Should magnesium therapy be considered for the treatment of coronary heart disease? I. A critical appraisal of current facts and hypotheses.

When given at physiological doses, therapy with magnesium corrects the alterations in cellular function resulting from magnesium deficiency, whereas at higher dosages, which induce hypermagnesaemic levels, magnesium possesses pharmacological effects, such as the inhibition of the calcium influx: this may alter the electrophysiological properties of heart cells, decrease catecholamine secretion, influence the synthesis of prostacyclin and/or alter platelet function. The evidence that magnesium deficiency has untoward effects in patients with ischaemic heart disease is only circumstantial and direct proof that magnesium deficiency causes cardiac disorders is at present lacking. A ubiquitous calcium-channel blockade mechanism is the main and well-established way of action whereby magnesium acts at pharmacological levels; other mechanisms may be involved as well but at present remain questionable or unsettled. On the basis of the present knowledge, beneficial effects may thus be expected from high dose intravenous magnesium therapy in the setting of acute myocardial infarction with respect to mortality rates, even when there is concurrent thrombolytic therapy, as recently demonstrated by the large LIMIT-2 study, although this could not be confirmed from the ISIS-4 trial. High dose intravenous magnesium is also a first choice therapy for terminating torsade de pointes ventricular tachycardia but cannot be considered an established therapy for other cardiac rhythm disturbances nor for settings other than acute myocardial infarction in the case of ischaemic heart disease. The preliminary evidence that magnesium deficiency has a high prevalence in patients with ischaemic heart disease and that it may have a detrimental influence on the course of ischaemic heart disease needs to be validated by larger prospective and controlled clinical studies. Magnesium therapy in ischaemic heart disease thus proves a promising approach which, however, requires that the respective pharmacological and physiological effects be distinguished and further delineated and that the type and stage of ischaemic heart disease be characterized.