Ancrod (Arvin) as an alternative to heparin anticoagulation for cardiopulmonary bypass

Clinical implications of differential antivenom efficacy in neutralising coagulotoxicity produced by venoms from species within the arboreal viperid snake genus Trimeresurus

Snake envenomation globally is attributed to an ever-increasing human population encroaching into snake territories. Responsible for many bites in Asia is the widespread genus Trimeresurus. While bites lead to haemorrhage, only a few species have had their venoms examined in detail. We found that Trimeresurus venom causes haemorrhaging by cleaving fibrinogen in a pseudo-procoagulation manner to produce weak, unstable, short-lived fibrin clots ultimately resulting in an overall anticoagulant effect due to fibrinogen depletion. The monovalent antivenom 'Thai Red Cross Green Pit Viper antivenin', varied in efficacy ranging from excellent neutralisation of T. albolabris venom through to T. gumprechti and T. mcgregori being poorly neutralised and T. hageni being unrecognised by the antivenom. While the results showing excellent neutralisation of some non-T. albolabris venoms (such as T. flavomaculaturs, T. fucatus, and T. macrops) needs to be confirmed with in vivo tests, conversely the antivenom failure T. hageni, and the very poor results against T. gumprechti and T. mcgregori, despite being conducted in the ideal scenario of preincubation of antivenom:venom, indicates that the likelihood of clinically relevant cross-reactivity for these species is low (T. gumprechti and T. mcgregori) to non-existent (T. hageni). These same latter three species were also not inhibited by the serine protease inhibitor AEBSF, suggesting that the toxins leading to a coagulotoxic effect in these species are non-serine proteases while in contrast T. albolabris coagulotoxicity was completely impeded by AEBSF, and thus driven by kallikrein-type serine proteases. There was a conspicuous lack of phylogenetic pattern in venom variation, with the most potent venoms (T. albolabris and T. hageni) being distant to each other on the organismal tree, and with the three most divergent and poorly neutralised venoms (T. gumprechti, T. hageni, and T. mcgregori) were also not each others closest relatives. This reinforces the paradigm that the fundamental dynamic evolution of venom results in organismal phylogeny being a poor predictor of venom potency or antivenom efficacy. This study provides a robust investigation on the differential venom effects from a wide range of Trimeresurus species on coagulation, highlighting differential fibrinogenolytic effects, while also investigating the relative antivenom neutralisation capabilities of the widely available Thai Red Cross Green Pit Viper antivenom. These results therefore have immediate, real-world implications for patients envenomed by Trimeresurus species.

Basal but divergent: Clinical implications of differential coagulotoxicity in a clade of Asian vipers

Envenomations by Asian pitvipers can induce multiple clinical complications resulting from coagulopathic and neuropathic effects. While intense research has been undertaken for some species, functional coagulopathic effects have been neglected. As these species' venoms affect the blood coagulation cascade we investigated their effects upon the human clotting cascade using venoms of species from the Azemiops, Calloselasma, Deinagkistrodon and Hypnale genera. Calloselasma rhodostoma, Deinagkistrodon acutus, and Hypnale hypnale produced net anticoagulant effects through pseudo-procoagulant clotting of fibrinogen, resulting in weak, unstable, transient fibrin clots. Tropidolaemus wagleri was only weakly pseudo-procoagulant, clotting fibrinogen with only a negligible net anticoagulant effect. Azemiops feae and Tropidolaemus subannulatus did not affect clotting. This is the first study to examine in a phylogenetic context the coagulotoxic effects of related genera of basal Asiatic pit-vipers. The results reveal substantial variation between sister genera, providing crucial information about clinical effects and implications for antivenom cross-reactivity.

Isolation and pharmacological characterization of a new cytotoxic L-amino acid oxidase from Bungarus multicinctus snake venom

ETHNOPHARMACOLOGICAL RELEVANCE

Bungarus multicinctus snake belongs to Elapidae family and is widely distributed in southern China. It is widely used in traditional Chinese medicine with the effect of dispelling wind and removing obstruction in the meridians. Moreover, it is also as a chief ingredient of many polyherbal formulations for the treatment of cancer.

AIM OF THE STUDY

To evaluate the antitumor activity of Bungarus multicinctus snake venom components and isolate, characterize the most effective anti-tumor component of Bungarus multicinctus snake venom.

MATERIALS AND METHODS

The in vitro antitumor activity of Bungarus multicinctus venom components was detected by cytotoxicity assay and cell apoptosis assay. A unique LAAO from Bungarus multicinctus venom named as BM-Apotxin was isolated and characterized by Sephadex G-75 gel filtration, Sephadex G-25 desalting, Q ion-exchange chromatography and subsequent amino acids sequence determination. The LAAO activity and enzyme kinetics of BM-Apotxin was detected by microplate assay.

RESULTS

BM-Apotxin, a 65KDa glycoprotein, which contributed to the most anti-tumor effects of Bungarus multicinctus venom. BM-Apotxin can selectively kill tumor cells, with less cytotoxicity to the normal cells. BM-Apotxin is an L-amino acid oxidase (LAAO) with high sequence identity to other snake venom LAAOs. Its anti-tumor activity is mainly due to the hydrogen peroxide produced from LAAO oxidation. But the catalase did not reverse its anti-tumor effect completely. Like other snake venom LAAOs, BM-Apotxin can oxidize many L amino acids, not D amino acids. The optimum substrate for BM-Apotxin is L-Phe. Moreover, BM-Apotxin deglycosylation can significantly reduce the LAAO activity and anti-tumor activity of BM-Apotxin.

CONCLUSION

This study will facilitate the study on anti-tumor mechanism of snake venom and drug development based on Bungarus multicinctus venom.

Cardiopulmonary Bypass Without Heparin

Due to familiarity, short half-life, ease of monitoring, and the availability of a reversal agent, heparin remains the anticoagulant of choice for cardiac operations requiring cardiopulmonary bypass (CPB). However, occasionally patients require CPB but should not receive heparin, most often because of acute or subacute heparin-induced thrombocytopenia (HIT). In these cases, if it is not feasible to wait for the disappearance of HIT antibodies, an alternative anticoagulant must be selected. A number of non-heparin anticoagulant options have been explored. However, current recommendations suggest the use of a direct thrombin inhibitor such as bivalirudin. This review describes the use of heparin alternatives for the conduct of CPB with a focus on the direct thrombin inhibitors.

Heparin-Induced Thrombocytopenia

Heparin's anticoagulation effect makes it the principal component in the immediate treatment of all thrombotic diseases. After hemorrhage, the most important complication of heparin is thrombocytopenia, the decrease in the number of blood platelets. Ten cases of "heparin-induced thrombocytopenia" are described, and guidelines for diagnosing heparin-induced thrombocytopenia in patients who present for cardiac and vascular surgery are given. Methods of treating patients with heparin-induced thrombocytopenia, including use of arachidonic acid derivatives, antiplatelet agents, other anticoagulants, heparinoids, natural and synthetic thrombin inhibitors, hirudin, and defibrinogenation with ancrod, are discussed.

Human cytokine response to Texas crotaline envenomation before and after antivenom administration

OBJECTIVE

The aim of this study was to characterize the human cytokine response to Texas crotaline envenomation before and after antivenom administration.

METHODS

This study enrolled crotaline bite victims presenting to a regional trauma center and children's hospital from March to November 2007 and age-matched unbitten controls. Blood spot cards were obtained from bite victims at presentation and at 1 and 6 hours after antivenom administration. One control sample was drawn from each of the age-matched controls selected from urgent care patients presenting for minor complaints. Samples were delivered to a laboratory using a proprietary method for quantitative evaluation of a large number of biomarkers in parallel with bead-based multiplex immunoassays.

RESULTS

After obtaining informed consent, 14 crotaline bite victims (age range, 5-85 years; median age, 45 years; 50% female) (Snakebite Severity Score, 2-7; median, 3) and 14 age-matched controls were enrolled. There were 7 copperhead (Agkistrodon contortrix) bites, 4 rattlesnake (probably Western Diamondback Crotalus atrox) bites, 2 cottonmouth (Agkistrodon piscivorus) bites, and 1 bite from a snake that was not identified by the victim. In t tests, the means in the presentation samples for apolipoprotein A-I (Apo A-I), Apo C3, interleukin 4 (IL-4), myeloperoxidase, plasminogen activator inhibitor 1 (PAI-1), epidermal growth factor, and regulated upon activation, normal t-cell expressed and secreted were significantly lower and Apo H was significantly higher in the bite patients than in the controls. In the 1-hour sample, α(1)-antitrypsin, Apo A-I, Apo C3, eotaxin, IL-4, myeloperoxidase, and PAI-1 levels were lower and prostatic acid phosphatase and cancer antigen 125 levels were higher in the bite patients than in the controls. And in the 6-hour sample, α(1)-antitrypsin, Apo A-I, Apo C3, endothelin-1, IL-4, macrophage inflammatory protein 1β, myeloperoxidase, and epidermal growth factor levels were lower and Apo H level was higher in the bite patients than in controls (all P values < .05).

CONCLUSIONS

Crotaline venom produces a broad cytokine response in human bite victims. In particular, IL-4, myeloperoxidase, and Apo A-I and C3 levels remain altered despite antivenom therapy, whereas PAI-1 and regulated upon activation, normal t-cell expressed and secreted levels seem to normalize after antivenin as other markers are affected. Understanding this profile and further study of the markers identified might lead to improved therapies and better prognostic indicators.

Successful use of bivalirudin for cardiac transplantation in a child with heparin-induced thrombocytopenia

Bivalirudin, a direct thrombin inhibitor, has recently emerged as a promising option for anti-coagulation during cardiopulmonary bypass in patients who cannot receive heparin. There is limited experience with the use of bivalirudin in children. We present the case of a child with heparin-induced thrombocytopenia with thrombosis (HIT Type II) who underwent successful orthotopic cardiac transplantation using bivalirudin as the primary anti-coagulant for cardiopulmonary bypass.

Aortic Valve Repair in a Patient with Congenital Afibrinogenemia

We describe the management of cardiopulmonary bypass (CPB) in a patient with congenital afibrinogenemia (AF). Although this state is akin to the state after hirudin administration, where CPB has been successfully performed, heparinization is still essential to preserve other clotting factors and prevent excessive bleeding. Aprotinin further helps in preservation of clotting factors. There are case reports of thrombosis associated with AF, but aprotinin can be safely used because it is, by definition, an anticoagulant. Cryoprecipitate effectively restores the fibrinogen and produces normal clotting.

Bivalirudin anticoagulation for cardiopulmonary bypass in a patient with heparin-induced thrombocytopenia

PURPOSE

To describe the perioperative management in a heparin-induced thrombocytopenia (HIT) positive patient who had prosthetic valve endocarditis and an aortic root abscess. The patient underwent high-risk cardiac re-operation with the use of the alternative anticoagulant, bivalirudin.

CLINICAL FEATURES

A 62-yr-old patient who underwent stentless tissue aortic valve replacement with a Toronto-SPV valve in 1998, was admitted to hospital with symptoms of stroke. A heparin infusion was started and further investigation revealed positive blood cultures. The patient developed HIT which was confirmed by laboratory tests. Echocardiographic examination performed one month later showed vegetations on the aortic tissue valve and a small aortic root abscess. The patient still tested positively for the presence of HIT antibodies and was treated conservatively with antibiotics. A repeat echocardiographic examination showed progression of the aortic root abscess and it was decided to proceed with urgent redo aortic valve surgery. Anticoagulation for cardiopulmonary bypass (CPB) was achieved with the use of a direct thrombin inhibitor (DTI), bivalirudin. Following an uneventful wean from CPB, hemostasis was achieved within 40 min. The postoperative course was uncomplicated and the patient was discharged from hospital on the seventh postoperative day.

CONCLUSION

Bivalirudin is a DTI, which can be used as an alternative anticoagulant for CPB in HIT positive patients. This case report showed a favourable outcome with bivalirudin for urgent complex redo cardiac surgery requiring CPB.

Anticoagulation management and cardiac surgery in patients with heparin-induced thrombocytopenia

Unfractionated heparin (UFH) is the gold standard for anticoagulation during cardiopulmonary bypass (CPB). Of patients undergoing CPB operations, 25% to 50% develop heparin-dependent antibodies during the postoperative period, typically between day 5 and 10, if UFH is continued during the postoperative course. In 1% to 3% of all patients undergoing CPB operation with UFH anticoagulation, these antibodies activate platelets causing a prothrombotic disorder, known as heparin-induced thrombocytopenia (HIT), which can lead to life-threatening thromboembolic complications. If urgent cardiac operation with the use of CPB in patients with positive antibody titer is required, different anticoagulatory approaches are available, such as lepirudin, bivalirudin, and danaparoid or UFH in combination with platelet antagonists, such as epoprostenol or tirofiban. In patients with previous HIT but no detectable antibodies, UFH alone can be used only during CPB, but alternative anticoagulation has to be used pre- and postoperatively.

Snake venom serine proteinases: sequence homology vs. substrate specificity, a paradox to be solved

Snake venom glands synthesize a variety of serine proteinases capable of affecting the haemostatic system. They act on macromolecular substrates of the coagulation, fibrinolytic, and kallikrein-kinin systems, and on platelets to cause an imbalance of the haemostatic system of the prey. In this review we describe their biochemical/biophysical characteristics, biological activities as well as aspects of their evolution and structure-activity relationship.

Diagnosis and treatment of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a major side effect secondary to the administration of heparin. This syndrome is serious and potentially life threatening. This response is the result of antibodies formed against the platelet factor 4 (PF4)/heparin complex. The incidence of this immune-mediated syndrome has been estimated to be 1-3% of all patients receiving heparin therapy. The occurrence of HIT in patients requiring full anticoagulation for cardiopulmonary bypass (CPB), therefore, presents a serious challenge to the cardiac surgery team. The diagnosis of HIT should be based on both clinical and laboratory evidence. While functional assays, platelet aggregation tests, and the serotonin release assay can be used to support the diagnosis, the negative predictive value of these tests is generally less than 50%. In contrast, although non-functional antibody detection assays are more sensitive, they have a low specificity. HIT can be treated in several ways, including cessation of all heparin and giving an alternative thrombin inhibitor, platelet inhibition followed by heparin infusion, and the use of low molecular weight heparins. In this presentation, the pathology and current diagnostic tests, as well as the successful management of patients with HIT undergoing CPB at New York Presbyterian Hospital, are reviewed.

[Extracorporeal circulation with danaparoid sodium for valve replacement in thrombocytopenia induced by type II heparin]

A type II heparin-induced thrombocytopenia (HIT) was diagnosed in a 64-year-old woman at day 20 of intravenous unfractionated heparin (UFH) therapy, given after myocardial infarction treated by angioplasty and intracoronary stent. The infarction was complicated by a mitral insufficiency that led to a mitral valve replacement. Cardiopulmonary bypass was successfully performed with sodium danaparoid (Orgaran), as an alternative to UFH, without thrombotic or haemorrhagic complications and the follow-up was uneventful.

Alternatives to unfractionated heparin for anticoagulation in cardiopulmonary bypass

Despite the progress made in the development of cardiopulmonary bypass (CPB) equipment, systemic anticoagulation with unfractionated heparin and post-bypass neutralization with protamine are still used in most perfusion procedures. However, there are a number of situations where unfractionated heparin, protamine or both cannot be used for various reasons. Intolerance of protamine can be addressed with extracorporeal heparin removal devices, perfusion with (no) low systemic heparinization and, to some degree, by perfusion with alternative anticoagulants. Various alternative anticoagulation regimens have been used in cases of intolerance to unfractionated heparin, including extreme hemodilution, low molecular weight heparins, danaparoid, ancrod, r-hirudin, abciximab, tirofiban, argatroban and others. In the presence of heparin-induced thrombocytopenia (HIT) and thrombosis, the use of r-hirudin appears to be an acceptable solution which has been well studied. The main issue with r-hirudin is the difficulty in monitoring its activity during CPB, despite the fact that ecarin coagulation time assessment is now available. A more recent approach is based on selective blockage of platelet aggregation by means of monoclonal antibodies directed to GPIIb/IIIa receptors (abciximab) or the use of a GPIIb/IIIa inhibitor (tirofiban). An 80% blockage of the GPIIb/IIIa receptors and suppression of platelet aggregation to less than 20% allows the giving of unfractionated heparin and running CPB in a standard fashion despite HIT and thrombosis. Likewise, at the end of the procedure, unfractionated heparin is neutralized with protamine as usual and donor platelets are transfused if necessary. GPIIb/IIIa inhibitors are frequently used in interventional cardiology and, therefore, are available in most hospitals.

Cardiopulmonary bypass in patients with heparin-induced thrombocytopenia and thrombosis

Heparin-induced thrombocytopenia and thrombosis (HITT) is an immunomediated disorder induced by the administration of heparin for therapeutic purposes. The presence of this condition in patients requiring full heparinization for cardiopulmonary bypass constitutes a formidable challenge for the cardiac surgeon. In this review, the clinical and experimental experience described in the literature are discussed in the perspective of the normal coagulation and the pathophysiology of HITT and in the light of a variety of old and new alternative anticoagulants.

Cardiopulmonary bypass in humans: bypassing unfractionated heparin

Seven anticoagulants besides unfractionated heparin have been used for human cardiopulmonary bypass (CPB), mainly in patients with heparin-induced thrombocytopenia. The collective experience with these alternative anticoagulants provides a perspective on current efforts aimed at improving CPB anticoagulation. Unfortunately, each alternative currently lacks a standard dosing schedule and a reliable method of monitoring the adequacy of its anticoagulant effect during CPB. Most also lack proven antidotes. Thus, unfractionated heparin remains the anticoagulant of choice for standard CPB.

Management strategies for heparin-induced thrombocytopenia in heart-transplant candidates: case report and review of the literature

Management of anticoagulation in patients with heparin-induced thrombocytopenia (HIT) undergoing surgery requiring cardiopulmonary bypass (CPB), such as cardiac transplantation, represents a difficult clinical problem and no clear management strategy exists. The cases of 2 patients with HIT who underwent cardiac transplantation using differing anticoagulation strategies are presented with a discussion of potential advantages and pitfalls of each approach used.

Cardiopulmonary bypass with danaparoid sodium and ancrod in heparin-induced thrombocytopenia

Heparin is the standard anticoagulant for patients undergoing cardiopulmonary bypass. There are some patients for whom heparin is unsuitable and ancrod (a defibrinogenating enzyme) has been used as an alternative. We present a patient with heparin-induced thrombocytopenia in whom treatment ancrod was ineffective. The addition of danaparoid sodium (a heparinoid) allowed safe cardiopulmonary bypass. We discuss the reasons for this and suggest that the combination of ancrod and danaparoid sodium is a logical one in such cases.

Heparinless cardiopulmonary bypass with active-site blocked factor IXa: a preliminary study on the dog

OBJECTIVE

Cardiopulmonary bypass is a potent stimulus for activation of procoagulant pathways. Heparin, the traditional antithrombotic agent, however, is often associated with increased perioperative blood loss because of its multiple sites of action in the coagulation cascade and its antiplatelet and profibrinolytic effects. Furthermore, heparin-mediated immunologic reactions (that is, heparin-induced thrombocytopenia) may contraindicate its use. Cardiopulmonary bypass with a selective factor IXa inhibitor was tested to see whether it could effectively limit bypass circuit/intravascular space thrombosis while decreasing extravascular bleeding, thereby providing an alternative anticoagulant strategy when heparin may not be safely administered.

METHODS

Active site-blocked factor IXa, a competitive inhibitor of the assembly of factor IXa into the factor X activation complex, was prepared by modification of the enzyme's active site by the use of dansyl glutamic acid-glycine-arginine-chlormethylketone. Twenty mongrel dogs (five were given standard heparin/protamine; 15 were given activated site-blocked factor IXa doses ranging from 300 to 600 microg/kg) underwent 1 hour of hypothermic cardiopulmonary bypass, and blood loss was monitored for 3 hours after the procedure.

RESULTS

Use of activated site-blocked factor IXa as an anticoagulant in cardiopulmonary bypass limited fibrin deposition within the extracorporeal circuit as assessed by scanning electron microscopy, comparable with the antithrombotic effect seen with heparin. In contrast to heparin, effective antithrombotic doses of activated site-blocked factor IXa significantly diminished blood loss in the thoracic cavity and in an abdominal incisional bleeding model.

CONCLUSION

These initial studies on the dog suggest that administration of activated site-blocked factor IXa may be an effective alternative anticoagulant strategy in cardiopulmonary bypass when heparin is contraindicated, affording inhibition of intravascular/extracorporeal circuit thrombosis with enhanced hemostasis in the surgical wound.

The contribution of Canadian anaesthetists to the evolution of cardiac surgery

PURPOSE

There have been great improvements in the management of patients with heart disease over the past 50 yr much of which has been due to the development of surgical procedures for the correction of acquired and congenital cardiac abnormalities. A great deal has been written about the surgeons and the innovative procedures they developed. They were undoubtedly courageous, imaginative, knowledgeable and skillful. Little is written about the anaesthetists who often worked in the laboratory with the surgeons and provided anaesthesia for patients having this surgery which, in the early days, was experimental. The purpose of this article is to present the contributions made by Canadian anaesthetists to the evolution of cardiac surgery.

PRINCIPAL FINDINGS

The contributions have been important over five clearly discernable eras and have been identified through publications. Canadian anaesthetists wrote about their experience giving anaesthesia for mitral commissurotomy, relief of pulmonic stenosis, ligation of patent ductus arteriosus, resection of aortic coarctation, correction of simple congenital heart defects under hypothermia and myocardial revascularization. When open heart surgery was introduced, Canadian anaesthetists working both in the United States and Canada were amongst the first to publish on surgery supported by cardiopulmonary bypass and anaesthesia for these procedures.

CONCLUSION

An analysis of the literature and personal, verbal and written communications with anaesthetists who experienced the trials and tribulations of anaesthesia for these early surgical procedures clearly indicates that Canadians were at the forefront in advancing anaesthesia for cardiac surgery.

Enoxaparin for unstable angina and ancrod for cardiac surgery following heparin allergy

OBJECTIVE

To describe a patient who presented with heparin allergy and required alternate anticoagulation for unstable angina and coronary artery bypass surgery. To review therapeutic alternatives to porcine heparin for patients with hypersensitivity or intolerance to standard heparin anticoagulation.

CASE SUMMARY

A 74-year-old man with a 15-year-old coronary artery bypass graft presented to the emergency room with unstable angina and was scheduled for urgent coronary artery revascularization. A bolus dose of porcine heparin was administered followed by a continuous infusion. Shortly afterward the patient developed a type I allergic reaction to the porcine heparin that was confirmed by rechallenge. Three alternatives to porcine heparin were tried, including bovine lung heparin, low-molecular-weight heparin (enoxaparin), and ancrod. The patient was found to be cross-sensitive to bovine lung heparin, but tolerated enoxaparin for unstable angina without cross-sensitivity. Anticoagulation for cardiopulmonary bypass was achieved with an infusion of ancrod that was later reversed with cryoprecipitate. The patient was discharged postoperatively on day 5 without the complication of excessive bleeding.

DISCUSSION

Type I allergic reaction to unfractionated heparin is a rare occurrence and could be the result of a variety of factors. Possible causes for the reaction include a porcine protein, a preservative contained in the heparin solution, or a hapten formed between heparin and a plasma protein. We considered four alternatives to heparin anticoagulation: rush desensitization, bovine lung heparin, low-molecular-weight heparin, and ancrod. The patient was cross-sensitive to bovine lung heparin, but was able to tolerate low-molecular-weight heparin (enoxaparin). This was unexpected because enoxaparin is derived from unfractionated porcine heparin. Testing for cross-sensitivity had no value in this case, as two negative subcutaneous test doses were followed by dramatic reactions when the drugs were given intravenously. Although enoxaparin has been used for anticoagulation during bypass surgery, there is more experience with ancrod as an alternative to heparin. Repeat bypass surgery, which normally results in above-average blood loss, was successfully performed with a very low fibrinogen concentration (< 0.15 g/L) during ancrod anticoagulation.

CONCLUSIONS

We conclude that ancrod was a safe and effective alternative to heparin for coronary artery bypass surgery in this patient in whom a heparin product had caused a hypersensitivity reaction. We discovered on two occasions that a negative subcutaneous test dose for heparin allergy did not predict a severe type I allergic reaction when the heparin was later administered intravenously. Furthermore, we found that a low-molecular-weight heparin administered subcutaneously for a short period of time did not cause cross-sensitivity in a patient with a type I allergy to unfractionated heparin.

Heparin-induced thrombocytopenia and thrombosis: presentation after cardiopulmonary bypass

Heparin-induced thrombocytopenia and thrombosis syndrome was diagnosed in a 63-year-old woman 11 days after coronary artery bypass grafting. Her only presenting complaints were incisional leg pain and vague chest discomfort. The syndrome was suspected when her platelet count was found to be 37,000/microL. A subsequent ventilation-perfusion lung scan showed findings highly probable for pulmonary embolism. An inferior venacavogram obtained before a pulmonary angiogram revealed a large retrohepatic thrombus at the right atrial junction. The patient was successfully treated with the defibrinogenating agent ancrod (Arvin). A diagnosis of heparin-induced thrombocytopenia and thrombosis syndrome should be considered and heparin therapy should be avoided in patients with low platelet counts who have been previously treated with heparin.

Ancrod infusion for anticoagulation during and after PTCA in a patient with heparin-induced thrombocytopenia

Ancrod is a rapid-acting defibrinogenating agent derived from the venom of the Malayan pit viper which has been used successfully as an alternative to heparin sulfate for anticoagulation during peripheral vascular procedures and coronary artery bypass surgery. We describe the first use of ancrod for anticoagulation before and during percutaneous transluminal coronary angioplasty (PTCA) in a patient with heparin-associated thrombocytopenia.

Anticoagulation and hemostasis in cardiac surgical patients

Optimizing anticoagulation and hemostasis during cardiopulmonary bypass and perioperatively helps to ensure the best possible clinical outcome. This article reviews the pharmacology of unfractionated and low-molecular weight heparin, aprotinin, desmopressin, dextran, antiplatelet agents, warfarin, and direct thrombin inhibitors. Their use is discussed in the context of coronary artery surgery, valvular surgery, and mechanical cardiac support devices, as well as in the management of acute ischemic syndromes, atrial fibrillation, and prevention and treatment of venous thromboembolism. Progress in the development and utilization of these anticoagulants and antiplatelet agents has supported the major advances that have been achieved in cardiac surgery.

Heparinless cardiopulmonary bypass with ancrod

A case is reported of a 22-year-old man with heparin-induced thrombocytopenia and thrombosis syndrome and a right atrial foreign body (Greenfield filter). Heparinless cardiopulmonary bypass for removal of the foreign body was conducted by pretreatment with ancrod, a rapid-acting antifibrinolytic of pit viper venom origin. Treatment protocol and a literature review are included in this article.

In vivo effect of a thrombin-like enzyme on platelet plug formation induced in mesenteric microvessels of mice

Ancrod caused defibrinogenation and exhibited ex vivo antiplatelet activity in experimental rabbits. In this study, platelet thrombus was induced by irradiation of the mesenteric microvessels with filtered light in mice pretreated with fluorescein sodium intravenously. Ancrod (0.5-2 U/kg) dose-dependently, significantly prolonged the time lapse of inducing platelet plug formation in mesenteric venules when it was intravenously infused. At these doses, ancrod depleted plasma fibrinogen and displayed ex vivo antiplatelet aggregation induced by collagen. Ancrod (1 U/kg) prolonged the occlusion time about 2.1 folds (from control 103.2 +/- 17.0 to 211.2 +/- 26.3 seconds) with a duration longer than 60 min. On the other hand, PGI2 briefly prolonged the occlusion time about 1.5 folds when it was given by continuous infusion (250-500 ng/kg/min). Heparin (100-250 U/kg) had no significant effect in this model. Therefore, ancrod may be used as a therapeutic agent not only in treatment of venous thrombosis and possibly in prevention of arterial thrombosis.

Response to heparinization in adults and children undergoing cardiac operations

The activated clotting time is an unreliable index of anticoagulation status during cardiopulmonary bypass procedures. However, modern instrumentation (Hemotec Hepcon HMS) now allows the monitoring of free heparin levels via automated protamine titration. In the present study, the standard procedure of anticoagulation at Killingbeck Hospital, Leeds, was investigated. Twenty-two pediatric patients and 20 adult patients undergoing open heart procedures involving cardiopulmonary bypass were given empirical doses of heparin (3 mg/kg body weight bolus), and activated clotting time was maintained at a level greater than 450 seconds using the Hemochron Timer. Heparin neutralization was performed at the termination of the bypass period using an empirical equivalent (3 mg/kg) of protamine sulfate. Mean free heparin concentration (+/- standard deviation) fell from 2.26 (+/- 0.45) mg/kg to 1.39 (+/- 0.34) mg/kg over the period 10 to 40 minutes on bypass in children. In adults, free heparin level declined from 2.56 (+/- 0.58) mg/kg to 1.81 (+/- 0.58) mg/kg over the same period. The biological half-life for heparin was 60 minutes in adults and 35 minutes in pediatric patients. Empirical protamine dosing resulted in excess protamine administration when compared with Hepcon titrated dose requirements: for children: median (range), 80 (12 to 350) versus 33 (12 to 97) mg, p less than 0.001; and for adults: 350 (200 to 500) versus 130 (61 to 237) mg, p less than 0.001. In conclusion, empirical heparin administration (3 mg/kg) does not result in "steady-state" anticoagulation during cardiopulmonary bypass, and empirical administration of protamine takes no account of interindividual differences in heparin sensitivity and biological half-life, which may be assessed using the Hepcon HMS.

Does the preparation of heparin influence anticoagulation during cardiopulmonary bypass?

Various preparations of heparin from different manufacturers are commercially available. The influence of bovine lung heparin (BLH) and porcine mucosal heparin (PMH) on anticoagulation and heparin plasma concentration was investigated in four groups of 10 patients undergoing elective aortocoronary bypass grafting either after single dose or repetitive dose (after 60 minutes) of one of these heparin preparations. Heparin plasma concentration increased significantly after injection of heparin (BLH: minimum, 1.67 U/mL; maximum, 2.10 U/mL; PMH: minimum, 1.69 U/mL; maximum, 2.15 U/mL). Sixty minutes after the initial dose, heparin plasma levels were higher in the patients who received PMH. Supplemental heparin doses 60 minutes after the loading dose increased plasma heparin concentration only with porcine mucosal heparin. Elimination of heparin in the urine was not different among the groups. Fibrinogen and antithrombin III concentrations, as well as activated clotting time (ACT; always greater than 400 seconds) and partial thromboplastin time (PTT; always greater than 300 seconds), did not differ among the groups, indicating effective anticoagulation during the bypass period with both types of heparin. It can be concluded that sufficient anticoagulation can be achieved with either kind of heparin. PMH seems to be longer acting and a repeat dose in these patients seems to be necessary only if cardiopulmonary bypass lasts longer than 90 minutes.