Effects of combined changes in serum calcium and potassium on QT interval. A study by Holter electrocardiographic monitoring during hemodialysis.

Holter electrocardiographic recordings were performed for 24 hours in 20 patients on chronic hemodialysis to evaluate the effect of changes in serum calcium and potassium during a 5-hour hemodialysis period on the QT interval. Hemodialysis caused an acute increase in serum calcium from a predialysis value of 9.6 +/- 1.3 mg/dl to 11.5 +/- 1.2 mg/dl and a decrease in serum potassium from 4.9 +/- 0.6 mEq/L to 3.5 +/- 0.4 mEq/L. The Q-oTc interval shortened from a predialysis value of 0.240 +/- 0.023 sec to a minimum of 0.215 +/- 0.022 sec during the 5th hour of hemodialysis. This Q-oTc interval shortening was correlated strongly with an increase in serum calcium and was statistically significant only in subjects showing an increase in serum calcium of more than 2 mg/dl (p less than 0.05). The Q-eTc interval increased from a predialysis value of 0.392 +/- 0.030 sec to 0.414 +/- 0.024 sec during the 4th hour of hemodialysis. This Q-eTc interval prolongation was correlated with a decrease in serum potassium. It was concluded that increased serum calcium during hemodialysis caused shortening of the Q-oTc interval, that the degree of shortening was proportional to the magnitude of increase in serum calcium, and that changes in serum calcium and the Q-oTc interval were concurrent. It was also concluded that hemodialysis resulted in prolongation of the Q-eTc interval. This change was possibly caused by a decrease in the level of serum potassium during the procedure.