Hyponatraemia: a strong predictor of mortality in adults with congenital heart disease

We studied the prevalence of hyponatraemia and its prognostic implications in a large population of adult patients with congenital heart disease (ACHD). A total of 1004 ACHD patients were retrospectively entered in this study (mean age 36.2 +/- 14.4 years, 48.7% male). Cox regression was used to estimate mortality associated with hyponatraemia, adjusted for potential confounders using both multivariable regression and propensity score matching. Mean sodium concentration in this ACHD cohort was 137.6 +/- 2.6 mmol/L. The overall prevalence of hyponatraemia in this cohort was 15.5% and was highest in congenitally corrected transposition (33.3%), after Fontan operation (29.6%), and in patients with Eisenmenger syndrome (22.0%). Predictors of hyponatraemia were worse functional class, cyanosis, higher serum creatinine levels, and treatment with diuretics. Patients were followed for a median of 4.1 years, during which there were 96 deaths. Hyponatraemia was a strong predictor of death, independent of age, previous surgery, functional class, systemic ventricular function, creatinine levels, and the use of diuretics (adjusted HR 2.82, 95% CI: 1.72-4.63, P < 0.0001). Hyponatraemia is relatively common in ACHD. Hyponatraemia carries a three-fold higher risk of death in ACHD and is a simple, cheap but powerful marker of mortality.