Prolonged Q-Tc interval and decreased lymphocyte magnesium in congestive heart failure.

Lymphocyte Mg concentration was measured in 2 patients with congestive heart failure, on long-term diuretic treatment, and was found to be lower than normal. The patients exhibited prolonged Q-Tc intervals on ECG analysis. During treatment with Mg sulfate, the Q-Tc interval normalized as the lymphocyte Mg approached control values. An Mg-sparing diuretic was added to the therapeutic regimen.