Mechanisms of altered myocardial contractility during hemodialysis: importance of changes in the ionized calcium to plasma potassium ratio.

Hemodialysis is associated with alterations in myocardial contractility, but duration and precise determinants responsible for these changes are unknown. We investigated the effect of several variables, established to influence left ventricular (LV) contractility, which normally changed during dialysis: the plasma concentrations of ionized calcium, potassium, bicarbonate, and magnesium and the removal of uremic toxins. The influence of three different isovolemic bicarbonate-dialysis procedures in 16 patients with normal (group 1) and hypertrophied myocardium (group 2) was assessed by echocardiography prior to and up to 44 h following each dialysis. During the first procedure, ionized calcium and potassium concentration decreased, but LV performance remained unchanged in both groups. The second procedure with increased ionized calcium and decreased potassium concentration resulted in an improvement of mean circumferential fiber shortening (VCF from 1.15 to 1.56 circ/s (P less than 0.001) in group 1 and from 1.05 to 1.16 circ/s (P less than 0.05) in group 2. The positive inotropic effect declined gradually up to 12 h (group 1) and 2.5 h (group 2) respectively. In the third procedure when ionized calcium was increased and potassium concentration remained unchanged contractility did not improve. Removal of uremic toxins, decrease in magnesium, and increase in bicarbonate concentrations were comparable during each procedure. These results suggest that the ionized calcium to potassium ratio is the important determinant of dialysis-related augmentation in LV contractility. In LV hypertrophy the expected contractile response is diminished indicating a depressed inotropic state.