of the infusion to patients deficient in K and/or Mg is clearly effective in improving the rate of conversion to NSR. The researchers conclude, "An electrolyte imbalance seems to be an independent factor predisposing to atrial fibrillation. Serum K/Mg levels should always be measured in patients presenting with recent onset AF, because electrolyte supplementation (if needed) seems to be a very effective, safe and inexpensive method in the restoration of sinus rhythm."

Cybulski, J, et al. A new-onset atrial fibrillation: the incidence of potassium and magnesium deficiency. The efficacy of intravenous potassium/magnesium supplementation in cardioversion to sinus rhythm. Polish Heart Journal, Vol. 60, 2004, pp. 580-81