Effects of iloprost in patients with critical limb ischemia: Results of a cohort study from the COPART registry

BACKGROUND

Iloprost has been proposed as an alternative to amputation in Critical Limb Ischemia (CLI) patients when revascularization was unsuccessful or not possible. Nonetheless, there is limited evidence of its benefit. The main objective was to evaluate the effectiveness of iloprost and the secondary objective was to evaluate its safety.

METHODS

In this cohort study including CLI patients from the COPART registry from 2006/10 to 2021/01, patients exposed to iloprost were matched with up to three unexposed patients according to age, sex, and Propensity Score (PS) for exposure to iloprost. The main outcome combined the occurrence of all-cause death and major amputations; survival was assessed over one-year using Kaplan-Meier estimates and Cox model analyses. Major Adverse Cardiovascular Events (MACE) were chosen as the safety outcome; the association with iloprost was estimated using a logistic regression model.

RESULTS

Among 1850 CLI patients, 201 were exposed to iloprost (71.6% men; median age: 72 years vs. 72.1%; 75 years for unexposed). In 134 exposed patients matched to 375 unexposed patients, 14 major amputations and 24 deaths occurred in exposed patients (28.4%) vs. 33 and 46 respectively in the unexposed patients (20.9%). The hazard ratio (HR) was of 1.49 (95% Confidence Interval: 1.01-2.20). The association remained in the subgroup of "no option" patients (HR: 1.74; [1.01-2.20]). Regarding safety, 21/201 (10.7%) exposed patients experienced MACE vs. 146/1649 (9.41%) unexposed patients (unadjusted Odds Ratio [OR]: 1.17 [0.72-1.90]; adjusted OR: 1.23 [0.72-2.11]).

CONCLUSION

The study did not find any benefit of iloprost in CLI patients and even suggested a deleterious effect.

P14.81 Importance of early spectral variations during a longitudinal 60-month follow-up MRI and 1H-MRS in 135 treated glioblastoma patients

BACKGROUND

To better understand glioblastomas tumor metabolism and metabolic responses to chemotherapy, radiotherapy and antiangiogenic treatments during a longitudinal 60-month follow-up MRI and 1H-MRS in 135 treated glioblastoma patients.

MATERIAL AND METHODS

135 patients all biopsied and treated by surgery and STUPP protocol underwent MRI (Sagittal T1, FLAIR, T2*, Diffusion, Perfusion, CoronalT2 and 3DT1 post-Gadolinium) and 1H-MRS (PRESS with multiple TEs: 35ms, 144ms and 288ms on a 6 to 12cm3 volume) exams on 1.5T and 3T GEMS. 92/135 patients underwent resection. MRS data were processed under jMRUI yielding amplitudes, areas under curves and ratios of tCho/tCr, tNAA/tCr, Lip+Lact/tCr, Lact/tCr, Glc/tCr, Glx/tCr and Gln/tCr. Statistical analysis of longitudinal MRI perfusion and spectroscopic data (every 2–3 months above 30 months and 6–9 months over).

RESULTS

Spectroscopic profiles and ratios improve under STUPP protocol and then worsen depending on the percentage of resection. Biopsied patients: a progressive decrease in ratios of tCho/tCr (0–24 months), Lact/tCr (0–18 months) and Glc/tCr (0–18 months) and Glx/tCr (0–12 months) and then increase at respectively 24, 18, 28 and18 months. Resected patients: a progressive decrease in ratios of tCho/tCr (0–9 months), Lact/tCr (0–15 months) and Glc/tCr (0–15 months) and Glx/tCr (0 and 18 months) and then increase at respectively 32, 20, 18 and 24 months. MRI Gadolinium enhancing tumor and necrosis volumes, Diffusion and FLAIR volumes changed less compared to spectroscopic profiles and ratios which do change more.

CONCLUSION

1H-MRS allows non-invasive follow-up of treated glioblastomas tumors. Despite inter-subjects variability, spectroscopic and metabolic changes often come well before clinical deterioration and sometimes before clinical improvement. Therefore, 1H-MRS could be more sensitive and could detect changes earlier than MRI and sometimes is predictive of survival and response to treatment. The analysis of spectral profiles of long survivors is interesting and could help to better understand tumor metabolism and therapeutic responses.

P14.91 Study glycolytic metabolism in 1H-MRS monovoxel in the most aggressive part of 62 glioblastomas before and after 18 months of treatment

BACKGROUND

To study the relationship between glycolytic metabolism, tumor proliferation, survival and treatment response in patients with glioblastoma (GBM).

MATERIAL AND METHODS

Patients: 62 patients with glioblastoma, all having a STUPP Protocol (radiotherapy and concomitant chemotherapy), were selected and separated into 2 groups: Biopsies (30) and resections (32). In total, 269 NMR spectra (PRESS at GE 1.5T and 3T; multi-TEs TE=35ms and TE=144ms) were acquired. Processing: MRS data were processed with jMRUI software and quantitated using HLSVD and QUEST algorithms. Statistical analysis of longitudinal MRS data (every 3 months)

RESULTS

1H-MRS glucose (Glc/tCr) and lactate (Lac/tCr) measurements are highly correlated before the beginning of treatment. This correlation is less obvious after 3, 6, 9 and 12 months of treatment. Proliferation is also strongly correlated with Lactate and Glucose before the beginning of treatment in both groups, whereas these correlations decrease in resected patients.The variability of ratios follow-up is higher in biopsied patients. Tumoral proliferation (tCho/tCr) and Glucose ratio (Glc/tCr) levels decreased along the follow-up. Although, the Lac/tCr ratio progressively decreased, its level remains high until 6 months. After 15 months of treatment, glucose increased although the lactate decreased.

CONCLUSION

The study of glycolytic metabolism in GBM could be used to evaluate the response to treatment. Being able to have a treatment response biomarker at 3 months, especially for patients who could not be resected could help to monitor and adapt treatment. The increase of Glucose at the end of the follow-up shows the interest of spectral and metabolic follow-up of glioblastoma after 18 months of treatment.

P14.100 Measurements of glioblastoma response to recurrence using spectroscopic measurements and MRI volumetry

BACKGROUND

Glioblastoma is the most aggressive and common primary malignant brain tumor in adults. The prognosis of patients with glioblastoma remains poor with a median life expectancy of 15 to 17 months and a survival rate of 5% at five years.Spectroscopy is becoming more and more used and the ratios studied allow in some cases a better prediction, at the recurrence, of the survival between certain ratios such as: Cho / Cr, NAA / Cr, Lac / Cr. Being able to combine all these ratios can allow us to obtain an additional survival index to take into account.This is why our study assesses whether MRS is coupled with volume, it is predictive of survival of the patient at 7 months.

MATERIAL AND METHODS

Population: 30 Patients with glioblastoma treated with the STUPP protocol with and without bevacizumab at recurrence over a period of 36 months. Patients divided into three different groups depending on the type of resection (subtotal (20), partial (13), and biopsy (7)).MRI sequences every 2 months on MRI 3T and 1.5T. Sequences we used: diffusion, T2, T2 *, FLAIR, 3D FLAIR, 3D T1 with gadolinium injection; also monovoxel spectroscopy (TE at 35 and 144 ms, sometimes 288 ms). The volume variations (calculated by Aw.Server and ITK) are evaluated according to the RANO criteria.The MRS ratios (calculated by jMRUI) were clinically used are Cho / Cr (tumor proliferation), NAA / Cr (infiltration) and Lac / Cr (glycolytic metabolism). Longitudinal analyzes of volumes and ratios.

RESULTS

30 patients included in this study. The analysis of the results is that proliferation and / or glycolytic metabolism are more informative and predictive when there is absence of contrast enhancement, hyperperfusion or large volume variation. The global index (choline + lactate / NAA) could be a relevant criterion of judgment to better study the aggressiveness of the tumor and better predict the evolution of tumor volumes and survival. Intra-inter-operator differences on 2 segmentation software.

CONCLUSION

The study shows us and confirms that the widest possible resection is to favor. Spectroscopy ratios vary earlier than the volumetry and give more information on the tumor processes and is sometimes predictive of survival.

P14.122 Integrin α5 is a poor prognostic factor in patients with glioblastoma treated by the Stupp protocol

BACKGROUND

Integrin α5β1 was suggested to be involved in glioblastoma (GBM) aggressiveness through preclinical studies and genomic analysis of several cohorts of patients. However, protein expression data are still missing to confirm this hypothesis. Our aim was to investigate the prognostic value of integrin α5 protein expression level in GBM.

MATERIAL AND METHODS

We retrospectively determined the protein expression level of integrin α5 using immunochemistry in tumors from patients treated in 6 French centers. Paraffin sections of GBM were labeled by immunofluorescence and analyzed by confocal microscopy. The corresponding clinical and survival data have been identified and analyzed. The primary end-point was overall survival (OS).

RESULTS

Out of 297 patients newly diagnosed with GBM between 2006 and 2013, 152 met the inclusion criteria (scheduled for initial treatment with the Stupp protocol, age > 18 years) and 95 tumor samples were suitable for immunohistochemical analysis. The median age is 58 years, (64 men, 34 women). Most of patients received macroscopic (43%) or partial (36%) surgery. In univariate analysis using the Log Rank test, high integrin α5 expression level was associated with poor prognosis (PFS: hazard ratio (HR) = 1,696, p=0,0355; OS: HR=1,598, p = 0,0508). Corresponding median OS were 15,6 versus 19,2 months. Similarly, OS was significantly reduced with age (> 60 years), lower resection degree, higher RPA (recursive partitioning analysis) score and non-methylated MGMT (O-6-methylguanine-DNA methyltransferase) promoter. In the subgroup of patients who received the full initial protocol (temozolomide treatment together with radiotherapy and later as adjuvant treatment; n=58) mean OS was strongly reduced when integrin α5 expression level was high (15,6 versus 22,8 months, p=0,0162) suggesting an impact of integrin signaling on temozolomide response in GBM.

CONCLUSION

Our study validates for the first time that the high protein level expression of α5 integrin is associated with poor prognosis in GBM. It also confirms its potential as a therapeutic target and its likely role in resistance to temozolomide as previously shown in preclinical study.

P14.92 Study of Glutaminergic and Glutamatergic Metabolism in 1H-MRS Monovoxel in the Most Aggressive Part of 62 Glioblastoma Before and After 18 months Treatment

BACKGROUND

To study the relationships between glutaminergic metabolism (Glx/tCr), tumor proliferation (tCho/tCr) and other metabolic activities in patients with glioblastoma (GBM).

MATERIAL AND METHODS

Patients: 62 patients with glioblastoma, all having a STUPP Protocol (radiotherapy and concomitant chemotherapy), were selected and separated into 2 groups: Biopsies (30) and resections (32). In total, 269 NMR spectra (PRESS at GE 1.5T and 3T; multi-TEs TE=35ms and TE=144ms) were acquired. Processing: MRS data were processed with jMRUI software and quantitated using HLSVD and QUEST algorithms. Statistical analysis of longitudinal MRS data (every 3 months)

RESULTS

Glx/tCr and Lac/tCr ratios are correlated with the tumoral proliferation (tCho/tCr) before the beginning of treatment. This correlations decreases over time in biopsied and resected patients. In biopsied patients, the evolution of lactate (Lac/tCr) and Glx (Glx/tCr) ratios is similar along the follow-up with a progressive decrease in tumor proliferation (tCho/tCr). However, in resected patients, the evolution of lactate (Lac/tCr) and Glx (Glx/tCr) ratios is similar until 6 months and differ above: a progressive decrease of Lac/tCr and Glx/tCr until 18 months with a higher level of Glx/tCr.

CONCLUSION

Despite the difficulties to separate glutamine from glutamate (post-processing improvement is ongoing), spectroscopic measurements of Glx changes before clinical deterioration. The increase of Glx is longer (in time) than the Lactate increase after 6 months of treatment in the resected patients could be predictive of the observed increase of tumor proliferation at 12 months of treatment.The study of glutaminergic metabolism in the GBM could be used to evaluate the response to treatment. Being able to predict the increase of tumor proliferation in resected patients could allow a faster treatment adaptation.

[Educational assessment of the first computerized national ranking exam in France in 2016: Opportunities for improvement]

In June 2016, 8124 medical students in their sixth year of graduation passed the first computerized national ranking exam (CNRE) in France after which they will have to choose what medical specialty they will be practicing all their life. We conducted the first educational assessment of this CNRE according to two criteria: the relevance of the questions and the cognitive domain mainly required to answer these questions. We propose two improvements for the future CNRE: promote student reasoning in the multiple choices questions, reduce to 10 the number of multiple choice questions in the progressive clinical cases and increase by 9 their total number (from 18 to 27), and use a majority of mini-clinical cases for isolated multiple choice questions in order to focus students on reasoning instead of simple knowledge restitution.

Up-regulation of Tissue Factor Expression by Platelet-derived Growth Factor in Human Vascular Smooth Muscle Cells in Culture

Human vascular smooth muscle cells (SMCs) isolated from normal adult arteries were investigated for the expression of Tissue Factor (TF) procoagulant activity at their membrane surface and TF antigen in lysed cells. In growing conditions, SMCs expressed high levels of TF activity and antigen. When cells were made quiescent by 72 h of subculture in serum-poor medium, these levels fell to about one third of the initial values. Platelet-derived growth factor BB (PDGF) up-regulated in a dose-dependent manner TF expression with a significant increase (1.8 fold) within five hours. PD 98059, a specific inhibitor of mitogen-activated protein kinase (MAPK) pathway involved in cell response to PDGF, also prevented TF up-regulation. Short-term treatment by Pentoxifylline and dibutyryl cAMP also completely prevented induced TF up-regulation, but remained without effect on baseline levels of quiescent, unstimulated cells. At their effective concentrations, pentoxifylline and dibutyryl cAMP also inhibited the activation of MAPK induced by PDGF. The rapid induction of TF upon growth factor stimulation may be important in circumstances where SMCs proliferate, such as vascular events or vessel development.

[College of the French Vascular Medicine Teachers (CEMV) statement: Arterial Doppler waveforms analysis (simplified Saint-Bonnet classification)]

Lower extremity peripheral artery disease is a frequent disease. Arterial Doppler waveforms analysis is a key element in vascular medicine, especially to diagnose lower peripheral artery disease. Although Doppler waveforms are often used, descriptions are highly heterogeneous. This review presents the simplified Saint-Bonnet classification that is tought to vascular medicine residents in order to homogenize arterial flow description.

[Assessing post-hospitalization therapeutic ranges in elderly patients treated for atrial fibrillation with vitamin k antagonists]

BACKGROUND

In France, anticoagulants are among the most recommended treatments for serious accidents, particularly among the elderly.

OBJECTIVES

The purpose of this study was to evaluate the impact of practical and validated tools designed to reduce the negative effects of vitamin K antagonist (VKA) treatments by assessing patients before and after the tools were implemented.

METHODS

An exhaustive before and after multi-centric cohort study was performed in the Agen territory. The follow-up period corresponded to the six-month period post-hospitalization. The principal criterion was the time in the therapeutic range (TTR) at values of 2 to 3 according to the Rosendaal method.

RESULTS

The overall time spent in the follow-up period before and after the implementation of the tools in 65- and 74-year-old patients was 58% and 64%, respectively (P=0.584). After the treatments, the TTR in the 85- to 90-year-old patients was 71.1%. An increase was observed in the number of subjects with a TTR≥70% after the implementation of the tools according to age, particularly in the 85- to 90-year-old patients (8 vs. 41; [P=0.01]). Prescription help software revealed a tendency of improvement in TTR values from 61% to 68% (P=0.472). In addition, longer therapeutic periods corresponded to longer patient lifespans (r=0.86).

CONCLUSION

This study demonstrates the feasibility and advantages of implementing tools to improve the efficacy of VKA treatment in primary care, particularly for patients from 85 to 90 years old. The results should promote the implementation of this type of treatment method at the national level.

Inhibition of Tissue Factor Synthesis by Disruption of ERK Kinases and PKC Signaling Pathways in Human Vascular SMCs

Tissue Factor (TF), the receptor for plasma VII/VIIa and the initiator of blood coagulation, is inducible in vascular smooth muscle cells (SMCs) by growth factors and bacterial lysopolysaccharides (LPS) and is expressed in vivo after vascular injury. As TF expression is a determinant of the thrombogenicity of vascular lesions, we investigated the signal pathways involved in this process.

Human vascular SMCs were obtained from normal arteries and made quiescent by serum deprivation. Baseline TF antigen and activity were up-regulated by various agonists: fetal calf serum (FCS), LPS, and platelet derived growth factor (PDGF) being the most effectives but with different kinetics. TF expression induced by LPS was transient with a maximum 6 h after stimulation and returned to baseline levels after 24 h whereas TF expression induced by serum or PDGF was sustained for at least 24 h. Rapid and transient activation of Extracellular signal-Regulated Kinase (ERK) was observed after stimulation by PDGF and FCS, but not by LPS. The role of ERK, Ras and protein kinase C activities were investigated using specific inhibitors, PD 98059, manumycin A and calphostin C respectively. For TF induction by LPS, PKC activity was required and the ERK/Ras pathway was not involved. In contrast, the effect of PDGF was strictly ERK and Ras dependent, but partially prevented by PKC inhibitors. TF induction by FCS was ERK dependent but partially Ras and PKC dependent. In conclusion, TF expression appears to be a non-specific response of SMCs to numerous stimuli through multiple signal pathways which differ according to the inducing agent.

Clinical Prediction of Lower Limb Deep Vein Thrombosis in Symptomatic Hospitalized Patients

We evaluated two clinical scores for the prediction of deep venous thrombosis (DVT) in hospitalized patients (Wells’ and Kahn’s). We included 273 patients referred to the vascular exploration unit for the suspicion of DVT. A clinical questionnaire was filled in by the practitioner and the scores were calculated from this form. 66 of the 273 patients had a DVT. When Wells’ score was 3, a DVT was found by duplex echography in 51% patients ; when the score was 0, a DVT was found in 9%. Kahn’s score was not adapted to this population. We then developed a new simple score (cancer, palsy or plaster immobilization, warmth, superficial venous dilation, unilateral pitting edema, other diagnosis). A DVT was found in 76% patients with a score of 3 and in 11% in those with a score of 0. We therefore propose a 6-item score whose main advantages are simplicity and usefulness in routine practice.

Effects of Heparin and Related Sulfated Polysaccharides on Tissue Factor Expression Induced by Mitogenic and Non-mitogenic Factors in Human Vascular Smooth Muscle Cells

Smooth muscle cells (SMCs) of the intima are generally quiescent and non proliferative. Their proliferation due to different stimulations occurs in myointimal hyperplasia and is regularly present in athero-genesis or after transluminal angioplasty leading to vascular occlusive stenosis. In the course of these pathologies, the Tissue Factor (TF) synthesis was upregulated and rapidly expressed at the membrane of the SMCs. Heparin is known to inhibit SMCs proliferation induced by FCS. We evaluated the inhibitory effect of heparin on the expression of TF induced by various mitogenic (FCS, PDGF-BB and EGF) and non-mitogenic (bacterial LPS) agents. Inhibition by heparin of SMCs proliferation induced by the same agonists was also determined.

Quiescent human vascular SMCs from normal adult arteries were treated for 1 h by heparin and related sulfated polysaccharides before stimulation by the agonists. All the agonists up-regulated the expression of TF antigen and activity. TF expression induced by the growth factors was inhibited by heparin (IC 50: 10-30 μg/ml), and other sulfated polysaccharides (IC 50: 1-5 μg/ml). SMCs proliferation, late activation of the extracellular signal-regulated kinases (ERK1/2), and PKC activity were inhibited by heparin (IC 50: 30-50 μg/ml) in SMCs stimulated by FCS but not in SMCs treated by PDGF or EGF. In contrast, heparin had no effect on LPS-induced TF expression nor on LPS-induced PKC activation. These results indicate that, besides its well known effect on SMC proliferation, heparin displays an inhibitory effect on cell mediated blood clotting processes through regulation of the TF expression.

Effect of the Antioxidants Selenium and Beta-carotene on HIV-related Endothelium Dysfunction

Patients infected with HIV are at increased risk of atherosclerosis, and have evidence of endothelium dysfunction. The hypothesis was tested that HIV-related endothelium dysfunction is related to loss of antioxidants. This was done by the supplementation of the antioxidants selenium and beta-carotene. We supplemented the diet of 10 HIV-sero-positive subjects with 100 μg selenium daily, 11 subjects with 30 mg beta-carotene twice daily while 15 subjects were not supplemented. Plasma was obtained at outset and after a year, and tested by ELISA for endothelial cell, platelet and inflammatory markers.

The non-supplemented patients experienced increases in von Wille-brand factor and soluble thrombomodulin (both p < 0.01). There were no changes in any of the indices in the patients taking selenium or beta-carotene.

Increased von Willebrand factor and soluble thrombomodulin in the non-supplemented patients imply increased damage to the endothelium over the year of the study. Therefore we interpret the lack of increase in the patients taking antioxidants as evidence of the protection of the endothelium by these agents.

[Cerebral vasoreactivity: Concordance of breath holding test and acetazolamide injection in current practice: 20 cases of asymptomatic carotid artery stenosis]

INTRODUCTION

Cerebral vasoreactivity (CVR) is the ability of the brain's vascular system to keep cerebral blood inflow stable. Impaired CVR is a risk marker of stroke in patients with asymptomatic carotid stenosis. The gold standard to assess CVR with transcranial ultrasound is acetazolamide (ACTZ) injection. The breath holding test (BHT) might be easier to perform. CVR proved to be efficient in laboratory conditions but not in routine practice.

OBJECTIVES

To study the validity of BHT versus ACTZ in routine practice in a vascular exploration unit in patients with asymptomatic carotid stenosis.

METHODS

Study of concordance of BHT and ACTZ, to assess CVR in patients consecutively explored on the same day.

RESULTS

Eighteen patients with 20 carotid stenosis were included. The temporal window was missing in 20% of cases. Only 11 out of the 20 procedures were analyzed. Concordance was low between BHT and ACTZ to assess CVR (k=0.3714).

CONCLUSION

BHT cannot replace ACTZ injection. It might be a first-step test so that ACTZ injection might be avoided if CVR is normal. Our present results must be confirmed by further study enrolling many more patients.

[Prevalence and prognosis of aspirin resistance in critical limb ischemia patients]

OBJECTIVES

To assess the prevalence and the association between aspirin resistance in critical limb ischemia patients using the VerifyNow^® bed-side platelet test, and occurrence of cardiovascular morbidity and/or death at one year.

MATERIALS AND METHODS

National multicenter prospective observational study related to COPART II centers. From 2010 through 2014, 64 subjects hospitalized for critical limb ischemia and already treated by aspirin before the VerifyNow^® test were included. A VerifyNow^® test>550 ARU was defined as aspirin resistance. Critical limb ischemia was defined according to the TASC I criteria. The primary outcome was a composite including death, acute coronary syndrome, stroke and major amputation during the one-year follow-up period.

RESULTS

In all, 9/64 patients were aspirin resistant, the status was confirmed in one case. The prevalence of aspirin resistance was 14.06%. There was no significant difference between aspirin resistant and aspirin non-resistant groups in terms of cardiovascular history and glycemia status. Neither was there significant difference between the two groups in terms of survival.

CONCLUSION

Aspirin resistance was not predictive of poorer survival in critical limb ischemia patients. However, our population was limited. Considering that a clear definition of aspirin resistance and standardized diagnostic tests are lacking, complementary studies might be useful.

Pigmented skin patches without scleroderma as a predominant clinical symptom revealing systemic sclerosis

Skin induration remains the major clinical symptom of systemic sclerosis (SSc), an autoimmune disease with potentially life-threatening visceral involvement. However, skin induration can be absent in some patients, making the diagnosis difficult to confirm and leading to delay in management. Skin pigmentation abnormalities have been reported in patients with SSc, and can be important to recognize for diagnosis. We report two patients who developed hyperpigmented skin patches without any sign of scleroderma, as a major clinical skin symptom of incipient SSc.

[Paroxysmal nocturnal hemoglobinuria: An unknown cause of thrombosis?]

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired disorder of hematopoietic stem cells. Somatic mutation in the phosphatidylinositol glycan class A (PIG-A), X-linked gene, is responsible for a deficiency in glycosphosphatidylinositol-anchored proteins (GPI-AP). The lack of one of the GPI-AP complement regulatory proteins (CD55, CD59) leads to hemolysis. The disease is diagnosed with hemolytic anemia, marrow failure and thrombosis. Thromboembolic complication occurs in 30% of patient after 10 years of follow-up and is the first event in one out of 10 patients. The two most common sites are hepatic and cerebral veins. These locations are correlated with high risk of death. Currently, these data are balanced with the use of a monoclonal antibody (Eculizumab), which has significantly improved the prognosis with a survival similar to general population after 36 months of follow-up. Anticoagulant treatment is recommended after a thromboembolic event but has no place in primary prophylaxis.