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December 1984

Documented Sudden Cardiac Death in Prolonged QT Syndrome

Arch Intern Med. 1984;144(12):2430. doi:10.1001/archinte.1984.00350220166040

To the Editor.  —The recent article by Vlay et al1 documented accurately the mechanism of sudden cardiac death in a patient with a prolonged QT interval, with a premature ventricular beat initiating fatal ventricular tachycardia. Electrolyte imbalance was mentioned by the authors in their discussion regarding the pathogenesis of QT prolongation; however, they did not document parameters of magnesium deficiency, despite the well-known propensity for magnesium deficiency to result in QT prolongation, which indeed has been suggested by some to be a good clinical marker of intracellular magnesium deficiency.2 Magnesium deficiency in this context is exceedingly important, not only for its effect on the QT interval per se, but also its known associations with refractory ventricular tachyarrhythmias3 and potentially sudden death syndromes.The patient described by Vlay et al had several common predisposing factors to severe magnesium deficiency: namely, advanced age, congestive heart failure with loop diuretic

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