Effects of magnesium and potassium on Wolff-Parkinson-White syndrome

To investigate the effects of electrolytes on anterograde conduction via accessory pathways, 12 patients with Wolff-Parkinson-White syndrome received, while in sinus rhythm, intravenous KCl (7 mEq in 200 mL of 0.9% NaCl), MgSO4 (10 mL 20% in 200 mL of 0.9% NaCl), NaCl (0.9%, 200 mL), and procainamide (maximal dose, 10 mg/kg of body weight over a 5-minute period) in a randomized fashion. NaCl had no effect on preexcitation. Procainamide abolished preexcitation in seven patients, of whom five had a similar response with MgSO4 and four with KCl. The finding that potassium and magnesium transiently abolish preexcitation in some Wolff-Parkinson-White patients deserves further study, especially during tachyarrhythmias in patients with accessory pathways.