ANAEMIA PREDICTS PROLONGED QT INTERVAL IN PREDIALYSIS CHRONIC KIDNEY DISEASE PATIENTS

摘要

Background. Patients with advanced chronic kidney disease (CKD) have increased cardiovascular mortality of multifactorial aetiology including cardiac arrhythmias. Prolonged QT interval may be responsible for some of the cardiac deaths. This prospective cross sectional study investigated the QTc in predialysis chronic kidney disease patients compared with age and sex matched controls subjects. It also investigated association between QTc and variables that may affect it.Methods. Ninety one patients in CKD stages 3 to 5 and thirty two control subjects matched for age and sex were studied using standard 12-lead electrocardiogram.Results. Fifty four (59.3%) of CKD patients had abnormal QTc defined as QTc ≥0.44. This was observed in all the stages of CKD studied (67% for CKD stage 3, 62% for stage 4 and 58% for stage 5). There was no statistical difference in the frequency of abnormal QTc between the stages of CKD, p = 0.707. All the control subjects had normal QTc with a mean of 0.38±0.02. BMI, SBP, DBP, Hb, and aetiology of CKD correlated with QTc. Only Hb predicted the presence of prolonged QTc in CKD. Conclusion. The QTc interval is significantly prolonged in predialysis CKD patients in this study. This abnormality was present in stages 3 to 5 CKD. This may be a contributing factor to the high cardiovascular mortality in CKD patients. Anaemia was predictive of prolonged QTc in this study. It is reasonable to recommend an ECG as part of the evaluation of all patients with CKD. Introduction Patients with chronic kidney disease are at significantly increased risk for both morbidity and mortality from cardiovascular disease,1,2.. Cardiovascular disease accounts for at least 50% of deaths in end stage renal disease 3. The increase in cardiovascular risk associated with CKD may be due to several mechanisms, including age, haemodynamic overload due to hypertension and anaemia, left ventricular hypertrophy, dyslipidaemia, a high prevalence of diabetes mellitus and impaired glucose tolerance, prothrombin changes, neurohormonal overactivity, and divalent ion abnormalities.4, 5 More recently other factors known as ‘new or non-classic’ factors have been identified. These include homocysteine, inflammation, and oxidative stress6, 7. This increased risk of cardiovascular mortality may exist in mild renal insufficiency 8-10 and progresses with the severity of renal disease.11, 12. Dialysis patients are a high risk group for all cause death. The death rate for all US dialysis patients between 1996 and 1998 was 231/1000 patient years.13 Cardiac disease is the major cause of death in dialysis patients, accounting for approximately 45% of all-cause mortality.13 Sudden cardiac death may be implicated in 60% of all cardiac deaths in dialysis patients. In the USRDS database, ‘cardiac arrest; cause unknown ‘ accounted for 47% of all cardiac deaths and another 13% were attributed to arrhythmia.14 Prolonged QT interval, a measure of heterogeneity of vascular repolarization, has been linked with increased risk of sudden death in dialyzed patients and it may be more prolonged, after haemodialysis.15-17 This cross sectional, prospective study was designed to study the QTc in patients with CKD stages 3 to 5 at first presentation before the commencement of renal substitution. The mean QTc of the patients was compared with that of age and sex matched control subjects. The association between the QTc and other factors was studied. Materials and Methods Chronic kidney disease patients attending the Nephrology Clinic of University of Nigeria Teaching Hospital, Enugu, a tertiary health institution were recruited for the study. The study was conducted between February 2003 and January 2004 after approval by the hospital’s Ethics Committee. Informed consent was obtained from each patient and control subject. Chronic kidney disease was defined as by the National Kidney Foundation Quality Outcome Initiative guidelines (K/DOQI)18. Patients were recruited if they were