Myocardial magnesium depletion associated with prolonged hypomagnesemia: a longitudinal study in heart transplant recipients

Department of Cardiological Sciences, St. George's Hospital Medical School, London, England.

OBJECTIVES. This study was carried out to establish prospectively the incidence and relation of hypomagnesemia and myocardial magnesium depletion after heart transplantation. BACKGROUND. No serial in vivo study of the relation of serum with tissue magnesium has been described. Myocardial magnesium depletion is associated with intracellular calcium overload, an increased incidence of cardiac arrhythmia and changes in coronary vasculature similar to those seen in the accelerated atherosclerosis that compromises graft survival after transplantation. METHODS. In a prospective study in 19 consecutive patients, serum and myocardial magnesium content were measured serially for 9 months after heart transplantation. Blood cyclosporine was assayed simultaneously. RESULTS. The incidence of hypomagnesemia was 100% during the 9-month study period, with lowest levels at 3 months (mean 0.80 vs. 0.64 mmol/liter, p less than 0.002). Myocardial magnesium depletion developed in 94% and was persistent in 55%; the lowest levels occurred at 6 months (mean 33.6 vs. 30.1, mumol/g, p less than 0.04). Hypomagnesemia predated decreases in myocardial magnesium by 2 to 6 weeks. Peak cyclosporine levels correlated positively with the decrease in serum magnesium. Clinical events were rare. CONCLUSIONS. This is the first report of serial measurement of tissue magnesium. Persistent hypomagnesemia is invariably accompanied by myocardial magnesium depletion in the transplanted heart. Reciprocal calcium overload and adverse changes in coronary vasculature would be expected from previous studies and merit further investigation. Should the implications of this study extend to the native heart, myocardial magnesium depletion may contribute to the high incidence of fatal arrhythmic events observed in patients with heart failure, who commonly have persistent hypomagnesemia.

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