Anticoagulant Effects of Low-Molecular-Weight Heparins in Healthy Cats

Preventing Cardiogenic Thromboembolism in Cats: Literature Gaps, Rational Recommendations, and Future Therapies

Cardiogenic arterial thromboembolism (CATE) is a devastating complication in cats with cardiomyopathies with significant morbidity and mortality. Despite recent advances in the diagnosis and treatment of CATE, its recurrence and mortality remain high. This highlights the urgent need for a greater understanding of CATE pathophysiology so that novel diagnostic tests and therapeutics can be developed. This comprehensive review aims to summarize existing literature on pathophysiology, clinical diagnosis, and current recommendations on the prevention and treatment of CATE. It also identifies and describes knowledge gaps and research priorities in the roles of immunothrombosis and procoagulant platelets in the pathogenesis of CATE.

Effects of a single subcutaneous dose of enoxaparin on veterinary viscoelastic coagulation monitor variables in healthy cats: Double blind, placebo controlled cross-over trial

BACKGROUND

Cats placed on anticoagulant medication require frequent monitoring. The veterinary viscoelastic coagulation monitor (VCM-Vet) could provide a convenient and cost-effective monitoring, enabling therapeutic decision making.

HYPOTHESIS/OBJECTIVES

Enoxaparin will lead to changes in VCM-Vet variables and these will correlate with antiXa activity.

ANIMALS

Twenty-one healthy cats.

METHODS

Cats were randomized to receive either enoxaparin (1 mg/kg) subcutaneously or 0.9% NaCl (equal volume) and crossed over with a 7-day washout period. The investigators were blinded to group allocation until data analysis. Jugular blood samples were drawn at time 0, and 2, 4, and 8 hours after injection for VCM-Vet analysis within 2 min of collection. Citrated plasma was frozen at -80°C for antiXa activity analysis. A Generalized Linear Model was completed to assess changes between baseline measurements and all time points.

RESULTS

Significant differences between the enoxaparin-treated cats and controls at for T0h and T2h were found and presented as mean ± SD for clotting time (enoxaparin, 593.4 ± 78.0 s; control, 448.5 ± 50.3 s, P < .001), clot formation time (enoxaparin, 183.1 ± 41.7 s; control, 155.4 ± 28.0 s, P = .001), and alpha angle (enoxaparin, 52.4 ± 6.1°; control, 56.9 ± 3.7 s, P = .003). AntiXa activity was significantly different between T0 and all other timepoints for the enoxaparin group (P < .001). There was no correlation between changes in clotting time and antiXa activity.

CONCLUSIONS AND CLINICAL IMPORTANCE

The VCM-Vet detects a difference at 2 hours after single-dose enoxaparin administration and it can be useful for anticoagulant therapy monitoring in cats.

Programmed prodrug breaking the feedback regulation of P-selectin in plaque inflammation for atherosclerotic therapy

Inflammation is the main driver of the aggravation of arteriosclerosis, and the complex inflammatory response in plaque is usually the result of the interaction of various cells and cytokines. Therefore, it is difficult to comprehensively regulate the inflammatory process of arteriosclerosis by intervening a single target, resulting in the poor effect of existing treatment method. Based on our clinical findings that P-selectin stably and highly expressed in patients' plaque endothelial cells, the programmed prodrug, low molecular weight heparin-indomethacin nanoparticles (LI NPs), were established as anti-inflammatory agent to multiphase inhibit arteriosclerosis by cascade interference of P-selectin. Structurally, LI NPs was obtained by simple esterification of low molecular weight heparin and indomethacin without any additives, guaranteeing the biocompatibility and applicability of LI NPs. Functionally, LI NPs could interfere with P-selectin in the inflammatory process, such as inhibiting macrophage adhesion, reducing the secretion of inflammatory factors, and inducing macrophage apoptosis. In the arteriosclerosis mice model, LI NPs significantly reduced the plaque area and showed satisfactory curative effect, which is related to the intervention of the multiphase inflammation between endothelial cells and macrophages. In conclusion, the programmed prodrug LI NPs offered a promising approach for the clinical therapy of arteriosclerosis.

Retrospective Evaluation of Intravenous Enoxaparin Administration in Feline Arterial Thromboembolism

Simple Summary

Feline arterial thromboembolism is a painful disease characterized by acute ischemic necrosis of one or more limbs due to cardiac diseases, hyperthyroidism, or neoplasia. Among others, medical treatment consists of preventing new thrombus formation primarily using heparin products, such as enoxaparin. This retrospective study reports clinical data, regain of perfusion, short-term outcome, and complications of 36 affected cats treated with a novel intravenous enoxaparin protocol. Furthermore, we aimed to report monitoring and management of the intravenous enoxaparin treatment for this disease. In our population, visible hemorrhage was rare. The most common causes of death/euthanasia were cardiac instability, acute kidney injury, neurological abnormalities, and limb necrosis. The hospital discharge rate was 47% overall and was significantly different between single limb (83%) and dual limb (29%) thromboembolism. Our study supports the intravenous use of enoxaparin in combination with oral clopidogrel for cats with thromboembolism as an alternative treatment method.

Abstract

Induction of a hypocoagulable state is imperative in the treatment of feline arterial thromboembolism. Publications in human medicine report the use of enoxaparin intravenously in selected cases. The aim of our retrospective study was to report the regain of perfusion, short-term outcome, and complications of cats treated with a novel intravenous enoxaparin protocol (1 mg/kg bolus injection followed by 3 mg/kg/day continuous infusion) combined with oral clopidogrel administration. The secondary aim was to report the monitoring of enoxaparin with anti-Xa activity. There were 36 cats included. The probability of reaching limb reperfusion was significantly (p = 0.0148) higher with anti-Xa activity within or above the target range compared to results below the target range (19/21, 90% versus 11/20, 55%). The complications observed were acute kidney injury (15/36, 42%), hemorrhage (2/36, 6%), and neurological signs (6/36, 17%). The most common causes of death/euthanasia were cardiac instability, acute kidney injury, neurological abnormalities, and limb necrosis. The hospital discharge rate was 83% (10/12) for single limb and 29% (7/24) for dual limb thrombosis; the difference was significant (p = 0.0039). The median hospitalization time for the survivors was 119.5 (95–480) h. Our study supports the use of intravenous continuous rate infusion of enoxaparin in combination with oral clopidogrel for cats with aortic thromboembolism. We report similar discharge rates and lower hemorrhage rates than previously reported with thrombolytic treatment.

Thromboelastography in cats with cholestatic liver disease

OBJECTIVES

While thromboelastography (TEG) has helped define a complex state of hemostasis in dogs and humans with hepatobiliary disease, it has not been explored in cats with cholestatic liver disease (CLD). The objective of this study was to describe TEG parameters in cats with CLD and to compare these parameters with conventional plasma-based coagulation tests, white blood cell (WBC) count and biochemical indicators of liver disease grade and severity.

METHODS

Eighteen cats with CLD, defined by a serum bilirubin ⩾3 mg/dl and a greater than two-fold increase in serum alanine aminotransferase (ALT) and/or alkaline phosphatase (ALP) activity, were prospectively enrolled. All cats received vitamin K1 subcutaneously for 24-36 h prior to acquisition of blood for kaolin-activated TEG analysis, prothrombin time (PT) and activated partial thromboplastin time (aPTT). Patient total solids, packed cell volume, platelet count, WBC count, and serum liver enzymes and bilirubin were extracted from the medical record and correlated with coagulation test results.

RESULTS

TEG global clot strength (TEG G) values defined 9/18 (50%), 5/18 (28%) and 4/18 (22%) cats as hypercoagulable, normocoagulable or hypocoagulable, respectively. TEG G was significantly negatively correlated with PT, aPTT and serum ALP activity and positively correlated with total solids. Five cats (5/18, 28%) were hyperfibrinolytic with clot lysis at 60 mins (LY 60) >15.3%. LY 60 was significantly positively correlated with PT.

CONCLUSIONS AND RELEVANCE

By TEG analysis, cholestatic cats replete with vitamin K1 display a variety of coagulation profiles. Indications of synthetic failure (prolonged PT and aPTT) were associated with hypocoagulable and hyperfibrinolytic TEG parameters. High disease activity (serum ALP) was associated with a hypocoagulable state.

A prospective evaluation of oral Yunnan Baiyao therapy on thromboelastographic parameters in apparently healthy cats

OBJECTIVE

To determine the effect of Yunnan Baiyao (YB) on hemostatic parameters measured by thromboelastography (TEG) in apparently healthy cats administered 1 capsule of YB orally twice daily for 1 week.

DESIGN

Prospective study of client-owned cats at a small animal specialty hospital.

SETTING

One private referral center.

ANIMALS

Twenty client-owned adult cats were prospectively enrolled.

INTERVENTIONS

All cats underwent echocardiographic examination by the same board-certified cardiologist to rule out occult cardiomyopathy. Blood samples were collected for analysis of baseline CBC, fibrinogen, and kaolin-activated TEG values. Cats were administered 1 capsule (250 mg/capsule) of YB twice daily orally for 1 week and the physical examination, CBC, fibrinogen, and TEG were re-evaluated. Any side effects attributed to YB were noted at this time.

MEASUREMENTS AND MAIN RESULTS

Three cats were excluded as 2 cats were identified with underlying cardiomyopathy and another cat had a cystic mass in the cranial mediastinum identified via echocardiography. Seventeen cats were treated with YB; however, 1 cat could not complete the study due to severe vomiting associated with YB administration. The remaining 16 cats completed the study, although 2 additional cats experienced transient vomiting. Yunnan Baiyao administration was associated with a significant decrease in HCT and red blood cell count, although no cat became anemic. None of the TEG parameters significantly changed compared to baseline after 1 week of YB therapy.

CONCLUSIONS

The results of this study suggest YB at a dose of 1 capsule orally twice daily in cats fails to produce any significant change in hemostatic parameters as measured by TEG, although it did significantly reduce HCT and red blood cell count. Yunnan Baiyao was tolerated for most of the cats, although 3 of 17 (17.6%) cats experienced vomiting. Clinicians should be aware of these effects before considering the use of YB in cats.

Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE): Domain 4-Refining and monitoring antithrombotic therapies

OBJECTIVES

To systematically review the evidence for therapeutic monitoring of antithrombotic drugs in small animals, develop guidelines regarding antithrombotic monitoring, and identify knowledge gaps in the field.

DESIGN

First, a standardized, systematic literature review was conducted to address predefined PICO (Population/Patient, Intervention, Control, Outcome) questions, with categorization of relevant articles according to level of evidence and quality. Preliminary guidelines were developed by PICO worksheet authors and the domain chair. Thereafter, a Delphi-style survey was used to develop consensus on guidelines regarding therapeutic monitoring of antithrombotics in dogs and cats.

SETTING

Academic and referral veterinary medical centers.

RESULTS

PICO questions regarding the utility of therapeutic monitoring were developed for 6 different antithrombotic drugs or drug classes, including aspirin, clopidogrel, warfarin, unfractionated heparin, the low molecular weight heparins, and rivaroxaban, The majority of the literature pertaining to therapeutic monitoring of antithrombotic drugs was either performed in experimental animal models of disease or involved studies of drug pharmacokinetics and pharmacodynamics in healthy laboratory animals. There was a paucity of high level of evidence studies directly addressing the PICO questions, which limited the strength of recommendations that could be provided. The final guidelines recommend that therapeutic monitoring should be performed when using warfarin or unfractionated heparin in dogs and cats at risk of thrombosis. There is insufficient evidence to make strong recommendations for therapeutic monitoring of aspirin or low molecular weight heparin in dogs and cats at this time.

CONCLUSIONS

As in other CURATIVE domains, significant knowledge gaps were highlighted, indicating the need for substantial additional research in this field. Ongoing investigation of the role of therapeutic monitoring of antithrombotic therapies will undoubtedly facilitate improved outcomes for dogs and cats at risk of thrombosis.

American College of Veterinary Emergency and Critical Care (ACVECC) Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE) guidelines: Small animal

OBJECTIVES

To systematically review available evidence and establish guidelines related to the risk of developing thrombosis and the management of small animals with antithrombotics.

DESIGN

Standardized, systematic evaluation of the literature (identified by searching Medline via PubMed and CAB abstracts) was carried out in 5 domains (Defining populations at risk; Defining rational therapeutic use; Defining evidence-based protocols; Refining and monitoring antithrombotic therapies; and Discontinuing antithrombotic therapies). Evidence evaluation was carried out using Population, Intervention, Comparison, Outcome generated within each domain questions to address specific aims. This was followed by categorization of relevant articles according to level of evidence and quality (Good, Fair, or Poor). Synthesis of these data led to the development of a series of statements. Consensus on the final guidelines was achieved via Delphi-style surveys. Draft recommendations were presented at 2 international veterinary conferences and made available for community assessment, review, and comment prior to final revisions and publication.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Over 500 studies were reviewed in detail. Worksheets from all 5 domains generated 59 statements with 83 guideline recommendations that were refined during 3 rounds of Delphi surveys. A high degree of consensus was reached across all guideline recommendations.

CONCLUSIONS

Overall, systematic evidence evaluations yielded more than 80 recommendations for the treatment of small animals with or at risk of developing thrombosis. Numerous significant knowledge gaps were highlighted by the evidence reviews undertaken, indicating the need for substantial additional research in this field.

Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE): Domain 3-Defining antithrombotic protocols

OBJECTIVES

To systematically examine the evidence for use of a specific protocol (dose, frequency, route) of selected antithrombotic drugs, in comparisons to no therapy or to other antithrombotic therapies, to reduce the risk of complications or improve outcomes in dogs and cats at risk for thrombosis.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence (LOE) and quality (Good, Fair, or Poor), and development of consensus on conclusions via a Delphi-style survey for application of the concepts to clinical practice.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Databases searched included Medline via PubMed and CAB abstracts. Eight different antithrombotic drugs were investigated using a standardized Patient, Intervention, Comparison, Outcome (PICO) question format both for dogs and cats, including aspirin, clopidogrel, warfarin, unfractionated heparin (UFH), dalteparin, enoxaparin, fondaparinux, and rivaroxaban, generating a total of 16 worksheets. Most studies identified were experimental controlled laboratory studies in companion animals (LOE 3) with only four randomized controlled clinical trials in companion animals (LOE 1).

CONCLUSIONS

Overall, evidence-based recommendations concerning specific protocols could not be formulated for most antithrombotic drugs evaluated, either because of the wide range of dosage reported (eg, aspirin in dogs) or the lack of evidence in the current literature. However, clopidogrel administration in dogs and cats at risk of arterial thrombosis, notably in cats at risk of cardiogenic thromboembolism, is supported by the literature, and specific protocols were recommended. Comparably, aspirin should not be used as a sole antithrombotic in cats with cardiomyopathy. Using the available safety profile information contained in the literature, the panel reached consensus on suggested dosage schemes for most antithrombotics. Significant knowledge gaps were highlighted, which will hopefully drive novel research.

Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE): Domain 2-Defining rational therapeutic usage

OBJECTIVES

To systematically review available evidence to determine when small animals at risk of thrombosis should be treated with antiplatelet agents and anticoagulants, which antiplatelet and anticoagulant agents are most effective, and when multimodal therapy is indicated.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence (LOE) and quality (Good, Fair, or Poor), and development of consensus on conclusions via a Delphi-style survey for application of the concepts to clinical practice. Draft recommendations were presented at 2 international veterinary conferences and made available for community assessment, review, and comment prior to final revisions and publication.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Databases searched included Medline via PubMed and CAB abstracts. Twelve Population Intervention Comparison Outcome questions were devised and generated corresponding worksheets investigating indications for use of antithrombotic drugs in small animals. Seventy-eight studies were reviewed in detail. Most studies assessed were experimentally controlled laboratory studies in companion animals (56 LOE 3) with smaller numbers of LOE 2 (1), LOE 4 (5), LOE 5 (6), and LOE 6 (4) studies assessed. Only 5 randomized controlled clinical trials were identified (LOE 1, Good-Fair). The 12 worksheets generated 21 guidelines with 17 guideline statements that were refined during 3 rounds of Delphi surveys. A high degree of consensus was reached across all guideline recommendations during the Delphi process.

CONCLUSIONS

Overall, systematic evidence evaluations generated 2 strong recommendations, 19 weak recommendations (formulated as suggestions), 9 situations where the evidence was insufficient to make strong recommendations, and 8 situations where no relevant evidence was retrieved to aid guideline generation. Numerous significant knowledge gaps were highlighted by the evidence reviews undertaken, indicating the need for substantial additional research in this field.

Haematology and coagulation profiles in cats with congenital portosystemic shunts

Objectives The objectives of this study were, first, to report the haematological parameters and coagulation times for cats with a congenital portosystemic shunt (CPSS) and the influence of surgical shunt attenuation on these parameters; and, second, to identify any association between prolongation in coagulation profiles and incidence of perioperative haemorrhage. Methods This was a retrospective clinical study using client-owned cats with a CPSS. Signalment, shunt type (extra- or intrahepatic), degree of shunt attenuation (complete or partial), haematological parameters, prothrombin time (PT) and activated partial thromboplastin time (aPTT) test results, and occurrence of any perioperative clinical bleeding complications were recorded for cats undergoing surgical treatment of a CPSS at the Royal Veterinary College, UK, between 1994 and 2011. Results Forty-two cats were included. Thirty-six (85.7%) had an extrahepatic CPSS and six (14.3%) had an intrahepatic CPSS. Preoperatively, mean cell volume (MCV) and mean cell haemoglobin (MCH) were below the reference interval (RI) in 32 (76.2%) and 31 (73.8%) cats, respectively. Red blood cell count and mean cell haemoglobin concentration (MCHC) were above the RI in 10 (23.8%) and eight (19.1%) cats, respectively. Postoperatively, there were significant increases in haematocrit ( P = 0.044), MCV ( P = 0.008) and MCH ( P = 0.002). Despite the significant increase in MCV postoperatively, the median MCV postoperatively was below the RI, indicating persistence of microcytosis. Preoperatively, PT was above the upper RI in 14 cats (87.5%), and aPTT was above the upper RI in 11 cats (68.8%). No cat demonstrated a perioperative clinical bleeding complication. Conclusions and relevance Cats with a CPSS are likely to present with a microcytosis, but rarely present with anaemia, leukocytosis or thrombocytopenia. Surgical attenuation of the CPSS results in a significant increase in the HCT and MCV. Coagulation profiles in cats with a CPSS are likely to be prolonged, irrespective of shunt type, but do not appear to be associated with an increased risk of clinical bleeding.

Feline Cardiogenic Arterial Thromboembolism: Prevention and Therapy

Feline cardiogenic arterial thromboembolism (CATE) is a devastating disease whereby 33% of cats survive their initial event, although approximately 50% of mortality is from euthanasia. Short-term management focuses on inducing a hypocoagulable state, improving blood flow, and providing supportive care. Ideally, all cats should be given 72 hours of treatment to determine the acute clinical course. Preventive protocols include antiplatelet and/or anticoagulant drugs, with the only prospective clinical trial demonstrating that clopidogrel is superior to aspirin with a lower CATE recurrence rate and longer time to recurrent CATE. Newer anticoagulant drugs hold great promise in the future of managing this disease.

Reference values for rotational thromboelastometry (ROTEM) in clinically healthy cats

OBJECTIVE

To establish reference intervals for rotational thromboelastometry (ROTEM) using feline blood.

DESIGN

Prospective study.

SETTING

University teaching hospital.

ANIMALS

Twenty-three clinically healthy cats between 1 and 15 years.

INTERVENTION

For each cat, whole blood was collected via jugular or medial saphenous venipuncture, and blood was placed into a serum tube, a tube containing potassium-EDTA, and tubes containing 3.2% sodium citrate. The tubes were maintained at 37°C for a maximum of 30 minutes before coagulation testing.

MEASUREMENTS AND MAIN RESULTS

ROTEM tests included the EXTEM, INTEM, FIBTEM, and APTEM assays. In addition, prothrombin time, activated partial thromboplastin time, thrombin time, and fibrinogen concentration (Clauss method) were analyzed for each cat. Reference intervals for ROTEM were calculated using the 2.5-97.5^th percentile for each parameter, and correlation with the standard coagulation profile was performed. Compared to people, clinically healthy cats had similar values for the EXTEM and INTEM assays, but had lower plasma fibrinogen concentrations (0.9-2.2 g/L), resulting in weaker maximum clot firmness (MCF, 3-10 mm) in the FIBTEM test. In 18 cats, maximum lysis (ML) values in the APTEM test were higher than in the EXTEM test, which seems unlikely to have occurred in the presence of aprotinin. It is possible that the observed high maximum lysis values were due to clot retraction rather than true clot lysis. Further studies will be required to test this hypothesis.

CONCLUSIONS

Cats have a weaker clot in the FIBTEM test, but have a similar clot strength to human blood in the other ROTEM assays, which may be due to a stronger contribution of platelets compared to that found in people. In cats, careful interpretation of the results to diagnose hyperfibrinolysis is advised, especially with the APTEM test, until further data are available.

Heparinase-modified thromboelastography in cats

BACKGROUND

Evaluation of underlying hemostatic function is challenging when feline patients are receiving an anticoagulant medication. Discontinuing the anticoagulant to obtain accurate results for hemostatic testing may lead to thrombotic complications. The addition of heparinase to blood samples may mitigate the effects of exogenous heparin and allow hemostatic testing.

METHODS

Tissue factor (TF)-activated thromboelastography (TEG) was performed using citrated whole blood from 19 cats. Assays were performed using citrated whole blood, with and without addition of unfractionated heparin to a concentration of 0.2 U/mL. For each blood sample, TEG assays were performed using a standard cup and a heparinase-coated cup.

KEY FINDINGS

For TEG variables R, k, α-angle, and MA, mean values were not statistically different when citrated blood was used with standard or heparinase-coated cups. Heparinized blood assayed in standard cups displayed a significantly increased R and k, and significantly decreased α-angle and MA when compared to heparinized blood assayed in heparinase-coated cups. TEG variables for heparinized blood assayed in heparinase cups was not statistically different from those of the citrated whole blood without added heparin.

SIGNIFICANCE

Heparinase modified, TF-activated, TEG reverses heparin effects in feline-citrated blood.

In vitro effects of 6 % hydroxyethyl starch 130/0.42 solution on feline whole blood coagulation measured by rotational thromboelastometry

Background

The artificial colloid, hydroxyethyl starch (HES), is recommended for intravascular volume expansion and colloid-osmotic pressure enhancement in dogs and cats. A well-known side effect of HES solutions in humans and dogs is coagulopathy. However, HES-associated coagulopathy has thus far not been investigated in cats. The goal of this study was to assess the in vitro effects of 6 % HES 130/0.42 on feline whole blood samples using rotational thromboelastometry (ROTEM). A further goal was to develop feline reference intervals for ROTEM at our institution. In this in vitro experimental study, blood samples of 24 adult healthy cats were collected by atraumatic jugular phlebotomy following intramuscular sedation. Baseline ROTEM analyses (using ex-tem, in-tem and fib-tem assays) were performed in duplicate. Additionally, ROTEM analyses were performed on blood samples after dilution with either Ringer’s acetate (RA) or 6 % HES 130/0.42 (HES) in a 1:6 dilution (i.e. 1 part solution and 6 parts blood).

Results

Coefficients of variation of duplicate measures were below 12 % in all ex-tem assays, 3 of 4 in-tem assays but only 1 of 3 fib-tem assays. Reference intervals were similar albeit somewhat narrower than those previously published. Dilution with both solutions lead to significantly prolonged CT (in-tem), CFT (ex-tem and in-tem), and reduced MCF (ex-tem, in-tem, and fib-tem) and alpha (ex-tem and in-tem). Compared to RA, dilution with HES caused a significant prolongation of CT in fib-tem (P = 0.016), CFT in ex-tem (P = 0.017) and in-tem (P = 0.019), as well as a reduction in MCF in in-tem (P = 0.032) and fib-tem (P = 0.020), and alpha in ex-tem (P = 0.014). However, only a single parameter (CFT in ex-tem) was outside of the established reference interval after dilution with HES.

Conclusions

In vitro hemodilution of feline blood with RA and HES causes a small but significant impairment of whole blood coagulation, with HES leading to a significantly greater effect on coagulation than RA. Further studies are necessary to evaluate the in vivo effects and the clinical significance of these findings.

Management of cardiac emergencies in small animals

Cardiac emergencies are life-threatening conditions that must be diagnosed quickly to avoid delays in therapy. A timely and accurate diagnosis leads to early relief of symptoms and improved survival. This article provides both a comprehensive review and updated management recommendations for common cardiac emergencies in dogs and cats. Specifically, the article confers updates for the efficient clinical recognition of decompensated cardiac patients, including focused echocardiography, cardiac biomarkers, and electrocardiogram interpretation. This article also reviews the latest recommendations for the treatment of heart failure (including the use of pimobendan) and the management of arrhythmias, pericardial effusion, and aortic thromboembolism.

Current diagnostic trends in coagulation disorders among dogs and cats

The diagnostic workup to differentiate hemorrhage caused by vascular injury from a systemic hemostatic imbalance typically involves a combination of broad screening tests and specific assays. The characterization of 3 overlapping phases of primary hemostasis, secondary hemostasis, and fibrinolysis provides a simple diagnostic framework for evaluating patients with clinical signs of hemorrhage. New techniques such as flow cytometry, thrombin-generation assays, thrombelastography, and anticoagulant drug monitoring are under investigation for veterinary patients; however, their ability to improve diagnosis or treatment requires further study in clinical trials.

Arterial thromboembolism: risks, realities and a rational first-line approach

PRACTICAL RELEVANCE

Feline arterial thromboembolism (ATE) is a common but devastating complication of myocardial disease, often necessitating euthanasia. A combination of endothelial dysfunction and blood stasis in the left atrium leads to local platelet activation and thrombus formation. Embolisation of the thrombus results in severe ischaemia of the affected vascular bed. With the classic 'saddle thrombus' presentation of thrombus in the terminal aorta, the diagnosis can usually be made by physical examination. The prognosis is poor for cats with multiple limbs affected by severe ischaemia, but much better where only one limb is affected or motor function is present.

PATIENT GROUP

Cats with left atrial enlargement secondary to cardiomyopathy are typically predisposed, although cats with hyperthyroidism, pulmonary neoplasia and supravalvular mitral stenosis may also be at risk.

MANAGEMENT

Analgesia is the main priority, and severe pain should be managed with methadone or a fentanyl constant rate infusion. Congestive heart failure (CHF) requires treatment with furosemide, but tachypnoea due to pain can mimic signs of CHF. Thrombolytic therapy is not recommended, but antithrombotic treatment should be started as soon as possible. Aspirin and clopidogrel are well tolerated.

EVIDENCE BASE

Several observational studies of ATE have been reported. No randomised, blinded, controlled studies have been reported in cats at risk, for either treatment or prevention of ATE, although such a study comparing aspirin and clopidogrel in cats is currently under way.

Comparing citrated native, kaolin-activated, and tissue factor–activated samples and determining intraindividual variability for feline thromboelastography

Thromboelastography (TEG) is a point-of-care whole blood test of hemostasis. While TEG is becoming more widely used in veterinary medicine, few studies describe the use of TEG in cats. The objectives of the current study were to: 1) document the range of TEG variables produced in healthy cats using 3 sample types (citrated native, kaolin-activated, and tissue factor–activated), and 2) determine if there was a significant difference between 2 separate samples obtained from individual healthy cats on the same day. Jugular venipuncture was performed in 20 cats, and citrated blood collected for TEG. TEG analysis was performed on citrated native, kaolin-activated, and tissue factor–activated blood for each sample. Two hours later, the procedure was repeated from the opposite jugular vein, yielding a total of 120 analyses. Reaction time ( R), alpha angle (α), kappa value (κ), and maximum amplitude (MA) were recorded from each tracing. No significant differences were found between TEG tracings from the first and second venipuncture samples. Significant differences were found between sample types for R, α, κ, and MA. Means for citrated native/kaolin-activated/tissue factor–activated methods were R = 4.1/3.7/0.6 min; κ = 2.5/1.8/2.2 min; α = 59.9/65.1/70.4 degrees; MA = 47.4/49.9/44.7 mm. A limitation of this study was the small number of cats used. Thromboelastography analysis may be a suitable method of evaluating hemostasis in cats.

Pharmacokinetics of the low molecular weight heparin dalteparin in cats

Low molecular weight heparin (LMWH) is used as an anticoagulant in cats although only limited pharmacokinetic data are available in this species. The aim of the present study was to establish the pharmacokinetics of dalteparin in cats based on anti-FXa heparin activities. Groups of clinically healthy cats (six animals per treatment) received individual LMWH injections at three different doses intravenously (IV) (25, 50, 100 anti-factor Xa international units [IU anti-FXa]/kg) or subcutaneously (SC) (50, 100, 200 IU anti-FXa/kg). Blood samples were collected before and at various times after injection. Anti-FXa activity was measured with a chromogenic substrate test. Following IV injection, maximum plasma heparin activities (C(max)) were 0.67 ± 0.14, 1.44 ± 0.22 and 2.87 ± 0.38 IU anti-FXa/mL, respectively. The calculated mean half-life (t(½)) was between 39 and 57 min and was not significantly dose-dependent (P=0.139). The volume of distribution (35-39 mL/kg) was almost equivalent to the plasma volume. After SC injection, C(max) values of 0.41 ± 0.10, 0.86 ± 0.17 or 1.91 ± 0.16 IU anti-FXa/mL, respectively, were calculated at 91-110 min post-injection. The t(½) values were between 106 and 122 min and were not significantly influenced by dose (P=0.784). The bioavailability after SC injection was approximately 100%. The high bioavailability of the SC administered LMWH dalteparin in cats was consistent with other species and indicated predictable blood levels. However, the comparatively short t(½) may indicate the necessity of multiple daily injections, which should be verified in clinical trials.

Defects in coagulation encountered in small animal critical care

Critically ill small animals are at risk for developing coagulation abnormalities. The processes of inflammation and coagulation are intertwined, and severe inflammation can lead to disturbances of coagulation. Severe coagulation dysfunction is associated with increased morbidity and mortality. Pathophysiology, diagnosis, and treatment of coagulation dysfunction are discussed. Defects in coagulation in small animal patients are complex and a consensus on diagnosis and treatment has yet to be reached.

Viscoelastic coagulation testing: technology, applications, and limitations

Use of viscoelastic point-of-care (POC) coagulation instrumentation is relatively new to veterinary medicine. In human medicine, this technology has recently undergone resurgence owing to its capacity to detect hypercoagulability. The lack of sensitive tests for detecting hypercoagulable states, along with our current understanding of in vivo coagulation, highlights the deficiencies of standard coagulation tests, such as prothrombin and partial thromboplastin times, which are performed on platelet-poor plasma. Viscoelastic coagulation analyzers can provide an assessment of global coagulation, from the beginning of clot formation to fibrinolysis, utilizing whole blood. In people, use of this technology has been reported to improve management of hemostasis during surgery and decrease usage of blood products and is being used as a rapid screen for hypercoagulability. In veterinary medicine, clinical use of viscoelastic technology has been reported in dogs, cats, foals, and adult horses. This article will provide an overview of the technology, reagents and assays, applications in human and veterinary medicine, and limitations of the 3 viscoelastic POC analyzers in clinical use.

Thromboembolic Conditions, Aetiology Diagnosis and Treatment in Dogs and Cats

In veterinary medicine, thrombo-embolism (TE) is an under-appreciated medical condition that requires immediate recognition. Since TE is multifactorial and its mode of presentation may vary, veterinarians face great difficulties in making a definitive diagnosis in a timely manner. In addition, most of the underlying conditions that give rise to TE are life-threatening and an aggressive diagnostic and therapeutic approach is required. Not only does the diagnosis and treatment of this condition require the collaboration of many specialties, the costs of therapy can be excessive with a high risk of recurrence. As such, owners have to be thoroughly informed before the therapy commences. While TE has been well-characterized in humans and is associated with significant morbidity and mortality, little information of similar quality is available in veterinary medicine. In addition, TE in animals is distinct from its human counterpart and we cannot simply adapt what is known from human clinical trials. With the promise of improvements in imaging modalities that improve our diagnostic capabilities, the window of opportunity to treat TE increases. This article focuses on aetiology, clinical presentation, diagnosis, and treatment of dogs and cats affected by TE.

Thromboelastography results on citrated whole blood from clinically healthy cats depend on modes of activation

Background

During the last decade, thromboelastography (TEG) has gained increasing acceptance as a diagnostic test in veterinary medicine for evaluation of haemostasis in dogs, however the use of TEG in cats has to date only been described in one previous study and a few abstracts. The objective of the present study was to evaluate and compare three different TEG assays in healthy cats, in order to establish which assay may be best suited for TEG analyses in cats.

Methods

90 TEG analyses were performed on citrated whole blood samples from 15 clinically healthy cats using assays without activator (native) or with human recombinant tissue factor (TF) or kaolin as activators. Results for reaction time (R), clotting time (K), angle (α), maximum amplitude (MA) and clot lysis (LY30; LY60) were recorded.

Results

Coefficients of variation (CVs) were highest in the native assay and comparable in TF and kaolin activated assays. Significant differences were observed between native and kaolin assays for all measured parameters, between kaolin and TF for all measured parameters except LY60 and between native and TF assays for R and K.

Conclusion

The results indicate that TEG is a reproducible method for evaluation of haemostasis in clinically healthy cats. However, the three assays cannot be used interchangeably and the kaolin- and TF activated assays have the lowest analytical variation indicating that using an activator may be superior for performing TEG in cats.

Thrombin physiology and pathophysiology

OBJECTIVES

To review the role of thrombin in physiology and clinical disease and to discuss the pharmacology of antithrombosis.

DATA SOURCES

Original research articles, scientific reviews, textbooks.

HUMAN DATA SYNTHESIS

Thrombin and thrombin receptors are involved in a variety of physiologic and pathologic processes resulting in a great deal of interest in thrombin-related pharmacologic intervention.

VETERINARY DATA SYNTHESIS

Although there is little clinical research data available on thrombin specifically in veterinary patients, some of the original research on protease activated receptors was performed at veterinary institutions and many of the human molecular biology studies have been done on animals including dogs.

CONCLUSION

Thrombin plays a significant role in coagulation, anticoagulation, and fibrinolysis. Antithrombotic treatment is focused on preventing thrombosis while maintaining hemostasis. Pharmaceutical agents are selected for the specific component of the coagulation pathway associated with a specific disease process, for a proven prophylactic benefit with procedures that carry a risk of thromboembolism, for rapidity of onset and ease of reversibility, for limited monitoring requirements, and for oral formulation and bioavailablity. Recent insight into other aspects of thrombin physiology presents an opportunity for pharmacologic intervention in a variety of other processes such as inflammation and sepsis, peripheral blood cell activation and chemotaxis, vascular endothelial and smooth muscle activity, cellular development and tissue repair, mitogenesis, neoplasia, and the function of nervous tissue following injury.

Cardiogenic arterial thromboembolism causing non-ambulatory tetraparesis in a cat

A 1-year-old oriental cat was presented with a peracute onset of tetraparesis and vocalisation. Clinical findings were suggestive of multi-site thromboembolic disease, and this was confirmed on post-mortem examination. An echocardiogram showed severe restrictive cardiomyopathy and spontaneous echogenic contrast. To the author's knowledge, this is the first reported case of tetraparesis secondary to cardiogenic arterial thromboembolic disease. Thromboembolic disease should be included as a differential diagnosis for any cat presented with a peracute onset of paresis or paralysis, even if there is no history of cardiac disease.