BACKGROUND Hyponatremia is a well-known risk factor for worse outcomes in heart failure (HF) patients. The impact of hyponatremia according to the ejection fraction (EF) is unclear. We evaluated the prognostic value of hyponatremia according to HF type.

METHODS AND RESULTS The Korea Acute Heart Failure (KorAHF) registry consecutively enrolled 5625 patients. Hyponatremia was defined as serum sodium level<135mmol/L at hospital admission. HF with preserved and reduced ejection fraction were defined as an LVEF ≥50% and LVEF ≤40%, respectively. Among 5103 patients with available EF, 2088 (60%) had HFrEF, and 1284 (25%) had HFpEF. There was no difference in serum sodium level between the groups (HFrEF: 137.4±4.7mmol/L vs. HFpEF: 137.5±5.0mmol/L, P=0.710). Hyponatremic patients had higher in-hospital mortality or urgent heart transplantation in all (11.3% vs. 4.5%, P<0.001), in HFrEF (13.1% vs. 4.9%, P<0.001), and in HFpEF (6.0% vs. 1.9%, P<0.001). After adjustment for significant covariates, hyponatremia was associated with 1.5 fold increased risk for 1-year post-discharge death in the HFrEF group (HR, 1.52; 95% CI, 1.24-1.86), but not in the HFpEF group (HR, 1.16; 95% CI, 0.84-1.61). During admission, the sodium status changed in 22% of the patients and the discharge sodium status had greater prognostic value.

CONCLUSIONS Hyponatremia is independent of HF type. Hyponatremia is a significant risk factor for adverse in-hospital outcomes; however its long-term prognostic value is only limited to patients with HFrEF, but not for those with HFpEF.