The prognostic significance of serum sodium in a population undergoing cardiac resynchronisation therapy

PURPOSE: To determine the prognostic implications of changes towards hyponatremia at varying time-points in the treatment of patients undergoing cardiac resynchronisation therapy (CRT). METHODS: A retrospective series of 249 patients was studied from 2002 to 2013. The population was categorized on the basis of serum sodium profile at baseline, at 1 month and at 6 month follow up visits following successful CRT implantation. The composite endpoint was all-cause mortality and heart failure hospitalisation (defined by the need for intravenous diuretic therapy) following CRT implantation. RESULTS: A total of 249 patients (67.8 ± 12.5 years; NYHA class III/IV 75; LVEF 27.2 ± 8.8%) were followed up for a median of 5.5 years. Hyponatremia at baseline, 1 month or 6 months follow up did not predict the composite endpoint. 26% of patients showed hyponatremia at baseline prior to CRT implantation, while it was present in 19.9% of patients 1 month (p = 0.003) and in 16% (p < 0.001) 6 months after CRT implantation. There was a significantly worse outcome for those patients who developed hyponatremia 6 months after CRT implantation. In multivariate analysis, the intake of loop diuretics (HR 1.76 [1.04–2.95], p = 0.03) and renal impairment (urea > 7.0 mmol/l) (HR 1.61 [1.05–2.46], p = 0.03) at baseline were associated with an increased risk of unplanned heart failure hospitalisation and all-cause mortality after CRT implantation. CONCLUSIONS: A change towards hyponatremia when observed 6 months after CRT implantation may predict a worse clinical outcome. Additionally, renal impairment and higher diuretic doses are associated with an increased risk of mortality in the population analysed.