Inotropic effects of ionic contrast media: The role of calcium binding additives

Renografin‐76 (RG76) regularly depresses myocardial contractility during coronary angiography. Angiovist‐370 (AV370) is a contrast medium similar to RG76 except the calcium sequestering agents sodium citrate and EDTA in RG76 have been replaced by calcium EDTA (an additive that does not bind additional calcium). To determine if the calcium sequestering agents contribute to the mechanical depression produced by ionic contrast media, this study compared the inotropic response of RG76 to that of AV370. Additionally, saline solutions containing sodium citrate + EDTA and calcium EDTA at concentrations found in the respective contrast media were also compared. In 10 open chest dogs the percent change and duration of the inotropic response following intracoronary injections of RG76 and AV370, as well as solutions of sodium citrate + EDTA and calcium EDTA were compared using Walton‐Brodie strain gauges. Injections, 2 cc, of RG76 and AV370 produced a biphasic response characterized by an initial negative inotropic response followed by a more prolonged positive inotropic response. The magnitude (67 ± 3% vs 59 ± 2%; p < 0.001) and duration (34 ± 3 vs 24 ± 2 sec; p < 0.001) of the initial negative inotropic response was greater with RG76 than with AV370. The magnitude of the secondary positive inotropic response with RG76 was not different from that obtained with AV370 (31 ± 12% vs 28 ± 10%; p > 0.3). This positive response was not affected by b̃‐adrenergic blockage with 0.2 mg/kg of timolol. Similarly, 4 cc of sodium citrate + EDTA produced a significantly greater magnitude (56 ± 5%) and longer (42 ± 7 sec) negative inotropic response than calcium EDTA (17 ± 2% and 15 ± 3 sec) or 0.9% saline (18 ± 8% and 13 ± 2 sec; p < 0.001). The results suggest that the calcium sequestering agents sodium citrate + EDTA produce significant negative inotropic effects contributing to the mechanical depression produced by RG76. However, the calcium binding additives are not solely responsible for the depression in contractility produced by ionic contrast media. Contrast media lacking calcium binding additives may be preferable for coronary angiography.