Clotting

Aspelin P et al. Effects of iodinated contrast media on blood and endothelium.Eur Radiol 2006[27].





Additional statements:

• The mechanisms of contrast media effect on platelets are unclear and there are no clinical data to date to suggest a clinically significant effect of contrast media upon platelet-induced coagulation.
• In-vitro tests reveal that all contrast media inhibit blood coagulation but to different extents. In specific assays, coagulation times are shorter for non-ionic monomers but always longer than controls.
• Clinical data are less easy to evaluate due to patient- and procedure-related variability (haemostatic system, vessel wall condition, use of guidewires, catheters, balloons, stents). Due to the rapid clearance of contrast media, their anticoagulant effect tends to be local rather than systemic, and their effect may not be significant if measured in distant peripheral blood vessels .
• Syringe material greatly influences the tendency for clot formation. In syringes containing contrast media and blood, the coagulation rates in order of increasing propensity are : polypropylene < styrene acrylonitrile < glass. Likewise, catheter and guidewire materials have thrombogenic effect - in increasing order: polyethylene < polyurethane < teflon.
• In-vitro studies demonstrate that contrast media impede fibrinolysis and delay the onset of lysis by recombinant tissue-type plasminogen activator (rt-PA), urokinase and streptokinase. This effect is reduced by increasing the concentration of the lysis agent. Contrast media cause fibrin to form in long/thin fibrils which are more resistant to fibrinolysis .
• The clinical relevane of in-vitro observations is often equivocal. Many in-vitro studies employ prolonged incubation periods and very high (often non-physiological) concentrations of contrast media. In contrast, contrast media are rapidly diluted and excreted after intravascular injection in humans. Additionally, in-vitro studies fail to account for patient- and procedure-related factors.
• All contrast media have anticoagulant properties, and ionic contrast media tend to be more thrombogenic than non-ionic contrast media. Acute/ subacute thrombus formation remains a topic of debate, including the use of low-osmolar, ionic, contrast media in preference to low-osmolar, nonionic, contrast media in coronary interventions. However, the general consensus is that good angiographic technique is the most important factor to reduce thrombotic complications. Drugs and interventional devices that decrease the risk of thromboembolic complications during interventional procedures may minimize the importance of the effects of contrast media.