Background: Hyponatremia is a well-known predictor of mortality in patients with acutely decompensated heart failure. Associations between hyponatremia and other prognostic variables in acutely decompensated heart failure, such as amino-terminal pro-B type natriuretic peptide remain unclear.
Methods and results: Six hundred twenty-eight patients presenting to the emergency department with acutely decompensated heart failure were studied. All were hospitalized. Serum sodium (Na) concentration at presentation was examined as a function of mortality at 1 year, alone and relative to other predictors of death. Hyponatremia (Na < or =135 mmol/L) was diagnosed in 24%(n=149) patients. Compared with those without hyponatremia, those affected were less likely to be male or to have hypertension or coronary artery disease but were more likely to have severe symptoms, to be anemic, and to have higher amino-terminal pro-B-type natriuretic peptide (NT-proBNP) concentrations (all P< or =0.05). When examined as a function of Na deciles (ranging from Na <132 mmol/L to Na < or =142 mmol/L), a U-shaped association was found between Na level and 1-year mortality. In multivariate Cox proportional hazards analysis, hyponatremia was an independent predictor of 1-year mortality (hazards ratio=1.72; 95% CI=1.22 to 2.37; P=0.001) as was an NT-proBNP concentration above the median value of 4690 pg/mL (hazards ratio=1.49; 95% CI=1.10 to 2.00; P=0.009). Those with hyponatremia and more elevated NT-proBNP were more likely to develop worsening renal function during their hospitalization and had highest rates of 1-year death. Notably, however, hyponatremia predicted only 1-year mortality in those with an elevated NT-proBNP.
Conclusion: Hyponatremia is associated with adverse outcome in patients with acutely decompensated heart failure; however, the prognostic value of low Na is mainly evident in those with more pronounced elevation of NT-proBNP concentrations.