Cell-associated magnesium and QT dispersion in hemodialysis patients

Background: Impaired magnesium (Mg) homeostasis has been implicated in a variety of cardiovascular disturbances, including ventricular arrhythmias and changes in the interval between the onset of wave Q to the end of wave T (QT interval) on electrocardiogram. Cardiac arrhythmias are common in patients on hemodialysis therapy. Methods: We investigated the relationship between QT interval corrected for heart rate (QTc) dispersion and Mg content in peripheral blood mononuclear cells (PBMC) of chronic hemodialysis patients treated with high-dose calcium carbonate providing Mg in excess (group I; n = 18) or low-dose calcium carbonate and smaller Mg load (group II; n = 13). Results: Mean Mg content in PBMC of group I patients (27.9 ± 4.2 [SD] μmol/L/mg protein) was significantly greater than in group II patients (10.4 ± 4.1 μmol/L/mg protein; P < 0.05) and greater in both groups than in healthy control subjects (2.75 ± 0.6 μmol/L/mg protein; P < 0.05). Mean QTc dispersion was significantly longer (74.6 ± 21.4 milliseconds) in group I than group II (37.8 ± 13.1 milliseconds; P < 0.02) and longer in both groups than in controls (27.3 ± 9.6 milliseconds; P < 0.05). After dialysis, in both groups of patients, cell-associated Mg (c-a Mg) levels and QTc dispersion were significantly greater (P < 0.05) than before dialysis started. One week after stopping calcium carbonate treatment, group I patients showed significant reductions in predialytic c-a Mg levels (to 19.5 ± 9.8 μmol/L/mg protein; P < 0.05) and QTc dispersions (to 48.9 ± 23.7 milliseconds; P < 0.05). Plasma Mg and other electrolyte concentrations prior to and during hemodialysis did not correlate with QTc dispersion. Conclusion: Prolongation of QTc dispersion in patients on chronic hemodialysis therapy could be, at least in part, a consequence of increased concentrations of c-a Mg resulting from excess daily Mg intake.