Prognostic importance of hyponatremia in acute ST-elevation myocardial infarction

PURPOSE: To determine the prevalence and prognostic implications of hyponatremia in the setting of acute ST-elevation myocardial infarction. METHODS: The study sample consisted of 1047 consecutive patients presenting with acute ST-elevation myocardial infarction. Plasma sodium concentrations were obtained on admission and at 24, 48, and 72 hours thereafter. Infarct size was determined by echocardiographic examination that was performed on day 2 or 3 of hospitalization. RESULTS: Hyponatremia, defined as a plasma sodium level < 135 mmol/L (< 135 mEq/L), was present on admission in 131 patients (12.5%). and developed during the first 72 hours of hospitalization in 208 patients (19.9%). Plasma sodium levels decreased to less than or equal to 130 mmol/L in 45 patients (4.3%). In a multivariate logistic regression analysis, hyponatremia was independently associated with 30-day mortality. The risk of 30-day mortality associated with hyponatremia on admission (odds ratio [OR] = 2.0; 95% confidence interval [0]: 1.0 to 3.9; P = 0.04) was similar to that of hyponatremia developing after admission (OR = 2.4; 95% CI: 1.5 to 4.2; P = 0.002). The risk of 30-day mortality increased with the severity of hyponatremia, with an odds ratio of 2.1 in patients with sodium levels between 130 and 134 mmol/L (95% CI: 1.2 to 3.5; P = 0.007) and 3.4 in those with levels < 130 mmol/L (95% CI: 1.5 to 7.8; P = 0.002). CONCLUSION: Hyponatremia on admission or early development of hyponatremia in patients with acute ST-elevation myocardial infarction is an independent predictor of 30-day mortality, and prognosis worsens with the severity of hyponatremia. Further studies are required to determine if plasma sodium levels may serve as a simple marker to identify patients at highrisk. (C) 2004 by Elsevier Inc.