Background
Hyponatremia is a common electrolyte disorder reported to be a predictor of poor prognosis among hospitalized patients, but individuals with high levels also tend to have less favorable outcomes. This study investigated whether sodium level on admission is predictive of in-hospital outcome in patients with ST-elevation myocardial infarction (STEMI) treated with primary angioplasty.
Material and Method
Included were 1858 patients admitted with STEMI for primary angioplasty. Sodium level was measured on admission and analyzed as hypo- versus normonatremia and by grouping patients into sodium quintiles. The relationships between sodium level and in-hospital mortality as well as the composite of death or heart failure were assessed.
Results
Ninety-six patients had hyponatremia on admission. The hypo- and normonatremic groups were comparable with respect to baseline characteristics and in-hospital management. Hyponatremics had higher rates of in-hospital mortality (13.5% vs. 3.8%, p<0.001) composite of death and heart failure (27.8% vs. 18.4%, p=0.022). After adjustment for covariates, hyponatremia independently correlated with in-hospital mortality (HR: 3.89, 95%CI: 1.59-9.56, p=0.003) and the combined endpoint (HR: 1.73, 95%CI: 1.01-2.99, p=0.047). Patients in the lowest and highest sodium quintiles were 3.27 (95%CI: 1.34-8.02, p=0.009) and 2.65 (95%CI: 1.07-6.60, p=0.036) times more likely to die during hospitalization than those in the 2nd quintile (best survival). In the adjusted model, only patients in the lowest quintile had significantly increased risk of in-hospital death (HR: 6.35, 95%CI: 1.83-21.72, p=0.004).
Conclusions
Hyponatremia is a simple laboratory marker independently associated with increased risk of death in STEMI patients treated with primary angioplasty.

Keywords: Patient Admission, Myocardial Infarction - therapy, Hyponatremia, Registries, Hospital Mortality, Angioplasty, Sodium - blood