Arterial Clot Research Articles

Upregulation of Thrombo-Inflammatory Pathways May Contribute to Increased Thrombotic Risk in Polycythemia Vera and Essential Thrombocythemia

Thrombosis is a major cause of morbidity and mortality in polycythemia vera (PV) and essential thrombocythemia (ET) patients. Known risk factors for thrombosis include: age > 60 years, history of thrombosis, high leukocyte count and JAK2V617F positivity. Several studies have failed to show correlation between increased platelet count and thrombosis, though qualitative abnormalities in multiple blood cell lineages have been shown. The mechanistic basis of thrombosis in PV/ET, however remains unknown. To better understand the pathophysiology of thrombosis in PV and ET, we studied transcript levels of selected thrombotic, inflammatory and hypoxia inducible factor (HIF) pathway genes in granulocytes and platelets of these patients.Genes selected for the study include: F3 gene encoding tissue factor (TF); P-selectin (SELP); serpin peptidase inhibitor clade E member 1 (SERPINE1, encoding plasminogen activator inhibitor I, PAI1); thrombospondin 1 (THBS1); interleukin 1 receptor associated kinase 1 (IRAK1); interleukin 1 receptor accessory protein (IL1RAP). We also interrogated these HIF regulated genes: vascular endothelial growth factor A (VEGFA) and solute carrier family 2 (SLC2A1, encoding glucose transporter 1). Transcript level of these selected genes in granulocytes and platelets was determined by QT-RT PCR using TaqMan Expression Assays (Applied Biosystems, CA).Thirty-three patients with PV (all JAK2V617F positive), and 12 ET patients (7 JAK2V617F , 3 calreticulin mutated and 1 triple negative) were included in the study. There were 25 females and 20 males with a mean age of 60.7 years. Of these, 23 patients had a history of thrombosis (15 females and 8 males). Fifteen patients had abdominal and 8 had other thromboses, including stroke, deep vein thrombosis, pulmonary embolism, cerebral venous sinus thrombosis or arterial clots in microvasculature. In granulocytes, we observed a higher expression of all these genes in PV/ET patients compared to normal controls. Transcript levels of SELP, THBS1 and IRAK1 were elevated in PV and ET patients with thrombosis, compared to those who did not have thrombosis (Figure 1). In platelets, all the tested genes had higher transcript levels in PV/ET patients compared to controls, except IRAK1, which had lower expression. Thrombotic patients had higher transcripts of F3, SERPINE1, IL1RAP, VEGFA and SLC2A1 than those without thrombosis(Figure 2). We are now comparing TF activity with its F3 transcript and the effects of therapy with hydroxyurea and pegylated interferon on the expression of these genes.TF is a principal initiator of coagulation and we found high levels of F3 transcripts in PV/ET patients by QT-RT PCR. We also found, in a different cohort of PV patients, increased transcripts of F3 in granulocytesby unbiased RNA sequencing. However, monocytes are the principal source of TF (Osterud, Thromb Res. 2010), and indeed, control monocytes we evaluated had higher transcripts of F3 than granulocytes or platelets. Unlike controls, it is possible that granulocytes and platelets may transcribe F3 in PV/ET patients. In ongoing analysis, the expression levels of F3, and TF activity in PV/ET monocytes is being evaluated.We also analyzed the whole transcriptome in a different cohort of PV patients (9 with and 16 without thrombosis) by RNA Seq. In this cohort, granulocyte analysis revealed that 2,025 genes were overexpressed and 2,137 genes downregulated. Functional annotation results are shown in the Table. In PV patients with thrombosis, 644 genes were upregulated and 573 genes downregulated. About 10 % of these upregulated genes are associated with inflammation and coagulation pathways, including SERPINE1.Alternative splicing variants of SELP, THBS1 and IL1RAP were detected. Alternative splicing variants with aberrant expression were found in 884 genes in PV, and 35 genes in PV patients with thrombosis. Analysis of platelets is ongoing.In conclusion, transcripts of thrombo-inflammatory and HIF-regulated genes are increased in granulocytes and platelets in PV and ET patients, which may play a role in increased thrombotic risk. The transcripts of these genes differ in granulocytes and platelets, reflecting the fact that their transcription is tissue specific. The differences in gene expression may identify patients with higher risk for thrombosis and possible therapeutic targets. [Display omitted] [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Intracranial Thrombus Morphology and Composition Undergoes Time-Dependent Changes in Acute Ischemic Stroke: A CT Densitometry Study.

The aim of our study was to assess whether cerebral artery clots undergo time-dependent morphological and compositional changes in acute ischemic stroke. We performed a retrospective chart review of patients admitted within 5 h from symptom onset to three European stroke centers and evaluated non-contrast-enhanced CT (NECT) for hyperdense artery signs (HAS) in 2565 scans. The occlusion site, density of HAS expressed in Hounsfield units (HU), area of HAS, and relative density (rHU) (HU clot/HU non-affected artery) were studied and related to time from symptom onset, clinical severity, stroke etiology, and laboratory parameters. A HAS was present in the middle cerebral artery (MCA) in 185 (7.2%) and further explored. The mean time from symptom onset to CT was 100 min (range 17–300). We found a time-dependent loss of density in the occluded M1 segment within the first 5 h (N = 118, 95% CI [−15, −2], p = 0.01). Further, the thrombus area in the M2 segment decreased with time (cubic trend N = 67, 95% CI [−63, −8], p = 0.02). Overall, and especially in the M2 segment, a lower clot area was associated with higher fibrinogen (−21.7%, 95% CI [−34.8, −5.8], p = 0.009). In conclusion, our results disclosed time-dependent changes of intracranial thrombi with regard to occlusion site, density and area.

Single-Phase Versus Multiphase CT Angiography in Middle Cerebral Artery Clot Detection—Benefits for Less Experienced Radiologists and Neurologists

CT angiography (CTA) is recommended as a standard of stroke imaging. We investigated accuracy and precision of standard or single-phase CTA as compared with novel technique or multiphase CTA in clot detection in the middle cerebral artery. Twenty single-phase CTA and twenty multiphase CTA with prevailing M2 occlusion were assessed by 10 radiologists and 10 neurologists blinded to clinical information (7 less experienced and 3 experienced). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated as compared with reading by two seniors. Reliability was calculated using Krippendorff's alpha (K-alpha). Sensitivity, specificity, PPV, and NPV of single-phase CTA compared with multiphase CTA for M2 clot presence were, respectively, .86, .75, .90, and .67 versus .88, .82, .92, and .72. For secondary or distal clots, sensitivity, specificity, PPV, and NPV of single-phase CTA compared with multiphase CTA were .41, .83, .50, and .78 versus .65, .77, .71, and .67. Agreement increased significantly in favor of multiphase CTA for detection of primary clots from moderate (.43) to substantial (.65) in less experienced radiologists and from slight (.10) to moderate (.30) in less experienced neurologists. Agreement significantly increased for distal or secondary clot detection in favor of multiphase CTA from fair (.24) to moderate (.49) in experienced radiologists and from slight (.12) to moderate (.46) in experienced neurologists. Multiphase CTA is a reliable imaging tool in M2 clot detection and might represent a beneficial imaging tool in clot detection for less experienced physicians.

Non-Association of Methylenetetrahydrofolate Reductase (MTHFR) Polymorphisms with Homocysteine Levels, Venous or Arterial Thromboses in 1,141 North-Central Appalachian Patients

<p class="cco-body"><strong><span lang="EN-GB">Objectives</span></strong><span lang="EN-GB">: MTHFR polymorphism testing has been used by clinicians for thrombophilia risk assessment. We questioned the utility of such testing.</span></p><p class="cco-body"><strong><span lang="EN-GB">Methods</span></strong><span lang="EN-GB">: 1,141 patients age 18 and above had MTHFR testing for both C677T and A1298C polymorphisms, 2006 through 2012. Available plasma homocysteine levels were obtained and ICD-9 billing codes were grouped to identify venous or arterial clots in these patients.</span></p><p class="cco-body"><strong><span lang="EN-GB">Results</span></strong><span lang="EN-GB">: 901 women and 240 men were tested; median age in women was 33 years (range 18-86); median age in men was 47 years (range 18-83). County of residence mapping confirmed that this MTHFR tested population was from north-central Appalachia. Only 144 (13%) of the 1,141 patients had no polymorphism at either the C677T or the A1298C locus; only 4 patients (0.4%) had 3 or more polymorphisms; 993 patients (87%) had either one or two polymorphisms. </span></p><p class="cco-body"><span lang="EN-GB">We found polymorphism frequency pattern similar in both sexes. Although men had higher homocysteine levels, MTHFR polymorphisms did not associate with homocysteine levels in either sex. In 901 women tested, the ICD-9 coded incidence of arterial clots was 20%, and of venous clots was 21%; in 240 men tested, the incidence of arterial clots was 48% and of venous clots was 40%. MTHFR polymorphisms did not associate with arterial or venous clots in either sex. </span></p><p class="cco-body"><span lang="EN-GB">Based on CPT billing codes, a minimal cost estimate was $137,000 for performing these 1,141 MTHFR tests.</span></p><p class="cco-body"><strong><span lang="EN-GB">Conclusions</span></strong><span lang="EN-GB">: MTHFR testing was costly and did not add useful information during thrombophilia evaluation in this patient population. </span></p>

Anticoagulation manager: development of a clinical decision support mobile application for management of anticoagulants.

Patients with certain clotting disorders or conditions have a greater risk of developing arterial or venous clots and downstream embolisms, strokes, and arterial insufficiency. These patients need prescription anticoagulant drugs to reduce the possibility of clot formation. However, historically, the clinical decision making workflow in determining the correct type and dosage of anticoagulant(s) is part science and part art. To address this problem, we developed Anticoagulation Manager, an intelligent clinical decision workflow management system on iOS-based mobile devices to help clinicians effectively choose the most appropriate and helpful follow-up clotting tests for patients with a common clotting profile. The app can provide physicians guidance to prescribe the most appropriate medication for patients in need of anticoagulant drugs. This intelligent app was jointly designed and developed by medical professionals in CDC and engineers at Georgia Tech, and will be evaluated by physicians for ease-of-use, robustness, flexibility, and scalability. Eventually, it will be deployed and shared in both physician community and developer community.

Dietary Nitrate and the Epidemiology of Cardiovascular Disease: Report From a National Heart, Lung, and Blood Institute Workshop.

In view of continuing unanswered questions regarding the geographical and demographic distribution of cardiovascular disease, and recent discoveries about the effects of dietary nitrate on cardiovascular physiology, the National Heart, Lung, and Blood Institute (NHLBI) convened a workshop to

Factors influencing intracranial vessel densities on unenhanced computed tomography: differences between hemispheres

The aim was to identify the factors influencing intracranial vessel density (VD). The Hounsfield units of the dense vessel and the contralateral side were measured in 34 patients with arterial clots, 20 with venous clots, and 196 without clots and correlated with skull thickness, density and dimensions, gender, age, red blood cell count (RBC), hemoglobin (HB), hematocrit (HT), creatinine, and sodium. Positive correlations were found between VD and HT, RBC, HB, creatinine, and occipital bone density. Density differences between the right and left intracranial vessels were more accurate (sensitivity/specificity/accuracy=0.91/0.93/0.93 and 0.75/0.87/0.85, respectively) for detecting clots than VD alone. HT, RBC, and HB are the main factors that correlate with VD.

Attenuation of EPA and DHA‐Mediated Platelet Inhibition Effects Following Heterogeneous Agonist Treatment

Agonist‐induced platelet activation following vascular damage is a critical event for the propagation of thrombi formed as a part of either hemostasis or thrombosis. Several studies have indicated this activation can be impaired after platelet membrane enrichment with the polyunsaturated omega‐3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). This attenuated platelet function represents a potential mechanism behind the anti‐thrombotic benefits of EPA and DHA observed in many human trials. However, nearly all platelet studies with EPA and DHA examined the alterations to platelet activation in response to a single agonist, rather than with multiple agonists that mimic the more complex heterogeneous environment of a developing arterial clot. We therefore asked if high levels of EPA and DHA could still inhibit platelet activation if platelets were stimulated with a combination of agonists designed to simulate the activating conditions found in the thrombus inner core (using thrombin and collagen) or outer shell (using ADP and thromboxane A2). To test this question, we treated platelets with EPA and DHA concentrations in vitro that raise the membrane content of both fatty acids to levels analogous to subjects taking EPA and DHA supplements. After this modification, the platelets were stimulated with the agonist combinations and measured for an activation response. Surprisingly, inherent measures of platelet activation using these agonist combinations, including adhesion, aggregation, granule release, and integrin activation were either only mildly affected or non‐significantly altered after EPA and DHA membrane enrichment. We also tested the ability of the core agonist combination to stimulate platelet‐derived thrombin generation, a catalytic process thought to be necessary for rapid thrombus core development. Contrary to the other measures of platelet function, thrombin generation was still consistently impaired by elevated EPA and DHA levels. We conclude that elevated levels of EPA and DHA in the developing clot environment do not readily inhibit most events of platelet activation. Instead, the impairment of amplified thrombin generation in the platelet‐rich arterial clot may provide a more likely candidate for how EPA and DHA prevent detrimental cardiovascular events.Support or Funding InformationResearch reported in this abstract was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20GM103443, a South Dakota/National Science Foundation EPSCoR RII Track 1 grant, the Sanford Program for Undergraduate Research, and an American Physiological Society Undergraduate Summer Research Fellowship.

Technical Results of Vacuum-Assisted Thrombectomy for Arterial Clot Removal in Patients with Acute Limb Ischemia

PurposeTo assess the efficacy and safety of a vacuum-assisted thrombectomy (VAT) catheter system for treating patients with acute limb ischemia (ALI). Materials and MethodsA retrospective study evaluated VAT systems (Penumbra, Alameda, California) in a consecutive series of 30 patients with ALI. ALI was defined as clinical symptoms within 2 weeks of presentation. The primary endpoint was improvement in blood flow across a lesion by improvement in Thrombolysis in Myocardial Infarction (TIMI) score that was adapted to peripheral arteries. Concomitant balloon angioplasty or stent placement in addition to VAT was considered a complementary treatment. Additional thrombectomy treatments, such as thrombolysis and mechanical thrombectomy, were considered technical failures. Target lesions were grouped anatomically into above-the-knee (ATK) or below-the-knee (BTK) lesions. ResultsIn 30 patients, 33 lesions (ATK, n = 13; BTK, n = 20) were treated. No complications were attributed to the VAT systems. The primary endpoint was obtained in 24/33 (72.7%) lesions (BTK, 17/20 [85.0%]; ATK, 7/13 [53.9%]; P = .050 by χ2 test). TIMI scores were similar at baseline but differed after VAT between the ATK and BTK groups (P < .025 by t test). ATK lesions required more concomitant angioplasty or stent placement, or both (P < .015 by χ2 test). ConclusionsVAT is a safe, technically successful short-term therapeutic option for thrombus removal in patients with ALI.

Hyperdense Artery Sign, Clot Characteristics, and Response to Intravenous Thrombolysis in Han Chinese People with Acute Large Arterial Infarction

Whether the presence of hyperdense artery sign (HAS) correlates with clot characteristics and response to intravenous thrombotic therapy (IVT) remains to be determined. Given that the existent literature was mainly from the Western nations, the current study aimed to examine the relationships among HAS, clot characteristics, and outcome of IVT in a Han Chinese sample in Taiwan. The specific objectives are (1) to correlate HAS with clot characteristics and (2) to explore relationships between HAS and effectiveness/complication of IVT. We enrolled 75 patients treated with IVT following acute large arterial infarctions. All patients had a baseline brain computed tomography and a follow-up image at 24 hours after thrombolysis. Correlations were explored between HAS and clot characteristics. Multivariable logistic regressions were employed to examine the relationships between HAS and response to IVT at 24 hours, including early improvement and all forms of intracerebral hemorrhage (ICH). In this Han Chinese sample in Taiwan, 50.7% of the patients had HAS and 64% had early improvements following IVT. Those with HAS tended to have clots lodging at main trunks of cerebral arteries but no significant associations were found between HAS and stroke etiology. In multivariable logistic regressions, HAS predicted neither early improvement nor ICH complication. Instead of clot etiology, we found that it might be clot location that correlated with HAS. HAS was not associated with early improvement or ICH complication after IVT in this Han Chinese sample. We also showed that some other patient characteristics were likely to influence outcomes of IVT, which warrant clinical attention.

N-terminal Pro-brain Natriuretic Peptide, High-sensitivity Troponin and Pulmonary Artery Clot Score as Predictors of Right Ventricular Dysfunction in Echocardiography

We investigated the ability of cardiac biomarkers and total pulmonary artery (PA) clot score to predict right ventricular dysfunction (RVD) on admission and at seven-month follow-up in subjects with acute pulmonary embolism (APE). Sixty-three normotensive patients with APE were divided into two groups: patients with (n= 32, age 58±19 years) and without (n=31, age 55±16 years) echocardiographic RVD. Transthoracic echocardiography (TTE), N-terminal pro-brain natriuretic peptide (NT-proBNP), and high-sensitivity troponin T (hsTnT) were assessed upon arrival and repeated at seven months. Total PA clot score was determined on admission. The age- and sex dependent NT-proBNP on admission, on day 5, and at seven months exhibited the best sensitivity (admission 94%, day 5 100%, seven months 100%) and negative predictive value (NPV) (89%, 100%, 100%) for detecting RVD. Six patients (10%) had persistent RVD at seven months. Total PA clot score showed only low to moderate sensitivity (77%) and PPV (7%) for detection of RVD at seven months. Normal age- and sex dependent NT-proBNP on admission or measured five days later seems to be useful in exclusion of RVD at follow up. Total PA clot score shows only to be of modest benefit for predicting persistent RVD.

A Study on Hereditary Thrombophilia and Stroke in a Cohort from Sri Lanka

Thrombophilia is an enhanced tendency of arterial or venous blood clot formation. The frequently assessed hereditary thrombophilia mutations associated with stroke are methylenetetrahydrofolate reductase (MTHFR) c.677C>T, Factor V (F5) c.1691G>A (Leiden), and prothrombin (F2) c.20210G>A. The aim of this study was to describe the prevalence of the 3 mutations in ischemic stroke patients in Sri Lanka. A database of clinical details and genetic test results of stroke patients referred for thrombophilia screening from June 2006 to April 2014 was maintained prospectively and analyzed retrospectively. A total of 400 ischemic stroke patients (319 arterial, 66 venous, and 15 location unreported) were screened for hereditary thrombophilia. Patients with the MTHFR c.677C>T, F5 c.1691G>A, and F2 c.20210G>A mutations were 17.3%, 3.3%, and .5% of the total cohort, respectively. F5 mutation was present in a statistically significant number of patients with venous thrombosis (P = .005) compared to patients with arterial thrombosis. The MTFHR and F2 mutations showed no such significant association. The mean age of patients with MTHFR, F5, and F2 mutations was 29 (±15), 34 (±11), and 38 (±5.6) years, respectively. MTHFR c.677C>T is the predominant mutation and the only mutation that had patients with the homozygous mutant genotype. Venous thrombosis showed a significant association with the F5 c.1691G>A mutation.

Thrombelastography does not predict clinical response to rtPA for acute ischemic stroke.

Thrombelastography (TEG) measures coagulation in venous blood. We hypothesized that TEG, by reflecting clot subtype and ex vivo fibrinolysis, might predict fibrinolytic response to tPA as reflected by rapid clinical improvement or hemorrhagic transformation of the infarct. 171 acute ischemic stroke patients treated with tPA were prospectively enrolled. Venous blood for TEG was drawn before and 10 min after tPA bolus. We measured rapid clinical improvement (RCI = 8 point improvement on NIHSS or total NIHSS of 0, 1 at 36 h), Hemorrhagic transformation (HT = any blood on imaging within 36 h), and hyperdense middle cerebral artery sign (HDMCA = biomarker for erythrocyte-rich clot). Multivariable regression models compared TEG parameters after adjusting for potential confounders. No differences in pre- or post-tPA TEG were found between patients with or without RCI. Also, there was no correlation between TEG and HDMCA. Clotting was slightly prolonged in patients with HT (p = 0.046). We failed to find a robust association between TEG and clinical response to tPA. It is likely that arterial clot lysis is determined by factors unrelated to coagulation status as measured by TEG in the venous circulation. It is unlikely that TEG will be useful to predict clinical response to tPA, but may help predict bleeding.

Initial experience of coiling cerebral aneurysms using the new Comaneci device

We present our initial patient experience with an innovative temporary bridging device, the Comaneci (Rapid Medical, Israel), to assist in the coiling of cerebral aneurysms. The Comaneci device confers the...

COMPARISON BETWEEN ANTICOAGULATION ALONE AND THROMBOLYSIS PLUS ANTICOAGULATION ON CLOT BURDEN AND RIGHT VENTRICULAR FUNCTION DURING HOSPITALIZATION IN NORMOTENSIVE ACUTE PULMONARY EMBOLISM PATIENTS WITH RIGHT VENTRICULAR DYSFUNCTION

To compare the effects between thrombolysis plus anticoagulation therapy and anticoagulation alone therapy on pulmonary artery (PA) clot burden and right ventricular (RV) function during hospitalization in normotensive acute pulmonary embolism (APE) patients with RV dysfunction. A total of 80

Breaking up is hard to do: tenecteplase in acute stroke

Stroke is a leading cause of death and disability worldwide, with few effective acute treatments. For patients with ischaemic stroke who present promptly to a properly equipped hospital and receive intravenous alteplase within 4·5 h, chance of regaining excellent functional outcome is greatly increased. 1 Lees KR Bluhmki E von Kummer R et al. Time to treatment with intravenous alteplase and outcome in stroke: an updated pooled analysis of ECASS, ATLANTIS, NINDS, and EPITHET trials. Lancet. 2010; 375: 1695-1703 Summary Full Text Full Text PDF PubMed Scopus (1598) Google Scholar The treatment effect decays rapidly with time, and patients with larger clot burden or more severe strokes often do not respond to alteplase. Many attempts have been made to determine whether alternative drugs or devices might be more effective than alteplase, but breaking up arterial clots has proven hard to do. Alteplase versus tenecteplase for thrombolysis after ischaemic stroke (ATTEST): a phase 2, randomised, open-label, blinded endpoint studyNeurological and radiological outcomes did not differ between the tenecteplase and alteplase groups. Evaluation of tenecteplase in larger trials of patients with acute stroke seems warranted. Full-Text PDF

Abstract T P57: TEG Does Not Correlate with Clot Subtype or Clinical Response to tPA

Background: Thromboelastography (TEG) measures coagulation status in venous blood. tPA thrombolysis is affected by multiple variables including whether clots are erythrocyte or platelet-rich. We hypothesized that TEG would correlate with clot subtype and response to tPA including rapid clinical improvement (RCI), recanalization, and hemorrhagic transformation (HT). Methods: 176 acute ischemic stroke patients between 11/09 and 06/14 treated with tPA were prospectively enrolled. Venous blood for TEG was drawn before and 10 minutes after tPA bolus. Pre-tPA measures of speed and strength of clot formation (R, Delta, K, Angle, MA, and G) and post-tPA measure of clot lysis (LY30) were analyzed. Hyperdense artery (HDA) on CT was a biomarker for erythrocyte-rich clot. RCI was defined as 8 point improvement on NIHSS or total NIHSS of 0,1 at 36 hours. HT was defined as any blood on follow up imaging within 36 hours. Recanalization was defined as resolution of baseline vascular occlusion on follow up CT or MR angiogram within 36 hours. Multivariable linear regression models compared TEG parameters after adjusting for potential confounding and interactive effects. Results: No differences in pre- or post-tPA TEG were found between patients with (n=32) or without (n=102) RCI. Also, there was no correlation between TEG and HDA on CT. Clot strength was decreased in patients with recanalization (lower MA and G, p = 0.02 and p = 0.03). Clotting was slightly prolonged (longer delta, p = 0.046) in patients with HT. Discussion: Our data do not show a robust association between TEG and clot subtype or clinical response to tPA. It is likely that arterial clot lysis is determined by factors unrelated to coagulation status as measured by TEG in the venous circulation. Though we found a correlation between TEG and recanalization, the number of patients with recanalization data was too small to detect an effect on clinical outcome. Similar to our previous findings, speed of clot formation may be related to risk of bleeding. Conclusion: It is unlikely that TEG will be useful in guiding tPA therapy. Future research should focus on local arterial influences on clot lysis. Further study of TEG in hemorrhage is indicated.

Elastic Behavior and Platelet Retraction in Low- and High-Density Fibrin Gels

Fibrin is a biopolymer that gives thrombi the mechanical strength to withstand the forces imparted on them by blood flow. Importantly, fibrin is highly extensible, but strain hardens at low deformation rates. The density of fibrin in clots, especially arterial clots, is higher than that in gels made at plasma concentrations of fibrinogen (3–10 mg/mL), where most rheology studies have been conducted. Our objective in this study was to measure and characterize the elastic regimes of low (3–10 mg/mL) and high (30–100 mg/mL) density fibrin gels using shear and extensional rheology. Confocal microscopy of the gels shows that fiber density increases with fibrinogen concentration. At low strains, fibrin gels act as thermal networks independent of fibrinogen concentration. Within the low-strain regime, one can predict the mesh size of fibrin gels by the elastic modulus using semiflexible polymer theory. Significantly, this provides a link between gel mechanics and interstitial fluid flow. At moderate strains, we find that low-density fibrin gels act as nonaffine mechanical networks and transition to affine mechanical networks with increasing strains within the moderate regime, whereas high-density fibrin gels only act as affine mechanical networks. At high strains, the backbone of individual fibrin fibers stretches for all fibrin gels. Platelets can retract low-density gels by >80% of their initial volumes, but retraction is attenuated in high-density fibrin gels and with decreasing platelet density. Taken together, these results show that the nature of fibrin deformation is a strong function of fibrin fiber density, which has ramifications for the growth, embolization, and lysis of thrombi.

PAI-1 mediates the antiangiogenic and profibrinolytic effects of 16K prolactin.

The N-terminal fragment of prolactin (16K PRL) inhibits tumor growth by impairing angiogenesis, but the underlying mechanisms are unknown. Here, we found that 16K PRL binds the fibrinolytic inhibitor plasminogen activator inhibitor-1 (PAI-1), which is known to contextually promote tumor angiogenesis and growth. Loss of PAI-1 abrogated the antitumoral and antiangiogenic effects of 16K PRL. PAI-1 bound the ternary complex PAI-1-urokinase-type plasminogen activator (uPA)-uPA receptor (uPAR), thereby exerting antiangiogenic effects. By inhibiting the antifibrinolytic activity of PAI-1, 16K PRL also protected mice against thromboembolism and promoted arterial clot lysis. Thus, by signaling through the PAI-1-uPA-uPAR complex, 16K PRL impairs tumor vascularization and growth and, by inhibiting the antifibrinolytic activity of PAI-1, promotes thrombolysis.

Management of acute limb ischemia in the pediatric population

Acute limb ischemia (ALI) in pediatric patients is rare but may lead to limb loss and life-long complications. This study reviewed the experience of a Canadian tertiary pediatric center with the medical and operative management ofALI. The medical records of inpatients diagnosed with ALI of the upper or lower limb between 1999 and 2012 were reviewed. Patient demographics, arterial clot site and etiology, intervention, anticoagulation type and duration, and short-term and long-term complications were analyzed. A total of 151 patients (45% female) presented with signs of limb ischemia, of whom 38% were aged<30days, 46% were between 1 and 12months, and 16% were between 1 and 18years. Ninety-four percent of those injuries involved the lower limbs. Ninety-one percent were due to vessel catheterization, 5% were idiopathic, 1% were congenital, and 4% traumatic. Ninety-four percent were managed nonoperatively. Patients were treated with a combination of thrombolysis, unfractionated or low-molecular-weight heparin, aspirin or warfarin, or both (duration, 1 day-13 years). All patients were monitored after discharge at our institution or at their referring hospital (average, 3.4± 2.8years). Fifteen percent had complications related to ALI or anticoagulation (most commonly limb length or thigh circumference discrepancy, or intracranial hemorrhage). Nineteen percent of patients died of unrelated causes (sepsis, multiorgan dysfunction, or cardiac failure). In contrast with adults, ALI in children can generally be managed nonoperatively with anticoagulation, likely because of their greater ability to develop arterial collaterals. Long-term follow-up by a multidisciplinary team of pediatric and surgical specialists and allied health professionals is integral to achieving a successful outcome in children with ALI.