Objectives Hyponatraemia is a well-known predictor of clinical outcomes in heart failure (HF). However, the mechanism remains poorly understood. Previous reports suggest that hyponatraemia is related to right HF. We sought to evaluate the association between right ventricular (RV) dysfunction and hyponatraemia, and the impact of this relationship on the prognosis of patients with acute heart failure (AHF).

Methods This is a nested case–control study of the Korean Acute Heart Failure registry. Among 2935 AHF patients enrolled prospectively and consecutively at four tertiary hospitals in Korea from 2011 to 2014, 116 patients with severe persistent hyponatraemia, defined as serum sodium level <130 mmol/L at admission and <135 mmol/L before discharge, were matched with 232 controls, based on propensity scores for hyponatraemia. RV function was assessed with fractional area change (FAC) by echocardiography.

Results RV dysfunction (FAC <35%) was more prevalent in patients with severe persistent hyponatraemia than in those without (81.0% vs 33.6%, p<0.001). Hyponatraemia was strongly associated with RV dysfunction (adjusted OR 8.00, 95% CI 4.50 to 14.22, p<0.001), but not with left ventricular dysfunction (adjusted OR 1.21, 95% CI 0.74 to 1.50, p=0.308). RV dysfunction was an independent predictor of all-cause mortality, after adjustment for hyponatraemia (adjusted HR 2.20, 95% CI 1.53 to 3.15, p<0.001), while hyponatraemia was not (adjusted HR 1.33, 95% CI 0.94 to 1.87, p=0.108).

Conclusions In patients with AHF, hyponatraemia was more common with RV dysfunction. RV dysfunction, rather than hyponatraemia, was more significantly related with patients’ prognosis. Thus, the utility of RV dysfunction instead of hyponatraemia per se should be considered in HF risk models.

Trial registration number Korean Acute Heart Failure registryNCT01389843;Results.