Torsades de pointes et hypomagnésémie

Abstract

The authors report a case of « Torsades de pointeoccurring in a patient subjected to intensive surgical care and presenting several causes of magnesium loss : mutilating abdominal surgery, exteriorized gastric fistula, administration of Henle's loop diuretics, electrolytic disorders and exclusive parenteral nutrition without any magnesium Mg supplement. The arrhythmia appeared in the third week and the usual treatment was ineffective. The level of plasma magnesium was below the measurable values on three separate occasions. The administration of magnesium sulphate corrected the dysrhythmia which did not recur. Experimental and clinical data demonstrating the antiarrhytmic effect of magnesium are recalled. The electrophysiological explanation is based on the inhibition of potassium and calcium flow across the cell membrane; magnesium ion has a stabilizing membrane effect and an antagonistic effect on ectopic automaticity. They are particularly important on slowly depolarizing tissue (nodal cells) or partially depolarized cells (ischaemic or digitalis treated cardiac tissue). In intensive care, circumstances for magnesium depletion by digestive or renal losses and by lack of parenteral magnesium supplement are frequently combined. Systematic intravenous administration of magnesium is necessary when such conditions are found and whenever ventricular or auricular dysrhythmias occur.