Usefulness of hyponatremia in the acute phase of ST-elevation myocardial infarction as a marker of severity.

Whether hyponatremia (sodium <135 mEq/L) in the acute phase of ST-segment elevation myocardial infarction is just a marker of "more ill" patients or decreased sodium concentration is able to exert a direct adverse effect on the cardiovascular system is still unknown. The aim of this study was to assess the prognostic impact, in the short and long terms, of admission hyponatremia in 1,231 consecutive patients with ST-segment elevation myocardial infarctions all submitted to primary percutaneous coronary intervention. In this series, 286 patients (23.2%) had sodium values <135 mEq/L. Patients with hyponatremia were older (p = 0.018) and more frequently had diabetes (p = 0.040). Anterior myocardial infarction was more frequent in patients with hyponatremia, who showed a higher incidence of 3-vessel coronary artery disease and advanced Killip class. Higher mortality rates were observed in patients with hyponatremia during intensive cardiac care unit stay and at follow-up. On multivariate regression analysis, admission sodium concentration was not independently related to early death, nor did it show any relations with long-term mortality on Cox regression analysis. In conclusion, the main findings of the present investigation are as follows: (1) hyponatremia is a common finding, being associated mainly with older age, diabetes, and advanced Killip class; (2) patients with hyponatremia had higher rates of in-hospital and long-term mortality; and (3) hyponatremia, also when assessed by means of the propensity score model, was not independently associated with increased risk for death in the short and long terms. These data therefore strongly suggest that the presence of hyponatremia in the acute phase of ST-segment elevation myocardial infarction should be considered a marker of more ill patients.