604 LETTER Mayo Clin Proc, April 1990, Vol 65

5. GroUman JH Jr, Lui CK, Astone RA, Lurie MD: Throm­boembolic complications in coronary angiography asso­ciated with the use of nonionic contrast medium. Cathet Cardiovasc Diagn 14:159-164,1988

6. GroUman JH Jr: Reply to letter to the editor. Cathet Cardiovasc Diagn 16:146,1989

7. Hwang MH, Piao ZE, Murdock DK, Messmore HL, Giardina JJ, Scanlon PJ: Risk of thromboembolism during diagnostic and interventional cardiac proce­dures with nonionic contrast media. Radiology 174:453-457, 1990

8. Fareed J, Walenga JM, Saravia GE, Moncada RM: Thrombogenic potential of nonionic contrast media? Radiology 174:321-325, 1990

D r . K i n g r e p l i e s

Dr. Robertson's commentary about the complex issue of thrombogenic potential of nonionic contrast media is timely and important when the appropriate use of the nonionic contrast agents is being discussed. The recent studies by Fareed, Hwang, and Kopko and their associates' ^ addressed the issue of the relative lack of anticoagulation that the nonionic contrast media seem to possess. Although most studies have dealt with in vitro situations, it is not unreasonable to be concerned about possible in vivo thrombogenic complications when these new nonionic agents are used, especially in coronary angiography and cere­bral angiography. Also, one should be concerned when certain patients are already at high risk for thrombogenic complications.

In the report by Fareed and colleagues,' certain risk factors for possible nonionic contrast media-induced thrombosis were identified (Table 1). In addition, Fareed and associates showed that throm­bin generation was dramatically increased with use of nonionic contrast agents when glass syringes were used in angiography. Thus, their conclusion was that nonionic contrast media should be used only with plastic syringes.

In light of Dr. Robertson's commentary and stud­ies that have been reported recently, it is apparent that the potential for thrombotic complications is higher with nonionic contrast agents than with ionic

Table 1.—Risk Factors for Nonionic Contrast Media-Induced Thrombosis

1. Antithrombin III deficiency 2. Protein C or protein S deficiency 3. Hyperfibrinogenemia 4. Thrombocytosis 5. Increased factor VIII levels 6. Hemoconcentration 7. Hyperviscosity syndrome 8. Paraproteinemias 9. Leukemias (increase in number of leukocytes)

10. Hemolysis 11. Oral contraceptives and smoking

From Fareed and associates.' By permission of the Radio­logical Society of North America, Inc.

contrast agents. In addition, extreme care and me­ticulous technique should be used during angiog­raphy to prevent the mixing of blood and the contrast medium. It is now apparent that large-scale prospec­tive clinical trials should be conducted to determine the clinical significance of the thrombogenic risk with nonionic contrast media. Until then, maintaining a continuous saline drip flowing through the intravas­cular catheter and systemic or local administration of heparin (or both) are two commonly used safety pre­cautions that may provide an improved safety margin until further information is gained from future clini­cal studies.

Bernard F. King, M.D.

REFERENCES 1. Fareed J, Walenga JM, Saravia GE, Moncada RM:

Thrombogenic potential of nonionic contrast media? Radiology 174:321-325, 1990

2. Hwang MH, Piao ZE, Murdock DK, Messmore HL, Giardina JJ, Scanlon PJ: Risk of thromboembolism during diagnostic and interventional cardiac proce­dures with nonionic contrast media. Radiology 174:453-457, 1990

3. Kopko PM, Smith DC, Bull BS: Thrombin generation in nonclottable mixtures of blood and nonionic contrast agents. Radiology 174:459-461, 1990