Serum, lymphocyte, and erythrocyte potassium, magnesium, and calcium concentrations and their relation to tachyarrhythmias in patients with acute myocardial infarction.

Serum, lymphocyte, and erythrocyte potassium, magnesium, and calcium levels were measured in 215 patients during the five days following acute myocardial infarction. Serum potassium fell from 4.25 +/- 0.05 to 4.08 +/- 0.06 mmol/liter (p less than 0.001), magnesium from 0.93 +/- 0.01 to 0.85 +/- 0.01 mmol/liter (p less than 0.001), and calcium from 2.4 +/- 0.02 to 2.2 +/- 0.08 mmol/liter (p less than 0.001). Lymphocyte potassium increased from 18.1 +/- 1.5 to 51.6 +/- 4.3 pmol/100 cells (p less than 0.001) and magnesium from 2.0 +/- 0.1 to 8.2 +/- 0.8 pmol/100 cells (p less than 0.001), whereas calcium decreased from 2.9 +/- 0.27 to 1.4 +/- 0.25 pmol/100 cells (p less than 0.001). Erythrocyte cations remained constant. There was a larger increase in lymphocyte potassium in patients with tachyarrhythmias than in patients without (70.4 and 46.9 pmol/100 cells, respectively, p less than 0.001), whereas the presence of a high lymphocyte magnesium level was associated with a significant decrease in the development of tachyarrhythmias, despite high potassium concentrations. It is suggested that lymphocyte cation concentrations mirror myocardial interstitial concentrations and that a high interstitial magnesium level has a protective effect on the increased cell excitability due to, and despite, a high interstitial potassium level.