Left Ventricular Contractility Varies Directly with Blood Ionized Calcium

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 (Vcf_c).

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, Vcf_c, 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), Vcf_c fell to 0.89 ± 0.04 circ/sec (P < 0.001 compared with medium); at high Ca²⁺ (1.68 ± 0.07 mmol/L) Vcf_c 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.