Introduction: Numerous studies have shown that during heart failure (HF) exacerbation patients with hyponatraemia have higher mortality, longer hospital stay and higher incidence of rehospitalisation due to HF. To date there has not been effective therapy for hyponatriaemia in AHF. Until now, research related to hyponatriaemia in HF patients did not focus on serum chloride levels, mostly due to traditional view of chloride as a secondary electrolyte whose levels are dependent on sodium levels and acid-base balance. The present study investigated the relationship between serum chloride and follow-up sodium levels in acute heart failure (AHF) patients with normal initial sodium level. (1)

Patients and Methods: The present study was performed as a prospective, single-centre, observational research with a total of 152 hospitalized AHF patients in University Hospital Centre “Sestre milosrdnice”. Patients have been divided in four groups depending on values of sodium and chloride. Patients were monitored on the second, third and seventh day of hospitalisation and follow up was done after three months. We statistically calculated the likelihood of these groups for developing hyponatriaemia after three months and mortality.

Results: Compared to patients with initial normochloraemia and normonatriaemia, patients with initial hypochloraemia and normonatriaemia had a statistically significant higher incidence of hyponatraemia after a 3-months follow-up. Binary logistic regression revealed a significantly increased in-hospital mortality in the hypochloraemic/normonatriaemic group. Interestingly, ejection fraction at admission was the highest in hypochloraemic/normonatriaemic patients, although that group of patients had significantly increased in-hospital mortality. The lowest ejection fraction was in a group of patients with hypochloraemic/hyponatraemic patients. The N-terminal precursor Brain Natriuretic Peptide (NT-proBNP) levels at admission were significantly lower in hypochloraemic/normonatriaemic compared to other groups.

Conclusion: Our study showed that initial low serum chloride concentration is predictive of developing hyponatraemia and associated with increased in-hospital mortality in HF patients. Chloride levels could be used to detect high-risk patients and start appropriate therapy early enough to prevent poor outcome of AHF patients.