#1650 Synergistic effects of mineral bone disorder (MBD) markers and iron metabolism markers on QT prolongation in maintenance haemodialysis patients

Abstract Background and Aims Prolonged QT interval is known to be common in maintenance haemodialysis (HD) patients, and QT prolongation is a risk for the development of fatal arrhythmias and cardiovascular complications. Previously, we showed that low Ca and low or high P before dialysis were associated with QT prolongation in HD patients. In this study, we aimed to investigate the effect of abnormalities in MBD markers such as Ca and P on QT time when added to abnormalities in markers of iron metabolism, a known cardiac prognostic factor due to abnormal energy metabolism in the myocardium. Method A cross-sectional study was conducted on adult maintenance HD patients enrolled in the 2020 Japanese Society for Dialysis Therapy Annual Survey. Patients with dialysis frequency less than 3 times per week and patients with absent serum Ca, serum P, transferrin saturation (TSAT), serum ferritin, and QTc were excluded. After describing patient characteristics, an analytical-epidemiological study was conducted with serum Ca, P, TSAT, and serum ferritin as exposure and QTc >500 msec as outcome. Exposure was defined as cut off values for Ca, P, TSAT, and serum ferritin of 8.4/10, 3.5/6, 20/40, and 100/300, respectively according to JSDT guideline. Adjusted variables in the multivariate analysis were age, gender, history of dialysis, BMI, and presence or absence of diabetes, previous cardiovascular disease, P adsorption medication, vitamin D analogue use, calcimimetics use. Missing values were addressed using Multiple Imputation by Chained Equations. All analyses were performed using STATA 18.0. The significance level was set at 5%. Results 169 705 patients were analysed. Among all subjects, 65.6% were male, mean age was 69.7 years (standard deviation (SD) 12.4), 50.6% had comorbid diabetes, 24.1% had previous cardiovascular disease, and mean serum Ca and P levels were 8.6 mg/dL (SD 0.7) and 5.2 mg/dL (SD 35.8), respectively. The mean QTc was 452 msec (SD 37.9). In multivariate analysis, the increased risk of QT prolongation in the low Ca, low P, and high P categories was further increased with low TSAT and cancelled with high TSAT (Table). In contrast, no such effect was appeared for ferritin. Conclusion The present study suggests that the association between lower serum Ca and lower and higher serum P levels and QTc prolongation in maintenance haemodialysis patients may be enhanced at low TSAT levels and weakened at normal and high TSAT levels.