IgG-class anti-PF4/heparin antibodies and symptomatic DVT in orthopedic surgery patients receiving different anti-thromboembolic prophylaxis therapeutics

Weight-Based Aspirin Dosing May Further Reduce the Incidence of Venous Thromboembolism Following Primary Total Joint Arthroplasty

BACKGROUND

Obesity poses a challenge to thromboembolic prophylaxis following total joint arthroplasty (TJA). The purpose of this study is to evaluate a weight-based aspirin dosing regimen for prevention of venous thromboembolism (VTE) following TJA.

METHODS

This is a retrospective observational study of 2403 patients who underwent primary total hip or knee arthroplasty at one institution. A weight-based aspirin dosing regimen for VTE prophylaxis was administered to 1247 patients: patients weighing ≥120 kg received 325 mg aspirin twice daily (BID) and those weighing <120 kg received 81 mg aspirin BID for 4 weeks. In total, 1156 patients in the comparison cohort received 81 mg aspirin BID. VTE and gastrointestinal bleeding events were identified through chart review at 42 days and 6 months postoperatively. A multivariable logistic regression was performed to adjust for covariates.

RESULTS

The weight-based aspirin cohort had a significantly lesser incidence of VTE at 42 days (P = .03, relative risk [RR] 0.31, 95% confidence interval 0.12-0.82) and 6 months (P = .03, RR 0.38, 95% confidence interval 0.18-0.80). There was no difference in VTE incidence between total hip arthroplasty and total knee arthroplasty cases (P = .8). There was no difference in gastrointestinal bleeding events between the cohorts at 42 days (P = .69) or 6 months (P = .92). Subanalysis of patients weighing ≥120 kg demonstrated a significant difference between the cohorts with a VTE incidence of 3.48% and 0% in the 81 mg and weight-based cohorts, respectively (P = .02).

CONCLUSION

Patients prescribed a weight-based aspirin regimen had significantly fewer VTEs after TJA compared to historical controls with an RR reduction of 69% at 6 weeks and 62% at 6 months postoperatively. This suggests the need to factor patient weight when determining postoperative VTE prophylaxis with aspirin.

Factors predisposing to thrombosis after major joint arthroplasty

BACKGROUND

Total joint arthroplasty is one of the most common options for end stage osteoarthritis of major joints. However, we must take into account that thrombosis after hip/knee arthroplasty may be related to mutations in genes encoding for blood coagulation factors and immune reactions to anticoagulants [heparin-induced thrombocytopenia (HIT)/thrombosis]. Identifying and characterizing genetic risk should help to develop diagnostic strategies or modify anticoagulant options in the search for etiological mechanisms that cause thrombophilia following major orthopedic surgery.

AIM

To evaluate the impact of patients’ coagulation profiles and to study specific pharmacologic factors in the development of post-arthroplasty thrombosis.

METHODS

In 212 (51 male and 161 female) patients that underwent primary total hip arthroplasty (100) or total knee arthroplasty (112) due to osteoarthritis during a period of 1 year, platelet counts and anti-platelet factor 4 (PF4)/heparin antibodies were evaluated pre/postoperatively, and antithrombin III, methylenetetrahydrofolate reductase, factor V and prothrombin gene mutations were evaluated preoperatively. In a minimum follow-up of 3 years, 196 patients receiving either low-molecular-weight heparins (173) or fondaparinux (23) were monitored for the development of thrombocytopenia, anti-PF4/heparin antibodies, HIT, and thrombosis.

RESULTS

Of 196 patients, 32 developed thrombocytopenia (nonsignificant correlation between anticoagulant type and thrombocytopenia, P = 0134.) and 18 developed anti-PF4/heparin antibodies (12/173 for low-molecular-weight heparins and 6/23 for fondaparinux; significant correlation between anticoagulant type and appearance of antibodies, P = 0.005). Odds of antibody emergence: 8.2% greater in patients receiving fondaparinux than low-molecular-weight heparins. Gene mutations in factor II or V (two heterozygotes for both factor V and II) were identified in 15 of 196 patients. Abnormal low protein C and/or S levels were found in 3 of 196 (1.5%) patients, while all patients had normal levels of von Willebrand factor, lupus anticoagulant, and antithrombin III. Four patients developed HIT (insignificant correlation between thrombocytopenia and antibodies) and five developed thrombosis (two had positive antibodies and two were heterozygotes for both factor II & V mutations). Thrombosis was not significantly correlated to platelet counts or HIT. The correlation of thrombosis to antibodies, factor II, factor V was P = 0.076, P = 0.043, P = 0.013, respectively.

CONCLUSION

Screening of coagulation profile, instead of platelet monitoring, is probably the safest way to minimize the risk of post-arthroplasty thrombosis. In addition, fondaparinux can lead to the formation of anti-PF4/heparin antibodies or HIT.

Heparin-induced thrombocytopenia (HIT): Identification and treatment pathways

Heparin-induced thrombocytopenia (HIT) is a major health problem, especially in cardiac surgery theaters, cardiac catheterization labs, and intensive care units. Some patients with HIT develop serious thrombotic complications like limb ischemia and gangrene, while others may not develop such complications and have only mild thrombocytopenia. Current laboratory diagnostic tools incur significant time delays before confirming HIT, therefore upon clinical suspicion, treatment of HIT should start immediately while awaiting laboratory results. This is a review of the types, phases, pathophysiology, clinical presentation and diagnosis of HIT, and its current management strategies.

Induction of anti-PF4/heparin antibodies after arthroplasty for rheumatic diseases

Heparin-induced thrombocytopenia (HIT) is an immune complication of heparin therapy caused by antibodies to complexes of platelet factor 4 (PF4) and heparin. These pathogenic antibodies against PF4/heparin bind and activate cellular FcγRIIa on platelets to induce a hypercoagulable state culminating in thrombosis. Recent studies indicate several conditions, including joint surgery, induce spontaneous HIT, which can occur without exposure to heparin. To determine the real-world evidences concerning the incidences of venous thromboembolism (VTE) after total joint arthroplasty for rheumatic disease, we conducted a multicenter cohort study (J-PSVT) designed to document the VTE and seroconversion rates of anti-PF4/heparin antibody in 34 Japanese National hospital organization (NHO) hospitals. J-PSVT indicated that prophylaxis with fondaparinux, not enoxaparin, reduces the risk of deep vein thrombosis in patients undergoing arthroplasty. Multivariate analysis revealed that dynamic mechanical thromboprophylaxis (intermittent plantar device) was an independent risk factor for seroconversion of anti-PF4/heparin antibodies, which was also confirmed by propensity-score matching. Seroconversion rates of anti-PF4/heparin antibodies were significantly reduced in rheumatoid arthritis (RA) patients compared with osteoarthritis (OA) patients, which may link with the findings that IgG fractions isolated from RA patients not OA patients contained PF4. Our study indicated that a unique profile of anti-PF4/heparin antibodies is induced by arthroplasty for rheumatic diseases.

Obesity and Venous Thromboembolism in Total Knee Arthroplasty Patients in an Asian Population

BACKGROUND

Venous thromboembolism (VTE) is a known complication of total knee arthroplasty (TKA). In addition, obesity has been implicated as a risk factor and justification for chemoprophylaxis for VTE. We wanted to review the prevalence of VTE among our patients and evaluate the incidence rates of VTE among nonobese and obese patients.

METHODS

We reviewed 894 patients who underwent elective unilateral total knee arthroplasty by a single surgeon from March 2003 to November 2014 in our center. Any patients with clinically significant symptoms or signs of VTE such as deep venous thrombosis (DVT) or pulmonary embolism (PE) were diagnosed radiologically. The patient demographics analyzed included age, gender, body mass index, the number of comorbid diseases, and a history of hyperlipidemia.

RESULTS

We found the incidence of VTE of 0.67% in our patients (6 patients of 894). Four of the 6 patients (66.7%) who developed DVT and PE belonged to nonobese group. The frequency of VTE in nonobese patients was 0.65% and 0.73% in the obese patients. There were no significant differences in age, number of comorbidities, and a history of hyperlipidemia between those who developed DVT and PE and those who did not.

CONCLUSION

With the low prevalence of VTE among our study population, including patients with obesity, advanced age, multiple comorbidities, or hyperlipidemia, the practice of routine chemoprophylaxis should be reviewed.

Management of the multiple phases of heparin-induced thrombocytopenia

The clinical course of heparin-induced thrombocytopenia (HIT) may be separated into five sequential phases: 1. suspected HIT, 2. acute HIT, 3. subacute HIT A, 4. subacute HIT B, and 5. remote HIT. Each phase confronts the clinician with a unique set of management questions. In this review, the phases of HIT are defined and key management questions associated with each phase are discussed. Among patients with Suspected HIT, I use the 4Ts score to determine which patients have a sufficiently high probability of HIT to justify discontinuation of heparin and initiation of a non-heparin parenteral anticoagulant. An algorithm for selecting an appropriate non-heparin anticoagulant based on the patient's clinical stability, renal and hepatic function, drug availability, and physician comfort is provided. In patients with Acute HIT, I generally avoid prophylactic platelet transfusion and inferior vena cava filter insertion because of a potential increased risk of thrombosis. I perform 4-limb screening compression ultrasonography. In patients with symptomatic thromboembolism or asymptomatic proximal deep-vein thrombosis, I treat with anticoagulation for three months. In patients without thrombosis, I discontinue anticoagulation upon platelet count recovery. I do not transition patients to an oral anticoagulant until platelet count recovery (i. e. Subacute HIT A). I increasingly choose direct oral anticoagulants over vitamin K antagonists in this setting because of their greater convenience and safety. In Subacute HIT B and Remote HIT, I use heparin for cardiovascular surgery, whereas I use bivalirudin in patients with Acute HIT and Subacute HIT A in whom surgery cannot be delayed.

Effects of a Foot Pump on the Incidence of Deep Vein Thrombosis After Total Knee Arthroplasty in Patients Given Edoxaban: A Randomized Controlled Study

We conducted a randomized clinical trial to compare the effectiveness of the A-V Impulse System foot pump for reducing the incidence of deep-vein thrombosis (DVT) after total knee arthroplasty (TKA) in patients under edoxaban thromboprophylaxis. Patients undergoing primary TKA at our institution between September 2013 and March 2015 were enrolled after obtaining informed consent. The patients were randomized to use the foot pump (n = 58) and not to use the foot pump (n = 62). Both groups were given prophylactic edoxaban. Primary outcomes were any DVT as detected by bilateral ultrasonography up to postoperative day 10 (POD10) and pulmonary embolism (PE) up to POD28. The safety outcomes were bleeding and death of any cause up to POD28. Plasma D-dimer levels were measured before TKA and on POD10 after TKA. Immunoglobulin G (IgG)-class anti-PF4/heparin antibodies were measured using an IgG-specific enzyme-linked immunosorbent assay. The incidences of any DVT up to POD28 were 31.0% and 17.7% in patients with or without the foot pump, respectively. The incidences of major bleeding up to POD28 were 5.1% and 4.8% in patients with or without the foot pump, respectively. Foot pump use did not significantly reduce the incidence of DVTs in patients undergoing TKA under edoxaban thromboprophylaxis. Although seroconversion of anti-PF4/heparin antibodies was confirmed in one-fourth of patients, the seroconversion rates did not differ between patients with (20.7%) or without (25.8%) foot pump use. This study shows that the A-V Impulse system foot pump did not affect the incidence of DVT under edoxaban thromboprophylaxis in patients undergoing TKA. Seroconversion of anti-PF4/heparin antibodies was detected in a significant number of patients who underwent TKA under antithrombotic prophylaxis using edoxaban.

Risk of venous thromboembolism after total knee arthroplasty in patients with rheumatoid arthritis

OBJECTIVE

To compare the incidence of venous thromboembolism (VTE) following total knee arthroplasty (TKA) between patients with rheumatoid arthritis (RA) and those with osteoarthritis (OA).

METHODS

The subjects were composed of 1084 Japanese patients with OA and 204 with RA. Primary effectiveness outcomes were any deep vein thrombosis (DVT) as detected by bilateral ultrasonography up to postoperative Day 10 (POD10) and pulmonary embolism (PE) up to POD28. The main safety outcomes were bleeding and death from any cause up to POD28. Plasma D-dimer levels were measured before and at POD10 after TKA.

RESULTS

The study cohort was composed of 1288 patients from 34 hospitals. There was no death up to POD28. PE occurred in 2 patients with OA and in no patients with RA. The incidence of primary effectiveness outcome was 24.3% and 24.0% in patients with OA and RA, respectively. The incidence of major bleeding up to POD28 was 1.3% and 0.5% in patients with OA and RA, respectively. No differences in the incidence of VTE (symptomatic/asymptomatic DVT plus PE) or bleeding were noted between patients with RA and OA. D-dimer levels on POD10 were significantly higher in patients with OA compared with those with RA. Also, D-dimer levels on POD10 were significantly lower in patients receiving fondaparinux than in patients without pharmacological prophylaxis.

CONCLUSION

Despite some differences in demographic data, patients with RA and OA have equivalent risks of VTE and bleeding following TKA.

Risk factors for venous thromboembolism of total hip arthroplasty and total knee arthroplasty: a systematic review of evidences in ten years

Background

Risk factors for venous thromboembolism (VTE) of total joint arthroplasty (TJA) have been examined by many studies. A comprehensive systematic review of recent findings of high evidence level in this topic is needed.

Methods

We conducted a PubMed search for papers published between 2003 and 2013 that provided level-I and level-II evidences on risk factors for VTE of TJA. For each potential factors examined in at least three papers, we summarize the the number of the papers and confirmed the direction of statistically significant associations, e.g. “risk factor” “protective factor” or “controversial factor”.

Results

Fifty-four papers were included in the systematic review. Risk factors found to be associated with VTE of both total hip arthroplasty and total knee arthroplasty included older age, female sex, higher BMI, bilateral surgery, surgery time > 2 hours. VTE history was found as a VTE risk factor of THA but an controversial factor of TKA. Cemented fixation as compared to cementless fixation was found as a risk factor for VTE only of TKA. TKA surgery itself was confirmed as a VTE risk factor compared with THA surgery.

Conclusions

This systematic review of high level evidences published in recent ten years identified a range of potential factors associated with VTE risk of total joint arthroplasty. These results can provide informations in this topic for doctors, patients and researchers.

Emphasis on the Role of PF4 in the Incidence, Pathophysiology and Treatment of Heparin Induced Thrombocytopenia

Heparin Induced Thrombocytopenia (HIT) is caused by antibodies that recognize platelet factor 4 (PF4) associated with polyanionic glycosaminoglycan drugs or displayed on vascular cell membranes. These antibodies are elicited by multimolecular complexes that can occur when heparin is administered in clinical settings associated with abundant PF4. Heparin binding alters native PF4 and elicits immune recognition and response. While the presence of heparin is integral to immunogenesis, the HIT antibody binding site is within PF4. Thus HIT antibodies develop and function to cause thrombocytopenia and/or thrombosis only in the presence of PF4. Future emphasis on understanding the biology, turnover and regulation of PF4 may lead to insights into the prevention and treatment of HIT.

Heparin-induced thrombocytopenia after total knee arthroplasty, with subsequent adrenal hemorrhage

Heparin-induced thrombocytopenia (HIT) is a life-threatening immune-mediated adverse effect of chemoprophylaxis for venous thromboembolic events. We present the case of a 44-year-old man who developed bilateral adrenal hemorrhage (BAH) as a sequela of HIT after bilateral total knee arthroplasty. In our review of clinical management of HIT-induced BAH, we discuss the 21 published cases of this phenomenon, 14 of which occurred after orthopedic surgery. Given the potentially fatal consequences and the importance of early intervention, physicians should be on the alert for recognizing HIT-induced BAH in patients experiencing shock unresponsive to fluid resuscitation. In addition, chemoprophylaxis with alternative agents such as a synthetic pentasaccharide factor Xa inhibitor and oral direct thrombin inhibitors that are associated with lower risks of HIT in orthopedic patients merits exploration.

How I treat heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia is a prothrombotic adverse drug effect induced by platelet-activating antibodies against multimolecular complexes of platelet factor 4 and heparin. Diagnosis rests on a clinical assessment of disease probability and laboratory testing. Management involves immediate discontinuation of heparin and initiation of an alternative anticoagulant. Because of the frequency of thrombocytopenia among heparinized patients, the limited specificity of widely available immunoassays, the limited availability of more specific functional assays, and clinicians' fears of missing a case of true disease, overtesting, overdiagnosis, and overtreatment have become common. As a result, a substantial number of thrombocytopenic patients are unnecessarily exposed to costly alternative anticoagulants and their attendant risk of bleeding. In this review, we describe not only our approach to the evaluation and management of patients with heparin-induced thrombocytopenia, but also the measures we use to minimize misdiagnosis and unnecessary treatment of patients without the disease. In addition, we propose areas of investigation for improvement of the diagnosis and management of this potentially fatal disorder.

Recent advances in heparin-induced thrombocytopenia

PURPOSE OF REVIEW

Heparin-induced thrombocytopenia (HIT) is a prothrombotic complication of heparin therapy caused by antibodies against platelet factor 4/heparin complexes. Progress in our understanding of HIT has translated to improvements in treatment and patient outcomes. The objective of this review is to examine recent advances and highlight areas of future inquiry in the epidemiology, diagnosis, and management of this potentially fatal disorder.

RECENT FINDINGS

Risk factors for the development of HIT related to heparin administration are well described. Recent identification of host-related risk factors adds to our understanding of disease epidemiology. The limited specificity of clinical diagnosis and widely used immunologic assays for HIT results in frequent overdiagnosis. Novel clinical decision rules and laboratory assays to improve diagnosis are in development. Fondaparinux, bivalirudin, and desirudin have recently been added to the HIT armamentarium.

SUMMARY

Despite these advances, critical issues remain to be addressed. Future research efforts will focus on the identification of novel clinical risk factors and biomarkers that will enable recognition of individuals at greatest risk, optimization of diagnostic strategies and use of currently available therapeutics, and development of new drugs that not only reduce thrombotic complications, but also minimize bleeding risk, are well tolerated in patients with organ dysfunction, and facilitate transition to outpatient therapy.

HIT paradigms and paradoxes

The current major problem with HIT is its overdiagnosis. This concept follows from the HIT central paradigm: HIT is caused by a subset of antibodies against platelet factor 4 (PF4)/heparin complexes that have strong platelet-activating properties. Prospective studies show that only a minority of sera containing such antibodies exhibit platelet-activating properties. Ironically, the earliest tests for HIT--platelet activation assays--remain today the most diagnostically useful, particularly the washed platelet assays. But the wider application of PF4-dependent immunoassays, and their much greater sensitivity for the larger subset of non-platelet-activating (and non-HIT-inducing) antibodies, has resulted in HIT overdiagnosis in many centres. Studies of anti-PF4/heparin immunization in diverse clinical situations have provided insights into the factors that influence the HIT immune response. Besides the conundrum of anticoagulant-induced thrombosis (including its potentiation of coumarin-induced microthrombosis), HIT evinces numerous other paradoxes: (i) it is a platelet-activating disorder with venous thrombosis as its predominant clinical manifestation; (ii) 'delayed-onset' (or 'autoimmune') HIT can lead to dramatic worsening of HIT-associated thrombosis despite cessation of heparin; (iii) partial thromboplastin time (PTT) monitoring of direct thrombin inhibitor treatment - and confounding of PTT monitoring by HIT-associated consumptive coagulopathy - infers that the worst subset of HIT patients may fail this therapeutic approach; (iv) the highly sulfated pentasaccharide anticoagulant, fondaparinux, can (rarely) cause HIT yet appears to be an effective treatment for this disorder; and (v) the transience of the HIT immune response means that many patients with previous HIT can safely receive future heparin.