Rivaroxaban and apixaban are less effective than enoxaparin for the prevention of catheter-induced clotting in vitro

Trousseau syndrome: management of refractory VTE

Managing recurrent and refractory venous thromboembolism (VTE) in patients with cancer presents unique challenges. This review outlines the complexities and therapeutic strategies for recurrent VTE in cancer patients, which includes distinguishing thrombus acuity, differentiating between tumor and bland thrombi, and evaluating potential contributing factors including anticoagulant adherence, extrinsic tumor compression, drug interactions, and anticoagulant-specific considerations such as heparin-induced thrombocytopenia or antithrombin deficiency. Different anticoagulation strategies are discussed, including the administration of escalated-dose low molecular weight heparin (LMWH) as well as the indications and rationale for switching between direct oral anticoagulants or LMWH.

Development and validation of an in vitro model to study thrombin generation on the surface of catheters in platelet-poor and platelet-rich plasma

INTRODUCTION

Coagulation activation on medical devices remains a significant problem as it can lead to dramatic thromboembolic complications. Understanding its poorly described mechanisms and finding optimal pharmacological prevention means is crucial to improve patient safety.

METHODS

We developed an in vitro model to study thrombin generation (TG) initiated by the contact of plasma with the surface of catheters. Interventional cardiology catheters were cut into segments and inserted in the bottom of multi-well plates; TG was then measured with the calibrated automated thrombogram (CAT). Model performance (analytical, intra- and inter-individual variability) was investigated and compared with activation of thrombin generation by tissue factor (TF) or contact pathway activator (ellagic acid), in the presence (PRP) and absence (PPP) of platelets. Model response to unfractionated heparin (UFH) was also assessed.

RESULTS

TG was greater when measured in presence of catheter segments, compared to conditions without activators. The analytical variability of the model was good (CV ≤ 5 %), both with PPP and PRP. Intra-individual variability was between 15 and 30 % with PPP and between 10 and 15 % with PRP. Inter-individual variability was between 15 and 30 % with both kinds of plasma samples. The analytical performance of the catheter-initiated TG model was equivalent to that observed when TG was initiated with TF or ellagic acid. Catheter-initiated TG was measurable until 0.1 IU/mL UFH with PPP and until 1.0 IU/mL UFH with PRP, highlighting the crucial requirement of platelets.

CONCLUSION

Our model is suitable for studying TG initiated with catheters. Inhibition of TG by UFH is overestimated in the absence of platelets.

Dabigatran for Treatment and Secondary Prevention of Venous Thromboembolism in Pediatric Congenital Heart Disease

BACKGROUND

Congenital heart disease (CHD) is common in children and associated with greater risk of thrombotic complications. Management of these complications with standard-of-care treatment is suboptimal for these children.

METHODS AND RESULTS

The effectiveness and safety of dabigatran were demonstrated in pivotal pediatric studies for the treatment of acute venous thromboembolism (VTE; NCT01895777) and secondary VTE prevention (NCT02197416). We report safety and efficacy outcomes from subgroup analyses of these studies for children with CHD (diagnosed according to local practice) and those without. In NCT01895777, 17/21 (81.0%) and 16/27 (59.3%) patients with CHD (including cyanotic) treated with dabigatran and standard of care, respectively, met the primary end point (complete thrombus resolution, freedom from recurrent VTE, and freedom from VTE-related death; odds ratio [OR], 0.34 [95% CI, 0.08-1.23]). In patients without CHD, 41.0% (n=64) versus 34.9% (n=22) achieved this end point with the respective treatments (OR, 0.77 [95% CI, 0.42-1.41]). Although numerical differences were observed, no heterogeneity in treatment effect of dabigatran on the composite primary end point was detected in patients with and without CHD (interaction P =0.2674). In NCT02197416, recurrent VTE at 12 months occurred in 0/17 patients with CHD versus 3/194 (1.5%) without. No patient with CHD experienced major or clinically relevant nonmajor bleeding events.

CONCLUSIONS

Data on favorable anticoagulant alternatives for the unmet needs of children with CHD are emerging, and our exploratory results suggest that dabigatran could be an appropriate treatment choice, although challenging sample size limitations in pediatric studies require cautious interpretation of findings.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifiers: NCT01895777, NCT02197416.

When Direct Oral Anticoagulants Should Not Be Standard Treatment: JACC State-of-the-Art Review

For most patients, direct oral anticoagulants (DOACs) are preferred over vitamin K antagonists for stroke prevention in atrial fibrillation and for venous thromboembolism treatment. However, randomized controlled trials suggest that DOACs may not be as efficacious or as safe as the current standard of care in conditions such as mechanical heart valves, thrombotic antiphospholipid syndrome, and atrial fibrillation associated with rheumatic heart disease. DOACs do not provide a net benefit in conditions such as embolic stroke of undetermined source. Their efficacy is uncertain for conditions such as left ventricular thrombus, catheter-associated deep vein thrombosis, cerebral venous sinus thrombosis, and for patients with atrial fibrillation or venous thrombosis who have end-stage renal disease. This paper provides an evidence-based review of randomized controlled trials on DOACs, detailing when they have demonstrated efficacy and safety, when DOACs should not be the standard of care, where their safety and efficacy are uncertain, and areas requiring further research.

Histidine-rich glycoprotein attenuates catheter thrombosis

Factor XII (FXII) knockdown attenuates catheter thrombosis in rabbits. Because histidine-rich glycoprotein (HRG) modulates FXIIa activity, we hypothesized that HRG depletion would promote catheter thrombosis. To test this, rabbits were given either antisense oligonucleotides (ASOs) against HRG or FXII, a control ASO, or saline. The activated partial thromboplastin time (aPTT), prothrombin time (PT), and catheter-induced thrombin generation were determined in blood collected before and after treatment. Compared with the controls, the HRG- and FXII-directed ASOs reduced hepatic messenger RNA and plasma levels of HRG and FXII, respectively, by >90%. Although HRG knockdown shortened the aPTT by 2.5 fold, FXII knockdown prolonged it by fourfold; neither of the ASOs affected the PT. Catheter segments shortened the lag time and increased peak thrombin in the plasma from control rabbits; effects were significantly enhanced and attenuated in the plasma from rabbits given the HRG- and FXII-directed ASOs, respectively. Catheters were then inserted into the right external jugular vein of the rabbits, and the time for catheter occlusion was determined. The catheter occlusion times with the control ASO or saline were 62 ± 8 minutes and 60 ± 11 minutes, respectively. The occlusion time was significantly reduced to 34 ± 9 minutes, with HRG knockdown and significantly prolonged to 128 ± 19 minutes with FXII knockdown. HRG levels are decreased with sepsis or cancer, and such patients are prone to catheter thrombosis. Because HRG modulates catheter thrombosis, our findings suggest that HRG supplementation may prevent this problem.