Venous Clots Research Articles

Association of ischemic stroke, hormone therapy, and right to left shunt in postmenopausal women

Postmenopausal hormone therapy (HT) increases the risk of venous thrombosis and ischemic stroke. We postulated that HT might increase the risk of ischemic stroke by promoting venous clots that travel to the brain through a right to left shunt (RLS). A total of 2,389 records were studied. After eliminating the premenopausal patients, and those with TIAs and non-ischemic strokes, the medical records of 1846 postmenopausal women hospitalized at four institutions for ischemic stroke were reviewed to identify those who had undergone an adequate study to assess for RLS. The proportion of women with a shunt in users and non-users of HT was compared in stroke patients and in a reference population consisting of postmenopausal women undergoing elective cardiac catheterization. There were 363 (20%) records that had complete data and were included in the analysis. A shunt was more prevalent in patients with a cryptogenic stroke than in patients with a stroke of known cause (55/88 (63%) vs. 53/275 (19%), P < 0.001). In patients with a stroke of known cause, the frequency of a shunt was similar to that in reference women 31/136 (23%), and the proportion of women with a shunt was similar in non-users and current users of HT (14% vs. 20%, P = 0.40). However, among patients with a cryptogenic stroke, the prevalence of a shunt was 1.5 times higher in current users than non-users of HT (82% vs. 56%, P = 0.04). Approximately 23% of older women have a RLS. HT in these women may increase the risk of ischemic stroke by promoting paradoxical embolism.

Drug focus on warfarin — an anticoagulant medication

Warfarin is a commonly prescribed anticoagulant medication used for the treatment and prevention of venous and arterial blood clots. This update article about warfarin covers the following: how it works, what it is used for, the potential side effects, when it should be avoided and practical considerations of warfarin therapy.

Abstract T P347: Metabolomic Analysis of PFO-Related Stroke Shows Immediate and Persistent Decrease of Homocysteine Post PFO Closure

Background: PFO, an independent stroke risk factor, enables direct mixing of venous and arterial circulation. As we have found previously, PFO serves not only as a conduit for venous clots, but also enables harmful factors such as serotonin (5HT) to avoid pulmonary filtration to remain within circulation at elevated levels, potentially contributing to a prothrombotic state. We hypothesize that in addition to 5HT, other factors may also be involved. In the context of endovascular PFO closure, a bedside model to understand PFO circulatory signaling, we performed a full metabolomic profile of mediators that may respond to PFO closure. Method: Non-migraine stroke patients were recruited in accordance with IRB approval, plasma was sampled from left and right atria pre and post closure and also from venous blood 3 months post PFO closure. A discovery metabolite screening was performed in 14 patients who underwent PFO closure, and analysis was performed using one-way ANOVA. Result: After stringent data filtering (537 metabolites, one-way ANOVA, p-value &lt;0.01), we identified significant changes in a panel of small molecules after PFO closure - the most prominent change being in homocysteine (HCY). While relative HCY levels (expressed as peak area) in the left atrium (LA) and right atrium (RA) were comparable pre-closure (pre-LA: 5.61 ± 0.09; pre-RA: 5.30 ± 0.48), HCY immediately decreased in LA post PFO closure (post-LA: 4.56 ± 0.04) and HCY level remained low in peripheral venous blood at 3-month follow-up (4.57 ± 0.06; p = 0.0036). Conclusion: We found PFO closure to lower HYC immediately in left atrial (arterial) blood, and this effect persists in peripheral venous circulation at 3 months post procedure. Since high level of HYC is independently associated with stroke and heart disease, our results suggest that mechanical PFO repair may improve circulatory profile of PFO stroke patients. Studies in a larger patient cohort and validation of other important metabolites are ongoing.

JAK2V 617 F-positive endothelial cells contribute to clotting abnormalities in myeloproliferative neoplasms

The Janus kinase 2 (JAK2) V617F mutation is the primary pathogenic mutation in patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs). Although thrombohemorrhagic incidents are the most common causes of morbidity and mortality in patients with MPNs, the events causing these clotting abnormalities remain unclear. To identify the cells responsible for the dysfunctional hemostasis, we used transgenic mice expressing JAK2V617F in specific lineages involved in thrombosis and hemostasis. When JAK2V617F was expressed in both hematopoietic and endothelial cells (ECs), the mice developed a significant MPN, characterized by thrombocytosis, neutrophilia, and splenomegaly. However, despite having significantly higher platelet counts than controls, these mice showed severely attenuated thrombosis following injury. Interestingly, platelet activation and aggregation in response to agonists was unaltered by JAK2V617F expression. Subsequent bone marrow transplants revealed the contribution of both endothelial and hematopoietic compartments to the attenuated thrombosis. Furthermore, we identified a potential mechanism for this phenotype through JAK2V617F-regulated inhibition of von Willebrand factor (VWF) function and/or secretion. JAK2V617F(+) mice display a condition similar to acquired von Willebrand syndrome, exhibiting significantly less high molecular weight VWF and reduced agglutination to ristocetin. These findings greatly advance our understanding of thrombohemorrhagic events in MPNs and highlight the critical role of ECs in the pathology of hematopoietic malignancies.

Comparison of arterial and venous whole blood clot initiation, formation, and strength by thromboelastography in anesthetized swine

Thromboelastography (TEG) analysis was used to determine if differences exist between venous and arterial samples in anesthetized swine, using identical sampling techniques for each of the samples. We hypothesized that TEG parameters would not differ between native whole blood venous and arterial samples. Thirty male Landrace swines were included in the study. Both the femoral artery and vein were catheterized using standard cut-down techniques and with identically sized catheters to rule out any catheter size effects on the results. Standard TEG parameters for native whole venous and arterial blood samples (r, K, α, MA, G, and coagulation index) were measured or calculated, and t-test or Mann-Whitney rank-sum test used for comparison when appropriate. Significant differences were detected for r (venous < arterial), K (venous < arterial), α (venous > arterial), and coagulation index (venous > arterial) TEG parameters. No significant differences were measured for MA or G. These differences are important, especially when temporal changes in TEG are utilized to monitor patient stability and fluid therapy protocols using trends in coagulation properties. Taken together, these results suggest that clots are more likely to form at a faster rate in venous samples compared to arterial samples, but the overall clot strength does not differ. Therefore, if TEG analysis is being used to monitor coagulation profiles in a patient, care should be taken to use the same site and technique if results are to be used for comparative purposes.

Nitrite Regulation Of Platelet Reactivity Under Physiological Conditions

Nitric oxide (NO) is generated by serial reduction pathway of nitrate and nitrite or by activity of endogenous nitric oxide synthase (NOS), and modulates platelet function and hemostasis. We have shown by aggregometry and flow cytometric analysis of P-selectin that nitrite in the presence of erythrocytes inhibits platelet aggregation and activation after its reduction to NO at low oxygen tension [PLoS One. 2012; 7: e30380. 10.1371/journal.pone.0030380]. We then investigated how nitrite may affect overall clotting processes by regulating platelet function using thrombelastography (TEG), a method used to assess platelet function, fibrin clot formation, and fibrinolysis in blood and/or plasma. We measured the effect of NO donors and nitrite on three TEG parameters, reaction time (R, time to initial fibrin formation), α angle (velocity of clot growth) and maximum amplitude (MA, clot strength), in healthy volunteers. The NO donor (DEANONOate) inhibited all three TEG parameters in response to two independent platelet activators (ADP and AA), in platelet rich plasma (PRP) or whole blood diluted with plasma to yield 20% hematocrit (Hct) to model blood in the microcirculation in vivo. At DEANONOate concentrations ranging from 0-1 μM, R values were progressively prolonged from 1.9 to 3.6 (p=0.008), α angle was decreased from 17.8 to 9.5 (p=0.01) and maximum clot amplitude was reduced from 9.0 to 4.4 (p=0.001) in 20% Hct with ADP stimulation. In contrast, nitrite did not affect clotting parameters in PRP, but exhibited moderate inhibitory effects in 20% Hct at concentrations from 0-10 μM; R values were slightly prolonged from 1.6 to 2.7 (p=0.12), α angle was decreased from 21.8 to 12.8 (p=0.07) and maximum clot amplitude was reduced from 11.0 to 5.0 (p=0.02). This inhibitory effect of nitrite on clotting was greatly enhanced under hypoxic conditions (blood pO2 46.5±11.6 mmHg); R values from 1.4 to 4.0 (p=0.003), α angle from 21.7 to 7.8 (p=0.002), and maximum clot amplitude from 10.0 to 3.4 (p=0.0003). These results suggest that the nitrite effect may be greatest in the microcirculation and be important in differences between arterial and venous clotting. In conclusion, our results show TEG parameters indicate NO inhibition of platelet-mediated blood clotting and that the physiological effect of factors which determine NO bioavailability, such as reduction of blood and tissue nitrite, could be used to predict hemostasis. Disclosures: Schechter: National Institutes of Health: Dr. Alan Schechter is listed as a co-inventor on several patents issued to the National Institutes of Health for the use of nitrite salts for the treatment of cardiovascular diseases., Dr. Alan Schechter is listed as a co-inventor on several patents issued to the National Institutes of Health for the use of nitrite salts for the treatment of cardiovascular diseases. Patents &amp; Royalties.

Circulation Editors’ Picks

<i>Circulation</i> Editors’ Picks

Catheter-directed thrombolysis for double inferior vena cava with deep venous thrombosis: A case report and literature review

Double inferior vena cava (DIVC) with deep venous thrombosis (DVT) is rare, and there is only one reported case of DIVC with DVT treated by catheter-directed thrombolysis. We report a case of a 32-year-old man with an extensive venous clot involving the infrarenal segment of a double IVC who received filter implantation and catheter-directed thrombolysis.

Use of a Trellis Device for Endovascular Treatment of Venous Thrombosis Involving a Duplicated Inferior Vena Cava

Congenital anomalies of the inferior vena cava (IVC) are increasingly recognized with CT and venography techniques. Although many patients with IVC anomalies are asymptomatic, recent studies have suggested an association with venous thromboembolism. We report the case of a 62-year-old woman with extensive venous clot involving the infrarenal segment of a duplicated left IVC who underwent pharmacomechanical thrombectomy and tissue plasminogen activator catheter-directed thrombolysis with complete deep venous thrombosis resolution. To our knowledge this is the first reported case in the English literature of the use of a Trellis thrombectomy catheter in the setting of duplicated IVC.

1017

Introduction: Pulmonary embolism (PE) is a serious complication among critically ill patients with major trauma. New options for achieving the goal of universal PE prophylaxis in this high-risk population are needed. The Angel™ Catheter combines the functions of an inferior vena cava (IVC) filter and a multilumen central venous catheter. The device is designed for bedside placement to provide both prophylaxis against PE and access to the central venous system. Hypothesis: The objective of this first-in-man pilot clinical trial were to assess the safety and effectiveness of the Ange™Catheter for severely ill medical and surgical patients at increased risk of PE and to evaluate the feasibility of conducting a large clinical trial of this device. Methods: This prospective pilot interventional study was conducted from December 2011 to March 2012. Patients in the intensive care unit (ICU) were recruited for the study and were followed up for 30 days after device retrieval. All patients were at high risk of PE but were not receiving medical thromboprophylaxis because of either increased risk of bleeding or ongoing bleeding. Results: This study included 8 critically ill patients in the ICU. The principal diagnosis resulting in ICU admission was trauma for 7 patients (87%) and subarachnoid hemorrhage for one (13%). Six of the trauma patients had multiple bone fractures and abdominal trauma, and one had a traumatic brain injury. At the time of device insertion, 3 patients had ongoing bleeding and one had a pulmonary embolism. The Angel™ Catheter was placed via the femoral vein with ultrasound guidance in 5 of 8 patients (62.4%) and was advanced to the infrarenal IVC without fluoroscopic guidance. In one patient, the filter trapped a large venous clot and prevented a PE. The mean length of time to catheter retrieval was 4 days (±1.6 days). All devices were retrieved without complications. No new PEs, major bleeding, or catheter-related blood stream infections were diagnosed. One patient died as a result of a septic shock 3 weeks after removal of the catheter. Conclusions: This pilot study supports the safety of the Angel™ Catheter and provides the basis for a future large pivotal clinical trial.

Incidental venous thromboembolism in oncology patients

Khorana AA, O’Connell C, Agnelli G, Liebman HA, Lee AYY, On Behalf of the Subcommittee on Hemostasis and Malignancy of the SSC of the ISTH. Incidental venous thromboembolism in oncology patients. J Thromb Haemost 2012; 10: 2602–4.

Genetic and Clinical Determinants Influencing Warfarin Dosing in Children With Heart Disease

Warfarin is a common anticoagulant with narrow therapeutic window and variable anticoagulation effects. Single gene polymorphisms in cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase (VKORC1) have been shown to impact warfarin dosing in adults. Insufficient data exists on genetic and clinical factors which influence warfarin dosing in children. Pediatric patients with heart disease who received long-term warfarin therapy were tested for VKORC1 and CYP2C9 polymorphisms. Clinical and demographic data were reviewed in those children who achieved stable therapeutic international normalized ratio (INR). Multiple linear regression modeling was used to assess relationships between stable warfarin doses and genetic or clinical variables. Fifty children were tested for VKORC1 and CYP2C9 polymorphisms; 37 patients (M 26: F 11) had complete data, achieved stable therapeutic INR, and were included in dose variability analysis. There were predominance of white race 73% and male sex 70.3%. The mean age was 9.6 years (1.8-18.6 years). The mean weight was 37.8 kg (7.7-95 kg). Fontan physiology and mechanical cardiac valves were two most common indications for chronic warfarin therapy (25/37 or 67.6%). Twelve patients (32.4%) had ≥ 2 indications for warfarin therapy. Three patients had documented venous or arterial clots, and 5 patients had strokes. Congenital heart disease was present in 29 patients (78.4%), including Fontan physiology (20), complex biventricular physiology (4), and congenital mitral valve disease (5). Acquired heart disease was present in 8 patients (21.6%), including Kawasaki disease with coronary aneurysms (3), acquired mitral valve disease (3), and Marfan syndrome (2). Stable warfarin dose (mg/kg/day) was strongly associated with VKORC1 polymorphism (p < 0.0001) and goal therapeutic INR (p = 0.009). Negative correlations were observed between stable warfarin dose and age, weight, height, and BSA (p = 0.04, 0.02, 0.02, and 0.02 respectively). Factors which did not influence warfarin dose included CYP2C9 polymorphism (p = 0.17), concurrent medications (p = 0.85), sex (p = 0.4), race (p = 0.14), congenital heart disease (p = 0.09), and Fontan physiology (p = 0.76). The gene-dose effect was observed in children with homozygous wild type VKORC1 CC, who required higher warfarin dose compared to those carrying heterozygous TC or homozygous TT (p = 0.028 and 0.0004 respectively). The full multiple linear regression model revealed that VKORC1 genotypes accounted for 47% of dosing variability; CYPC29 accounted for 5%. Overall, the combination of VKORC1, CYP2C9, age, and target INR accounted for 82% of dosing variability. In children with heart disease, VKORC1 genotypes, age, and target INR are important determinants influencing warfarin dosing in children with heart disease. Future warfarin dosing algorithm in children should factor both genetic and clinical factors.

Simple and accurate bedside diagnostic kit for determining haemophilia A and B: a revised version

Simple and accurate bedside diagnostic kit for determining haemophilia A and B: a revised version

The role of prothrombin time (PT) in evaluating green pit viper (Cryptelytrops sp) bitten patients

Viper bites cause consumptive coagulopathy resulting in hypofibrinogenaemia. Whole-blood clotting time is a standard test used to assess bleeding risk. Prothrombin time (PT) and activated partial thromboplastin time (APTT) are better standardised assays that are widely available, but their diagnostic accuracy in viper bites remains unknown. Adult patients presumed bitten by green pit vipers (Cryptelytops sp.) were enrolled. Conventional venous clotting time (VCT), 20min whole-blood clotting time (20WBCT), PT with international normalized ratio (INR) and APTT were determined. A fibrinogen level below 1.0g/litre was used as the gold standard. There were 97 patients. The average age was 46.1 years and 49.5% were men. VCT >30min, INR >1.2 and fibrinogen level <1.0g/litre were found in 9.3, 10.3 and 7.2%, respectively. The sensitivities of VCT >30min, 20WBCT (N=55), INR and APTT were 57.0%, 85.7%, 85.7% and 57.1%, respectively. The respective specificities were 94.4%, 95.8%, 95.6% and 72.4%. Three hypofibrinogenaemic patients who did not receive antivenom because of VCT <30min had persistently normal VCT and went home without clinical bleeding. In conclusion, PT with INR can be an alternative test for evaluation of coagulopathy in green pit viper bitten patients with potentially improved inter-laboratory standardisation.

Anesthesia Dogmas and Shibboleths

Anesthesia Dogmas and Shibboleths

Mouse Models, Risk Factors, and Treatments of Venous Thrombosis

Deep vein thrombosis and pulmonary embolism are collectively called venous thromboembolism (VTE) and are a major cause of morbidity and mortality in the United States and Europe. March is deep vein thrombosis awareness month in the United States, and each year Arteriosclerosis, Thrombosis, and Vascular Biology marks this event with a series of reviews on VTE. This year we have 3 excellent articles on (1) mouse models of venous thrombosis, (2) risk factors for VTE in humans, and (3) the new generation of oral anticoagulants that are available to treat VTE. See accompanying articles on pages 556, 563, and 569 The first review, by Diaz et al1 describes how the use of mouse models has increased our understanding of the mechanisms of initiation, propagation, and resolution of venous clots. The obvious advantage of mice is that we can determine the effect of the loss or mutation of any given gene on thrombosis. Indeed, work with P-selectin knockout mice suggested a role for P-selectin in venous thrombosis that was subsequently confirmed in nonhuman primates. It will be interesting to see whether P-selectin inhibitors will be successfully developed as anticoagulant drugs. Mice have several disadvantages, however, including their small size, their resistance to thrombosis, and the surgical challenges of working with small vessels. Diaz et al1 evaluate 4 inferior vena cava (IVC) thrombosis models. The ferric chloride model induces oxidative damage to the vessel wall that produces an occlusive thrombosis. The advantage of this model is that it is …

Circulation: Clinical Summaries

Circulation: Clinical Summaries

Risk of Blood Clots Higher for Oral Contraceptives With Certain Progestins

This article evaluates the risk of developing venous thrombeombolism among women taking oral contraceptives. A study of women in Denmark revealed that women taking oral contraceptives were three times more likely to develop the condition than women who were not. The risk of venous thrombeombolism and blood clots varied depending on whether the contraceptive was combined progestin-only or intrauterine. Despite the increased risks the researchers note that the benefits of oral contraceptives still outweigh the potential downsides.

Role of Microparticles in Hemostasis and Thrombosis

Abstract SCI-10 Microparticles (MPs) (also known as or microvesicles) are submicron plasma membrane vesicles released from activated or apoptotic cells. Current estimates indicate that MPs are ∼200 nm in diameter. They are formed as membrane blebs and have phosphatidylserine exposed on the surface due to a loss of membrane asymmetry. MPs containing tissue factor (TF) are highly procoagulant. We recently developed an assay to measure TF activity of MPs isolated from plasma. We found that healthy individuals contain low levels of TF+ MPs, but levels are increased in many pathological conditions associated with thrombosis, such as sepsis, cardiovascular disease, sickle cell disease, diabetes mellitus, and cancer. We have analyzed the role of TF+ MPs in various murine models of thrombosis and in different patient populations. Work in collaboration with Bruce and Barbara Furie demonstrated that leukocyte-derived TF+ MPs contributed to microvascular thrombosis in a model of laser injured cremaster arterioles using healthy mice. Further studies have been performed using different murine models of disease. Arterial thrombosis is mostly caused by rupture of atherosclerotic plaques and leads to myocardial infarction and stroke. In hypercholesterolemic LDLR−/− mice we observed increased levels of hematopoietic cell-derived TF+ MPs that were associated with a prothrombotic state. These TF+ MPs may enhance thrombosis after plaque rupture. Indeed, we observed more fibrin deposition in the laser injury model of thrombosis in hypercholesterolemic mice than controls. Importantly, we found that simvastatin reduced TF expression in mononuclear cells and levels of TF+ MPs in the plasma in these hypercholesterolemic mice. Venous thrombosis occurs without significant damage to the vessel wall and is associated with embolization of clot fragments that can block pulmonary arteries. Venous clots appear to form due to changes in the vessel wall, stasis, and/or increased coagulability of the blood. We have analyzed levels of TF+ MPs in murine cancer models and cancer patient samples. We and other have found that tumors release TF+ MPs into the circulation. In one study, we found that pancreatic patients with the highest levels of MP TF activity develop thrombosis. These results suggest that TF+ MPs may enhance venous thrombosis in cancer patients by binding to activated endothelium. Further studies are needed to determine if levels of TF+ MPs in the circulation can be used to identify patients at risk for thrombosis. Disclosures: Mackman: Merck: Consultancy; Daiichi: Consultancy; Daiichi: Research Funding.

Combination Treatment of Essential Thrombocythemia with Hydroxyurea and Anagrelide

Abstract 5177 BACKGROUND: Hydroxyurea and anagrelide are therapeutic options for essential thrombocythemia (ET) with distinct mechanism of actions and side effect profiles. However, therapeutic goals may not be achieveable due to drug intolerance or disease resistance. Here we report our successful clinical experience with combination treatment with hydroxyurea and anagrelide. METHODS: Medical records of six patients who were on the combination treatment for the ET were retrospectively reviewed. All had history of unsuccessful monotherapy with either hydroxyurea or anagrelide. RESULTS: All patients were female with median age of 59.5 years. All were positive for the V617_ jak2 mutation. Two had prior major thromboses (portal vein; ischemic stroke), and one had Raynaud's disease. Reasons for failure of hydroxyurea monotherapy were leukopenia and/or inadequate platelet reduction, while reasons for anagrelide failure were palpitations and orthostasis. Rather than discontinue the primary drug, doses were lowered to a tolerable level and the second agent was added. These patients have been treated with the combination of hydroxyurea and anagrelide for a mean duration of 4.89+ years. Combination regimen achieved 64% reduction of platelet counts (mean best platelet counts during treatment 328×109/L), while maintaining adequate leukocyte counts (range 3.64–7.88 × 109/L). Relatively low daily doses of hydroxyurea (mean 684mg/day) and anagrelide (1.7mg/day) were required. Adverse events noted during the combination therapy were one case with rectal bleeding and two cases of myelofibrosis. One patient returned to monotherapy due to persistent headache to low-dose anagrelide. No arterial or venous thromboses bleeding events have occurred. CONCLUSION: This is the longest follow-up experience of hydroxyurea and anagrelide combination therapy in ET that has been resistant to monotherapy or where high monotherapy doses could not be tolerated. The low-dose combination regimen was able to achieve clinical and laboratory response in all patients with a low incidence of medication side effects. This strategy is made more attractive by data that hydroxyurea may be more effective in prevent arterial events while anagrelide was found more effective in preventing venous clots, but conclusions on superior efficacy of the combination would require formal study. We recommend that rather than substitute for an agent that has had partial success or is causing dose-related side-effects, the dose can be adjusted and a second agent added. Disclosures: No relevant conflicts of interest to declare.