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 (= QTmax - QTmin) 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 QTc interval and QTc 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 QTc interval remained stable (dCa++1.5) or decreased (dCa++1.75), but no significant change was noted in QTc 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 QTc interval (403 +/- 27 vs. 419 +/- 33 ms, P < 0. 05) and QTc dispersion increased (38 +/- 19 vs. 49 +/- 18 ms, P < 0. 05). The change in the QTc 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 QTc 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.