Prognostic Significance of Hyponatremia in ST-elevation Myocardial Infarction/Heart Failure Patients

ST-elevation myocardial infarction (STEMI) and heart failure (HF) are common, big-budget, debilitating and expanding diseases. Cardiovascular diseases, especially STEMI and heart failure have been known to cause 17.3 million deaths worldwide annually. Hyponatremia, delineated as a serum sodium (sNa) concentration <135 mmol/l, is a frequently seen electrolyte disturbance in practice and the prevalence, clinical impact; the prognostic factor of low SNa in STEMI/heart failure patients vary widely. The aim of this review is to assess its existence and comparing survival difference between hypo and normonatremic patients. A comprehensive review of the published articles was conducted using database PubMed. We found a total of over 1400 articles. The inclusion criteria used for this review were age >65 years, published within the last 10 years, written in English, performed on human subjects and of studies such as reviews and randomized controlled trials (RCTs), especially for heart failure MeSH words. By applying this inclusion criterion, we found out 40 relevant articles which included 26 cohort studies, four clinical trials, four review articles, and six RCTs. In the analysis of 7,06,899 patients with STEMI/heart failure, hyponatremia was significantly linked to causing all-cause mortality, both short and long term (hazard ratio [HR] as continuous variable: 1.06; 95% confidence interval [CI]: 1.01-1.11; P = 0.026; HR as categorical variable: 1.71; 95% CI: 1.06-2.75; P = 0.028). The rates of rehospitalization were also higher (odds ratio, 1.68; 95% confidence interval, 1.32-2.14) along with prolonged hospital stays as well as a greater cost burden as compared to patients with normal serum sodium. It was existent not only in patients with reduced ejection fraction (HFrEF) but also in subjects with preserved ejection fraction (HFpEF) (HR 1.40, 95% CI 1.12 to 1.75, P = 0.004). Rise of first follow-up and discharge sodium does seem to have positive linkage on survival as well (hazard ratio [HR] 0.429, 95% CI 0.191-0.960, P = 0.04). Hyponatremia is the most frequently encountered electrolyte abnormality in clinical practice and has a poor prognosis in both STEMI and heart failure patients. It exacerbates both short and long term mortality, rehospitalization rates, as well as the average length of stay in the hospital. Although it is still a mystery whether hyponatremia is just a marker of iller patients or the core of poor prognosis in patients with STEMI and HF, one thing is certain: timely recognition of patients at risk for developing hyponatremia could help to commence early treatment.