Contrast, coagulation, and fibrinolysis

Effects on Erythrocyte Aggregation and Blood Coagulation from Iohexol Solutions with and without Sodium Chloride

Solutions of the nonionic monomeric contrast medium iohexol (300 mg I/ml) with and without added NaCl were investigated for effects on red blood cell aggregation and blood coagulation. Three volumes of a test solution were mixed in test tubes with one volume of human blood. During 30 min samples of the mixture were taken for investigation. Six test solutions were used: 1) iohexol, 2) iohexol+glucose 280 mM, 3) iohexol+NaCl 150 mM, 4) glucose 280 mM, 5) glucose 140 mM+NaCl 75 mM, 6) NaCl 150 mM. Test solutions with NaCl caused no aggregation. Test solutions without NaCl always caused macroscopic red cell aggregates. These aggregates always disappeared when saline was added to the sample. The macroscopic red cell aggregates could be dispersed to microscopic aggregates by shaking the test tubes. During the next 30 min macroscopic aggregates returned in the glucose solution but not in the iohexol solutions. In 30 min, blood mixed with iohexol solutions never coagulated while blood layered on top of the same iohexol solutions always coagulated. Blood mixed with solutions 5 and 6, both without iohexol, always coagulated. It is concluded that adding 150 mM NaCl to iohexol did not eliminate its ability to antico-agulate whole blood, but inhibited its ability to aggregate red cells. This inhibition was not caused by the osmotic effects of the added NaCl.

Coronary Angioplasty Using a Low Osmolar Nonionic Contrast Medium

This study was performed to investigate the occurrence of acute angiographic and clinical complications following PTCA using a low osmolar nonionic contrast medium. Five hundred consecutive PTCA procedures were analyzed retrospectively. The incidence of acute in-laboratory complications during PTCA as well as complications occurring during the hospital stay 24 to 48 hours after the procedure were recorded. Occlusion of the dilated artery or a side branch was observed in 19 (3.8%) of the procedures, major dissection in 34 (6.8%), and thrombus in 14 (2.8%). One patient died, 6 (1.2%) required emergency coronary artery bypass grafting (CABG), 4 (0.8%) required an emergency PTCA, and 7 (1.4%) suffered myocardial infarction (MI). Our results show that angiographic findings of thrombus, major dissection and occlusion were serious conditions that related to the clinical complications MI, emergency CABG and re-PTCA. Patients with unstable angina were risk patients for both angiographic and clinical complications. Low rates of intraarterial thrombus formation and coronary artery occlusion indicate good angiographic technique and anticoagulant and antiplatelet medication.

Blood Clot Formation in Angiographic Catheters

Human blood was injected into angiographic catheters filled with contrast media or flushing media. The catheters were allowed to stand at 37°C for 10, 20 or 30 min. Physiologic saline was then injected through the catheters, the catheter contents were shaken and filtered, and any clots were identified. Diatrizoate, ioxaglate, iohexol, iopamidol and iopromide were tested. Physiologic and heparinized saline were used as controls. At 10 min, clots were found in 65 per cent of the catheters filled with physiologic saline, in 25 per cent with non-ionic media, in 19 per cent with heparinized saline, and in 4 per cent with ionic contrast media. At 30 min, all catheters with physiologic saline, 85 per cent with non-ionic contrast media, 46 per cent with heparinized saline and 23 per cent with ionic contrast media contained a clot. Although all the contrast media were anticoagulants, a more careful angiographic technique is needed for non-ionic media. All the non-ionic agents showed equal results. Physiologic saline without heparin is not suitable for flushing during angiography.

Effect of the radiographic contrast material iopamidol on hemostasis: an observational study in thirty cardiac patients

BACKGROUND

In vitro studies have shown that nonionic radiographic contrast material may induce the generation of thrombin in blood, whereas ionic contrast agents, such as iohexol, do not. However, knowledge of the effects of contrast material on coagulation and fibrinolytic systems in vivo is limited.

OBJECTIVE

This study was designed to assess the effects of the nonionic radiographic contrast material iopamidol on hemostasis in patients undergoing coronary angiography or cardiac catheterization.

METHODS

Patients aged ≥18 years with chest pain and/or dyspnea who underwent coronary angiography or cardiac catheterization with intra-arterial contrast material were assessed for hemostasis. Blood samples were drawn before and 3 minutes after injection of iopamidol. Complete blood count and coagulation profile (bleeding time, clotting time, clot retraction time, euglobulin lysis time [ELT], prothrombin and partial thromboplastin times, coagulation factor I [CFI] level, and platelet factor 3 [PF-3] availability) were assessed. The natural coagulation inhibitors protein C, protein S, and antithrombin III (AT-III) also were measured.

RESULTS

Thirty patients (7 males, 23 females; mean [SD] age, 51.3 [20.2] years; range, 17-79 years) were included in this single-center study. All hematologic variables (hemoglobin, white blood cell count, and platelet count) decreased significantly (P<0.001, P<0.001, and P<0.05, respectively) after administration of iopamidol but remained within normal limits. Mean levels of protein C, protein S, and AT-III did not change significantly after administration of iopamidol. Bleeding time was not changed significantly, and PF-3 availability was prolonged in both groups, but the changes were not statistically significant.

CONCLUSIONS

In this study population, although hemostasis remained grossly intact after injection of nonionic contrast material, the coagulation system may have been affected by the accelerated consumption of CFI and platelets. The affected variables were platelets, clot retraction time, ELT, and natural coagulation inhibitors (protein C, protein S, and AT-III). Although the natural coagulation inhibitors remained within the normal range, the correlations were found significant. These changes in hemostasis affected the vascular phase. If the vascular compartment, especially the endothelium, remained intact, the infusion of nonionic agents in low concentrations might be safe for angiography and other procedures; however, more studies are needed.

Intra-arterial iodinated radiographic contrast material injection administration in a rat middle cerebral artery occlusion and reperfusion model: possible effects on intracerebral hemorrhage

BACKGROUND AND PURPOSE

Observations in human interventional stroke treatment led us to hypothesize that iodinated radiographic contrast material use may contribute to intracerebral hemorrhage. Effects of intra-arterial iodinated radiographic contrast material on hemorrhagic transformation after middle cerebral artery occlusion and reperfusion were studied in a placebo-controlled, blinded preclinical study in rats.

METHODS

Four groups of male Sprague-Dawley rats were studied: saline group (n=8), contrast group (n=12), heparin group (n=9), and contrast+heparin group (n=9). The middle cerebral artery was occluded for 5 hours using suture placement. Heparin was infused before suture removal and reperfusion. Saline and/or contrast were infused immediately during reperfusion. Incidence, location, and size of hemorrhage were determined by brain necropsy inspection at 24 hours.

RESULTS

There was a significant increase in incidence of cortical hemorrhage from control (37.5%), contrast (75.0%), heparin (77.8%) to contrast+heparin (100%; Cochran-Mantel-Haenszel correlation, P<0.01). Both pooled contrast groups (85.7%) and pooled heparin groups (88.9%) had higher rates of cortical intracerebral hemorrhage compared with the control group (P<0.05). Similar trends for increased cortical intracerebral hemorrhage were seen in the contrast-only (P=0.18) and heparin-only (P=0.18) groups. There was a trend for decreased infarct edema in rats receiving contrast versus those without (P=0.06).

CONCLUSIONS

Intraarterial iodinated radiographic contrast material may increase cortical intracerebral hemorrhage, similar to heparin. Iodinated radiographic contrast material effect may be additive to heparin effect on the incidence of cortical intracerebral hemorrhage.

Effects of iodinated contrast media on blood and endothelium

The aim of the study was to assess the effects of iodinated contrast media on blood components and endothelium based on experimental and clinical studies and to produce clinically relevant guidelines for reducing thrombotic and hematologic complications following the intravascular use of contrast media. A report was drafted after review of the literature and discussions among the members of the Contrast Media Safety Committee of the European Society of Urogenital Radiology. The final report was produced following discussion at the 12th European Symposium on Urogenital Radiology in Ljubljana, Slovenia (2005). Experimental data indicate that all iodinated contrast media produce an anticoagulant effect and that this effect is greater with ionic contrast media. Several of the in vitro and experimental in vivo studies on haematological effects of contrast media have not been confirmed by clinical studies. Low- or iso-osmolar contrast media should be used for diagnostic and interventional angiographic procedures, including phlebography. Meticulous angiographic technique is the most important factor for reducing the thrombotic complications associated with angiographic procedures. Drugs and interventional devices that decrease the risk of thromboembolic complications during interventional procedures minimize the importance of the effects of contrast media.

Changes in the fibrinolytic system during angiography with ionic and with nonionic contrast media

RATIONALE AND OBJECTIVES

The purpose of the study was to evaluate and compare changes in some parameters of the fibrinolytic system caused by the use of ionic and nonionic contrast media during angiography in certain groups of patients.

MATERIALS AND METHODS

Angiographic diagnostic procedures were performed in 126 patients (male and female) clinically suspected of having kidney cancer (38 patients), arteriosclerotic occlusive disease of lower extremities (44 patients), or dissection of cerebral artery (44 patients). The control group included 12 patients with clinical symptoms of the disease in whom angiographic examination excluded the presence of cerebral artery dissection or kidney cancer. Patients were randomly assigned to receive either an ionic (diatrizoate sodium) or a nonionic (iopromide) contrast medium. Immediately before and 30 minutes after administration, venous blood samples were obtained to determine select parameters of the hemostatic system.

RESULTS

There were no significant differences in the fibrinolytic parameters within the control group after contrast medium administration. The nonionic contrast medium (iopromide) caused a decrease in fibrinolytic activity in the patients, unlike the controls, which was particularly pronounced among the patients undergoing renal angiography.

CONCLUSION

The use of contrast media in some groups of patients led to transient changes in the fibrinolytic system. These results indicate that ionic contrast media should be used during angiographic procedures in patients at increased risk for thrombotic complications.

Systemic platelet effects of contrast media: implications for cardiologic research and clinical practice

BACKGROUND

Angiographic contrast media cause platelet activation and decrease aggregability in vitro. We have previously shown in vitro a significant antiplatelet effect of contrast media at the concentrations obtained locally in the coronary artery during angioplasty. It is not known, however, whether a systemic effect is present.

METHOD

Thirty patients undergoing diagnostic coronary angiography were prospectively randomized to receive the nonionic medium iohexol, ionic low-molecular-weight medium ioxaglate, or ionic high-molecular-weight medium diatrizoate. Platelet aggregability was measured before and after the investigation with whole blood electrical impedance aggregometry (WBEA) with collagen agonist and the PFA-100 (Dade, Miami, Fla) platelet function analyzer with combined shear, collagen, and adenosine diphosphate as agonists.

RESULTS

With WBEA, with iohexol no difference in impedance change was seen: (medians and ranges) before, 9.8 Omega (4.8-19.2 Omega) versus after, 9.6 Omega (2-19.2 Omega) (P not significant [NS]). With ioxaglate a significant fall was seen: before, 8.6 Omega (6.4-15.2 Omega) versus after, 6.6 Omega (0-12.4 Omega) (P =.004). With diatrizoate a significant and greater fall was seen: before, 10.8 Omega (6.4-17.6 Omega) versus after, 6.6 Omega (0-10.8 Omega) (P =.002). With PFA, no difference in closure time was seen with any medium: iohexol before, 99 seconds (79-142 seconds) versus after, 142 seconds (63-128 seconds) (P NS); ioxaglate before, 120 seconds (75-258 seconds) versus after, 95 seconds (74-258 seconds) (P NS); and diatrizoate before, 114.5 seconds (65-250 seconds) versus after, 100.5 seconds (72-300 seconds) (P NS).

CONCLUSIONS

Ionic but not nonionic contrast media have a systemic antiplatelet effect at diagnostic angiographic doses when measured with WBEA. Such an effect has not been shown before. This may explain the observed improved clinical outcome with ionic contrast media but also might confound platelet studies in coronary angioplasty.

Effects of nonionic contrast media on platelet aggregation: assessment by particle counting with laser-light scattering

Intravascular radiographic contrast media used in angiography, particularly nonionic contrast media, may cause activation of platelets. This study was designed to determine which properties of nonionic contrast media were potentially responsible for this action. Platelet aggregation after adenosine diphosphate stimulation was studied in the platelet rich plasma obtained from 37 patients who underwent left ventriculography using the highly sensitive method of particle counting with laser-light scattering. Platelet activation by contrast media was studied in the platelet rich plasma from healthy volunteers using flow cytometric analysis to detect platelet degranulation as P-selectin expression. There was a significant decrease in platelet aggregation in patients injected with ioxilan or iomeprol compared with patients injected with iohexol. There was a significant increase in P-selectin expression with the three groups of contrast media compared to control. The platelet activation with ioxilan or iomeprol was significantly less compared to the activation with iohexol. The comparison showed that previous generalization regarding platelet activation by nonionic contrast media might not be valid. It is presumed that the higher osmolality of iohexol may contribute to the increase in platelet aggregation and activation.

Thromboembolic events during chemotherapy for germ cell cancer: a cohort study and review of the literature

PURPOSE

To evaluate the risk of major thromboembolic complications in male germ cell cancer patients receiving cisplatin-based chemotherapy and to review the literature on this subject.

PATIENTS AND METHODS

One hundred seventy-nine germ cell cancer patients treated between January 1979 and May 1997 in our hospital were analyzed with respect to risk factors for developing thromboembolic events, such as baseline tumor characteristics, prior tumor therapy, administration of cytostatic agents, and the use of antiemetic drugs. The patients were treated with a variety of combination chemotherapy regimens, primarily cisplatin-containing combination regimens.

RESULTS

Of the 179 patients, 15 patients (8.4%) were identified who developed a total of 18 major thromboembolic complications in the time period between the start of chemotherapy and 6 weeks after administration of the last cytostatic drug in first-line treatment. Of these 18 events, three (16.7%) were arterial events, including two cerebral ischemic strokes, and 15 (83. 3%) were venous thromboembolic events, including 11 pulmonary embolisms. One (5.6%) of the 18 events was fatal. Liver metastases (odds ratio, 4.9; 95% confidence interval, 1.1 to 20.8) and the administration of high doses of corticosteroids (>/= 80 mg dexamethasone per cycle; odds ratio, 3.5; 95% confidence interval, 1. 2 to 10.3) as antiemetic therapy were identified as risk factors for the development of major thromboembolic complications.

CONCLUSION

Germ cell cancer patients who receive chemotherapy, in particular those who have liver metastases or receive high doses of corticosteroids, are at considerable risk of developing thromboembolic complications.

Differential effects of three radiographic contrast media on platelet aggregation and degranulation: implications for clinical practice?

We have determined the effects of three radiographic contrast media on platelet aggregation and degranulation in vitro. Aggregation was measured as loss of single platelets, and degranulation was measured as P-selectin expression using flow cytometry. Iopamidol added to hirudinized blood induced aggregation directly and also potentiated that induced by weak platelet agonists such as adenosine diphosphate (ADP). Iodixanol also potentiated platelet aggregation, but ioxaglate inhibited it. Iopamidol also caused marked platelet degranulation. The pro-aggregatory effect of iopamidol was evident in non-anticoagulated blood as well as in hirudinized blood, but not in citrated blood. In platelet-rich plasma (PRP) prepared from hirudinized blood neither iopamidol nor iodixanol directly induced platelet aggregation, but they rendered platelets hypersensitive to ADP. ADP antagonists inhibited the platelet aggregation and degranulation induced by iopamidol in whole blood, whereas aspirin, an inhibitor of thromborane A2 synthesis, did not. These data are consistent with clinical reports of increased thromboembolic risk with non-ionic low-osmolar media, and raise concerns about the routine use of these contrast media during diagnostic and interventional arteriographic procedures. Routine use of citrate in previous experiments may have masked a pro-aggregatory effect of some contrast media.

Differences between contrast media in the inhibition of platelet activation by specific platelet agonists

RATIONALE AND OBJECTIVES

The authors evaluated the ability of three x-ray contrast agents--a nonionic monomeric agent (iohexol), a nonionic dimeric agent (iodixanol), and an ionic dimeric agent (ioxaglate)--to either directly activate platelets or inhibit a platelet agonist from activating platelets.

METHODS

Fluorescence spectroscopy was used to detect the effect of contrast media on platelet activation. In this method, the platelet is first exposed to a fluorescent probe, which is de-esterified and trapped to Fluo-3 within the platelet. In the presence of calcium, the fluorescence emission from Fluo-3 is increased 80-fold. Thus, the increase in the free platelet calcium associated with platelet activation can be used to indicate platelet activation.

RESULTS

None of the agents were shown to directly activate platelets. However, wide differences in the ability of contrast media to inhibit platelet activation by a specific agonist were observed. Activation of platelets by epinephrine or arachidonic acid was not affected by any of the three contrast media studied. All three agents partially inhibited collagen activation of platelets, with ioxaglate the more potent inhibitor. Ioxaglate was the only agent to inhibit thrombin activation of platelets. Inhibition of adenosine diphosphate platelet activation was more extensive with ioxaglate than with iodixanol; iohexol produced no inhibition at all.

CONCLUSION

Direct activation of platelets by contrast media was not observed. Of greater importance is the finding that ionic contrast media, but not nonionic contrast media, inhibit thrombin activation of platelets by binding to the anion-binding exosite I, thus preventing thrombin from binding to and activating the platelet.

Effects of ionic and nonionic contrast media on endothelium and on arterial thrombus formation

BACKGROUND

The aims of the present study were to investigate whether ionic and nonionic contrast media (CM) affect: 1) the procoagulant and fibrinolytic activities of cultured human vessel endothelium; and 2) early events of tissue-factor-induced arterial thrombus formation under conditions which may follow a percutaneous transluminal coronary angioplasty (PTCA) procedure. The following 3 CM were studied: iohexol (nonionic monomer, Omnipaque); iodixanol (nonionic dimer, Visipaque); and ioxaglate (ionic dimer, Hexabrix). Saline (0.9%) and glucose (40 vol%) were used as control.

METHODS AND RESULTS

Exposing endothelium to 40 vol% CM for 10 min did not affect the selected parameters of cellular procoagulant (tissue factor), anticoagulant (thrombomodulin), fibrinolytic (tissue plasminogen activator) or antifibrinolytic (plasminogen activator inhibitor-1) activity or antigen. However, ioxaglate had a profound impact on the cell morphology, which was noted already after one minute of exposure. The cells contracted and rounded, exposing large areas of extracellular matrix. Iohexol showed this phenomenon to a considerably lesser extent, whereas iodixanol induced a slight swelling of the cells without detectable exposure of extracellular matrix. The effect of the respective CM on tissue-factor-driven thrombus formation at an arterial shear rate of 2600 s-1 was studied in an ex vivo parallel-plate perfusion chamber device. In this model, human native blood was passed over a tissue factor/phospholipid-rich surface following 30 s exposure to 100% CM. The CM was washed out by nonanticoagulated blood drawn directly from an antecubital vein by a pump positioned distal to the perfusion chamber. Such a pre-exposure of the procoagulant surface to iodixanol reduced the fibrin deposition around the platelet thrombi by 50% (p<0.01). However, iohexol and ioxaglate did not affect fibrin deposition. None of the 3 CM affected the recruitment of platelets in the thrombi, since similar values were obtained with pre-exposure to 40 vol% of saline.

CONCLUSION

Iodixanol appears to be most biocompatible with endothelium, and has a moderate inhibitory effect on fibrin deposition in flowing blood. This differs from iohexol, and in particular from ioxaglate, which induce endothelial changes in morphology with no effect on fibrin deposition. Since none of the CM affected the platelet aggregate formation, and since ioxaglate has been reported to have stronger anticoagulant and antithrombotic properties than iodixanol or iohexol in in vitro assays, it is apparent that these properties were not reflected in thrombus formation under the experimental conditions of high arterial shear.

Radiographic contrast media and the coagulation and complement systems

Intravascular contrast agents have several side effects including alterations of the hemostasis and the complement system. The effects on these systems may be one of the main causes of the "adverse contrast agent reaction." In vitro and in vivo evidence is provided that both ionic and nonionic contrast media activate the plasma kallikrein with consecutive activation of the factor XII-contact phase and stimulation of the bradykinin generation. Furthermore, activation of the complement cascade via the classic and the alternative pathways was described to a various extent for intravascular application of contrast agents. In non-reactors, these alterations are transient and only have a limited extent indicating that these reactions are within the regulatory capacity of the kallikrein-kinin-factor XII system. In reactors, however, significant evidence for an extended activation of the kallikrein system is associated with reduced levels of C1-esterase inhibitor. Therefore, patients with alterations in these systems should be regarded as candidates for adverse contrast agent reactions. Furthermore, contrast media influence the blood coagulation, especially in contact to artificial surfaces (plastic or glass). In vitro findings suggest that there is a broad scope of modifications caused by contrast agents indicating a modification of the risk of thromboembolism during angiography. Preliminary data suggest that an inhibition of clot formation is more effective with ionic compared with nonionic contrast agents. In summary, radiographic contrast agents have an impact both on the hemostasis and the complement systems. The effects may be of importance for adverse reactions as well as for thromboembolic complications during angiography.

Safety, tolerance, and pharmacokinetics of iodixanol injection, a nonionic, isosmolar, hexa-iodinated contrast agent

RATIONALE AND OBJECTIVES

A review of clinical-chemical parameters and tolerability of iodixanol is presented. Iodixanol is a newly developed dimeric, ratio 6 radiographic contrast medium formulated to be isotonic to plasma in all concentrations by the balanced addition of electrolytes. We summarize completed trials of iodixanol.

RESULTS

The increase in femoral blood flow following administration of iodixanol was significantly smaller than that seen with most other nonionic contrast media. Iodixanol appears to have less impact than other nonionic media on renal tubular function. Unlike iohexol and ioxaglate, the rate of adverse events after iodixanol administration was essentially the same for normal patients as for patients at increased risk for negative reactions (patients with previous adverse reactions to contrast administration). The risk following administration of iodixanol also appears to be similar in normal patients and in patients with other risk factors, including those with a history of congestive heart failure, renal insufficiency or disease, asthma, diabetes, hypertension, or vascular disease. A significant reduction in the sensation of injection-associated heat and pain was noted for iodixanol versus ioxaglate. Cardiac electrophysiologic measurements and contractility revealed minimal interference from iodixanol.

CONCLUSION

Iodixanol is a safe and effective nonionic, isotonic contrast medium that may offer clinical advantages.

Variable influence of heparin and contrast agents on platelet function as assessed by the in vitro bleeding time

Both heparin and contrast agents have anticoagulant effects which are well-documented but their effects on platelets are not well-characterized. The purpose of the present study was to evaluate the sequential effects of heparin and then a contrast agent on platelet function during an angiographic procedure. Blood samples from 54 patients were obtained at baseline, after a 5000 unit bolus of heparin and after administration of a contrast agent (iohexol, n = 30: diatrizoate, n = 24) during angiography. The in vitro bleeding time (IVBT) was determined on nonanticoagulated whole blood using a hollow fiber device under physiological flow conditions. Mean IVBT at baseline was 3.6 +/- 2.7 minutes and increased to 17.0 +/- 12.3 minutes after heparin (p < 0.01). After heparin, 44.5% of the patients still had a normal IVBT (< 9.0 minutes), 11% of the patients had a moderately increased IVBT and the remaining patients had a large increase in their IVBT. When contrast was given (167 +/- 52 mls) following heparin, mean IVBT was higher in those who received diatrizoate (23.3 +/- 9.4 minutes) compared with iohexol (15.0 +/- 10.9 minutes, p < 0.05). However, 15 patients (28%) continued to have a normal IVBT after contrast and of these 80% had received iohexol.

A randomized trial of low osmolar ionic versus nonionic contrast media in patients with myocardial infarction or unstable angina undergoing percutaneous transluminal coronary angioplasty

OBJECTIVES

The purpose of this study was to determine prospectively whether the differences in anticoagulant and antiplatelet effects of ionic and nonionic contrast media after angiographic or clinical outcomes in patients with unstable ischemic syndromes undergoing percutaneous transluminal coronary angioplasty.

BACKGROUND

The interaction of platelets and thrombin with the endothelium of injured vessels contributes to thrombosis and restenosis after coronary angioplasty. Case reports and retrospective observations have reported an increased risk of thrombosis with the use of nonionic contrast media.

METHODS

A total of 211 patients with acute myocardial infarction or unstable angina undergoing coronary angioplasty were randomized to receive nonionic or ionic low osmolar contrast media. Coronary angiograms were assessed by a technician blinded to the study contrast media, and clinical events were monitored by an independent nurse for 1 month.

RESULTS

Patients receiving the ionic media were significantly less likely to experience decreased blood flow during the procedure (8.1% vs. 17.8%, p = 0.04). After the angioplasty, residual stenosis, vessel patency, the incidence of moderate to large thrombi and use of adjunctive thrombolytic therapy were similar between the two groups. However, patients receiving ionic media had fewer recurrent ischemic events requiring repeat catheterization (3.0% vs. 11.4%, p = 0.02) and repeat angioplasty during the initial hospital stay (1.0% vs. 5.8%, p = 0.06). One month after angioplasty, patients receiving ionic contrast media reported significantly fewer symptoms of any angina (8.5 vs. 20.0%, p = 0.04) or of angina at rest (1.4% vs. 11.8%, p = 0.01) and a reduced need for subsequent bypass surgery (0% vs. 5.9%, p = 0.04), compared with patients receiving the nonionic media.

CONCLUSIONS

These findings demonstrate that in patients with unstable ischemic syndromes undergoing coronary angioplasty, the use of ionic low osmolar contrast media reduces the risk of ischemic complications acutely and at 1 month after the procedure. Therefore, low osmolar ionic contrast media should be strongly considered when performing interventions in patients with unstable angina or myocardial infarction.

Risk factors leading to arterial occlusion following diagnostic arteriography

OBJECTIVES

Arteriography may precipitate occlusive complications in stenotic vessels by a toxic effect on the vascular endothelium, leading to intra-arterial thrombosis. The aim of this retrospective study was to determine the incidence of arterial occlusion following arteriography.

METHODS

We studied 101 consecutive patients (71 male, 30 female; median age 72 years) undergoing percutaneous transluminal angioplasty (PTA) of stenotic lesions, which had been identified on diagnostic arteriograms performed a median of 109 days (range 6-519) previously. One hundred and thirty-one arterial stenoses suitable for PTA were identified in the patient cohort.

RESULTS

Seventeen patients (17%) progressed to occlusion in the period between diagnostic arteriography and PTA. Stenoses in the femoro-popliteal segment (21%) progressed to occlusion more frequently than lesions of the iliac arteries (3%). Independent risk factors were analysed to determine the risk factors predisposing to arterial occlusion following diagnostic arteriography. Both groups were well matched for age and sex. The mode of presentation, the presence of ischaemic heart disease, hypertension, diabetes or current smoking habits did not predict progression of disease to arterial occlusion. However, the rate of occlusion appeared to be influenced by the proportion of patients taking anti-platelet medication (51% in non-occluders as compared to 11% in patients who occluded, 95% CI 0.1 to 10), and to the length of time between arteriography and PTA (median of 92 days in non-occluders as compared to 125 days in patients who occluded, 95% CI 21 to 57).

CONCLUSIONS

These data demonstrate that occlusion of pre-existing arterial stenoses following diagnostic arteriography is significantly more frequent in patients not taking anti-platelet medication and when the time interval between arteriography and PTA exceeds 92 days. To minimise thrombotic arterial occlusion both diagnostic and therapeutic procedures should be performed simultaneously, but if a delay is unavoidable, patients should be treated with anti-platelet medication, which reduces the incidence of arterial occlusion.

Experimental investigation of hypercoagulant conditions associated with angiography

PURPOSE

To evaluate changes in blood coagulability after high-velocity intravascular fluid injections under conditions relevant to angiography.

MATERIALS AND METHODS

In 101 rabbits, fluids were injected at 1,000 psi (6,890 kPa) via a multiple-side-hole catheter in the abdominal aorta, while blood was simultaneously aspirated via a second downstream catheter. The fluids injected included saline, contrast media, blood, tissue plasminogen activator, and heparin. The aspirate was evaluated for clotting time with an activated clotting time (ACT) device, for elevated levels of plasma hemoglobin to confirm capture of at least part of the injection bolus in the sample, and sometimes for hematocrit or fibrin degradation products (FDP).

RESULTS

A single high-pressure injection of 2 mL of saline briefly accelerated the ACT of a blood-saline bolus (mean, 38% +/- 4). The mean volume of the hypercoagulable bolus was 15 mL. Systemic FDP levels became elevated within a few minutes after initial injection, suggesting activation of the fibrinolytic system by intravascular clot formation. Subsequent injections produced less hypercoagulability, probably reflecting the anticoagulant effects of FDP. Pressure-injected contrast agents had anticoagulant effects. The ACT was accelerated by up to 80% after injection of blood that had remained within the catheter for 3-10 minutes. Glove powder or gauze lint from wiping the guide wire markedly accelerated intracatheter clotting. Hypercoagulability after injection of clotting blood was partially prevented by injections with contrast agent and was completely inhibited by low-dose systemic heparinization.

CONCLUSION

A hypercoagulable bolus may occur after angiographically relevant high-pressure fluid injections. The major contributing factors appear to be high jet velocities and injection of small amounts of clotting blood. Heparinization provides a simple and effective means of prevention.

Roentgen contrast media and fibrinolysis

A review of the literature on the influence of contrast media (CM) on fibrinolysis showed that information currently available is contradictory, inconclusive and fragmentary. Results of some in vivo studies suggest that both ionic and nonionic CM increase fibrinolytic activity, either by lowering plasma plasminogen activator inhibitor 1 levels, by releasing endogenous tissue plasminogen activator and¿or by altering the fibrin meshwork of thrombi. Most in vitro studies on the subject contain results that are contradictory to those from in vivo studies. The discrepancies are due to obvious differences between systems which are, at best, only comparable under conditions of stagnant flow. Thus, great care should be exercised when extrapolating or interchanging data obtained in vivo and in vitro.

Platelet degranulation induced by some contrast media is independent of their nonionic vs ionic nature

We confirm that the phenomenon of platelet degranulation exists for both iohexol and diatrizoate, as reported earlier. In contrast to previous conclusions, however, we have determined that the degranulation is independent of the nonionic vs. ionic nature of the media per se, since degranulation was neither seen with nonionic iodixanol nor ionic ioxaglate. The degranulation, further, does not significantly augment platelet function, as measured by flowing whole blood platelet aggregometry.

Clinical pharmacology of iomeprol

The pharmacodynamic effects of iomeprol on the cardiovascular, central nervous, coagulation, and complement systems and on renal and thyroid functions using a wide range of intravenous and intraarterial radiological procedures were evaluated in Phase I, Phase II and Phase III clinical studies. The pharmacokinetics and metabolism of iomeprol were studied in healthy volunteers. Iomeprol 350 and 400 mgI/ml at doses ranging from 100 to 300 ml did not cause any significant changes of the basal haemodynamic parameters when used in CT of the chest and upper abdomen. No significant alterations of haemodynamic and ECG parameters were seen in patients who underwent cardiac-angiography or coronary angiography with iomeprol 400 mgI/ml. Intensive monitoring of haemodynamic and EEG parameters in patients undergoing conventional cerebral angiography with iomeprol 300 mgI/ml confirmed good toleration by the CNS. Neither renal and thyroid functions nor the coagulation and complement systems were significantly affected by iomeprol. Iomeprol was not metabolised and did not bind to plasma proteins. In healthy volunteers it was excreted almost exclusively by renal glomerular filtration (about 90% of the injected dose after 24 h). The pharmacokinetic behaviour of iomeprol was very similar to the behaviour of other nonionic, monomeric agents.

Pharmacodynamic effects of iomeprol for injection in experimental animals

Iomeprol for injection is a new nonionic triiodinated contrast medium for diagnostic radiology, which combines low osmolality with low viscosity. The effects of iomeprol for injection on the cardiovascular system, blood parameters, renal function and the central nervous system were studied after intravascular administration to several animal species of doses at least as high as the highest presumed clinical doses. The following observations were made with respect to the central circulatory system: moderate and short-lasting increases of left ventricular end-diastolic pressure and cardiac output, no significant effects on heart rate either in vitro or in vivo, some episodes of arrhythmia and ventricular fibrillations only at doses far higher than the highest presumed clinical ones, no significant increases in diastolic and systolic coronary flow. The following observations were made with respect to peripheral circulation: no significant changes on blood pressure, moderate and short-lasting increases in renal and pulmonary arterial flow, together with a decrease in peripheral vascular resistance, no crossing of the blood-brain barrier in healthy animals. Cardiovascular and haemodynamic changes were all significantly milder than those induced by ionic contrast media (CM) and were similar to effects caused by some other nonionic contrast media. When injected into the femoral artery of rats, iomeprol was shown to be less algogenic than iopamidol and iohexol. In comparison with the same reference CM, iomeprol affected to a lesser extent the filterability of red blood cells in vitro and showed a less marked effect on their deformability. When administered intravenously at very high dosages, iomeprol had no effect on the glomerular filtration rate, but increased both renal blood flow and diuresis. Proteinuria and enzymuria were also increased, albeit more transiently. The neurotolerance of iomeprol for injection after intravenous administration was higher than or at worst equal to that of iopamidol and iohexol. Iomeprol is therefore a promising new contrast agent particularly suitable for intravascular use in humans.

Effects of an ionic versus a nonionic low osmolar contrast agent on the thrombotic complications of coronary angioplasty

An increasing body of evidence suggests that the potential for thrombotic complications is greater with nonionic than with ionic contrast agents. This is a particularly important consideration in the highly thrombogenic setting of percutaneous transluminal coronary angioplasty (PTCA). To explore this issue further, 500 consecutive patients undergoing PTCA were prospectively randomized to receive the low osmolality ionic ioxaglate or the nonionic agent iohexol. The number of acute thrombotic in-laboratory events was significantly less in the ioxaglate than in the iohexol group (8 versus 18; P < 0.05), but there was no significant difference between the 2 groups as regards the number of out-of-laboratory acute rethrombotic events. With multivariate analysis, use of the nonionic agent rather than the ionic agent emerged as an independent predictor of acute in-laboratory rethrombosis. These data suggest that, in the performance of PTCA, an ionic, rather than a nonionic, should be the preferred contrast agent.

Ionic contrast agent-mediated endothelial injury causes increased platelet deposition to vascular surfaces

Contrast agent-mediated endothelial injury may be clinically relevant to the development of acute thrombosis after coronary interventions. We sought to investigate the extent to which contrast agents increase platelet deposition by measuring deposition of indium-111 radiolabeled platelets in an isolated perfused rabbit carotid artery model. Carotid artery segments were perfused at physiologic temperature, pressure, and shear. Vessels were subjected to angioplasty or no angioplasty before exposure to either buffer, diatrizoate (high osmolal/ionic), ioxaglate (low osmolal/ionic), or ioversol (low osmolal/nonionic). Subsequent deposition of indium-111 radiolabeled platelets was quantified. In vessels without balloon angioplasty, platelet deposition (platelets/cm2) was 110,000 +/- 95,000 for buffer perfused vessels, 280,000 +/- 210,000 for vessels perfused with diatrizoate, 290,000 +/- 160,000 for vessels perfused with ioxaglate, and 130,000 +/- 98,000 for vessels perfused with ioversol. After balloon angioplasty, platelet deposition was 1,300,000 +/- 590,000 for buffer controls, 1,800,000 +/- 320,000 for diatrizoate-perfused vessels, 1,500,000 +/- 450,000 for ioxaglate-perfused vessels, and 1,000,000 +/- 180,000 for ioversol-perfused vessels. In vessels without balloon angioplasty, diatrizoate and ioxaglate increased platelet deposition 2.5-fold and 2.6-fold, respectively, relative to buffer-perfused vessels (p < 0.05 and p < 0.01), whereas no increase was seen with ioversol. After balloon angioplasty, diatrizoate increased platelet deposition 1.4-fold over control (p < 0.05), whereas ioxaglate and ioversol showed no statistically significant increase. We conclude that ionic contrast media may cause more endothelial injury and associated localized platelet deposition than nonionic contrast media. These findings may be relevant to coronary interventions, specifically with regard to acute closure and chronic restenosis.

Use of nonionic or low osmolar contrast agents in cardiovascular procedures. American College of Cardiology Cardiovascular Imaging Committee

Low osmolar contrast agents produce less adverse electrophysiologic and hemodynamic alterations during cardiac catheterization. The nonionic agents probably reduce the risk of provoking myocardial ischemia during coronary arteriography or ventriculography. Patients also report less subjective sensation of discomfort during administration of low osmolar agents for cardiovascular procedures. However, nonionic agents have not been proved to reduce the incidence of several serious complications of cardiac catheterization, including acute renal failure and anaphylactoid reaction. Although evidence is inconclusive, there may be an increased risk of thromboembolic complications during cardiac catheterization when certain low osmolar nonionic agents are administered. Nonionic contrast agents have not been definitely proved to reduce the risk of death after cardiac catheterization.

Relationship of anticoagulation and radiographic contrast agents to thrombosis during coronary angiography and angioplasty: are there real concerns?

Radiographic contrast agents are essential for the performance of coronary angiography and angioplasty. Historical data show that thrombosis-related events have occurred since coronary angiography has been performed. Newer non-ionic agents have been shown to be safer than conventional high osmolar ionic agents especially in high risk patients, but concern has been raised about a potentially increased risk of thrombosis with the use of these agents. A review of basic and clinical evidence for this perception does not support the view that an increase in thrombosis-related events has occurred as a results of non-ionic contrast media use in coronary angiographic procedures.

Catastrophic thrombus development despite systemic heparinization during coronary angioplasty: possible relationship to nonionic contrast

Two cases of catastrophic thrombus formation during coronary angioplasty occurred shortly after the operators began using nonionic contrast. This occurred despite systemic heparinization, the adequacy of which was documented by activated clotting times (ACT). Both cases were resistant to balloon inflation and one was refractory to intracoronary thrombolysis. There is a considerable body of evidence documenting that low-osmolality contrast media, especially those that are nonionic, have less anticoagulant effect than standard contrast media. Several reports have also been published suggesting possible relationships between nonionic contrast and intravascular thrombus formation during coronary angiography and angioplasty. These data are reviewed and recommendations made for utilization of these contrast media.

Risk of thrombosis during coronary angioplasty with low osmolality contrast media

Studies in vitro have suggested that nonionic low osmolar contrast agents produce an increase in thrombogenicity. To determine the incidence of thrombi related to the use of nonionic low osmolar contrast media during coronary angioplasty, a double-blind randomized study was performed in 100 patients. Medication before angioplasty included oral aspirin (250 mg/day) in all cases. At the beginning of the procedure, aspirin (250 mg) and heparin (10,000 U) were intravenously administered. During the procedure patients were randomly assigned to receive either an ionic low osmolar contrast agent ioxaglate (n = 50), or a nonionic low osmolar contrast media iohexol (n = 50). The presence of thrombus was evaluated on the angiogram and on the guidewire immediately after its retrieval from the patients. Clinical, angiographic and procedural variables were similar in the 2 randomized groups. Angiographic evidence of thrombus was observed in 1 patient (2%) assigned to ioxaglate and in 11 patients (22%) assigned to iohexol (p less than 0.005). One patient (2%) from the ioxaglate group and 6 patients (12%) from the iohexol group showed thrombotic residues on the guidewire (p = not significant). Three patients had acute myocardial infarction, 1 patient (2%) receiving ioxaglate and 2 patients (4%) iohexol (p = not significant). There were no deaths. Thus, compared with an ionic low osmolar contrast media ioxaglate, the nonionic low osmolar contrast agent iohexol increases the incidence of thrombus during coronary angioplasty.

Influence of contrast media on thrombus formation during coronary angioplasty

The influence of contrast media on thrombus formation during percutaneous transluminal coronary angioplasty was assessed in 124 consecutive patients undergoing coronary angioplasty and receiving either ionic (n = 57) (Group I) or nonionic (n = 67) (Group II) contrast medium. The presence of thrombus was assessed by qualitative analysis of angiograms in identical pre- and postangioplasty projections by four observers who had no knowledge of other data. Quantitation of stenosis severity before and after angioplasty and qualitative analysis of lesion eccentricity and complexity and of the presence of dissection were also performed. Although the baseline clinical characteristics of the two groups (including presenting syndromes and procedural and angiographic variables) did not differ, more patients in Group II than Group I developed new thrombus during coronary angioplasty (18% vs. 4%, p less than 0.02). In particular, patients with a presenting syndrome of recent myocardial infarction or rest angina, or both, and patients with an eccentric coronary plaque were more likely to develop new thrombus if they received nonionic than if they received ionic contrast medium (p less than 0.05). Patients with new thrombus formation and patients with thrombus present both before and after angioplasty had a high incidence of acute procedural complications (36% and 23%, respectively). Patients in Groups I and II had a similar incidence of ischemic events during follow-up.

Urokinase-mediated thrombolysis: a dose-response relationship in cats. Work in progress

A cat model was developed to study thrombolytic agents. The infrarenal aorta was surgically exposed, all side branches were ligated, and both ends of the segment were occluded. After preformed clot was injected into the segment, proximal flow was restored and a distal stenosis was created. Urokinase was infused at rates varying from 4,000 to 250,000 U/h. Amount of remaining clot was quantified every 15 minutes with cine angiography. Pre- and postinfusion measurements of prothrombin time, partial thromboplastin time, thrombin time, and levels of fibrinogen and fibrin degradation products were obtained. A graph of thrombolysis rate versus infusion rate was obtained yielding maximal thrombolytic activity at 126,000 U/h and 90% of maximal activity at an infusion rate of 70,000 U/h. Levels of fibrin degradation products did not change. Prothrombin, partial thromboplastin, and thrombin times increased with increasing infusion rates, leveling off at 100,000 U/h, while fibrinogen levels decreased, with a plateau at 50,000 U/h.

In vivo effects of nonionic and ionic contrast media on beta-thromboglobulin and fibrinopeptide levels

Nonionic contrast media are suggested to cause increased thromboembolism (in vivo), platelet aggregation and procoagulant effect (in vitro) as compared with ionic contrast media. To study these effects in vivo, 30 consecutive patients undergoing routine angiography were prospectively randomized to three groups of 10 patients each. Group A received diatrizoate (ionic, high osmolality), Group B ioxaglate (ionic, low osmolality) and Group C iohexol (nonionic, low osmolality). In vivo platelet alpha-granule release and fibrin-1 formation were measured by radioimmunoassay of beta-thromboglobulin and fibrinopeptide A in peripheral venous samples. Levels were estimated at three stages during the procedure: before and after left ventriculography and after coronary angiography. No differences were noted (p = NS) when the ratios of beta-thromboglobulin and fibrinopeptide A were compared among the three groups. These data suggest that the newer nonionic contrast media do not demonstrate enhanced systemic platelet activation or fibrin formation as compared with standard ionic contrast media. However, larger randomized clinical studies are necessary to conclusively establish the suggested thromboembolic potential of nonionic contrast media.

Platelet and fibrin modification by radiographic contrast media

The effect of the radiographic contrast agents, iopamidol and diatrizoate, on fibrin assembly and structure as well as platelet surface charge was studied. Increasing the iopamidol concentration from 0 to 4.5 mM prolongs the fibrin gelation time from 20 to 105 seconds (an anticoagulant effect) and reduces the fibrin fiber mass/length ratio from 3.2 x 10(12) to 0.5 x 10(12) Da/cm (i.e., produces very thin fibrin fibers). Ultraviolet difference spectroscopy of fibrinogen showed both a 15-nm shift in the ultraviolet difference maximum for iopamidol (suggesting binding) and a perturbation of the aromatic amino acid side chain region for fibrinogen (suggesting a conformational change in fibrinogen) as the concentration of iopamidol was increased from 0 to 9 mg/ml. Binding of iopamidol to fibrinogen was also shown by affinity chromatography using a Sepharose-fibrinogen column. Electrophoretic quasi elastic light scattering was used to show platelet interaction with iopamidol as reflected in a reduction in the platelet electrophoretic mobility from 2.0 to 0.5 (microns-cm)/(V-sec) as the concentration of iopamidol was increased from 0 to 4.5 mM. In addition, the ionic radiopaque contrast agent, Renografin, was also studied and found to inhibit fibrin monomer assembly. Although iopamidol is not shown to be thrombogenic, iopamidol does appear to reduce platelet surface charge, bind fibrinogen, and modify fibrin clot structure.

Ionic versus nonionic contrast use

It has taken many years of research, development and intense scientific investigation to produce intravascular contrast media. Research on relations between chemical structure, animal toxicity, and water-solubility has produced a number of highly water-soluble, iodinated compounds for use in diagnostic radiology as intravascular contrast agents. The currently used intravascular agents may be classified into four groups according to their chemical structure: 1. Ionic monomers 2. Ionic monoacid dimers 3. Nonionic monomers 4. Nonionic dimers It is the objective of this publication to review the history and development of intravascular contrast media as well as their properties, general effects and clinical use. The four types of contrast media differ significantly in their chemical structure and physico-chemical properties, and these differences determine their osmotoxicity, chemotoxicity, and ion toxicity. We analyze the organ specific toxic effects of intravascular contrast media upon the central nervous system, the cardiovascular system, and the renal system. We also review the secondary effects, clinical manifestations, and the incidence of adverse events associated with different types of contrast. The choice of contrast media has become critical since the introduction of nonionic agents because their toxicological and pharmacological properties differ from those of the ionic agents. The application of basic concepts involved in the use of contrast media in excretory urography, computed tomography, angiography, and angiocardiography is discussed, and the advantages of the use of nonionic contrast agents are outlined. Economic and ethical issues are presented with emphasis upon strategies to reduce the risk associated with the injection of intravascular contrast and to curtail consumption according to rational principles of use.

Thromboembolic phenomena in clinical angiography: role of materials and technique

Interactions between blood and iodinated contrast agents and syringes and catheters are discussed with regard to clot formation and thromboembolic phenomena in angiography. Syringe and catheter materials are, to varying extents, contact activators of coagulation, whereas contrast agents inhibit coagulation and platelet aggregation. Current understanding of these phenomena is surveyed, and the implications for clinical angiographic technique are discussed.

Contrast media for angiography: physicochemical properties, pharmacokinetics and biocompatibility

Contrast agents are used as diagnostic molecules for the visualization of the vascular system. Despite their rapid pharmacokinetic distribution, and their excretion within a few minutes, their injection is associated with clinical symptoms of relative bioincompatibility. Allergoid reactions and disturbances of the hemostatic system represent the main fields of biological investigations. Due to the extent of clinical and experimental works the ubiquitous interactions between these molecules and cellular and/or protein systems have emerged. The development of a new family of low osmolality ionic or non-ionic contrast molecules had decreased the incidence of minor reactions, but did not modify the frequency of severe accidents and even led to the emergence of new iatrogenic syndromes. Despite extensive laboratory investigations there are still no predictive criteria nor any specific therapeutic prevention of these allergoid reactions. The suggested future line of investigation concerns the physicochemical interaction of CM and targeted biological systems which may allow the analysis and predictivity of these interactions at the molecular level.

Effect of heparin in nonionic contrast media on blood coagulation and its dose response curve

To investigate the local effect of heparin on blood clot formation and partial thromboplastin time (PTT), blood was withdrawn into the catheters filled with iopamidol and heparin at 0, 1, 2, 3, 5, and 10 U per ml concentrations as debubbling. After 30 min incubation, blood clotting was observed in all 8 experiments with heparin concentrations of 0 and 1 U per ml; in 3 of 8 with 2 U per ml; and in none with greater than or equal to 3 U per ml. PTT of blood and contrast mixture in catheters increased significantly when heparin concentrations were increased from 2 to 3 U per ml and reached a level of greater than 110 sec at 5 or more U per ml. Thus, the addition of heparin to nonionic contrast media at concentrations of 5 U per ml may be an easy measure with which to prevent blood clotting and reduce thromboembolic complications during coronary arteriography.

Cardiovascular effects of contrast agents

Iodinated radiologic contrast agents should, ideally, passively provide radiographic contrast in blood vessels and soft tissues but have no effects on physiology, hematology or biochemistry. In practice, no such agent exists although the nonionics most closely approach the ideal. All agents have a bewildering variety of effects on the cardiovascular system, which, in turn, engender a variety of neurogenic and humoral responses. The mechanisms underpinning these many phenomena appear to involve hyperosmolality, molecular structure, ionic content and balance. This review presents the current state of knowledge of these effects and their mechanisms, with emphasis on the differences between conventional ionic and more inert nonionic agents.

Effects of contrast media on endothelial cell monolayers under controlled flow conditions

To compare the biocompatibility of nonionic and ionic intravascular contrast media in a more physiologic in vitro system, key aspects of blood flow through a microvessel were simulated. Toward this end, monolayers of endothelial cells placed in a specially designed flow chamber, real-time imaging of the monolayers by brightfield and phase videomicroscopy, and real-time imaging and computer-aided quantitation at normal hematocrit levels of platelet adhesion/aggregation to sites of monolayer injury by means of epifluorescence videomicroscopy were used. At a concentration in culture medium of 20% by volume, it was found that monolayer morphology was least altered by iohexol when compared with diatrizoate and ioxaglate; monolayer production of prostacyclin was enhanced (p less than 0.001) by ioxaglate compared with saline controls; and at a concentration in citrated blood of 20% by non-red-cell volume, platelet adhesion/aggregation was reduced by all 3 contrast agents in the order diatrizoate greater than ioxaglate greater than iohexol.