Iohexol, platelet activation and thrombosis. II. Iohexol-induced platelet secretion does not affect collagen-induced or tissue-factor-induced thrombus formation in blood that is anticoagulated with heparin and aspirin

Addition of heparin to contrast media is associated with increased bleeding and peripheral vascular complications during percutaneous coronary intervention with bivalirudin and drug-eluting stents

BACKGROUND

Nonionic radiographic contrast media (CM) is reported to be thrombogenic while performing diagnostic or interventional procedures. To avoid thrombosis, heparin is often added to the CM. Bivalirudin, used to replace heparin during percutaneous coronary intervention (PCI), is reported to be associated with reduced bleeding complications. We aimed to evaluate the impact of adding heparin to the CM during PCI in patients (pts) who underwent sirolimus-eluting stent (SES) implantation when bivalirudin was utilized as the sole antithrombotic agent.

METHODS

A total of 664 pts with 756 lesions underwent standard PCI with SES for various coronary artery lesions. Pts were treated with either bivalirudin only (the bivalirudin group; 0.75 mg/kg bolus and 1.75 mg/kg/h infusion, n = 323 pts) or bivalirudin (same dose) plus low-dose heparin added to the CM (the heparin mix group; mean dose = 2101.8+/-882.5 U, n = 341 pts) during PCI. The periprocedural, in-hospital, and 30-day clinical outcomes were compared.

RESULTS

Baseline clinical and angiographic parameters were similar between both groups. Periprocedural, in-hospital, and 1-month clinical outcomes, including thrombotic complications, were similar between the two groups. There was no difference in the periprocedural thrombosis rate between the groups. In the heparin mix group, the overall incidence of hematoma was significantly higher (3.8% vs. 8.5%, P = .01), there was a trend toward higher rates of blood transfusion (2.6% vs. 6.6%, P = .06) and overall vascular complications (0.01% vs. 5.3%, P <.001), including pseudoaneurysm (PSA; 0.0% vs. 2.6%, P = .004), and pts who required surgical repair (0.3% vs. 1.8%, P = .07).

CONCLUSIONS

The routine addition of low-dose heparin to CM during contemporary PCI does not add any protection value and is associated with higher rates of bleeding and vascular complications.

Comparative tolerability of contrast media used for coronary interventions

Radiographic contrast media (CM) are necessary to provide x-ray absorption of the bloodstream; all other observed effects need to be regarded as adverse. Four types of CM are currently used in diagnostic and interventional cardiology: ionic high-osmolar CM (HOCM), either ionic or non-ionic low-osmolar CM (LOCM), and non-ionic iso-osmolar CM (IOCM). Focusing on the potential cardiovascular effects caused by the CM, there is a clear difference between HOCM and the LOCM or IOCM. HOCM have a poorer profile due to a higher incidence of hypotension and electrophysiological effects. To prevent contrast-induced nephropathy, HOCM should be avoided and patients should receive the minimal dose of LOCM or IOCM with intravenous hydration before and after the procedure. Clinical hyperthyroidism has been detected after CM use, but the condition appears, ultimately, to be self-limited and to occur mainly in elderly patients. When assessing the need for a CM in terms of improved patient safety, preventing serious complications should be the major factor determining the choice. CM should not be selected on the basis of minor adverse effects since these are, ultimately, of low clinical relevance. Thrombotic events, in contrast, carry a high clinical relevance and we consider that these should be the main issue governing current choice. Ionic LOCM appear to have better profile than other CM with respect to interaction with platelet function and coagulation. In relation to thrombotic events in randomised clinical studies, ionic CM have been associated, mainly, with favourable and some neutral results compared with non-ionic agents. Only one trial indicated a more pronounced antithrombotic effect of the non-ionic IOCM relative to the ionic LOCM. The antithrombotic advantages of ionic over non-ionic LOCM are, in part, balanced by a greater frequency of minor adverse effects such as nausea, vomiting or cutaneous rashes. A matter of concern is the delayed adverse effects observed with non-ionic IOCM. However, severe and life-threatening reactions are exceptional and there are probably no significant differences between IOCM and LOCM whether ionic or non-ionic. However, in patients with known allergies, non-ionic CM are to be recommended. On the basis of the available pre-clinical and clinical data, the ionic LOCM or the non-ionic IOCM are the agents to be recommended in percutaneous coronary interventions because of their antithrombotic advantages over non-ionic LOCM.

Methods and models to evaluate shear-dependent and surface reactivity-dependent antithrombotic efficacy

The purpose of the present communication is to evaluate the importance of blood flow and surface reactivity for measurement of antithrombotic drug activity or efficacy in selected model systems of thrombus formation. Such information is essential for proper evaluation of antithrombotic drug profiles. The continuous development of flow-dependent thrombosis models for in vitro (anticoagulated blood) and ex vivo (native blood) studies and their application in in vivo animal models from the early 1970s and onwards are briefly considered. Central to this process was the development of various types of perfusion chambers in which a thrombogenic surface is exposed to flowing blood. Such perfusion chambers have been inserted into arteriovenous (AV) shunts in baboon, pig, dog, and rabbit. These approaches have allowed reproducible testing of traditional and novel experimental antithrombotic drugs, and studies on novel drug strategies under well-defined shear conditions and surface reactivity. Shear-dependent antithrombotic efficacy in these models is observed with anticoagulants such as unfractionated heparin, low-molecular weight heparins, or selective inhibitors of thrombin, Factor Xa, or Factor VIIa. However, the degree of shear dependency depends on the nature of the thrombogenic surface, e.g., the inhibition is more pronounced on a tissue factor (TF)-rich surface than on a collagen-rich surface, particularly at venous or low arterial shear. Platelet antagonists such as the COX-1 inhibitor aspirin, inhibitors of thromboxane A2 (TxA2) synthetase, the TxA2 platelet receptor, and of von Willebrand factor (vWf) are shear dependent also, being more efficient at high arterial shear. In contrast, the platelet ADP antagonist clopidogrel, or antagonists to the active platelet membrane glycoprotein IIb-IIIa complex (GPIIb-IIIa) are shear independent. At extremely high arterial shear, which activates platelets and elicit aggregates of circulating platelets, aspirin looses its antithrombotic effect, whereas ADP and GPIIb-IIIa antagonists still interrupt thrombus formation. In general, results obtained with these models mimic and predict antithrombotic efficacy in man when comparison is possible. Information on antithrombotic efficacy in flow devices with various thrombogenic surfaces is now sufficiently available to suggest recommendations for experimental conditions, particularly with regard to blood flow and reactive surfaces.