Suppression of torsade de pointes by magnesium

Suppression of torsade de pointes by magnesium

It is well known that intravenous magnesium infusion is effective in suppressing polymorphic ventricular tachycardia with QT interval prolongation known as torsade de pointes. This effect is mediated through the blockade of L-type calcium channels and suppression of torsade de pointes can occur even without normalization of the prolonged QT interval. It may be noted that magnesium is a physiological calcium antagonist within the myocardial cell. High levels of magnesium suppresses calcium release from the sarcoplasmic reticulum and low levels of magnesium increases calcium release from the sarcoplasmic reticulum. Sarcoplasmic reticulum is an important intracellular store of calcium ions having important role in excitation contraction coupling in the myocardial cell.

In experimental animals magnesium has been shown to suppress early afterdepolarizations and ventricular arrhythmias induced by cesium.¹ Suppression of early afterdepolarization (EAD) by magnesium is by blocking the calcium influx so that the amplitude of EAD is reduced to subthreshold levels.

Intravenous magnesium has been used to suppress torsades induced by sotalol.² It was presumed that magnesium suppressed the early afterdepolarizations caused by sotalol.

Role of interventricular dispersion of repolarization and their reversal with magnesium has also been shown in experimental animals with acquired torsade de pointes.³

References

1. Bailie DS, Inoue H, Kaseda S, Ben-David J, Zipes DP. Magnesium suppression of early afterdepolarizations and ventricular tachyarrhythmias induced by cesium in dogs. Circulation. 1988;77:1395-402.
2. Arstall MA, Hii JT, Lehman RG, Horowitz JD. Sotalol-induced torsade de pointes: management with magnesium infusion. Postgrad Med J. 1992;68:289-90.
3. Verduyn SC, Vos MA, van der Zande J, van der Hulst FF, Wellens HJ. Role of interventricular dispersion of repolarization in acquired torsade-de-pointes arrhythmias: reversal by magnesium. Cardiovasc Res. 1997;34:453-63.