NDT Advance Access published online on March 22, 2005
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfh770
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1 Chair of Nephrology, Department of Internal Medicine, University of Messina, Italy
* To whom correspondence should be addressed. Background. The risk of developing cardiovascular diseases is higher in patients on haemodialysis than in the general population. These patients may develop arrhythmias that depend on the extra- and intracellular concentrations of potassium. ECG findings, particularly the QT interval and its dispersion (QTd) and the QTc (QT interval corrected for heart rate according to Bazett's formula) and its dispersion (QTcd), may be direct indicators of the risk of developing arrhythmia. Methods. Our cohort comprised 28 patients who were dialysed for 3.5-4 h three times per week, first with haemodiafiltration with a constant potassium concentration (HDF) in the dialysis bath then with haemodiafiltration with variable concentrations of potassium (HDFk). ECGs were done at different time intervals: at the start of dialysis (T0), at 15 (T15), 45 (T45), 90 (T90) and 120 min (T120) after the beginning of the session, and at the end of treatment (Tend). ECG-derived data (QT, QTd, QTc and QTcd) were measured. At the same time points, plasma electrolytes, intra-erythrocytic potassium and the electrical membrane potential at rest (REMP) of the erythrocytic membrane were measured. Results. Plasma potassium concentration diminished more gradually in HDFk than in HDF, the difference being statistically significant at T15 and T45 (P<0.05), and T90 (P<0.01). The intra-erythrocytic potassium concentration remained constant throughout the observation period. In both HDF and HDFk, REMP was lower at all points after T0 (P<0.05), but the reduction was greater and more significant in HDF than in HDFk at T15 and T120 (P<0.05). ECG revealed a statistically significant diminution in HDFk vs HDF in the measures of dispersion of QT and QTc at T15, T90, T120 and Tend (P<0.01) and of QTcd at T45 (P<0.05). The mean of QTd, adjusted for plasma potassium, increased over time in HDF with large alternate mean increase and decrease peaks and error intervals. In HDFk, instead, there was a progressive and constant diminution with minor error intervals. QTcd adjusted for plasma potassium had the same trend. A marked difference was found between the final values in standard HDF and those in HDFk. Conclusions. HDF and HDFk have significantly different effects on QTc. ECG data demonstrate that the risk of arrhythmia could be lower, with a variable removal of potassium during haemodialysis. With HDF but not HDFk, hyperpolarization of the cell membrane is detected, and this could have a destabilizing effect on different types of cardiac cell, giving rise to retrograde circuits.
Received August 22, 2004
Accepted December 22, 2004
Original Articles
The effect of two different protocols of potassium haemodiafiltration on QT dispersion
2 Department of Pathology and Experimental Microbiology, University of Messina, Italy
Michele Buemi, E-mail: buemim{at}unime.it
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