Effects of different dialysate calcium concentrations on heart rate variability and serum ionized calcium levels in maintenance hemodialysis patients

Aims: Heart rate variability (HRV), a marker of cardiac autonomic function, is suppressed in patients receiving maintenance hemodialysis (MHD) compared with the general population. However, data on modifiable dialysis-related factors influencing HRV remain limited. This study aimed to investigate the impact of different dialysate calcium concentrations on serum ionized calcium (iCa) levels and cardiac autonomic function, assessed by HRV, in MHD patients. Methods: This prospective observational study with repeated measures included patients receiving MHD. Baseline electrocardiography and transthoracic echocardiography were performed in all participants. Twenty-four–hour ambulatory electrocardiographic recordings were obtained using Holter monitors initiated immediately before the index hemodialysis (HD) session. The time domain measures of HRV were the standard deviation of all RR interval (SDNN), the mean of the standard deviation of all 5-minute RR intervals (SDNN index: SDNNI), the standard deviation of the average NN intervals over 5-minute segments (SDANN), and the square root of the mean difference between consecutive normal RR intervals (RMSSD). Serum iCa, magnesium, and potassium levels were measured at the beginning and at the end of the index HD session. Relative changes (Δ) in biochemical parameters were calculated as [(baseline value-4th hour value)]/baseline value. All clinical, biochemical, and HRV parameters were compared between groups stratified according to 1.25 mmol/L and 1.50 mmol/L calcium dialysate concentration. Results: A single 4-hour HD session using dialysate containing 1.25 mmol/L calcium was associated with a significant reduction in serum iCa levels and a greater relative change in iCa (∆iCa) compared with 1.50 mmol/L calcium dialysate. In the 1.25 mmol/L calcium dialysate group, all time-domain HRV parameters decreased, accompanied by greater relative changes. In contrast, treatment with 1.50 mmol/L calcium dialysate was related to increases in SDNNI, SDANN, and RMSSD values. After adjustment for potential confounders, multivariable regression analysis demonstrated that ∆iCa was independently associated with ∆SDANN. Conclusion: A single 4-hour HD session with 1.25 mmol/L calcium dialysate was associated with an acute decline in serum iCa levels and parallel changes in HRV indices, suggesting a potential link between dialysate calcium concentration and short-term autonomic modulation in MHD patients.