Poor Reliability of Common Measures of Anticoagulation in Pediatric Extracorporeal Membrane Oxygenation

Impact of Vascular Geometry on Thrombosis in Pediatric Patients With Modified Blalock-Taussig-Thomas Shunt: A Pilot Study

BACKGROUND

Thrombosis in modified Blalock-Taussig-Thomas shunts (mBTTS) poses a life-threatening risk for infants with shunt-dependent congenital heart disease. Although hemodynamics influence thrombosis, the specific geometric contributors remain unclear. This study aimed to identify key variables to inform future hemodynamic analysis, hypothesizing that brachiocephalic, subclavian artery, mBTTS, and/or pulmonary artery (PA) geometry play a critical role in clot formation.

METHODS AND RESULTS

We retrospectively analyzed 11 infants with hypoplastic left heart syndrome who underwent mBTTS placement. Using computed tomography and magnetic resonance imaging, we generated 3-dimensional models of the shunt and surrounding vasculature. Geometric variables related to shunt positioning and vascular insertion were measured and compared between patients with (n=5) and without (n=6) thrombotic occlusions. Significant differences in vascular geometry were observed between occluded and nonoccluded shunts. Occluded shunts had longer PA lengths (12.4 mm versus 8.4 mm, P=0.0130), increased variance in PA radius (0.03 versus 0.008, P=0.0216), greater PA tortuosity (1.03 versus 1.01, P=0.0043), and increased variance in torsion across the brachiocephalic and subclavian arteries (3200 mm-1 versus 17 500 mm-1, P=0.0390). These findings support our hypothesis that the vascular geometry surrounding the mBTTS plays a critical factor in clot formation. Additional variations in PA, brachiocephalic and subclavian artery geometry approached significance.

CONCLUSIONS

Significant geometric differences in the PA, brachiocephalic, and subclavian arteries were associated with mBTTS thrombosis, supporting the hypothesis that vascular geometry plays a critical role in clot formation. These findings provide a foundation for future hemodynamic analyses and may inform surgical planning to reduce thrombosis risk in patients with mBTTSs.

Bivalirudin as an anticoagulation strategy for acute hemodialysis in children: Two cases with a summary of recent literature

Unfractionated heparin is the most used anticoagulative agent for extracorporeal settings in children, including acute hemodialysis modalities. In certain situations, such as heparin-induced thrombocytopenia, alternatives must be applied. The direct thrombin inhibitor bivalirudin has come forth as an attractive substitute. Bivalirudin is currently only approved for adult use in specific percutaneous coronary intervention settings. However, it has a growing off-label popularity in different contexts for both adult and pediatric patients. Experience with bivalirudin in children is mainly limited to extracorporeal membrane oxygenation, ventricular assist devices and during cardiopulmonary bypass surgery. Literature about its use as anticoagulation strategy for pediatric hemodialysis is very scarce. Here, we present two pediatric cases where bivalirudin was used during acute hemodialysis, followed by a short summary of recent literature.

Single Ventricular Assist Device Care and Outcomes for Failed Stage I Palliation: A Single-Center Decade of Experience

Single ventricular assist device (SVAD) use before and after stage I palliation (S1P) is increasing with limited data on outcomes. To address this knowledge gap, we conducted a single-center retrospective review to assess pre- and post-SVAD clinical status, complications, and outcomes. We leveraged a granular, longitudinal, local database that captures end-organ support, procedural interventions, hematologic events, laboratory data, and antithrombotic strategy. We identified 25 patients between 2013 and 2023 implanted at median age of 53 days (interquartile range [IQR] = 16-130); 80% had systemic right ventricles and underwent S1P. Median SVAD days were 54 (IQR = 29-86), and 40% were implanted directly from ECMO. Compared to preimplant, there was a significant reduction in inotrope use ( p = 0.013) and improved weight gain ( p = 0.008) post-SVAD. Complications were frequent including bleeding (80%), stroke (40%), acute kidney injury (AKI) (40%), infection (36%), and unanticipated catheterization (56%). Patients with in-hospital mortality had significantly more bleeding complications ( p = 0.02) and were more likely to have had Blalock-Thomas-Taussig shunts pre-SVAD ( p = 0.028). Survival to 1 year postexplant was 40% and included three recovered and explanted patients. At 1 year posttransplant, all survivors have technology dependence or neurologic injury. This study highlights the clinical outcomes and ongoing support required for successful SVAD use in failed single-ventricle physiology before or after S1P.

Impact of inflammation and steroids on anti-coagulation in children supported on a ventricular assist device

Critically ill pediatric patients supported on ventricular assist devices (VADs) are increasingly being anticoagulated on bivalirudin, but with difficulty monitoring anticoagulation. Activated partial thromboplastin time (aPTT) has recently been shown to poorly correlate with bivalirudin plasma concentrations, while dTT had excellent correlation. However, aPTT is the more common monitoring test and dTT testing is rarely used. In addition, effects of frequent clinical VAD scenarios (such as inflammation) on the accuracy of aPTT and dTT testing remains uncertain. We reviewed the effects of clinical scenarios (infection/inflammation, chylothorax, and steroids administration) on anticoagulation monitoring in 10 pediatric VAD patients less than 3 years at Cincinnati Children's Hospital Medical Center from 10/27/2020 to 5/6/2022 using bivalirudin for anticoagulation. There were 16 inflammation/infection, 3 chylothorax, and 6 steroids events. Correlation between dTT and aPTT was significantly lower after infection/inflammation, with dTT increasing prior to inflammation/infection while aPTT remained unchanged. In addition, steroids are administered to VAD patients to reduce inflammation and thus additionally stabilize anticoagulation. However, this anticoagulation stabilization effect was reflected more accurately by dTT compared to aPTT. In children requiring VAD support utilizing bivalirudin anticoagulation, inflammation/infection is a common occurrence resulting in anticoagulation changes that may be more accurately reflected by dTT as opposed to aPTT.

Is it time to switch to bivalirudin for ECMO anticoagulation?

For decades, unfractionated heparin (hereafter, heparin) has been the primary anticoagulant used for extracorporeal membrane oxygenation (ECMO) support. More recently, however, bivalirudin, a direct thrombin inhibitor, has emerged as an alternative. This systematic review based on PRISMA guidelines, aims to summarize 16 comparative studies and 8 meta-analysis and review articles published from January, 2011 till May, 2023 which directly compares ECMO courses using heparin versus bivalirudin as the anticoagulant. While this comparison is complicated by the lack of a standardized definition of major bleeding or thrombosis, our overall findings suggest there is no statistical difference between heparin and bivalirudin in incidence of bleeding and thrombosis. That said, some studies found a statistical significance favoring bivalirudin in reducing major bleeding, thrombosis, and the need for transfusions. We also offer essential guidance for appropriately selecting an anticoagulant and monitoring its effect in ECMO settings.

Anticoagulation-Free Pediatric Extracorporeal Membrane Oxygenation: Single-Center Retrospective Study

OBJECTIVES

To analyze hemorrhage and thrombosis data related to anticoagulation-free pediatric extracorporeal membrane oxygenation (ECMO).

DESIGN

Retrospective cohort study.

SETTINGS

High-volume ECMO single institution data.

PATIENTS

Children (0-18 yr) supported with ECMO (>24 hr) with initial anticoagulation-free period of greater than or equal to 6 hours.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Utilizing consensus American Thoracic Society definitions for hemorrhage and thrombosis on ECMO, we evaluated thrombosis and associated patient and ECMO characteristics during anticoagulation-free period. Thirty-five patients met inclusion criteria from 2018 to 2021 having a median age (interquartile range [IQR]) of 13.5 months (IQR, 3-91 mo), median ECMO duration of 135 hours (IQR, 64-217 hr), and 964 anticoagulation-free hours. Increased RBC transfusion needs were associated with longer anticoagulation-free periods ( p = 0.03). We identified 20 thrombotic events: only four during the anticoagulation-free period and occurring in three of 35 (8%) patients. Compared with those without thrombotic events, anticoagulation-free clotting events were associated with younger age (i.e., 0.3 mo [IQR, 0.2-0.3 mo] vs 22.9 mo [IQR, 3.6-112.9 mo]; p = 0.02), lower weight (2.7 kg [IQR, 2.7-3.25 kg] vs 13.2 kg [5.9-36.4 kg]; p = 0.006), support with lower median ECMO flow rate (0.5 kg [IQR, 0.45-0.55 kg] vs 1.25 kg [IQR, 0.65-2.5 kg]; p = 0.04), and longer anticoagulation-free ECMO duration (44.5 hr [IQR, 40-85 hr] vs 17.6 hr [IQR, 13-24.1]; p = 0.008).

CONCLUSIONS

In selected high-risk-for-bleeding patients, our experience is that we can use ECMO in our center for limited periods without systemic anticoagulation, with lower frequency of patient or circuit thrombosis. Larger multicentered studies are required to assess weight, age, ECMO flow, and anticoagulation-free time limitations that are likely to pose risk for thrombotic events.

Heparin-based versus bivalirudin-based anticoagulation in pediatric extracorporeal membrane oxygenation: A systematic review

Introduction

Optimal anticoagulation therapy is essential for the prevention of thrombotic and hemorrhagic complications in pediatric patients supported with extracorporeal membrane oxygenation (ECMO). Recent data have demonstrated bivalirudin has the potential to surpass and replace heparin as the anticoagulant of choice.

Methods

We conducted a systematic review comparing the outcomes of heparin-based versus bivalirudin-based anticoagulation in pediatric patients supported on ECMO to identify the preferred anticoagulant to minimize bleeding events, thrombotic complications, and associated mortality. We referenced the PubMed, Cochrane Library, and Embase databases. These databases were searched from inception through October 2022. Our initial search identified 422 studies. All records were screened by two independent reviewers using the Covidence software for adherence to our inclusion criteria, and seven retrospective cohort studies were identified as appropriate for inclusion.

Results

In total, 196 pediatric patients were anticoagulated with heparin and 117 were anticoagulated with bivalirudin while on ECMO. Across the included studies, it was found that for patients treated with bivalirudin, trends were noted toward lower rates of bleeding, transfusion requirements, and thrombosis with no difference in mortality. Overall costs associated with bivalirudin therapy were lower. Time to therapeutic anticoagulation varied between studies though institutions had different anticoagulation targets.

Conclusion

Bivalirudin may be a safe, cost-effective alternative to heparin in achieving anticoagulation in pediatric ECMO patients. Prospective multicenter studies and randomized control trials with standard anticoagulation targets are needed to accurately compare outcomes associated with heparin versus bivalirudin in pediatric ECMO patients.

Correlation between partial thromboplastin time and thromboelastography in adult critically ill patients requiring bivalirudin for extracorporeal membrane oxygenation

STUDY OBJECTIVE

Thromboelastography (TEG) offers a more dynamic assessment of hemostasis over activated partial thromboplastin time (aPTT). However, the clinical utility of TEG in monitoring bivalirudin during extracorporeal membrane oxygenation (ECMO) remains unknown. The purpose of this study was to evaluate the correlation between aPTT and TEG in adult ECMO patients anticoagulated with bivalirudin.

DESIGN

Multicenter, retrospective, cohort study conducted over a 2-year period.

SETTING

Two academic university medical centers (Banner University Medical Center) in Phoenix and Tucson, AZ.

PATIENTS

Adult patients requiring ECMO and bivalirudin therapy with ≥1 corresponding standard TEG and aPTT plasma samples drawn ≤4 h of each other were included. The primary endpoint was to determine the correlation coefficient between the standard TEG reaction (R) time and bivalirudin aPTT serum concentrations.

MEASUREMENTS AND MAIN RESULTS

A total of 104 patients consisting of 848 concurrent laboratory assessments of R time and aPTT were included. A moderate correlation between TEG R time and aPTT was demonstrated in the study population (r = 0.41; p < 0.001). Overall, 502 (59.2%) concurrent assessments of TEG R time and aPTT values showed agreement on whether they were sub-, supra-, or therapeutic according to the institution's classification for bivalirudin. The 42.2% (n = 271/642) discordant TEG R times among "therapeutic" aPTT were almost equally distributed between subtherapeutic and supratherapeutic categories.

CONCLUSIONS

Moderate correlation was found between TEG R time and aPTT associated with bivalirudin during ECMO in critically ill adults. Further research is warranted to address the optimal test to guide clinical decision-making for anticoagulation dosing in ECMO patients.

Comparison of Bivalirudin Versus Heparin for Anticoagulation During Extracorporeal Membrane Oxygenation

The effect and safety of bivalirudin compared with heparin in patients undergoing extracorporeal membrane oxygenation (ECMO) remains unclear. Therefore, we conducted a systematic review and meta-analysis to compare the effectiveness and safety of heparin and bivalirudin in patients who underwent ECMO. We searched Embase, the Cochrane Central Register of Controlled Trials, and MEDLINE. Inclusion criteria included patients (1) undergoing ECMO and (2) receiving bivalirudin or heparin. We excluded studies where the majority of patients switched heparin to bivalirudin or vice versa during the clinical course. The primary outcome was short-term mortality. We presented the results of all analyses with the use of random-effects models. Eleven studies reported short-term mortality. The use of bivalirudin was associated with significantly lower short-term mortality, compared with heparin (odds ratio: 0.71, 95% confidence interval, 0.55-0.92; p = 0.01, I2 = 7%). In this meta-analysis of observational studies, the use of bivalirudin was associated with significantly lower short-term mortality, compared with heparin. Further prospective studies are warranted to clarify this finding.

Viscoelastic Testing in Pediatric Mechanical Circulatory Support

Pediatric mechanical circulatory support can be lifesaving. However, managing anticoagulation is one of the most challenging aspects of care in patients requiring mechanical circulatory support. Effective anticoagulation is even more difficult in pediatric patients due to the smaller size of their blood vessels, increased turbulent flow, and developmental hemostasis. Recently, viscoelastic testing (VET) has been used as a qualitative measure of anticoagulation efficacy in patients receiving extracorporeal membrane oxygenation (ECMO) and ventricular assist devices (VAD). Thromboelastography (TEG®) and thromboelastometry (ROTEM®) provide a global qualitative assessment of hemostatic function from initiation of clot formation with the platelet-fibrin interaction, platelet aggregation, clot strength, and clot lysis. This review focuses on the TEG®/ROTEM® and important laboratory and patient considerations for interpretation in the ECMO and VAD population. We summarize the adult and pediatric ECMO/VAD literature regarding VET values, VET-platelet mapping, utility over standard laboratory monitoring, and association with outcome measures such as blood product utilization, bleeding, and thrombosis.