Serum Sodium Level within the Low-normal Range is Associated with Long-term Clinical Outcomes in Patients with Acute Decompensated Heart Failure

Background: Although hyponatremia during hospitalization for acute decompensated heart failure (ADHF) has been reported to relate with poor prognosis, limited data is available regarding the impact of serum sodium level (sNa) within the low-normal range at admission on clinical events in patients with ADHF. Methods: We studied eligible ADHF patients admitted to the cardiac intensive-care unit from 2007–2011. All patients were categorized into 3 groups according to the admission sNa of <135 mmol/L (hyponatremia), ≥135 and <140 mmol/L (low-normal range), or ≥140 mmol/L (normal range). Association between admission sNa and long-term clinical events including all-cause deaths and/or ADHF re-hospitalizations, was assessed by multivariable Cox proportional regression. Results: Among 584 eligible patients, 208 (35.6%) were identified as low-normal range, and 99 (16.9%) were hyponatremia. In the multivariable analysis, compared with those with sNa ≥140 mmol/L, patients with hyponatremia had an increased risk for clinical events, (hazard ratio [HR], 1.53; P=.041), whereas HR of those with low-normal range attenuated and was insignificant (HR, 1.08; P=.625). However, HR of each category increased significantly with categories of sNa decreased (P-value for trend, 0.024). In addition, when sNa was treated as a continuous variable, the lower the sNa, the greater the risk of clinical events (P=.012). Conclusion: Low sNa on admission for ADHF, even within the low-normal range, can increase the risk of long-term mortality and/or ADHF rehospitalization.