Gadzooks, noniodinated contrast?

Abstract

Contrast-enhanced X-ray imaging remains the cornerstone of catheter-based diagnostic and therapeutic approaches to disorders of the cardiovascular system. Central to these procedures are intravascular agents that absorb X-ray within the diagnostic range, thus providing transient opacification of vessels and cardiac chambers. Materials used for this purpose have been derivatives of the tri-iodinated benzene ring and include the traditional (but essentially abandoned) high osmolal ionic, the low osmolal ionic, the low osmolal nonionic, and the isosmotic nonionic contrasts. An ideal intravascular contrast material would absorb X-ray while otherwise remaining physiologically inert. Iodine has a reasonable K-edge of absorption and is in general well tolerated. Iodinated contrasts, however, have been associated with a number of undesirable effects and considerable effort has been directed at the development of better tolerated agents over the last 40 years. Much of the toxicity of the traditional agents has been related to their hyperosmolality. This has been effectively addressed, as noted above, by the introduction of contrasts having progressively lower osmolalities such that agents isosmotic to plasma are now available. This has remarkably reduced the incidence of allergy-like reactions as well as the pain, heat, nausea, and vomiting that accompanied the administration of the traditional high osmolal contrasts. Reduction of contrast osmolality has also significantly reduced extent and frequency of hemodynamic and arrhythomogenic perturbations related to intracoronary and high-volume (e.g., ventricular, aortic, pulmonary arterial) injections. The low osmolal agents (especially the nonionic dimers) are so well tolerated that, when necessary in complex cases, we have administered over a liter of contrast without untoward reaction. This is not to say that even the best of iodinated contrast is risk-free because certainly such is not the case.