Risk Factors for In-Hospital Mortality in Patients with Hyponatremia in a Cardiology Setting

Aim. To identify risk factors for in-hospital mortality among patients with hyponatremia in a cardiology hospital.

Material and Methods. This single-center retrospective study included 119 patients (mean age 71.2 (12.7) years) admitted to a cardiology center from June 2024 to March 2025, who had at least one recorded instance of hypotonic hyponatremia (sodium level < 135 mmol/L). Patients with acute coronary syndrome and myocardial infarction were excluded. Statistical analysis was performed using logistic regression and ROC analysis.

Results. The prevalence of hyponatremia among the examined patients was 4.1%. In-hospital mortality reached 16.0% (19 deaths). Hypervolemic hyponatremia, typical for patients with chronic heart failure, was the most common type (48.7%). Compared to survivors, deceased patients more frequently had a history of myocardial infarction (52.6% vs. 21.2%), coronary artery stenting (36.8% vs. 8.2%), stage II chronic heart failure (21.1% vs. 4.0%), chronic kidney disease (73.7% vs. 29.3%), and cholelithiasis (31.6% vs. 12.1%). They also presented with a higher number of non-cardiac comorbidities: 4.0 [2.5; 5.0] vs. 2.0 [1.0; 4.0]. Deceased patients more often reported dyspnea (94.7% vs. 63.0%), had a higher respiratory rate (20.0 [16.5; 20.5] vs. 17.0 [16.0; 19.0]), lower oxygen saturation (96.0 [91.5; 97.0]% vs. 97.0 [96.0; 98.0]%), higher levels of creatinine (205.5 [160.6; 293.4] µmol/L vs. 116.8 [83.2; 165.2] µmol/L), potassium (5.0 (1.5) mmol/L vs. 4.4 (1.0) mmol/L), and troponin (2872.0 [186.0; 5456.0] ng/L vs. 30.4 [13.9; 1237.5] ng/L). They also exhibited lower sodium levels (128.0 [124.0; 132.0] mmol/L vs. 131.0 [129.0; 133.0] mmol/L), lower glomerular filtration rate (24.7 [15.8; 29.7] vs. 42.2 [32.6; 72.9] mL/min/1.73 m^2), larger left ventricular end-diastolic and left atrial dimensions, and lower left ventricular ejection fraction (35.5 [27.9; 54.3]% vs. 54.0 [40.0; 62.0]%). Multivariable regression analysis identified the following independent predictors of mortality: minimum sodium level (AOR 0.840; p=0.004), glomerular filtration rate (AOR 0.957; p=0.023), and left ventricular ejection fraction (AOR 0.947; p=0.022). The resulting predictive model demonstrated high discriminative power: AUC = 0.840 with a sensitivity of 71.4% and specificity of 88.2%.

Conclusion. Minimum serum sodium level is an independent risk factor for in-hospital mortality, particularly in patients with reduced glomerular filtration rate and left ventricular ejection fraction. Optimization of diagnostic protocols and implementation of more proactive methods for correcting electrolyte imbalances are necessary to reduce mortality rates.

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