The Impact of Hyponatremia in Aortic Valve Surgery Using Histidine–Tryptophan– Ketoglutarate Cardioplegia

ABSTRACT
Background: Histidine–tryptophan–ketoglutarate (HTK) cardioplegia is one of the most widely used methods of cardioplegia. This solution is hyponatremic compared to blood, and the rapid infusion of a substantial volume of hyponatremic solution will result in a notable reduction in serum natrium (Na) levels. The aim of this study was to analyze changes in serum Na concentration following HTK cardioplegia infusion in aortic valve surgery, and to investigate the association between hyponatremia and postoperative outcomes in patients who underwent aortic valve replacement surgery. Materials and Methods: This retrospective study involved 302 patients who underwent aortic valve replacement surgery between June 2023 and June 2024 at the Emergency Institute for Cardiovascular Diseases and Transplantation, Tîrgu Mureș, Romania. Based on their preoperative serum Na levels, the patients were divided into a low Na group (Na < 136 mEq/l) and a normal/high Na group (Na ≥136 mEq/l). Outcomes measured were operative shortterm mortality, as well as in-hospital postoperative complications such as neurological impairment, surgical reintervention, new onset atrial fibrillation (AFib), and sustained ventricular fibrillation (VF) or ventricular tachycardia (VT). Results: Before surgery, the mean Na concentration was 134.0 ± 1.3 mmol/l in the low Na group and 140.5 ± 3.2 mmol/l in the normal/high Na group. After surgery, the mean Na concentration decreased to 134.5 ± 3.4 mmol/l in the low Na group and to 135.5 ± 8.1 mmol/l in the normal/high Na group. Logistic regression analysis of the outcomes showed a significant association between low preoperative Na concentrations and surgical reintervention for hemorrhagic cause, being a risk factor (OR = 3.65; 95%CI 1.18–11.34; p = 0.025). The 7-day mortality was 7.6% in the low Na group vs. 1.1% in the normal/high Na group, and 30-day mortality was 10.9% in the low Na group vs. 1.6% in the normal/high Na group. We found a significant association between low preoperative Na levels and 7-day mortality (OR = 7.40; 95% CI 1.57–34.90; p = 0.011), as well as low preoperative Na levels and 30-day mortality (OR =7.36; 95% CI 2.05–26.42; p = 0.002). Conclusions: Our findings suggest that the occurrence of complications is primarily associated with preoperative rather than postoperative hyponatremia, even when there are minor deviations from the normal range.