Study Objective: To determine the effect of variations in blood ionized calcium (Ca2+) on myocardial contractility independent of changes in loading conditions and other biochemical variables.
Design: Hemodialysis done in a randomized, double-blind manner with dialysates differing in calcium concentration only. Left ventricular contractility was assessed using the load- and heart rate-independent relationship between end-systolic wall stress (<es) and rate-corrected velocity of fiber shortening (Vcfc).
Setting: In-hospital dialysis unit and echocardiography laboratory of a university medical center.
Patients: Seven patients with stable, chronic renal failure maintained on regular hemodialysis.
Interventions: Each patient was hemodialyzed three times within 1 week with dialysates differing in calcium concentration only. Ultrafiltration was adjusted to achieve the same postdialysis weight. Immediately after dialysis, two-dimensionally targeted M-mode echocardiographic and calibrated carotid pulse tracings were recorded over a wide range of left ventricular end-systolic wall stress values (a measure of left ventricular afterload) generated by either methoxamine or nitroprusside.
Measurements and Main Results: After dialysis, three statistically distinct levels of Ca2+ were achieved. When Ca2+ was 1.34 ± 0.03 mmol/L, Vcfc, calculated at a common level of afterload (<es = 50 g/cm2), was 1.01 ± 0.05 circ/sec; at low Ca2+ (1.02 ± 0.02 mmol/L), Vcfc fell to 0.89 ± 0.04 circ/sec (P < 0.001 compared with medium); at high Ca2+ (1.68 ± 0.07 mmol/L) Vcfc rose to 1.10 ± 0.03 circ/sec (P < 0.001 compared with medium and low).
Conclusion: Variations in Ca2+ are directly correlated with clinically significant changes in myocardial contractility.