Hyponatraemia and severity and outcome of myocardial infarction.

A total of 235 consecutive patients admitted to a coronary care unit were investigated for serum electrolyte and urea concentrations; activities of aspartate amino-transferase, lactate dehydrogenase, and lactate dehydrogenase isoenzymes; electrocardiographic changes; clinical state; and outcome. Hyponatraemia, hypochloraemia, and uraemia were common in patients with confirmed myocardial infarctions, the degree of infarction correlating well with all the above indices of severity. The day-to-day variability of plasma sodium, chloride, and potassium concentrations was often increased above normal. Disturbances were greater in patients given diuretics. It is concluded that plasma sodium concentration fall after infarction and that the extent and duration of the fall are indices of the severity of the infarction.