Differing mechanisms of clotting inhibition by ionic and nonionic contrast agents
Article Abstract:
The new nonionic contrast agents iopamidol (Isovue) and iohexol (Omnipaque) are highly biocompatible and an improvement over conventional contrast agents. They are, however, less effective in stopping bleeding than conventional high-osmolality agents when they are inadvertently contaminated by blood during an angiographic procedure. Consequently, they should be used in conjunction with precise technique. Poor technique raises the hazard that clots may be introduced into the patient. Ioxaglate, while ionic, has the advantage of possessing relatively low osmolality. Low osmolality a measurement of ions dissolved in a substance per unit of solvent, means that a contrast agent will produce less disturbance in the circulation and fewer adverse symptoms in the patient. Research was undertaken to determine how intravascular clotting could be initiated by these contrast agents. Ioxaglate exerted about twice the anticoagulant effect of the two nonionic agents, as measured by its effect in prolonging the activity of thrombin, an enzyme in shed blood which reacts with fibrinogen, converting it to fibrin, which forms the basis of a blood clot. It is about four times more potent when a recalcified whole-blood activated clotting time (RACT) test is used. It seems likely that ioxaglate inhibits coagulation prior to the generation of thrombin. The nonionic agents appear to prevent coagulation primarily after the production of thrombin. When enough thrombin was present to clot the diluted sample, there was also enough thrombin present to clot the parent mixture. Therefore, when thrombin formed, its presence was signaled by clotting in the blood-contaminated contrast agent. This attribute of ioxaglate is an advantage under conditions in which the contrast agent is inadvertently contaminated with blood. The absence of clots can be taken as reliable evidence that no thrombin is present and that the contaminated contrast agent will not cause clotting on reinjection. Similar conclusions cannot be drawn when blood inadvertently contaminates the nonionic agents iopamidol and iohexol. These findings underscore the necessity to maintain meticulous angiographic technique when using the newest nonionic contrast agents.
Publication Name: Radiology
Subject: Health
ISSN: 0033-8419
Year: 1989
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Angiography in the 1990s: diagnosis and therapy
Article Abstract:
Initial evaluation of a patient suspected of having or known to have peripheral vascular disease begins with a patient history and a noninvasive (without entering the body) examination. Peripheral vascular disease refers to disease, such as narrowing or obstruction, in the veins and arteries of the extremities. If this evaluation establishes the presence of such disease, and therapy requiring more extensive evaluation is indicated, angiography is the next logical step. Angiography is an invasive technique used to image blood vessels for evaluation; angiography requires insertion of a catheter into the vessel. Variations of this technique are also used for treating disease in the vessels. Percutaneous transluminal angioplasty (PTA) involves inserting the catheter into the vessel and inflating a balloon carried by the catheter in order to open a blockage of the vessel. This procedure can be as successful as direct surgical treatment, and is less invasive. PTA can also be done in conjunction with angiography. An article by Fellmeth and colleagues in the April 1990 issue of Radiology examined the benefits of performing angiography and PTA, if needed, in the same procedure; this saves both time and money and is less intrusive for the patient. The authors questioned whether the contrast materials used for angiography might interfere with the PTA. This was speculated because seven subjects who were examined with angiography had quick progressions in disease afterwards. Further analysis of these cases showed that the contrast material was not likely to be the cause. The interconnections between diagnostic and therapeutic uses of angiography will require the radiologist to become more involved in the clinical aspects of medicine. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: Radiology
Subject: Health
ISSN: 0033-8419
Year: 1990
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