Should we be less reactive about contrast reaction prophylaxis?

During our cardiology training, we were continually cautioned about the risk of contrast reactions, and warned that anaphylactic shock may be especially difficult to treat in patients with advanced cardiovascular disease or in those on beta-blockers. Therefore, over the past several decades in the United States, we have consistently utilized premedications to reduce the risk of contrast allergies in patients with a prior history of contrast reactions. However, the incidence of contrast reactions has been greatly reduced during the evolution from high osmolar ionic contrast to the current standard of isoor lowosmolar non-ionic agents. In fact, a recent publication that evaluated nearly 72,000 cardiac catheterizations found anaphylaxis in only 46 (0.06%), with severe anaphylaxis in only 11 patients (0.015%), and there was no association with the use of betablockers or ACE inhibitors. Unfortunately, there are no randomized trials in the era of nonionic contrast that demonstrate a reduction in anaphylactic reactions. Underpowered studies suggest a reduction in minor reactions, but since anaphylaxis is rare and unpredictable, huge studies would be needed to prove any benefit from pretreatment strategies. Most contrast reactions are nonallergic and are due to non-IgEmediated histamine release from basophils and/or mast cells, or other mechanisms such as complement activation and bradykinin formation. Breakthrough reactions despite premedication can occur in up to 50% of cases; conversely, in patient with prior reactions who received the same contrast without premedication, <1/3 had recurrent reactions. True allergic reactions are due to IgE-mediated drug allergy and fortunately severe reactions are very rare; in that setting, experts have noted that the efficacy of premedication is absent and the specific contrast agent the patient is allergic to should be avoided. But why worry about pretreatment for contrast allergies? It is the standard of care in the United States, and does not seem to be harmful ... that we know of. In this issue of Catheterization and Cardiovascular Interventions, Amr et al. compared 88 diabetics with contrast hypersensitivity who were pretreated with oral steroids prior to cardiac catheterization with 76 diabetics without hypersensitivity. Preand postprocedural glucose levels were significantly higher in diabetics treated with oral steroids, and there was a twofold increase in the need for intravenous insulin (67% vs. 32%). Further, diabetics who received steroids had significantly higher systolic blood pressures and more severe hypertension requiring use of IV anti-hypertensive medications (81% vs. 19%) peri-procedurally. There were no differences in 30-day MACE between groups, however event rates were extremely low, and the study was too small to determine clinical outcomes. Other limitations of this study include the fact that it was retrospective, there was no mention of whether diabetic medications were reduced or held prior to the procedure, no information provided on the occurrence of allergic reactions, the % undergoing revascularization after diagnostic angiography, and whether the differences noted in glucose or blood pressure may been influenced by baseline differences in renal function. Since hyperglycemia may affect rates of restenosis, it would have been nice to have longer term follow-up. However, this article shows potential harmful effects of steroid pretreatment and raises many important questions: