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

Resolution of Exercise-Induced Syncope After Stenting of the Azygos Vein in a Dog with Segmental Aplasia and Azygos Continuation of the Levopositioned Caudal Vena Cava

A 1-year-old Maltese-Poodle mixed breed dog was referred to the cardiology service because of severe exercise intolerance and daily exercise-induced syncopal episodes. Physical examination revealed no abnormalities. Echocardiography showed intermittent underfilling of the heart. Abdominal ultrasound examination revealed a segmental aplasia of the caudal vena cava between the kidneys and the liver, and azygos continuation of the cava. The azygos vein dorsal to the right kidney showed a severe aneurysm with stasis of blood. Computed tomographic angiography showed that the right crus of the diaphragm was probably responsible for the intermittent compression of the dilated azygos vein, which was thought to have subsequently led to insufficient venous return to the heart. The underfilled ventricles could not produce sufficient cardiac output, which caused the assumed cerebral hypoperfusion due to presumed systemic arterial hypotension. Under general anesthesia a self-expanding nitinol stent was implanted into the azygos vein at the level of the diaphragm. All clinical signs resolved immediately after surgery. The dog remained free from clinical signs (6 months after surgery). This is the first report that describes the successful treatment of this congenital vascular anomaly. Ultrasonography of the caudal vena cava should be performed in dogs with unexplained syncope.

Monitoring of Rivaroxaban Therapy in Hypercoagulable Dogs

BACKGROUND

Measurement of rivaroxaban efficacy using the rivaroxaban-specific anti-Xa assay (raXa) can be used for monitoring in veterinary medicine. Detection of rivaroxaban efficacy using other hemostatic tests would make monitoring timelier and more accessible.

OBJECTIVES

Compare results of raXa with prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen concentration, tissue factor (TF) and kaolin-activated thromboelastography (TEG), and thrombin generation (TG) in hypercoagulable dogs.

ANIMALS

Twelve client-owned dogs, diagnosed with hypercoagulability or thromboembolic disease, and prescribed rivaroxaban, were recruited from a tertiary referral hospital from 2020 to 2022.

METHODS

Prospective clinical trial. Jugular vein blood samples were collected before treatment, and 1 week and 1-3 months after initiation of rivaroxaban therapy. Hemostatic tests were performed at each visit (3 h after rivaroxaban dosing). TG curve parameters lag time, endogenous thrombin potential (ETP), peak, and time to peak (ttpeak) were assessed.

RESULTS

There was a significant linear relationship between raXa and PT (r2 = 0.74, p < 0.001), ETP (r2 = 0.83, p < 0.001), lag time (r2 = 0.87, p < 0.001), peak (r2 = 0.86, p < 0.001), and ttpeak (r2 = 0.86, p < 0.001). There was a weak linear relationship between raXa and kaolin-activated TEG parameter reaction time (R) (r2 = 0.49, p = 0.026). There was no significant relationship between raXa and aPTT, fibrinogen concentration and the remainder of the TEG variables (p > 0.05).

CONCLUSION AND CLINICAL IMPORTANCE

PT and TG correlated with raXa. PT performed at a reference laboratory appeared to be a convenient method to monitor a small cohort of dogs receiving rivaroxaban therapy.

A novel technique to characterize procoagulant platelet formation and evaluate platelet procoagulant tendency in cats by flow cytometry

Introduction

Cardiogenic arterial thromboembolism (CATE) is a life-threatening complication of hypertrophic cardiomyopathy (HCM) with a high mortality rate. As the primary responders in hemostasis, platelets play a crucial role in the progression of CATE. Procoagulant platelets are a subpopulation of activated platelets that facilitate thrombin generation to strengthen thrombus structure. Since their discovery, procoagulant platelets have gained a considerable amount of attention due to their potential role in thromboembolic complications. Uncovering the key phenotypic markers and agonists underlying the procoagulant response in feline platelets may provide diagnostic and therapeutic insights in the treatment of CATE. However, species differences in platelet physiology and the sensitive nature of feline platelets pose some significant challenges in studying procoagulant platelets in cats.

Objectives

To first devise a flow cytometric method to sequentially assess procoagulant platelet markers and to identify agonists that could induce procoagulant platelet phenotypes. Furthermore, a novel scoring system was established to evaluate the procoagulant tendency of platelets in cats.

Methods

Platelets were isolated from eight healthy cats and activated by thrombin in the presence or absence of collagen (COL) and convulxin (CVX). The following markers were measured sequentially by flow cytometry: (1) loss of mitochondrial membrane potential (ΔΨm), (2) phosphatidylserine (PS) externalization, and (3) P-selectin upregulation.

Results

Thrombin in the presence of CVX significantly reduced ΔΨm and induced P-selectin upregulation (p = 0.0078, p = 0.0128, respectively). In addition, thrombin-treated platelets in the presence of COL and CVX augmented PS externalization significantly (p = 0.043, p = 0.0172, respectively). Of the agonists tested, thrombin and CVX resulted in the highest procoagulant tendency score with 75% cats reaching a score ≥2/3. The number of cats with a procoagulant tendency score of 2 or 3 for thrombin and thrombin + COL was 4/8 (50%) and 5/8 (62.5%), respectively.

Discussion

Sequential analysis of procoagulant markers via flow cytometry may be an effective technique for studying procoagulant platelets in cats.

Comparison of the pharmacokinetics and pharmacodynamics of apixaban and rivaroxaban in dogs

BACKGROUND

Comparative pharmacokinetics and pharmacodynamics (PK/PD) of apixaban and rivaroxaban have not been studied in dogs and the propensity of these drugs to cause hypercoagulability after discontinuation is unknown.

HYPOTHESIS

Compare the PK/PD of clinical dosing regimens of PO apixaban and rivaroxaban administered repeatedly to healthy dogs and assess the effect of abrupt drug discontinuation on coagulation.

ANIMALS

Six University-owned, purpose-bred, middle-aged, mixed-breed dogs (4 male, 2 female).

METHODS

Dogs were given apixaban or rivaroxaban PO at 0.5 mg/kg q12h for 7 days with a 14-day washout period between drugs. Plasma drug concentrations were quantitated, and anticoagulant effects were measured using clotting times, calibrated anti-Xa bioactivity assays, and measurements of thrombin generation. The potential for rebound hypercoagulability was assessed by measuring D-dimers, thrombin-antithrombin (TAT) complexes, and antithrombin activity after drug discontinuation.

RESULTS

Plasma drug concentrations and anti-Xa bioactivities were closely correlated for both drugs, but drug concentrations varied considerably among dogs, despite consistent dose regimens. Thrombin generation variables were significantly correlated with the anti-Xa bioactivity of both drugs and no significant differences in the effects of apixaban and rivaroxaban on thrombin generation were observed. Drug discontinuation had no effect on D-dimer concentrations. The concentration of TAT complexes decreased after apixaban discontinuation and did not change after rivaroxaban discontinuation.

CONCLUSIONS AND CLINICAL IMPORTANCE

Repeated PO administration of apixaban or rivaroxaban to healthy dogs produced comparable anticoagulant effects measured by inhibition of thrombin formation. Rebound hypercoagulability after drug discontinuation was not observed and weaning of these drugs in clinical patients might not be necessary.

Methylprednisolone alone or combined with cyclosporine or mycophenolate mofetil for the treatment of immune-mediated hemolytic anemia in dogs, a prospective study

BACKGROUND

Benefit of adding a second-line immunosuppressive drug to glucocorticoids for the treatment of non-associative immune-mediated hemolytic anemia (naIMHA) in dogs has not been defined prospectively.

HYPOTHESIS/OBJECTIVES

Evaluate the effectiveness of different immunosuppressive protocols in naIMHA dogs.

ANIMALS

Forty-three client-owned dogs.

METHODS

Open label, randomized, clinical trial. Dogs were treated with methylprednisolone (M-group), methylprednisolone plus cyclosporine (MC-group) or methylprednisolone plus mycophenolate mofetil (MM-group). Dogs were defined as responders by disappearance of signs of immune-mediated destruction and hematocrit stabilization. Frequency of responders was compared between M-group and combined protocols (MC and MM-group evaluated together), and among the 3 different therapeutic groups at 14 (T14), 30 (T30), 60 (T60) days after admission. Frequency of complications, length of hospitalization and relapse were also compared. Death rate was evaluated at discharge, T60 and 365 (T365) days.

RESULTS

Proportion of responders was not significantly different between M-group and combined protocols (MC and MM-groups), nor among the 3 therapeutic groups at T14, T30, and T60 (P > .17). Frequency of relapse, complications, and length of hospitalization were not significantly different between M-group and dogs treated with combined protocols, nor among the 3 treatment groups (P > .22). Death was significantly more common only for MM-group compared with MC-group at T60 (+42.8%; 95% CI: 11.5-67.4; P = .009), and at T365 (+50%; 95% CI: 17.5-73.2; P = .003).

CONCLUSIONS AND CLINICAL IMPORTANCE

Combined immunosuppressive therapy did not improve hematological response in naIMHA.

Feline Aortic Thromboembolism: Recent advances and future prospects

PRACTICAL RELEVANCE

Feline aortic thromboembolism (FATE) is commonly encountered in clinical medicine, especially in emergency situations. This often devastating syndrome usually develops secondarily to severe heart disease, and has short- and long-term consequences.

CLINICAL FEATURES

The clinical presentation of FATE is consistent with peripheral ischemic neuropathy, usually in both pelvic limbs. Diagnosis is relatively straightforward, but can be assisted with Doppler ultrasound, point-of-care ultrasound or infrared thermal imaging.

RECENT ADVANCES AND FUTURE PROSPECTS

Interpretation of survival rates in cats with FATE has been hampered by historically high admission euthanasia, but recent studies suggest a survival rate with supportive care of 30-40%. Moreover, with advances in post-FATE thromboprophylaxis, median survival times of over 1 year are being achieved. Future directions include use of thrombolytic agents and treatment of common FATE sequelae such as acute kidney injury and reperfusion injury.

OUTLINE

This article, aimed at small animal veterinarians, including emergency practitioners, reviews key aspects of the clinical presentation, diagnosis and treatment options for FATE, with a view to guiding client and veterinarian decision-making. Three case studies are included to illustrate the practical application of information presented in the review.

EVIDENCE BASE

There are limited prospective studies on FATE, although the recent literature reflects a resurgence in clinical research interest in the past few years. Advances in FATE treatment will benefit many cats and it is important that research efforts continue to identify appropriate treatment modalities.

Case report: Severe hepatopathy following rivaroxaban administration in a dog

Rivaroxaban, a specific factor Xa inhibitor and commonly utilized anticoagulant, has been known to cause hepatotoxicity and liver failure in humans. Although rivaroxaban is frequently used in veterinary medicine, hepatotoxicity has not been previously reported in dogs. The current case report describes a dog that developed severe hepatopathy following rivaroxaban administration for a large right pulmonary artery thrombus. An estimated 6-year-old spayed female mixed-breed dog developed anorexia and lethargy 9 days after rivaroxaban administration began. Subsequent labwork revealed severe hepatocellular hepatopathy, and rivaroxaban was discontinued. Additional diagnostics did not reveal an underlying etiology, although hepatic cytology could be consistent with a toxic injury. The hepatopathy and clinical signs improved after rivaroxaban was discontinued. The time to onset, type of hepatopathy, and time to resolution were all similar to those reported for human cases. This case provides precedence to advocate for improved and closer monitoring of dogs receiving factor Xa inhibitors. In cases of suspected hepatotoxicity with no other identifiable cause, a risk-benefit analysis should be performed, and discontinuation of rivaroxaban administration or alternative anticoagulant medications should be considered.

Rivaroxaban versus enoxaparin plus clopidogrel therapy for hypertrophic cardiomyopathy-associated thromboembolism in cats

Background and Aim

Cardiogenic embolism (CE) is a common complication of feline hypertrophic cardiomyopathy (HCM), leading to severe clinical symptoms. This study compared the effects of rivaroxaban and enoxaparin combined with clopidogrel on cats.

Materials and Methods

This was a single-center, prospective, randomized controlled trial. In this study, rivaroxaban or enoxaparin plus clopidogrel was prescribed to 23 cats for at least one of the following events: Abnormal movement of the anterior mitral leaflet during systole, enlargement of the left atrium, spontaneous echocardiographic contrast, or presence of arterial thromboembolism. Oral rivaroxaban (2.5 mg, q24 h) was prescribed to six cats. Subcutaneous injections of enoxaparin (1 mg/kg, q24 h) plus oral clopidogrel (3 mg/kg, PO q24 h) for 60 days were administered to 17 cats. Renal insufficiency and bleeding complications were observed. Plasma concentrations of D-dimer, prothrombin time (PT), partial thromboplastin time, and international normalized ratio (INR) were evaluated. We analyzed the relationship between echocardiography parameters and the effects of coagulation. Blood samples were collected from all cats at baseline and at 1 and 2 months post-treatment.

Results

Rivaroxaban alone and in combination with enoxaparin and clopidogrel significantly affected PT and INR. In cats treated with 2.5 mg/kg rivaroxaban for 60 days, no bleeding or recurrence of thrombus formation was observed. These data support the use of rivaroxaban for the treatment of HCM-associated thromboembolism in cats.

Conclusion

Treatment of HCM-associated thromboembolism with rivaroxaban alone demonstrated clinical effectiveness with no clinical complications in cats.

Platelet function analyzer-200 closure curve analysis and assessment of flow-obstructed samples

BACKGROUND

The Platelet function analyzer-200 can determine the effect of clopidogrel in cats. Flow obstruction is an error that causes uninterpretable results. Closure curves and parameters initial flow rate (IF) and total volume (TV) are displayed by the PFA-200 and may allow interpretation of results in cases of flow obstruction. The primary hemostasis components (PHC) are calculated values that normalize these parameters.

OBJECTIVES

To determine if closure curves and research parameters allow detecting the effect of clopidogrel in cases of flow obstruction.

METHODS

A review of closure curves identified those with flow obstruction and paired analysis that did not. Non-flow-obstructed curves were used to categorize curves with respect to clopidogrel effects. IF, TV, PHC(1), and PHC(2) were evaluated to determine if these could be used to categorize if a sample exhibited the effects of clopidogrel. Curves were visually analyzed, and characteristics identified that were more common with or without the effect of clopidogrel. Visual analysis of curves was performed by blinded observers to determine if a visual analysis was able to predict the effect of clopidogrel.

RESULTS

Analysis of parameters was able to predict closure or non-closure in flow-obstructed curves. TV, PHC(1), and PHC(2) had area under the curve of the receiver operating characteristics of 0.79, 0.79, and 0.87. Visual curve analysis was unable to predict closure, with an average accuracy of only 55%, among three reviewers. Agreement between reviewers was poor (Fleiss' Kappa 0.06).

CONCLUSIONS

Visual curve analysis was unable to determine the effect of clopidogrel in flow-obstructed samples. Numerical parameters were able to detect the effect of clopidogrel with a high degree of accuracy in flow-obstructed samples.

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.

Secondary right atrial thrombosis in three dogs: Antithrombotics therapy and echocardiographic follow-up

Three dogs were diagnosed with right atrial thrombosis, thought to be secondary to systemic diseases. Specifically, two cases had hyperadrenocorticism and one case was diagnosed with pancreatitis with acute renal injury. In all cases, the thrombi were found within the right atrium, necessitating a differentiation from cardiac neoplasia. In all three cases, the structures assumed to be thrombi had irregular margins with interspersed hypoechoic regions, which were later confirmed as thrombi based on the responsiveness to therapy. All three cases were prescribed with the combination of clopidogrel and rivaroxaban.The thrombi gradually disappeared after initiation of the combination therapy. Complete resolution of right atrial thrombosis was noted in each dog treated with clopidogrel and rivaroxaban. This combination therapy appears to be safe and well tolerated. Diligent observation of the echocardiographic findings and clinical course allows the diagnosis of thrombosis.

Evaluation of thrombin generation in dogs administered clopidogrel

Introduction

The antiplatelet effect of clopidogrel can vary between patients. A modified thromboelastography (TEG) protocol (TEG-Platelet Mapping assay® [TEG-PM]) can be used for clopidogrel monitoring but is not widely available. Thrombin generation (TG) assays could offer a novel alternative. The main objective of this pilot study was to assess TG assay variables (lag time, peak, endogenous thrombin potential [ETP]) in dogs before and after 7 days of clopidogrel administration and compare with TEG-PM variables (maximum amplitude [MA]-ADP and percentage (%) inhibition).

Methods

Six healthy mix-breed dogs were enrolled in this pilot study. Blood samples for platelet count, TG assays, and TEG-PM were obtained at two time points, corresponding to baseline, and after 7 days of clopidogrel administration (mean 2.3 +/- 0.3 mg/kg PO q24 hours). Data were then compared with a Student's t-test.

Results

There was no significant change in TG assay variables performed on platelet poor plasma after 7 days of clopidogrel administration: lag time (Day 1: 1.8 +/- 0.2 min, Day 7: 1.8 +/- 0.2 min, p = 0.42); peak (Day 1: 76 +/- 7 nM, Day 7: 72 +/- 10 nM, p = 0.49); and ETP (Day 1: 399 +/- 27 nM*min, Day 7: 392 +/- 32 nM*min; p = 0.49). There were significant changes in TEG MA-ADP (Day 1: 19 +/- 8 mm, Day 7: 9 +/- 6 mm, p = 0.04) and % inhibition (Day 1: 58 +/- 27, Day 7: 99 +/- 0.3, p = 0.02).

Discussion

Clopidogrel administration did not lead to changes in TG assay variables performed on platelet poor plasma samples, despite concomitant changes in TEG-PM variables consistent with platelet inhibition. Based on this pilot study, thrombin generation performed on platelet poor plasma may not be a useful antiplatelet monitoring tool in dogs.

Right atrial thrombus formation in a dog after successful electrical cardioversion for atrial fibrillation

Right atrial masses in dogs are commonly diagnosed as malignant tumors. This report describes a dog with a right atrial mass that appeared after successful electrical cardioversion of atrial fibrillation and resolved with antithrombotic treatment. A 9-year-old mastiff was presented for acute vomiting, and occasional cough of several weeks' duration. Ultrasonographic and radiographic examinations of the abdomen and chest identified mechanical ileus, as well as pleural effusion and pulmonary edema, respectively. Echocardiography indicated a dilated cardiomyopathy phenotype. During anesthetic induction for laparotomy, atrial fibrillation developed. Electrical cardioversion successfully restored sinus rhythm. An echocardiogram performed 2 weeks later disclosed a right atrial mass, which had not been apparent before cardioversion. Repeat echocardiography after 2 months of clopidogrel and enoxaparin treatment failed to detect the mass. Intra-atrial thrombus formation is possible after successful cardioversion of atrial fibrillation and should be considered as a differential diagnosis for echocardiographically detected atrial masses.

Validation of Plateletworks ADP for the ProCyte Dx analyzer

BACKGROUND

Platelet function testing in cats allows determination of clopidogrel effect. Plateletworks assesses aggregation based on decreasing platelet counts on hematology analyzers in response to agonists. It has not been validated for the IDEXX ProCyte Dx analyzer. Ideal time to perform analysis and the utility of other platelet parameters have not been fully assessed.

OBJECTIVES

To validate Plateletworks ADP on the ProCyte Dx, to investigate the utility of various platelet parameters using Plateletworks ADP, and determine the ideal time to perform analysis.

ANIMALS

Twenty healthy cats recruited from the general population used for transference of reference intervals to a new analyzer, and 10 cats receiving clopidogrel to determine clopidogrel effect.

METHODS

Plateletworks ADP using the ProCyte Dx and ADVIA 2120i analyzer was run simultaneously in both healthy cats and cats receiving clopidogrel, and CBC results at different timepoints were compared between analyzers.

RESULTS

Aggregation was significantly different (P < .001) between analyzers. Cohen's kappa showed almost perfect agreement for determination of clopidogrel effect, and the area under the curve of the receiver operating characteristic was 1.0. Lower limits of the aggregation reference interval in healthy cats were 28.8% on the ProCyte Dx and 12.5% on the ADVIA 2120i. Coefficients of variation for platelet parameters were not different between analyzers. No significant changes in mean platelet volume, plateletcrit, large platelets, and mean platelet component were identified. No significant change in aggregation was observed within the first hour after phlebotomy.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our study validated the Plateletworks ADP system on the ProCyte Dx analyzer. Samples may be analyzed up to 1 h after collection.

Spontaneous remission of idiopathic minimal change disease in a cat

Case summary

A 5-year-old female neutered domestic mediumhair cat presented with acute onset hyporexia, lethargy, ascites, hypoalbuminaemia and ventral subcutaneous oedema. Further investigations revealed a bicavitary effusion, myocardial injury, hypercholesterolaemia and concurrent marked proteinuria. A panel of infectious disease tests yielded negative results. Nephrotic syndrome was suspected and renal biopsies were performed. Histopathology and electron microscopy confirmed a diagnosis of minimal change disease (MCD). The patient was successfully managed with benazepril, clopidogrel and a veterinary prescription renal diet. Follow-up two weeks later documented almost complete resolution of the cardiac abnormalities, absence of clinical signs and marked improvement in clinicopathological findings. The hypoalbuminaemia and proteinuria had resolved two months after presentation. At the time of writing, 13 months post-admission, the cat remained asymptomatic with no evidence of disease relapse.

Relevance and novel information

MCD is rarely described in the veterinary literature, with only four cases reported to date. To our knowledge, this report describes the first case of successfully treated MCD-associated nephrotic syndrome in a cat without the use of glucocorticoid treatment.

2022 Update of the Consensus on the Rational Use of Antithrombotics and Thrombolytics in Veterinary Critical Care (CURATIVE) Domain 1- Defining populations at risk

OBJECTIVES

To expand the number of conditions and interventions explored for their associations with thrombosis in the veterinary literature and to provide the basis for prescribing recommendations.

DESIGN

A population exposure comparison outcome format was used to represent patient, exposure, comparison, and outcome. Population Exposure Comparison Outcome questions were distributed to worksheet authors who performed comprehensive searches, summarized the evidence, and created guideline recommendations that were reviewed by domain chairs. The revised guidelines then underwent the Delphi survey process to reach consensus on the final guidelines. Diseases evaluated in this iteration included heartworm disease (dogs and cats), immune-mediated hemolytic anemia (cats), protein-losing nephropathy (cats), protein-losing enteropathy (dogs and cats), sepsis (cats), hyperadrenocorticism (cats), liver disease (dogs), congenital portosystemic shunts (dogs and cats) and the following interventions: IV catheters (dogs and cats), arterial catheters (dogs and cats), vascular access ports (dogs and cats), extracorporeal circuits (dogs and cats) and transvenous pacemakers (dogs and cats).

RESULTS

Of the diseases evaluated in this iteration, a high risk for thrombosis was defined as heartworm disease or protein-losing enteropathy. Low risk for thrombosis was defined as dogs with liver disease, cats with immune-mediated hemolytic anemia, protein-losing nephropathy, sepsis, or hyperadrenocorticism.

CONCLUSIONS

Associations with thrombosis are outlined for various conditions and interventions and provide the basis for management recommendations. Numerous knowledge gaps were identified that represent opportunities for future studies.

Clinical features and posttreatment monitoring of dogs administered rivaroxaban (2018-2020): 19 cases

OBJECTIVE

To describe a population of sick dogs administered rivaroxaban monitored with a rivaroxaban-calibrated anti-Xa activity assay (aXa).

DESIGN

Descriptive retrospective study.

SETTING

Two veterinary teaching hospitals.

ANIMALS

Client-owned dogs administered rivaroxaban and monitored with aXa from January 2018 to January 2020 were eligible for study.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Medical records were reviewed and 19 dogs with a variety of underlying disease processes were identified. Rivaroxaban was administered to 12 of 19 dogs (63%) with confirmed thrombosis, 4 of 19 dogs (21%) with a strong clinical suspicion of thrombosis, and in 3 of 19 dogs (16%) with no current evidence of thrombosis. The median rivaroxaban dose administered was 0.96 mg/kg/day (0.62-1.58 mg/kg/day), with 15 of 19 dogs (79%) receiving rivaroxaban once daily. Clopidogrel was concurrently administered to 11 of 19 dogs (58%). Complete or partial thrombus resolution was identified in 5 of 12 (42%) and 3 of 12 (25%) dogs, respectively. Rivaroxaban appeared safe, with only 1 of 19 dogs (5%), concurrently administered clopidogrel, developing evidence of mild hematuria. Posttreatment monitoring revealed that 8 of 19 dogs (42%) had aXa below the target (aXa range of 150-250 ng/ml associated with effective treatment and prevention of venous thrombosis in people). The remaining 3 to 19 dogs (16%) achieved this range, and 8 of 19 dogs (42%) exceeded the range. No significant relationship between the initial rivaroxaban dose administered and the corresponding aXa result was identified. There were also no significant differences in baseline clinicopathological variables in dogs in which aXa fell within or outside this range.

CONCLUSIONS

aXa was most commonly measured in dogs receiving rivaroxaban with confirmed or suspected thrombosis. Dogs in this study received a range of rivaroxaban dosages and attained variable aXa values that were not directly correlated with dosage.

Urinary 11-dehydrothromboxane B2 concentrations in 20 dogs with primary immune-mediated hemolytic anemia

BACKGROUND

Thromboembolic disease is a major cause of mortality in dogs with immune-mediated hemolytic anemia (IMHA). At present, no reliable biomarkers of individual patient thrombotic risk are available. In human medicine, increased urinary thromboxane concentrations have utility as markers of prothrombotic tendency in various situations.

HYPOTHESIS/OBJECTIVES

First, to determine if urinary 11-dehydrothromboxane B2 (u11-dTXB) concentrations are increased in dogs with primary IMHA compared to normal dogs; second, to assess whether u11-dTXB concentration is associated with survival, known prognostic indicators, or frequency of thrombosis in dogs with IMHA.

ANIMALS

Twenty client-owned dogs diagnosed with primary IMHA and 17 healthy dogs volunteered by hospital staff.

METHODS

Prospective case-control study. A previously validated ELISA was used to measure urine 11-dTXB concentrations, which were normalized to urine creatinine concentration (u11-dTXB:Cr). Samples were obtained at presentation from patients with primary IMHA. Standard clincopathological data at baseline and survival data were collected. Urinary 11-dTXB:Cr was compared between outcome subgroups, and correlated with known markers of disease severity.

RESULTS

Baseline u11-dTXB:Cr was significantly higher in dogs with IMHA than in healthy dogs (median, 3.75; range, 0.83-25.36 vs 0.65; 0.24-2.57; P = .003) but did not differ between dogs with IMHA that survived and did not survive to 30 days after presentation, nor between dogs with and without clinical suspicion of thrombotic disease.

CONCLUSIONS AND CLINICAL IMPORTANCE

Urinary 11-dTXB:Cr is increased in dogs with IMHA compared to healthy controls, consistent with a prothrombotic state. However, in this IMHA population u11-dTXB:Cr was not associated with survival or suspected thrombosis.

Usefulness of peripheral venous blood gas analyses in cats with arterial thromboembolism

Feline arterial thromboembolism (ATE) is a condition with a high mortality rate. Acid-base abnormalities may be beneficial to the prognosis of cats with ATE. Venous blood gas and electrolytes data on the first day of ATE presentation of 47 cats with ATE were retrospectively reviewed and analysed. The Cox and logistic regression were analysed to evaluate the relationship between acid-base parameters and death. The most common venous acid-base disorder was simple metabolic acidosis. Age, body weight, and partial venous pressure of carbon dioxide (PvCO2) differed between the dead and alive groups within 7 days of the onset of ATE presentation (p < 0.05). Cox-regression showed that increasing age (HR=1.175 [95% CI: 1.027-1.343], p = 0.019), increasing PvCO2 (HR=1.066 [95% CI: 1.010-1.125], p = 0.021) and PvCO2 more than 34 mmHg (HR=7.878 [95% CI: 1.036- 59.915], p = 0.046) were associated with increased hazard of death. Multivariable logistic regression showed that age > 5 years (OR=9.030, 95% CI: 1.258- 64.823; p=0.029), and PvCO2 > 34 mmHg (OR=21.764, 95% CI: 1.747-271.141; p=0.017) were associated with an increased risk of death, while concomitant administration of enoxaparin with clopidogrel (OR=0.111, 95% CI: 0.015-0.795; p=0.029) were associated with a decreased risk of death within 7 days of the onset of ATE presentation. This study demonstrated the power of venous blood gas analysis which may be used as prognostic indicators for cats with ATE.

The Feline Cardiomyopathies: 2. Hypertrophic cardiomyopathy

Practical relevance:

Hypertrophic cardiomyopathy (HCM) is the most common form of feline cardiomyopathy observed clinically and may affect up to approximately 15% of the domestic cat population, primarily as a subclinical disease. Fortunately, severe HCM, leading to heart failure or arterial thromboembolism (ATE), only occurs in a small proportion of these cats.

Patient group:

Domestic cats of any age from 3 months upward, of either sex and of any breed, can be affected. A higher prevalence in male and domestic shorthair cats has been reported.

Diagnostics:

Subclinical feline HCM may or may not produce a heart murmur or gallop sound. Substantial left atrial enlargement can often be identified radiographically in cats with severe HCM. Biomarkers should not be relied on solely to diagnose the disease. While severe feline HCM can usually be diagnosed via echocardiography alone, feline HCM with mild to moderate left ventricular (LV) wall thickening is a diagnosis of exclusion, which means there is no definitive test for HCM in these cats and so other disorders that can cause mild to moderate LV wall thickening (eg, hyperthyroidism, systemic hypertension, acromegaly, dehydration) need to be ruled out.

Key findings:

While a genetic cause of HCM has been identified in two breeds and is suspected in another, for most cats the cause is unknown. Systolic anterior motion of the mitral valve (SAM) is the most common cause of dynamic left ventricular outflow tract obstruction (DLVOTO) and, in turn, the most common cause of a heart murmur with feline HCM. While severe DLVOTO is probably clinically significant and so should be treated, lesser degrees probably are not. Furthermore, since SAM can likely be induced in most cats with HCM, the distinction between HCM without obstruction and HCM with obstruction (HOCM) is of limited importance in cats. Diastolic dysfunction, and its consequences of abnormally increased atrial pressure leading to signs of heart failure, and sluggish atrial blood flow leading to ATE, is the primary abnormality that causes clinical signs and death in affected cats. Treatment (eg, loop diuretics) is aimed at controlling heart failure. Preventive treatment (eg, antithrombotic drugs) is aimed at reducing the risk of complications (eg, ATE).

Conclusions:

Most cats with HCM show no overt clinical signs and live a normal or near-normal life despite this disease. However, a substantial minority of cats develop overt clinical signs referable to heart failure or ATE that require treatment. For most cats with clinical signs caused by HCM, the long-term prognosis is poor to grave despite therapy.

Areas of uncertainty:

Genetic mutations (variants) that cause HCM have been identified in a few breeds, but, despite valiant efforts, the cause of HCM in the vast majority of cats remains unknown. No treatment currently exists that reverses or even slows the cardiomyopathic process in HCM, again despite valiant efforts. The search goes on.

Anticoagulant profile of subcutaneous enoxaparin in healthy dogs

Our study objective was to identify a subcutaneous enoxaparin dosage that provided a consistent anticoagulant intensity in dogs. Our hypotheses were that a dose of 0.8 mg/kg would provide inconsistent anticoagulation, a higher dose would provide consistent anticoagulation over a greater duration of time, and viscoelastometry would effectively monitor the anticoagulant status. Six healthy dogs received two subcutaneous enoxaparin doses (0.8 and 2 mg/kg) for anti-Xa activity determinations and pharmacokinetic modeling. Based on calculations derived from these results, 1.3 mg/kg, SC, q8 h was administered for seven doses. Target ranges for anticoagulant intensity were defined as anti-Xa activity of 0.5-1 U/ml, and change from baseline of two viscoelastometric parameters: activated clotting time (ΔACT; ≥40 s), and clot rate (CRpost; ≤20 U/min). Following an initial injection at 1.3 mg/kg, anti-Xa activity of 5/6 dogs reached or exceeded the target range. Following the final dose, anti-Xa activity reached or exceeded the target range in all dogs, and ΔACT and CRpost values exceeded target for 2-6 and 4-12 h, respectively. At an enoxaparin dosage of 1.3 mg/kg, SC, q8 h, anti-Xa activity was consistently above the minimum threshold of the target range; however, the safety of this dosage remains to be determined.

Balloon expandable aortic stent-graft for the treatment of aortic aneurysm and rupture in a dog

OBJECTIVE

To describe the successful placement of an aortic stent graft in a dog suffering from aortic aneurysm and rupture.

CASE SUMMARY

A 4-year-old neutered female mixed breed dog weighing 25 kg was presented with a chief complaint of acute onset of weakness and respiratory distress. On presentation, the dog was lateral and unresponsive, hypothermic, tachycardic, and tachypneic. Pleural effusion was identified in the right hemi-thorax on thoracic-focused sonographic scan for trauma. Thoracic radiographs showed a fluid/soft tissue opacity in the cranial mediastinum and pleural effusion on the right side. Thoracocentesis yielded noncoagulating blood. Hematology revealed normal PCV and total plasma protein that decreased within 24 hours to 20% and 50 g/L (20%/5.0 g/dL), respectively. The dog was treated with IV fluids, tranexamic acid, and fresh frozen plasma. An aortic aneurysm with irregular mineralization of the right ventrolateral aortic wall was identified on computed tomography examination, which also demonstrated a peri-aortic hematoma. A decision was made to attempt treatment with a stent graft. Under general anesthesia, a marker catheter was inserted into the esophagus. A 10-Fr sheath was inserted into the right femoral artery, and an angiography catheter was advanced over a wire. After angiography, a stent graft (12-mm × 50-mm) was placed over the guide wire and deployed under fluoroscopic guidance. The dog recovered uneventfully, with no evidence of recurrent bleeding, and was discharged 2 days after the procedure with antimicrobials, anthelmintic, and antithrombotic treatment. At 90-day follow-up, the dog was doing well, and stent position was radiographically confirmed.

NEW OR UNIQUE INFORMATION PROVIDED

This report describes successful management of aortic aneurysm and dissection, an uncommon and challenging pathology in the veterinary practice with few available treatment options. Stent graft placement is a minimally invasive procedure in which a covered stent is placed over the lesion to prevent rupture.

Brachial artery thrombosis in a dog causing monoparesis mimicking nerve sheath tumor

There are few differential diagnoses for non‐orthopedic thoracic limb lameness in adult dogs aside from nerve tumors and disk‐associated nerve compression; this report introduces another etiology. A 9‐year‐old male castrated mixed dog presented with an episodic history of nonweight‐bearing thoracic limb lameness. Additional clinical signs included an atrophied thoracic limb with cool paw pads and painful axillary region. Magnetic resonance imaging, computed tomography, ultrasound, and exploratory surgery confirmed a chronic thrombus of the right brachial artery. No underlying cause for the thrombus was identified. The dog has been successfully managed on long‐term rivaroxaban and clopidogrel. Follow‐up ultrasound of the thrombus suggested early remodeling.

Pharmacokinetics and Biologic Activity of Apixaban in Healthy Dogs

Thrombosis is common in critically ill dogs and causes considerable morbidity and mortality. The direct factor Xa inhibitor apixaban is safe, efficacious, and convenient in humans. This study aimed to determine the pharmacokinetics (PK), bioactivity, protein binding, and bioavailability of apixaban following intravenous (IV) and oral (PO) administration to healthy dogs. Six healthy, adult, mixed-breed dogs were administered apixaban 0.18 mg/kg IV and then following a minimum 2-week washout period administered apixaban 0.2 mg/kg PO. Dogs were monitored using an apixaban-calibrated anti-Xa bioassay, prothrombin time (PT) and activated partial thromboplastin time (aPTT) and tissue-factor thromboelastography (TF-TEG). Plasma apixaban concentrations were measured using liquid chromatography-tandem mass spectrometry. Concentration-time plots were constructed, and PK modeling performed using compartmental methods. Administration of IV and PO apixaban was well-tolerated. Following IV administration, mean half-life was 4.1 h, and volume of distribution was 177 ml/kg. Apixaban was highly protein bound (98.6%). Apixaban concentrations and anti-Xa activity were highly correlated (R2 0.994, P < 0.0001). Intravenous apixaban significantly prolonged PT at time points up to 1 h, and aPTT at time points up to 0.25 h post-administration. Coagulation times were positively correlated with apixaban concentrations (PT R2 0.599, P < 0.0001; aPTT R2 0.430, P < 0.0001) and TF-TEG R-time was significantly prolonged 0.25 h post-administration. Following oral administration, mean bioavailability was 28.4%, lag time was 2 h, time to Cmax was 5 h and the apparent elimination half-life was 3.1 h. Oral apixaban significantly prolonged PT at 4, 6, and 8 h but aPTT and TF-TEG were not consistently affected by oral apixaban. Apixaban concentrations are best monitored using anti-Xa activity. Future studies should determine PK and bioactivity of other doses using commercial tablets and following multidose administration and establish safe, effective dosing ranges in sick dogs.

The Rare Occurrence of a Left Atrial Thrombus in a Dog

Intracardiac thrombi are rare in dogs. If they occur, they are mostly seen in the right atrium while only two case reports describing a mural left atrial thrombus in dogs are available. This case report describes a 14-year-old mixed-breed bitch that was presented at the clinic because of dyspnoea. The dog suffered from alopecia for about three years and displayed polyuria and polydipsia for a number of months. Clinical examination revealed intensified inspiratory and expiratory respiratory sounds and various heart sounds. Chest X-ray showed cardiomegaly (VHS 11) and a mixed bronchoalveolar lung pattern of the caudal lung. A transthoracic echocardiography was performed and showed a moderate mitral regurgitation, a highly dilated left atrium, a low-grade pulmonary insufficiency, and a minimal aortic and tricuspid insufficiency. Additionally, a free-floating ball thrombus was found in the left atrium. Hyperadrenocorticism was indicated by an ACTH stimulation test. The previous medical therapy of the referring veterinarian consisted of benazepril and furosemide and was complemented by clopidogrel. The pet owners declined any further clinical diagnostics and therapy. The dog died 19 days later. This is the first reported case of a dog with a free-floating left atrial thrombus. Specific therapeutic strategies for intracardiac thrombi in the dog are currently not available, and therefore, every patient should be treated individually.

Evaluation of point-of-care coagulation tests as alternatives to anti-Xa activity for monitoring the anticoagulant effects of rivaroxaban in healthy dogs

OBJECTIVE

To evaluate a panel of coagulation assays for their potential utility in rivaroxaban monitoring as alternatives to the rivaroxaban-specific anti-Xa activity (RIVA).

DESIGN

Prospective experimental study.

SETTING

University research laboratory.

ANIMALS

Five healthy neutered male Beagles.

INTERVENTIONS

Dogs were administered a median dose of 1.8 mg/kg rivaroxaban (range, 1.6-1.8 mg/kg) orally once daily for 2 consecutive days as part of a pharmacodynamic study. Blood was collected from a preplaced jugular catheter at time points relative to their rivaroxaban administration (0, 2, 4, 8, 24, 36, and 48 h) for measurement of RIVA, prothrombin time (PT), activated partial thromboplastin time, RapidTEG, and thrombin generation variables.

MEASUREMENTS AND MAIN RESULTS

One hundred forty data points were available for analysis. There was poor correlation between RIVA and RapidTEG variables: R time (R) (min) (r = 0.554, P < 0.0001), K time (K) (min) (r = -0.204, P = 0.016), alpha angle (degrees) (r = 0.152, P = 0.073), Maximum amplitude (MA) (mm) (r = 0.106, P = 0.215), and G value (G) (dynes/s) (r = 0.108, P = 0.205). A good correlation was noted between thrombin generation variables and RIVA: lag time (min) (r = 0.827, P < 0.0001), peak (nM) (r = -0.752, P < 0.0001), and endogenous thrombin potential (nM·min) (r = -0.762, P < 0.0001). There was an excellent correlation between PT and RIVA (r = 0.915, P < 0.0001) and a good correlation between activated partial thromboplastin time and RIVA (r = 0.772, P < 0 .0001).

CONCLUSIONS

Of all the coagulation tests investigated, the PT correlated best with RIVA. There is potential for PT being a convenient second-line monitoring option in dogs receiving rivaroxaban, but further work is necessary to validate other PT assays. Thromboelastography performed with strong activators correlated poorly with anti-Xa activity.

The influence of feeding and gastroprotectant medications on the Factor Xa inhibitory activity of orally administered rivaroxaban in normal dogs

OBJECTIVE

Rivaroxaban is a new anticoagulant option for dogs, yet its reported oral bioavailability is as low as 60%. The objective of this study was to examine the influence of feeding and gastroprotectant medications on the bioactivity (anti-Xa activity) of rivaroxaban in healthy dogs.

DESIGN

Prospective experimental study.

SETTING

University research laboratory.

ANIMALS

Five healthy neutered male purpose-bred Beagles.

INTERVENTIONS

Dogs were administered a median dose of 1.8 mg/kg rivaroxaban (range, 1.6-1.8 mg/kg) orally once daily for 2 consecutive days with either (1) no food, (2) food, (3) sucralfate 30 minutes before rivaroxaban, or (4) omeprazole at the same time as rivaroxaban. Blood was collected from preplaced jugular catheters immediately before and at 6 time points after rivaroxaban administration (2, 4, 8, 24, 36, and 48 hours). A rivaroxaban calibrated anti-Xa activity assay (RIVA) was used to monitor anticoagulant effect.

MEASUREMENTS AND MAIN RESULTS

Rivaroxaban administration resulted in significant increases in RIVA (P = 0.02), with peak activities occurring 2 to 4 hours after dosingduring each study arm. No feeding was associated with significantly higher RIVA at the 36-hour time point compared to all other treatment arms (P < 0.0001), and feeding resulted in high RIVA at the 48-hour time point compared with sucralfate administration (P = 0.003). No significant changes in RIVA were otherwise identified with respect to feeding or gastroprotectant administration (P = 0.2).

CONCLUSIONS AND CLINICAL IMPORTANCE

Although administration without food demonstrated an apparent increase in RIVA 36 hours after drug administration, clinically relevant differences among treatment groups were not identified in combined analyses of time points. Based on these results, dogs treated with rivaroxaban do not require special modification of feeding practices or gastroprotectant drug administration.

The Use of Antithrombotics in Critical Illness

Hypercoagulable tendencies may develop in critically ill dogs and to a less known extent, cats. Although the use of antithrombotics is well-established in critically ill people, the indications and approach are far less well-known in dogs and cats. The goal of this article was to review the relevant CURATIVE guidelines, as well as other sources, and to provide recommendations for critically ill patients with directions for future investigation.

Therapeutic Strategies for Treatment of Immune-Mediated Hemolytic Anemia

Immune-mediated hemolytic anemia is a common hematologic disorder in dogs. Disease management involves immunosuppression using glucocorticoids, potentially in combination with other medications such as azathioprine, cyclosporine, or mycophenolate mofetil. Therapeutic drug monitoring may enhance the utility and maximize the safety of cyclosporine and mycophenolate mofetil. The disease is proinflammatory and prothrombotic. Antithrombotic drug administration is therefore essential, and anticoagulant therapy should be initiated at the time of diagnosis. Additional therapies include red blood cell transfusion to support blood oxygen content. Future therapies may include therapeutic plasma exchange, anti-CD20 monoclonal antibodies, and complement inhibitors.

Surgical embolectomy in a cat with cardiogenic aortic thromboembolism

A seven-year-old, spayed female, domestic longhair cat was referred for management of a sudden aortic thromboembolism (ATE). Echocardiography showed hypertrophic cardiomyopathy with severe left atrial enlargement. Ultrasonography of the abdominal aorta confirmed a large thrombus at the level of the aortic trifurcation, involving both iliac arteries. Considering the recent onset and bilateral involvement of the iliac arteries, the cat underwent emergent surgical embolectomy (SE) of the aortoiliac embolus. A standard caudal celiotomy was performed and the abdominal aorta was identified. Vessel loops with tourniquets were placed around the abdominal aorta proximal to the thrombus and on both iliac arteries distal to the thrombus. A full-thickness incision was made in the ventral surface of the aorta. The aortic thromboembolus was removed. The trifurcation was subsequently flushed with sterile saline. The SE resulted in a good outcome, with both clinical and ultrasound signs of complete reperfusion of the rear limbs within a few hours. Long-term treatment included antiplatelet drugs, furosemide and benazepril. Eighteen months after surgery, the cat was free of clinical signs, without recurrence of ATE or congestive heart failure. Based on the present case, SE could be considered as a feasible alternative to traditional conservative treatment in cats with a very recent onset of bilateral ATE.

Use of rivaroxaban for treatment of cranial vena cava syndrome secondary to transvenous pacemaker lead thrombosis in a dog

A six-year-old Brussels griffon was presented for cervical swelling three months after implantation of a transvenous pacemaker. Transthoracic echocardiography demonstrated a thrombus associated with the pacemaker lead, partially obstructing right atrial inflow. The laboratory findings were consistent with protein-losing nephropathy. Initial medical therapy consisted of rivaroxaban (0.68 mg/kg orally every 24 hours), clopidogrel (2.5 mg/kg orally every 24 hours), and enalapril (0.5 mg/kg orally every 12 hours). Resolution of cervical and thoracic edema was noted within two weeks of initiating therapy. Recheck echocardiography two months and one year later revealed decreasing thrombus size despite worsening proteinuria. To the authors' knowledge, this is the first documented use of rivaroxaban for successful medical treatment of cranial vena cava syndrome caused by intracardiac pacemaker lead thrombosis in a hypercoagulable patient.

Clinical application of the American College of Veterinary Emergency and Critical Care (ACVECC) Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE) guidelines to small animal cases

OBJECTIVE

To illustrate the application of the Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE) guidelines to the management of dogs and cats at risk of developing thrombosis using a case-based approach.

ETIOLOGY

Dogs and cats become at risk of developing thrombosis from a wide range of conditions. These conditions often involve a specific insult followed by an inflammatory response and when combined with other contributing factors (eg, hypercoagulability, vascular endothelial injury, hemodynamic changes) create favorable conditions for thrombosis.

DIAGNOSIS

Development of thrombosis in small animals remains challenging to demonstrate. Compatible clinical signs, the presence of known risk factors, and supporting diagnostic tests may be highly suggestive of the development of thrombosis.

THERAPY

Therapeutic recommendations in accordance with the CURATIVE guidelines for dogs and cats are described in specific case vignettes presented. Discussion is centered on antithrombotic drug choices and dosing protocols, as outlined in Domains 2 and 3 of the CURATIVE guidelines. Where appropriate, guidelines related to therapeutic monitoring (Domain 4) and discontinuation of antithrombotics (Domain 5) were included.

PROGNOSIS

In small animals at risk of developing thrombosis, overall prognosis may be improved by following consensus-based recommendations on the use of antithrombotics as outlined in the CURATIVE guidelines. Whether such interventions have any impact on outcome requires further investigation.