Cardiac biomarkers are influenced by dialysis characteristics

INTRODUCTION: The cardiac biomarkers cardiac Troponin T (cTNT) and NT-proBNP tend to be elevated in nearly all hemodialysis patients. The high percentage and magnitude of these increased molecules is associated with cardiovascular morbidity and mortality in hemodialysis patients. This study investigates the impact of the dialysis procedure itself on cardiac biomarkers. METHODS: Standard chronic hemodialysis lasting 4-5 hs 3 times weekly and using polysulfone dialyzers (high-flux and low-flux) was performed. Blood flow rates varied between 250-350 ml/min. The cTNT levels of 49 chronic hemodialysis patients were measured twice (interval of 6 weeks) before and after a hemodialysis session by a third-generation assay (Elecsys Analyzer, Roche Diagnostics, Mannheim, Germany). NT-proBNP levels were measured with polyclonal antibodies capable of recognizing the N-terminal fragment of BNP. In a follow-up period of 42 months, cardiovascular events and death were assessed. RESULTS: The median concentration of cTNT prior to hemodialysis was 0.024 ng/ml (< 0.001-0.703). All dialysis patients presented high plasma levels of NT-proBNP (median 4,885 pg/ml). Oligoanuric patients had significantly higher cTNT and NT-proBNP levels prior to dialysis compared to patients with normal diuresis (p < 0.0001). cTNT and NT-proBNP levels increased significantly during the hemodialysis sessions in which a low-flux dialyzer was used (p < 0.0001) but remained unchanged when a high-flux dialyzer was utilized. Neither the predialytic nor the interdialytic changes in cTNT and NT-proBNP levels were influenced by blood flow. NT-proBNP levels increased markedly during hemodialysis sessions (p < 0.005) utilizing the low-flux dialyzer. Patients with a non-native fistula had significantly higher predialysis cTNT and NT-proBNP levels (p < 0.05). Patients with cardiovascular events had a significantly higher cTNT and NT-proBNP at the beginning of the study. CONCLUSION: Asymptomatic chronic hemodialysis patients have significantly higher levels of the cardiac biomarkers cTNT and NT-proBNP relative to the general population. The levels are associated with the time of measurement (before and after a hemodialysis session). Dialysis modalities like high-flux dialyzers influence cTNT and NT-proBNP levels and should be taken into account, particularly in patients with acute onset of cardiac ischemia. The elevation of cTNT and NT-proBNP levels after hemodialysis using a low-flux dialyzer are partly due to hemoconcentration. The significant association of cTNT and NT-proBNP with non-native fistulas (catheter or graft) may be due to the chronic inflammation commonly caused by these devices. Both cardiac biomarkers are of prognostic value determining cardiovascular events and death.