How does magnesium acts as an antiarrhythmic drug ?
Posted Jan 13 2010 5:57am
Magnesium is a powerful cell membrane stabilizing agent. It is well recognized to act on the cerebral motor cortical cells and suppress seizure , especially in eclampsia of pregnancy .
Mg SO4 is still the drug of choice for seizures of pregnancy. It was soon realised , the molecular basis of cellular excitability is similar for every cell . And thus , we got this great antiarrhythmic drug !
Magnesium is a cofactor in the enzyme Na /K ATPase in the myocyte cell membrane
Integrity of this enzyme is essential for proper maintenance of the intracellular potassium levels.
Many times hypokalemia can not be fully corrected by administration of K + alone .
Co- administration of magnesium increase the intracellular K + and hyperpolarize the cells and make it less excitable.
Further , magnesium competes with ca++ ions to enter the cells and thus it is a natural calcium blocker. This property also helps in controlling refractory calcium dependent cardiac arrhythmia.
Indications for magnesium
Torsades de pointes . Note: Magnesium does not shorten the QT interval significantly but still effective in torsades.
Any refractory VT especially , post MI.
Digoxin induced , hypokalemia dependent atrial tachycardias, MAT
It is administered 1-2mg boluses of 2-3 boluses.
Where we should not use magnesium ?
Routine Use of magnesium in recurrent non sustained VT following MI is not recommended .(Courtesy ISIS -4 trial )