The Effect of Sodium on the Fibrillatory Propensity of Nonionic Contrast Media

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Abstract
Removing sodium from standard ionic contrast media markedly increases the incidence of ventricular fibrillation in patients undergoing coronary angiography. Newer nonionic contrast media, iopamidol, iohexol, and ioversol contain only trace amounts of sodium. To determine whether sodium attenuates or potentiates ventricular fibrillation from nonionic contrast media, we measured the prolongation in QT interval and performed programmed electrical stimulation with one, two and three extra ventricular stimuli in 40 dogs during 4-mL intracoronary injections of iopamidol, iohexol, and ioversol. Solutions of each contrast medium with added NaCl at concentrations of 0.225%, 0.45%, and 0.9% were compared with standard contrast media. The addition of NaCl markedly increased the amount of QT interval prolongation produced by each contrast medium. With iopamidol, the amount of QT interval prolongation was 40 .+-. 11 msec with standard iopamidol, but was 58 .+-. 11 msec with 0.225% NaCl/iopamidol, 84 .+-. 17 msec with 0.45% NaCl/iopamidol, and 132 .+-. 42 msec with 0.9% NaCl/iopamidol (P < .001). Similar results were seen with iohexol and ioversol. Ventricular fibrillation was difficult to induce with standard solutions of these agents (even with three extra stimuli), but became progressively easier to induce when NaCl was added. Three extra stimuli produced ventricular fibrillation in zero of 11 dogs with standard iopamidol, zero of 11 with 0.225% NaCl/iopamidol, three of 11 with 0.45% NaCl/iopamidol, and eight of 11 with 0.9% NaCl/iopamidol (P < .001). Similar results were observed with iohexol and ioversol. The addition of choline chloride or dextrose did not increase ventricular fibrillation and QT interval prolongation. It is concluded that standard preparation of nonionic contrast media have a very low fibrillatory propensity. The addition of NaCl increases the amount of QT interval prolongation, making ventricular fibrillation easier to induce. The detrimental effects of added NaCl are due to the addition of the Na+ ion rather than the Cl- ion or an osmotic effect.