Fibrin modification by ionic and nonionic contrast media during cardiac catheterization

Abstract

T he rare but serious complication of thromboembolism during cardiac catheterization is believed to be a result of an imbalance between the prothrombotic nature of the invasive procedure and the antithrombotic effects of adequate catheter flushing and of the contrast agents themselves. Although thrombotic complications may occur as a result of an identifiable problem in procedural technique, thrombosis sometimes occurs without explanation.’ Both ionic and nonionic contrast media are known to have an inhibitory effect on platelet aggregation and blood clotting in vitro2-9; however, nonionic contrast has been shown to have a less inhibitory effect,3-5*7-9 and therefore could theoretically result in a greater tendency for thrombosis.tO Hwang et al” showed that use of the nonionic agents iohexol and iopamidol was associated with coronary thromboembolism during cardiac catheterization in dogs, whereas the ionic agents ioxaglate and diatrizoate were not associated with such clotting complications. It has also been observed that clots embolized into coronary arteries during catheterization are particularly difficult to dissolve with thrombolytic therapy.t2 Both the ionic contrast agent diatrizoate and the nonionic agent iopamidol have been shown in vitro to cause changes in fibrin assembly and structure, resulting in thin fibrin fibrils,6 which render the fibrin resistant to fibrinolysis. Fibrin with low mass/length ratio in certain disease states has been shown to be resistant to fibrinolysis.13 Demonstration of fibrin changes in vivo during cardiac catheterization would provide further evidence that the in vitro changes have clinical relevance, including providing a possible explanation for why contrast-induced thrombus is resistant to fibrinolysis. This study evaluates the effects of ionic and nonionic contrast media on fibrin assembly and structure by analyzing samples obtained at critical times and anatomic locations during cardiac catheterization. Twenty-three patients undergoing cardiac catheterization between March 14,1990, and July 12,1990, were prospectively studied. Exclusion criteria were as follows: history of bleeding disorder, hypercoagulable state, treatment with warfarin or heparin, hematocrit <30%, platelet count <150,000, abnormally elevated protime or partial thromboplastin time, uncontrolled angina at rest, or myocardial infarction within 3 months. The indication for cardiac catheterization was suspicion of coronary artery disease due to chest pain or a positive func-