There is evidence that supports platelet activation and dysfunction in both MPNs and in multiple myeloma. In the European Collaboration on Low-Dose Aspirin in Polycythemia Vera ECLAP trial, low-dose aspirin mg per day , when compared with placebo, reduced a composite end point of thrombotic complications without a significantly increased incidence of major bleeding.
The use of aspirin for secondary VTE prevention is perhaps best reserved for situations in which antiplatelet therapy is already strongly recommended for another indication eg, coronary stent placement , or anticoagulation is contraindicated or simply cannot be acquired due to cost or logistics. For example, in clinical case 2, aspirin could be an option for secondary thromboprophylaxis because she already has an existing cardiac indication for aspirin.
Although the combination of antiplatelet and anticoagulant therapy would likely reduce the risk for VTE compared with antiplatelet therapy alone, the marginal benefit in this patient who had 1 unprovoked DVT 3 years ago would likely not offset the bleeding risk. There are other intriguing hypotheses that would be interesting to test. Would selected persons undertaking long-distance travel benefit from taking low-dose aspirin? Which patients would benefit and for how long would such treatment be recommended?
For now, these questions remain unanswered. For many patients, aspirin is an inexpensive, safe and effective VTE-prevention strategy following total joint arthroplasty. Although ongoing clinical trials EPCAT III and PEPPER will further clarify the roles of low-dose aspirin and low-dose anticoagulants after joint replacement surgery, there is already robust evidence to support low-dose aspirin as part of a hybrid strategy after an initial period of low-dose anticoagulant administration.
For secondary VTE prophylaxis, aspirin is less effective than anticoagulants but more effective than placebo. Establishing that long-term aspirin use is clearly safer than long-term anticoagulant exposure especially compared with low-dose, oral factor Xa inhibitors has been surprisingly difficult.
Unless a safety benefit from aspirin can be established in well-designed prospective studies, patients who need long-term antithrombotic therapy for VTE will often choose a low-dose factor Xa inhibitor, once presented with the risk-benefit tradeoffs.
National Center for Biotechnology Information , U. Robert Diep and David Garcia. Author information Copyright and License information Disclaimer. Corresponding author. Conflict-of-interest disclosure: The authors declare no competing financial interests. This article has been cited by other articles in PMC. Visual Abstract. Open in a separate window. Learning Objectives Understand the evidence supporting the use of low-dose aspirin in the primary prophylaxis of VTE in specific medical and surgical contexts Understand the evidence related to the use of low-dose aspirin in the secondary prophylaxis of VTE Review the safety profile and bleeding risk of aspirin use in comparison with anticoagulation.
Clinical case 1 A year-old man with no prior medical history undergoes an elective total knee replacement for chronic degenerative disease. The physiology behind venous thrombosis Hemostasis is a balance between clot formation and clot degradation, a tightly regulated system of procoagulant and anticoagulant forces. Figure 1. Aspirin Mechanism of action Acetylsalicylic acid, also known as aspirin, was the first synthetic drug produced, in Dosing Aspirin is absorbed primarily in the stomach and upper small intestine.
Primary prophylaxis of venous thrombosis VTE DVT and PE is a well-established cause of morbidity and mortality in the medical and surgical patient populations. Table 1. Clinical case 2 A year-old woman with a history of coronary artery disease, morbid obesity, and a prior unprovoked proximal DVT 3 years ago presents to her primary care office prior to embarking on a long international flight to a low-resource setting.
The risks Long-term stroke-prevention trials in patients with atrial fibrillation provide an excellent assessment of the relative bleeding risk with aspirin compared with the anticoagulants. Table 2. Study reference Indication Aspirin dose compared with placebo No. Table 3. Study reference Indication Comparators No. Primary VTE prevention in selected medical populations In specific medical contexts, such as in some patients with myeloproliferative neoplasms MPNs and in some patients with multiple myeloma, aspirin is widely used to reduce the risk of both VTE and arterial thrombosis.
Conclusion For many patients, aspirin is an inexpensive, safe and effective VTE-prevention strategy following total joint arthroplasty. References 1. Thrombosis and platelets: an update. Eur Heart J. Mechanisms of venous thrombosis and resolution. Arterioscler Thromb Vasc Biol. Fibrinolysis and inflammation in venous thrombus resolution. Front Immunol. Sneader W. The discovery of aspirin: a reappraisal. Fitzpatrick FA. Cyclooxygenase enzymes: regulation and function.
Curr Pharm Des. Awtry EH, Loscalzo J. Effects of aspirin on clot structure and fibrinolysis using a novel in vitro cellular system. Antithrombotic properties of aspirin and resistance to aspirin: beyond strictly antiplatelet actions. Why does aspirin decrease the risk of venous thromboembolism? On old and novel antithrombotic effects of acetyl salicylic acid.
J Thromb Haemost. Blood Coagul Fibrinolysis. Marked increase of fibrin gel permeability with very low dose ASA treatment.
Thromb Res. Collaborative meta-analysis of randomised trials of antiplatelet therapy for prevention of death, myocardial infarction, and stroke in high risk patients. Aspirin dose for the prevention of cardiovascular disease: a systematic review. Low-dose aspirin is adequate for venous thromboembolism prevention following total joint arthroplasty: a systematic review. J Arthroplasty. Rates of venous thromboembolism occurrence in medical patients among the insured population.
Thromb Haemost. Relative impact of risk factors for deep vein thrombosis and pulmonary embolism: a population-based study. Arch Intern Med. The risk of VTE is highest immediately after hospitalization and remains elevated for up to 3 months after admission. Recently, two studies examined the benefit of extending thromboprophylaxis with oral options but did not provide definite evidence of net clinical benefit [ , ].
Routine use of extended thromboprophylaxis after discharge without individualized risk assessment is not recommended [ 9 ]. A recent publication in this VTE series explores the recent trials for extended VTE prophylaxis and suggests an algorithm to determine which patients may benefit from extended prophylaxis [ ]. Immune activation to fight bacterial, viral, and fungal pathogens stimulates a complex cascade of inflammatory cytokines [ ].
This in turn leads to activation of thrombin and vascular endothelial injury, increasing the risk of venous thromboembolic disease. This activation exists on a spectrum from beneficial to pathologic, and in severe inflammatory conditions, the risk of VTE can increase dramatically.
During ICU admissions, the need for prolonged immobilization, indwelling central venous catheters, and hypoxia due to acute respiratory distress syndrome are additional risk factors for development of thrombosis, which in part explains the high rate of VTE seen in patients with severe COVID infection [ ].
Several mechanisms contribute to the unusually high rate of venous thrombosis seen in COVID patients. Infection of pulmonary tissues via angiotensin-converting enzyme 2 ACE2 receptors leads to direct endothelial injury, and the immune response leads to the release of pro-thrombotic cytokines [ ].
Thromboelastographic studies have demonstrated a hypercoagulable state and decreased fibrinolysis in COVID patients [ , , ]. In addition to the conventional mechanism for PE, a preponderance of evidence suggests that immunothrombosis contributes to in situ development of pulmonary artery thrombi [ , , ].
In addition to these disease-specific factors, patients admitted with suspected or confirmed COVID are hypoxic and may be asked to limit their ambulation for the purpose of infection control, both of which are potent risk factors for VTE. Notably, the baseline risk of VTE is lower in China, and thromboprophylaxis is not routinely used in these patients. Recent data reveal that increased rates of VTE are seen even with the use of prophylaxis.
There are limitations and challenges with interpreting these early reports because of their mainly retrospective designs, short duration of follow-up, and consequent concerns about bias including publication and case ascertainment biases. However, intensifying anticoagulant therapy may increase the risk of bleeding, particularly in those who are critically ill.
Ongoing randomized trials will determine whether these approaches will improve patient outcomes. In patients with cancer, the risk of VTE is substantially increased due largely to tumor production of procoagulant and inflammatory substances which are released into the circulation.
Interactions between chemotherapy anticancer treatments and the development of VTE are also well established. Gemcitabine and Cisplatin chemotherapy are strongly associated with VTE risk [ , ]. All solid malignancies appear to increase the risk of VTE, and certain cancer sites including pancreatic and gastric cancer have particularly high rates of VTE during initial treatment.
Patients with hematologic malignancies are also at increased risk of VTE, except for some indolent lymphoma subtypes [ ]. Patients with cancer-associated thrombosis typically have a poor prognosis, and in these patients, VTE likely serves as an indicator for more aggressive disease.
Similar observations over many years have led to attempts to risk-stratify and prevent thrombosis in cancer patients. The Khorana score is the most widely known tool by which ambulatory cancer patients are risk-stratified using clinical and laboratory criteria.
Pancreatic cancer and stomach cancer each count for two points, and lymphoma, gynecologic, bladder, and testicular cancer count for one point. Multiple prospective and series have confirmed the validity of the Khorana score, and its use is endorsed by the most recent ASCO guidelines for VTE risk stratification in cancer [ 40 , , ]. The Khorana score is also valid for use in hospitalized cancer patients [ , ].
Attempts to validate the Khorana score for specific subpopulations of cancer have been less successful, and in studies of lung cancer, hepatocellular carcinoma, acute myeloid leukemia, and lymphoid malignancies, the Khorana score did not adequately stratify or predict VTE events [ , , , ].
Major bleeding events are more frequent in cancer patients, due to both the propensity of certain cancer subtypes to bleeding complications including gastrointestinal and genitourinary cancers and the tendency of cancer patients towards anemia and blood transfusion. The rates of major bleeding and fatal bleeding were also not statistically different between the study arms HR 1. The high discontinuation rates of the DOACs over time in both trials and in treatment trials highlight the challenges with adherence to DOACs in the prevention and treatment of VTE in patients with cancer [ , , ].
By leveraging our understanding of VTE risk to target patients at the highest risk of VTE, these studies have attempted to maximize the net clinical benefit of preventative treatments for VTE.
Similarly, patients at relatively low risk of VTE are spared the expense and potential bleeding complications of these treatments. Attempts to further refine the Khorana score include the Cancer-And-Thrombosis-Study CATS score, which combines tumor subtype and D-dimer levels to predict those at greatest risk of cancer-associated thrombosis [ ].
Further research is required to determine if additional clinical or laboratory parameters can be leveraged to improve our ability to predict the development of VTE and target prophylactic measures accordingly. Advances in technology and pharmacology have already improved our ability to predict and prevent VTE. At least two major barriers to improving VTE prevention still exist.
The first is the limitations on overall benefit to thromboprophylaxis inherent to current anticoagulant medications. The second barrier is the imperfect science of individualizing VTE risk stratification and the inherent complexity of predicting multifactorial and competing phenomena.
These final sections will discuss future directions in therapeutics and technology including the importance of antithrombotic options with less bleeding and technological advances including machine learning to refine risk stratification and facilitate their implementation. Over the past decade, the tolerability, acceptability, and quality of life for patients at risk of VTE have changed with the advent of effective oral therapies for VTE treatment and prevention.
In those with cancer, patient-reported quality of life is better with oral anticoagulant treatment compared to daily subcutaneous LMWH injection [ ]. After only one month on therapy, those taking subcutaneous injections experienced excess bruising, stress, worry and irritation, and frustration taking anticoagulants compared to those on oral therapy.
While not as rigorously studied, quality-of-life improvements with oral therapies are likely similar in the prophylactic setting.
Increased tolerability and ease of use has led to more widespread adoption and adherence to VTE prophylaxis in populations such as ambulatory cancer patients and post-operative patients. Oral options for prophylaxis reduce the time required for counseling and reviewing self-injection technique or administering subcutaneous medications by healthcare practitioners and increase patient adherence to anticoagulant medications.
Every effective anticoagulant medication for VTE prophylaxis also increases the risk of bleeding. The harms of bleeding—including substantial case fatality rates—may be under-appreciated. Many authors have argued that declining rates of VTE in hospitalized patients should be cause for re-appraisal and de-escalation of previous protocols for the use of VTE prophylaxis [ 7 , 8 ]. As the baseline rate of VTE changes, either through time or differing circumstance, we must balance the threats of both underuse and overuse of pharmacologic VTE prophylaxis.
Novel agents for pharmacologic prophylaxis are currently being developed that target factor XI and factor XII. Early studies with factor XI antisense oligonucleotides were successful in lowering factor XI levels and preventing VTE without significant effects on hemostasis and bleeding [ ]. Whether this result is confirmed with oral or long-acting parenteral factor XI inhibitors in larger studies is a question of significant interest. If these trials or other new agents are successful at reducing VTE without substantially increasing the risk of bleeding, existing approaches to VTE prevention could change dramatically.
Efforts to predict and prevent venous thromboembolic disease are predicated on our ability to accurately identify patients at risk. The benefits of thromboprophylaxis must be weighed against the financial costs and potential for increased bleeding.
Understanding which patients are at greatest risk can help medical practitioners and their patients to make intelligent decisions regarding the use of anticoagulants to prevent VTE. We must continue to collect and analyze large data sets on patient-specific and acquired risk factors, and how they interact, to improve existing risk assessment models.
Early successes with predicting VTE risk using biomarkers should prompt further research into the use of biomarkers in new situations. Biomarkers are only one aspect of prediction. The development and validation of prediction models should seek to increase the accuracy of prediction without sacrificing usability [ , ].
As we seek to individualize preventative efforts, the primary obstacles that affect implementation of risk assessment models will be the complications and complexity of any proposed algorithm. Scoring systems and other risk-assessment models can be implemented for use by health professionals if they are easily accessible and understood, but developing sufficient predictive power for VTE often requires the combination of several variables.
Scoring systems can quickly become time-consuming for use by physicians, and hiring additional data entry personnel adds significant cost. Predictive algorithms that appropriately consider and calculate bleeding risks for individual patients to avoid harms from VTE prophylaxis increase complexity and add additional workload. Scoring systems developed in the current age must not lose sight of the practical challenges of implementation by treating clinicians. Scoring systems and other decision support tools can be incorporated into EMRs for ease of access.
Studies indicate that computer alert interventions can increase adherence to appropriate VTE risk-stratification [ ], reduce costs by avoiding unnecessary thromboprophylaxis in low-risk patients [ ], and decrease preventable harm from VTE [ , , ]. Implementation of such systems should consider whether the absolute benefit is worth the additional burden on healthcare providers as long as direct provider input is required for the system to function. Smoother implementation of existing categorical scoring systems is laudable, but health technologies in the future will render such systems obsolete.
By taking continuous variables such as age or weight and reducing them to binary or ternary variables, we necessarily sacrifice some predictive value. Machine learning has the capacity to overcome these challenges by recognizing patterns in complex sets of information that accurately predict the risk of VTE and bleeding [ ].
When interpreted by such systems, continuous variables do not need to be reduced to categorical variables for ease of use. Additionally, new clinical events can be fed into machine learning algorithms continuously, which in turn would allow such systems to adjust the weight of variables in risk calculations quickly and precisely. Until such technology is available, institutional protocols for VTE prophylaxis should be regularly reviewed to ensure they reflect recent studies detailing risks and benefits of this common medical intervention.
Discussions at the institutional and individual level should seek to balance the complex relationship between the multifactorial risk factors for VTE and bleeding complications and strive for net clinical benefit in prescribing pharmacologic VTE prophylaxis.
In the last half-century, we have made tremendous progress in understanding the epidemiology and prevention of VTE. Patients considering exogenous hormonal therapies or pregnancy can be accurately informed about their risk for VTE, and patients undergoing surgery, medical hospitalization, cancer treatments, and those with COVID infection routinely receive preventative anticoagulant treatments when the benefits of such treatments are known to outweigh the risks.
As scoring systems and other decision support tools increase in accuracy and complexity, we risk overwhelming clinicians, or worse, turning them into data entry personnel. In the future, additional biomarkers for predicting VTE, safer medications, and machine learning algorithms will revolutionize prediction and prevention of this common disorder. All authors critically reviewed the draft and provided edits for the final manuscript. All authors have read and agreed to the published version of the manuscript.
National Center for Biotechnology Information , U. Journal List J Clin Med v. J Clin Med. Published online Aug 1. Author information Article notes Copyright and License information Disclaimer. Received Jun 26; Accepted Jul This article has been cited by other articles in PMC. Introduction Venous thromboembolism VTE is the third most common cause of vascular mortality worldwide and comprises deep-vein thrombosis DVT and pulmonary embolism PE [ 1 ].
Venous Thromboembolism Exists in a Hierarchy of Clinical Importance Venous thrombi consist predominantly of fibrin and red blood cells [ 27 ]. Age Is One of The Most Important Risk Factors Even in the presence of cancer, venous access devices, and medications that increase the risk of thrombosis, the incidence of venous thrombosis in children remains low until adulthood—late teens and early 20s. Open in a separate window.
Prevention: Acquired Risk Over the past three decades, structured protocols have been developed and validated to reliably risk-stratify patients based upon clinical features and laboratory testing into risk groups for VTE.
Figure 1. Summary of select scoring systems for predicting risk of venous thromboembolism. Medical Hospitalization Most hospitalizations are for non-surgical conditions.
COVID Infection Immune activation to fight bacterial, viral, and fungal pathogens stimulates a complex cascade of inflammatory cytokines [ ]. Cancer-Associated Thrombosis In patients with cancer, the risk of VTE is substantially increased due largely to tumor production of procoagulant and inflammatory substances which are released into the circulation. Future Directions for Prevention of Venous Thromboembolism Advances in technology and pharmacology have already improved our ability to predict and prevent VTE.
A More Palatable Approach to Pharmacologic Prevention Over the past decade, the tolerability, acceptability, and quality of life for patients at risk of VTE have changed with the advent of effective oral therapies for VTE treatment and prevention. Implementing and Improving Scoring Systems Efforts to predict and prevent venous thromboembolic disease are predicated on our ability to accurately identify patients at risk.
Conclusions In the last half-century, we have made tremendous progress in understanding the epidemiology and prevention of VTE. Author Contributions M. Conflicts of Interest M. References 1. Wendelboe A. Global Burden of Thrombosis: Epidemiologic Aspects.
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Hirsh J. Choi H. Thromboembolism in children with cancer: A retrospective multicenter study in Korea. Andrew M. Biss T. Clinical features and outcome of pulmonary embolism in children. Conventional therapy consists of intravenous heparin followed by oral anticoagulants usually given for three to six months. The recommended intensity of oral anticoagulants warfarin has been derived from clinical trials. Such therapy is usually quite effective. However, some patients develop recurrent disease after the oral anticoagulants are stopped.
A recent randomized study evaluated the optimal duration of oral anticoagulant therapy. There was no difference in mortality in the two groups. Recurrence was not seen while the patients were under treatment. When anticoagulants were stopped, recurrent thrombosis was documented in 18 percent of the patients treated for six weeks and in 9.
The period of greatest risk of recurrence for the six weeks patients was immediately after therapy was stopped. There was a linear increase in cumulative risk of 5 to 6 percent per year for both treatment groups during the following 18 months. For patients who have experienced idiopathic venous thrombosis, the risk of recurrence may continue even after several months of conventional therapy.
Further prophylactic therapy might be beneficial for the patients who are at risk for late recurrence. But, because of the presumed risk of bleeding and inconvenience of monitoring standard warfarin therapy, most physicians usually limit treatment to three to six months.
In , Simioni showed a cumulative recurrence rate of VTE of The factor V Leiden mutation is found in 4 to 6 percent of Caucasians and is the single most important cause of thromboembolism in a variety of conditions. Heterozygous carriers with the mutation have VTE at a younger age than do noncarriers. Among those with first VTE, the prevalence of the mutation is 15 to 40 percent and among those with a family history of VTE, as high as 50 percent.
However, in a large study of men participating in the Physicians Health Study, those individuals with the mutation had an increased rate of VTE over time. These age-specific incidence rate differences ranged from 1. These data suggest that confounders other than genetic predisposition are important in the development of VTE.
The INR was introduced by the World Health Organization to standardize control of anticoagulant therapy internationally. Multicenter, randomized, double-blind, placebo-controlled. A total of patients were randomized to usual care plus placebo and a total of patients to usual care plus a three-to-four year regimen of low-dose warfarin target INR 1. Double-blind INR assessment and dose adjustment were performed every three months to ensure patient safety and to monitor compliance. Primary endpoints included recurrent venous thromboembolism, major bleeding episodes, and all-cause mortality.
Separate analysis was performed of all-cause mortality in the total patient population and in those with factor V Leiden. The study consisted of 52 clinical centers, a laboratory coordinating center, the clinical coordinating center, and the data coordinating center.
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