Correlation Analysis Between QTc Interval And Body Composition In Maintenance Hemodialysis Patients And Its Predictive Value For All-Cause Mortality

Backgrounds and ObjectivesHemodialysis is one of the renal replacement treatments for patients with end stage renal disease（ESRD）.With the development of hemodialysis technology and the popularization of standard operation,the long-term survival rate of patients with maintenance hemodialysis（MHD）has improved greatly,but the mortality is still high compared with the general population.Relevant studies have reported that the 5-year survival rate of maintenance hemodialysis patients is about 39.8%～60.2%,and about a quarter of the patients die from sudden cardiac death（SCD）.QT interval reflects the whole process of ventricular muscle from depolarization to repolarization,and the prolonged QT interval is a risk factor for malignant arrhythmias and cardiac sudden death.The heart-rate corrected QT interval is called the QTc interval,and MHD patients have a significantly higher percentage of prolonged QTc intervals than general population.Previous studies have shown that QTc interval may be related to human composition in MHD patients,but there are few studies on the influencing factors of the QTc interval in MHD patients,especially the relationship between the QTc interval and human composition,as well as the effect of the prolonged QTc interval on all-cause death.The purpose of this study was to explore the correlation between QTc interval and human composition and the predictive value of prolonged QTc interval for all-cause death,so as to provide a new perspective and basis for the prevention of arrhythmia and SCD in MHD patients and the improvement of patient survival rate.MethodsMHD patients hospitalized in the department of nephrology,the First Affiliated Hospital of Zhengzhou University from January 2020 to December 2020 were selected as the research subjects.We collect and record the basic information of patients.Also,we collect venous blood of patients before dialysis on midweek dialysis day and collect relevant laboratory test results,including red blood cell count（RBC）,white blood cell count（WBC）,platelet count（PLT）,hemoglobin（Hb）,coefficient of variation of red blood cell distribution width（RDW-CV）,blood potassium（K）,blood calcium（Ca）,blood phosphorus（P）,albumin（Alb）,blood urea nitrogen（BUN）,creatinine（Cr）,uric acid（UA）,triglyceride（TG）,cholesterol（TC）,high density lipoprotein（HDL）,low density lipoprotein（LDL）,β₂-microglobulin（β₂-MG）,serum iron（Fe）,ferritin（FERR）,total iron binding capacity（TIBC）,25-hydroxyvitamin D₃[25-（OH）D₃],parathyroid hormone（iPTH）,C reactive protein（CRP）.Corrected serum calcium was calculated according to relevant formulas,and patients were stratified according to corrected serum calcium and potassium levels.Hypocalcemia was defined as Ca<2.0mmol/L,normal blood calcium was defined as 2.0mmol/L≤Ca≤2.7mmol/L,and 2mmol/L≤Ca≤2.2mmol/L was defined as normal but low calcium levels.Hypokalemia was defined as K<3.5mmol/L,normal blood potassium was defined as 3.5mmol/L≤K≤5.5mmol/L,and 3.5mmol/L≤K≤4mmol/L was defined as normal but low potassium levels.We also performed body composition tests on patients to obtain nutrition-related indicators and volume-related indicators,including fat tissue mass（FAT）,adipose tissue mass（ATM）,fat tissue index（FTI）,lean tissue mass（LTM）,lean tissue index（LTI）,body cell mass（BCM）,overhydration（OH）,total body water（TBW）,extracellular water（ECW）,intracellular water（ICW）,body mass index（BMI）.In addition,12-lead electrocardiogram was performed on the patients,and the QTc interval was calculated by Bazett formula,namely,QTc interval=QT/RR^1/2.QTc interval>440ms was considered as prolonged.According to this standard,patients were divided into prolonged QTc interval group（QTc interval>440ms）and normal QTc interval group（320ms≤QTc interval≤440ms）.Patients were followed up by telephone or during hospitalization every 3-6 months until death,cessation of hemodialysis treatment,or loss of follow-up.The end point event was all-cause death,that is,death from any cause during follow-up.SPSS 25.0 software was used for statistical analysis.All measurement data were tested for normality and homogeneity of variance.The measurement data conforming to normal distribution or approximately conforming to normal distribution were represented by （?）±s and comparison between groups was performed by t test.Data that did not conform to normal distribution or non-variance homogeneity were represented by M(P₂₅,P₇₅),and rank-sum test was used for comparison between groups.Enumeration data were expressed by number of cases and percentage,and chi-square test was used for comparison between groups.Pearson and Spearman correlation analysis was used to analyze the correlation between body composition indicators and QTc interval,and binary Logistic regression was used to analyze the influencing factors of QTc interval prolongation in MHD patients.Kaplan-meier survival analysis and log-rank test were used to analyze survival and compare the difference of cumulative survival between the prolonged QTc interval group and the normal QTc interval group.Cox regression analysis was used to discuss the influencing factors of all-cause death in MHD patients.P<0.05 was considered statistically significant.Results1.A total of 305 MHD patients were enrolled in this study,including 159 females and 146 males,aged from 21 to 87 years,with an average age of（51.1± 14.04）years and dialysis age of 36（12,60）months.There were 165 cases（54.1%）of chronic glomerulonephritis,68 cases（22.3%）of diabetic nephropathy,31 cases（10.2%）of hypertensive renal damage,41 cases（13.4%）of polycystic kidney and other diseases.78 cases（25.6%）were complicated with diabetes,284 cases（93.1%）were complicated with hypertension.There were 183 cases（60%）in the normal QTc interval group and 122 cases（40%）in the prolonged QTc interval group.There were no significant differences in gender,primary disease type,the percentage of diabetes mellitus and hypertension between the two groups（P>0.05）.2.Comparison of age,dialysis age,laboratory indexes and body composition analysis indexes between the two groups:Compared with the normal QTc interval group,the ratio of 2mmol/L≤Ca<2.2mmol/L and 3.5mmol/L≤K≤4mmol/L in the prolonged QTc interphase group was higher,the levels of PLT,LTI,TBW,ICW and BCM were significantly decreased,while the levels of CRP and FTI were increased.While other indexes,including age and dialysis age,had no significant difference between the two groups（P>0.05）.3.Correlation analysis of QTc interval and body composition in MHD patients showed that QTc interval was positively correlated with FTI（r=0.143,P=0.013）,while LTI（r=-0.164,P=0.004）,TBW（r=-0.135,P=0.019）,ICW（r=-0.164,p=0.004）and BCM（r=-0.176,P=0.002）were negatively correlated.4.With the prolongation of QTc interval as the dependent variable,the indexes with statistical differences in inter-group comparison were included as independent variables,and the "Forward:LR" was used for binary Logistic regression analysis.Statistical results showed that FTI（OR=1.070,95%CI:1.001～1.144,P=0.045）,2mmol/L≤Ca≤2.2mmol/L（OR=2.670,95%CI:1.319～5.403,P=0.006）and CRP（OR=1.014,95%CI:1.000～1.029,P=0.049）were independent risk factors for QTc interval prolongatian.5.Survival analysis of all-cause death in MHD patients:By the end of follow-up,a total of 24 patients died,including 9 patients in the normal QTc interval group and 15 patients in the prolonged QTc interval group.Kaplan-meier survival curve showed that the cumulative survival rate in the prolonged QTc interval group was significantly lower than that in the normal QTc interval group（Log-rank test χ²=5.606,P=0.018）.6.Univariate Cox regression analysis showed that age,prolongation of QTc interval,Alb,CRP,LTI,BCM,TBW and ICW were the influencing factors of all-cause death in maintenance hemodialysis patients（P<0.05）.Variables with P<0.2 in univariate Cox regression analysis were included in multivariate Cox regression and "forward:LR" method was used to enter the equation.The results showed that age and prolonged QTc interval were still independent influencing factors of all-cause death in maintenance hemodialysis patients,and prolonged QTc had a higher risk than age（HR=4.137,95%CI 1.117～15.320,P=0.034 vs.HR=1.052,95%CI 1.004～1.102,P=0.033）.ConclusionsFTI,normal but low calcium levels（2mmol/L≤Ca≤2.2mmol/L）and CRP were independently associated with prolonged QTc in MHD patients,and the risk of all-cause death was increased in patients with prolonged QTc interval.Monitoring QTc interval as well as related risk factors in high-risk patients and active intervention can reduce the risk of death in MHD patients to a certain extent.