Purpose: Hemodialysis (HD) patients present an elevated risk of ventricular arrhythmias and sudden death. This risk is correlated with QTc dispersion, assessed as the difference between maximum and minimum QT recorded on 12 leads. Our study aimed to estimate the difference between QT, QTc, QT dispersion and QTc in HD patients on standard HD and online hemodiafiltration (HDF) in pre- and post-dialysis vs. normal controls.
Methods: Nineteen uremic patients on standard HD (13 males, six females) and nine patients (six males, three females) treated with on-line HDF were studied. Seven normal subjects were the control group, matched for age and sex. No one was taking drugs that could interfere with electrocardiographic morphology and QT value. Basal anthropometric parameters were taken and simultaneous 12-lead electrocardiograms (ECGs) were recorded before and 30 min after HD. Serum concentration of creatinine (Cr), urea and electrolytes (Na, K, Mg, Ca, Pi) were monitored before and 30 min after HD, in the short interval section. QT interval was measured according to the Bazett formula, in the presence of different heart rates: QTc=QT/RR(0.5) (heart rate corrected QT interval).
Results: Anthropometric parameters were similar among the groups. Before dialysis, standard HD patients had lower calcium and higher potassium than the controls (Student's t-test): (p<0.01, p<0.004). ECGs in the two groups did not show essential differences. After dialysis calcium was higher and magnesium lower in HD patients than in controls: (p<0.0006, p<0.000); QT and QTc dispersion was higher in HD patients than in controls: (p<0.01, p<0.04). Before dialysis on-line HDF patients had lower magnesium (p<0.01) than controls; while there were no electrocardiographic differences between them. In the post-dialytic phase, calcium was higher and phosphates, magnesium and potassium were lower than in controls: (p<0.001, p<0.01, p<0.002, p<0.01); QT and QTc dispersion was higher in HD patients (p<0.03, ns). Controls did not demonstrate any correlation between electrolyte and electrocardiographic parameters; while QTc dispersion and phosphates positively and directly correlated in uremic standard HD patients after dialysis (r=0.48, p<0.02), and then QTc dispersion correlated negatively to Ca/P ratio (r=-0.63, p<0.003).