QTc dispersion increases during hemodialysis with low-calcium dialysate

Background. The risk of ventricular arrhythmias is known to increase during hemodialysis (HD) treatment, but the cause of this phenomenon has remained unidentified. QT dispersion (= QT(max) - QT(min)) reflects heterogeneity of cardiac repolarization, and increased dispersion is known to predispose the heart to ventricular arrhythmias and sudden cardiac death. Methods. We studied the effect of dialysate calcium concentration on cardiac electrical stability during HD treatment in 23 end-stage renal disease patients. Three HD treatments were applied with dialysate Ca++ concentrations of 1.25 mmol/L (dCa(++)1.25), 1.5 mmol/L (dCa(++)1.5), and 1.75 mmol/L (dCa(++)1.75). The QT(c) interval and QT(c) dispersion were measured before and after the three sessions. Results. With the dCa(++)1.5 and dCa(++)1.75 dialyses, serum Ca++ increased and the QT(c) interval remained stable (dCa(++)1.5) or decreased (dCa(++)1.75), but no significant change was noted in QT(c) dispersion. With dCa(++)1.25 HD, serum Ca++ decreased (1.24 +/- 0.11 vs. 1.20 +/- 0.09 mmol/L, P < 0.05), and both the QT(c) interval (403 +/- 27 vs. 419 +/- 33 ms, P < 0.05) and QT(c) dispersion increased (38 +/- 19 vs. 49 +/- 18 ms, P < 0.05). The change in the QT(c) interval correlated inversely with the change in serum Ca++ (r = -0.68, P < 0.0001). Except for serum Ca++ and plasma intact parathyroid hormone, predialysis and postdialysis values in other blood chemistry, blood pressure, heart rate, body weight, and total ultrafiltration were equal in the three dialysis sessions. Conclusion. This study is the first, to our knowledge, to demonstrate that HD increases QT(c) dispersion if a low-calcium (dCa(++)1.25) dialysate is used. This indicates that the use of low-calcium dialysate may predispose HD patients to ventricular arrhythmias and that perhaps it should be avoided, at least when treating patients with pre-existing cardiac disease.