SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Thrombus

171

Fibrin polymerization is a necessary part of hemostasis but clots can obstruct blood vessels and cause heart attacks and strokes. The polymerization reactions are specific and controlled, involving strong knob-into-hole interactions to convert soluble fibrinogen into insoluble fibrin. It has long been assumed that clots and thrombi are stable structures until proteolytic digestion. On the contrary, using the technique of fluorescence recovery after photobleaching, we demonstrate here that there is turnover of fibrin in an uncrosslinked clot. A peptide representing the knobs involved in fibrin polymerization can compete for the holes and dissolve a preformed fibrin clot, or increase the fraction of soluble oligomers, with striking rearrangements in clot structure. These results imply that in vivo clots or thrombi are more dynamic structures than previously believed that may be remodeled as a result of local environmental conditions, may account for some embolization, and suggest a target for therapeutic intervention.

Concepts: Protein, Stroke, Coagulation, Polymer chemistry, Fibrin, Hemostasis, Thrombus, Monomer

169

Atrial fibrillation, the commonest cardiac arrhythmia, predisposes to thrombus formation and consequently increases risk of ischaemic stroke. Recent years have seen approval of a number of novel oral anticoagulants. Nevertheless, warfarin and aspirin remain the mainstays of therapy. It is widely appreciated that both these agents increase the likelihood of bleeding: there is a popular conception that this risk is greater with warfarin. In fact, well-managed warfarin therapy (INR 2-3) has little effect on bleeding risk and is twice as effective as aspirin at preventing stroke. Patients with atrial fibrillation and a further risk factor for stroke (CHA2DS2-VASc >0) should therefore either receive warfarin or a novel oral agent. The remainder who are at the very lowest risk of stroke are better not prescribed antithrombotic therapy. For stroke prevention in atrial fibrillation; aspirin is rarely the right choice.

Concepts: Myocardial infarction, Stroke, Atrial fibrillation, Thrombosis, Warfarin, Thrombus, Anticoagulant, Heparin

145

Data on left atrial/left atrial appendage (LA/LAA) thrombus resolution after non-vitamin K antagonist (VKA) oral anticoagulant treatment are scarce. The primary objective of X-TRA was to explore the use of rivaroxaban for the resolution of LA/LAA thrombi in patients with nonvalvular atrial fibrillation (AF) or atrial flutter, with the CLOT-AF registry providing retrospective data after standard-of-care therapy in this setting.

Concepts: Stroke, Atrial fibrillation, Warfarin, Thrombus

92

Background Edoxaban is a direct oral factor Xa inhibitor with proven antithrombotic effects. The long-term efficacy and safety of edoxaban as compared with warfarin in patients with atrial fibrillation is not known. Methods We conducted a randomized, double-blind, double-dummy trial comparing two once-daily regimens of edoxaban with warfarin in 21,105 patients with moderate-to-high-risk atrial fibrillation (median follow-up, 2.8 years). The primary efficacy end point was stroke or systemic embolism. Each edoxaban regimen was tested for noninferiority to warfarin during the treatment period. The principal safety end point was major bleeding. Results The annualized rate of the primary end point during treatment was 1.50% with warfarin (median time in the therapeutic range, 68.4%), as compared with 1.18% with high-dose edoxaban (hazard ratio, 0.79; 97.5% confidence interval [CI], 0.63 to 0.99; P<0.001 for noninferiority) and 1.61% with low-dose edoxaban (hazard ratio, 1.07; 97.5% CI, 0.87 to 1.31; P=0.005 for noninferiority). In the intention-to-treat analysis, there was a trend favoring high-dose edoxaban versus warfarin (hazard ratio, 0.87; 97.5% CI, 0.73 to 1.04; P=0.08) and an unfavorable trend with low-dose edoxaban versus warfarin (hazard ratio, 1.13; 97.5% CI, 0.96 to 1.34; P=0.10). The annualized rate of major bleeding was 3.43% with warfarin versus 2.75% with high-dose edoxaban (hazard ratio, 0.80; 95% CI, 0.71 to 0.91; P<0.001) and 1.61% with low-dose edoxaban (hazard ratio, 0.47; 95% CI, 0.41 to 0.55; P<0.001). The corresponding annualized rates of death from cardiovascular causes were 3.17% versus 2.74% (hazard ratio, 0.86; 95% CI, 0.77 to 0.97; P=0.01), and 2.71% (hazard ratio, 0.85; 95% CI, 0.76 to 0.96; P=0.008), and the corresponding rates of the key secondary end point (a composite of stroke, systemic embolism, or death from cardiovascular causes) were 4.43% versus 3.85% (hazard ratio, 0.87; 95% CI, 0.78 to 0.96; P=0.005), and 4.23% (hazard ratio, 0.95; 95% CI, 0.86 to 1.05; P=0.32). Conclusions Both once-daily regimens of edoxaban were noninferior to warfarin with respect to the prevention of stroke or systemic embolism and were associated with significantly lower rates of bleeding and death from cardiovascular causes. (Funded by Daiichi Sankyo Pharma Development; ENGAGE AF-TIMI 48 ClinicalTrials.gov number, NCT00781391 .).

Concepts: Blood, Heart, Stroke, Atrial fibrillation, Warfarin, Thrombus, Atrial flutter, Embolism

82

To the Editor: In the Rivaroxaban Once Daily Oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation (ROCKET AF), investigators found that rivaroxaban was noninferior to warfarin in the prevention of stroke and systemic embolism in patients with atrial fibrillation.(1) In December 2014, four years after completion of the trial, the Food and Drug Administration (FDA) issued a recall notice for a medical device correction of the Alere INRatio Monitor System (formally known as the Hemosense INRatio device). The recall correction notice was issued because the FDA-approved and European . . .

Concepts: Stroke, Atrial fibrillation, Coagulation, Warfarin, Thrombus, Anticoagulant, Vitamin K, Embolism

81

Clinical guidelines recommend early discharge of patients with low-risk pulmonary embolism (LRPE). This study measured the overall impact of early discharge of LRPE patients on clinical outcomes and costs in the Veterans Health Administration population. Adult patients with ≥1 inpatient diagnosis for pulmonary embolism (PE) (index date) between 10/2011-06/2015, continuous enrollment for ≥12 months pre- and 3 months post-index date were included. PE risk stratification was performed using the simplified Pulmonary Embolism Stratification Index. Propensity score matching (PSM) was used to compare 90-day adverse PE events (APEs) [recurrent venous thromboembolism, major bleed and death], hospital-acquired complications (HACs), healthcare utilization, and costs among short (≤2 days) versus long length of stay (LOS). Net clinical benefit was defined as 1 minus the combined rate of APE and HAC. Among 6,746 PE patients, 95.4% were men, 22.0% were African American, and 1,918 had LRPE. Among LRPE patients, only 688 had a short LOS. After 1:1 PSM, there were no differences in APE, but short LOS had fewer HAC (1.5% vs 13.3%, 95% CI: 3.77-19.94) and bacterial pneumonias (5.9% vs 11.7%, 95% CI: 1.24-3.23), resulting in better net clinical benefit (86.9% vs 78.3%, 95% CI: 0.84-0.96). Among long LOS patients, HACs (52) exceeded APEs (14 recurrent DVT, 5 bleeds). Short LOS incurred lower inpatient ($2,164 vs $5,100, 95% CI: $646.8-$5225.0) and total costs ($9,056 vs $12,544, 95% CI: $636.6-$6337.7). LRPE patients with short LOS had better net clinical outcomes at lower costs than matched LRPE patients with long LOS.

Concepts: Pneumonia, Pulmonary embolism, Hematology, Thrombus, Vein, Ape, Propensity score, Deep vein thrombosis

46

The prevalence of both atrial fibrillation (AF) and diabetes mellitus (DM) are rising, and these conditions often occur together. Also, DM is an independent risk factor for stroke in patients with AF. We aimed to examine the safety and efficacy of rivaroxaban vs warfarin in patients with nonvalvular AF and DM in a prespecified secondary analysis of the ROCKET AF trial.

Concepts: Diabetes mellitus, Stroke, Atrial fibrillation, Coagulation, Warfarin, Thrombus, Anticoagulant, Vitamin K

43

Thrombin is a serine protease and regulator of haemostasis that plays a critical role in the formation of obstructive blood clots, or thrombosis, that is a life-threatening condition associated with numerous diseases such as atherosclerosis and stroke. To detect thrombi in living animals, we design and conjugate thrombin-sensitive peptide substrates to the surface of nanoparticles. Following intravenous infusion, these ‘synthetic biomarkers’ survey the host vasculature for coagulation and in response to substrate cleavage by thrombin, release ligand-encoded reporters into the host urine. To detect the urinary reporters, we develop a companion 96-well immunoassay that utilizes antibodies to bind specifically to the ligands, thus capturing the reporters for quantification. Using a thromboplastin-induced mouse model of pulmonary embolism, we show that urinary biomarker levels differentiate between healthy and thrombotic states and correlate closely with the aggregate burden of clots formed in the lungs. Our results demonstrate that synthetic biomarkers can be engineered to sense vascular diseases remotely from the urine and may allow applications in point-of-care diagnostics.

Concepts: Blood, Myocardial infarction, Stroke, Coagulation, Warfarin, Hematology, Thrombus, Embolism

39

 To assess the risk of pulmonary embolism, ischaemic stroke, and myocardial infarction associated with combined oral contraceptives according to dose of oestrogen (ethinylestradiol) and progestogen.

Concepts: Sexual intercourse, Myocardial infarction, Atherosclerosis, Stroke, Combined oral contraceptive pill, Thrombus, Ischemia, Embolism

33

Blood clotting is a precise cascade engineered to form a clot with temporal and spatial control. Current control of blood clotting is achieved predominantly by anticoagulants and thus inherently one-sided. Here we use a pair of nanorods (NRs) to provide a two-way switch for the blood clotting cascade by utilizing their ability to selectively release species on their surface under two different laser excitations. We selectively trigger release of a thrombin binding aptamer from one nanorod, inhibiting blood clotting and resulting in increased clotting time. We then release the complementary DNA as an antidote from the other NR, reversing the effect of the aptamer and restoring blood clotting. Thus, the nanorod pair acts as an on/off switch. One challenge for nanobiotechnology is the bio-nano interface, where coronas of weakly adsorbed proteins can obscure biomolecular function. We exploit these adsorbed proteins to increase aptamer and antidote loading on the nanorods.

Concepts: Blood, Coagulation, Fibrin, Platelet, Warfarin, Thrombus, Heparin, Tenase