Frequency and prognostic significance of QT prolongation in chronic renal failure patients

Cardiovascular mortality and morbidity are high in chronic renal failure (CRF) patients. Previous studies on non-uraemic patients with heart failure (HF), hypertension or diabetes mellitus (DM) showed that QT and QTc prolongation and dispersion represent cardiovascular risk factors. The patients with long QT interval have more often ventricular premature beats and sudden death than those with normal QT interval. The aim of our study was to evaluate the frequency and predictive value of QT and QTc prolongation in CRF patients, included or not in a chronic dialysis programme. On 68 patients (M/F = 36/32, mean age = 47.6 years), with CRF we analyzed QT and QTc interval with a digital 12 lead electrocardiogram-CARDIAX. 8/68 patients (11.8%) had long QT interval (>0.45"). After having calculated QT corrected (QTc) interval according to the heart rate, 28/68 patients (41.2%) had QT prolongation (>0.45"). Multivariate statistical analysis of clinical factors, but also of biological, electrocardiographic, echocardiographic data and 24 hours of ECG and blood pressure monitoring showed that QT prolongation is statistically significant (p < 0.05) correlated with: number of years of renal failure (p = 0.0001), serum concentrations of potassium and calcium (p = 0.0001) and diastolic BP (p = 0.05). QT prolongation in CRF patients is not dependent on the level of uremia or the type of chronic renal substitution (hemodialysis or continuous ambulatory peritoneal dialysis). There were no statistically significant correlations between QT prolongation and serum concentrations of Mg, PO4, HCO3 and Hb. Long QT interval was not dependent either on the dipper/nondipper profile of mean BP values or ejection fraction of left ventricle. In our study long QT interval was not statistically significant correlated with arrhythmias or sudden death. Despite the high incidence of QT prolongation in CRF patients (41.2%), short-term consequences are not as severe as those in cardiac patients. This is possibly explained by the different pathogenic mechanisms of arrhythmia in CRF when electrolytic disorders are the main cause for the development of arrhythmia. During a mean follow-up of 3.8 months (3-5.5) there were no cases of sudden death on patients with QT prolongation, and arrhythmia incidence was not statistically significant higher than in subjects with normal QT interval.