Background: Several studies have shown that hyponatremia is associated with increased risk of rehospitalization and death in patients with heart failure. In these studies, chronic heart failure (CHF) patients with persistent hyponatremia were compared only with CHF patients with a normal sodium level at hospital admission. Aims: In the present retrospective study, conducted in a cohort of patients with recent acute decompensated heart failure (ADHF), all with hyponatremia ascertained at the time of hospital admission, we aimed to evaluate the effect of the normalization of serum sodium on the composite endpoint of short-term rehospitalization and mortality. Methods: A retrospective study centered on medical records of patients hospitalized for ADHF in the period April 2013 to April 2016 was performed. Data regarding serum sodium measurements had to be collected from medical records of cardiology wards of two hospitals, and were then processed for statistical analysis. As an inclusion criterion for enrollment, patients had to be suffering from heart failure that had required at least one hospitalization. Moreover, they had to be suffering from a state of hyponatremia (serum sodium < 135 mEq/L) at admission on the occasion of the index hospitalization. Patients with hyponatremia at admission were divided into two groups, one comprising patients with hyponatremia that persisted at the time of discharge (persistent hyponatremia) and a second including patients who had achieved normalization of their serum sodium levels (serum Na⁺ ≥ 135 mEq/L) during hospitalization until discharge. For both groups, the risk of mortality and rehospitalization during a 30-day follow-up was assessed. Results: One hundred and sixty CHF patients with various degrees of functional impairment were enrolled in the study. Among them, 56 (35%) had persistent hyponatremia over the course of hospitalization. At multivariable Cox proportional-hazards regression analysis, the risk of having a 30-day unplanned readmission or death was significantly higher in patients with persistent hyponatremia compared to those who exhibited a sodium level normalized at discharge (adjusted hazard ratio = 3.0743; 95% CI: 1.3981-6.7601; p = 0.0054). Among the other variables included in the Cox regression model, the number of admissions in the last 12 months (p < 0.0001), the length of stay of the index admission (p = 0.0015) and the New York Heart Association (NYHA) class III at discharge (p = 0.0022) were also identified as risk factors associated with the composite endpoint of 30-day unplanned readmission or death. Conclusions: In the present retrospective study, the risk of 30-day rehospitalization or death was significantly higher in patients with recent ADHF and persistent hyponatremia in comparison with ADHF patients who had had their serum sodium normalized during the hospital stay. This association seemed to be independent of the heart failure severity.
Keywords: heart failure; hospitalization; hyponatremia; mortality.