Long-term prognostic impact of hyponatremia in the ST-elevation myocardial infarction

Aims. The aim of the study was to analyse in-hospital outcomes and long-term prognostic implications of reduced sodium serum level (S-Na) in the early phase of ST elevation myocardial infarction (STEMI) treated, primarily, with direct percutaneous coronary intervention (dPCI). Methods and results. The study included 218 consecutive patients (144 males, the mean age 64 +/- 13 years) with no history of heart failure admitted with acute STEMI. Out of them, 193 (88.5%) patients were treated with dPCI. The mean follow-up period was 39 +/- 21 months. Hyponatremia was defined as S-Na value < 135 mmol/L. A total of 72 (33%) patients reached hyponatremia level; 51(23.4%) of them at admission and 21 (9.6%) later during hospitalization. The hyponatremic patients more frequently presented with reduced left ventricular systolic function, Killip class III or IV and were at increased risk of developing cardiogenic shock compared to patients with normonatremia. Compared to the rest of the population, patients who developed hyponatremia later during hospitalization had higher incidence of acute renal failure; (12 patients/6.1% vs. 5 patients/25.5%, p < 0.05). The difference in long-term survival between the hyponatremia and normonatremia groups was significant (p = 0.01, log-rank test). The multiple analysis of variance identified decrease of S-Na levels at admission independently associated with total mortality (p = 0.05). Conclusion. Patients who developed hyponatremia in the early phase of STEMI were at higher risk of worse in-hospital clinical outcome. During the long-term follow-up, higher mortality rates were recorded in hyponatremic patients.