A reduction of prothrombin conversion by cardiac surgery with cardiopulmonary bypass shifts the haemostatic balance towards bleeding

Protocol for a phase 3, randomised, active-control study of four-factor prothrombin complex concentrate versus frozen plasma in bleeding adult cardiac surgery patients requiring coagulation factor replacement: the LEX-211 (FARES-II) trial

INTRODUCTION

Reduced thrombin generation is an important component of post cardiopulmonary bypass (CPB) coagulopathy. To replenish coagulation factors and enhance thrombin generation in bleeding surgical patients, frozen plasma (FP) and four-factor prothrombin complex concentrate (4F-PCC) are used. However, the efficacy-safety balance of 4F-PCC relative to FP in cardiac surgery is unconfirmed.

METHODS AND ANALYSIS

LEX-211 (FARES-II) is an active-control, randomised, phase 3 study comparing two coagulation factor replacement therapies in bleeding adult cardiac surgical patients at 12 hospitals in Canada and the USA. The primary objective is to determine whether 4F-PCC (Octaplex/Balfaxar, Octapharma) is clinically non-inferior to FP for haemostatic effectiveness. Inclusion criteria are any index (elective or non-elective) cardiac surgery employing CPB and coagulation factor replacement with 4F-PCC or FP ordered in the operating room for bleeding management. Patients will be randomised to receive 1500 or 2000 international units of 4F-PCC or 3 or 4 units of FP, depending on body weight. The primary endpoint of haemostatic treatment response is 'effective' if no additional haemostatic intervention is required from 60 min to 24 hours after the first initiation of 4F-PCC or FP; or 'ineffective' if any other haemostatic intervention (including a second dose of study drug) is required. An estimated 410 evaluable patients will be required to demonstrate non-inferiority (one-sided α of 0.025, power ≥90%, non-inferiority margin 0.10). Secondary outcomes include transfusions, bleeding-related clinical endpoints, coagulation parameters and safety.

ETHICS AND DISSEMINATION

The trial has been approved by the institutional review boards of all participating centres. Trial completion is anticipated at the end of 2024, and results will be disseminated via publications in peer-reviewed journals and conference presentations in 2025. The results will advance our understanding of coagulation management in bleeding surgical patients, potentially reducing the need for allogeneic blood products and improving outcomes in surgical patients.

TRIAL REGISTRATION NUMBER

NCT05523297.

The endogenous thrombin potential in patients with left ventricular assist device or heart transplant

Background

The Heartmate 3 (HM 3) is a left ventricular assist device featuring less shear stress, milder acquired von Willebrand syndrome, and fewer bleeding incidences than its predecessor the Heartmate II (HM II). The novel surface coating of the HM 3 suggests less contact activation of plasmatic coagulation. We hypothesized that patients with HM 3 exhibit fewer aberrations in their thrombin potential than patients with HM II. We compared these results with the thrombin potential of patients with heart transplantation (HTX).

Methods

Thrombin generation in plasma samples of patients with HM II (n = 16), HM 3 (n = 20), and HTX (n = 13) was analyzed 3 days after implantation/transplantation and after long-term support (3-24 months) with HM II (n = 16) or HM 3 (n = 12) using calibrated automated thrombography. Heparin in postoperative samples was antagonized with polybrene.

Results

Three days postoperatively HM II patients exhibited a lower endogenous thrombin potential (ETP) than HM 3 and HTX patients (HM II: 947 ± 291 nM*min; HM 3: 1231 ± 176 nM*min; HTX: 1376 ± 162 nM*min, p < 0.001) and a lower velocity index of thrombin generation (HM II: 18.74 ± 10.90 nM/min; HM 3: 32.41 ± 9.51 nM/min; HTX: 37.65 ± 9.41 nM/min, p < 0.01). Subtle differences in the thrombin generation profiles remained in HM II and HM 3 patients under long-term support (Velocity Index: HM II: 38.70 ± 28.46 nM/min; HM 3: 73.32 ± 32.83 nM/min, p < 0.05). Prothrombin fragments 1 + 2 were higher in HM II than in HM 3 patients (HM II: 377.7 ± 208.4 pM; HM 3: 202.1 ± 87.7 pM, p < 0.05) and correlated inversely with the ETP (r = -0.584, p < 0.05).

Conclusion

We observed a more aberrant thrombin generation in HM II than in HM 3 despite comparable anticoagulation and routine parameters. A trend toward lower values was still observable in HM 3 compared to HTX patients. Calibrated automated thrombography may be a good tool to monitor the coagulation state of these patients and guide anticoagulation in the future.

Assessing the individual roles of FII, FV, and FX activity in the thrombin generation process

Thrombin generation (TG) is known as a physiological approach to assess the hemostatic function. Although it correlates well with thrombosis and bleeding, in the current setup it is not sensitive to the effects of fluctuations in single coagulation factors. We optimized the calibrated automated thrombinography (CAT) method to quantify FII, FV and FX activity within the coagulation system. The CAT assay was fine-tuned for the assessment of FII, FV and FX by diluting the samples in FII-, FV-, or FX-deficient plasma, respectively, and measuring TG. Plasma FII levels correlated linearly with the ETP up to a plasma concentration of 100% FII. FV and FX levels correlated linearly with the peak height up to a plasma level of 2.5% FV and 10% FX, respectively. Sensitized CAT protocols were designed by adding a fixed volume of a pre-diluted patient sample to FII, FV, and FX deficient plasma in TG experiments. This approach makes the TG measurement dependent on the activity of the respective coagulation factor. The ETP or peak height were quantified as readouts for the coagulation factor activity. The intra- and inter-assay variation coefficients varied from 5.0 to 8.6%, and from 3.5 to 5.9%, respectively. Reference values were determined in 120 healthy subjects and the assays were clinically validated in 60 patients undergoing coronary artery bypass grafting (CABG). The sensitized CAT assays revealed that the contribution of FII, FV, and FX to the TG process was reduced after CABG surgery, leading to reduced prothrombin conversion and subsequently, lower TG.

Semi-automated thrombin dynamics applying the ST Genesia thrombin generation assay

Background

The haemostatic balance is an equilibrium of pro- and anticoagulant factors that work synergistically to prevent bleeding and thrombosis. As thrombin is the central enzyme in the coagulation pathway, it is desirable to measure thrombin generation (TG) in order to detect possible bleeding or thrombotic phenotypes, as well as to investigate the capacity of drugs affecting the formation of thrombin. By investigating the underlying processes of TG (i.e., prothrombin conversion and inactivation), additional information is collected about the dynamics of thrombin formation.

Objectives

To obtain reference values for thrombin dynamics (TD) analysis in 112 healthy donors using an automated system for TG.

Methods

TG was measured on the ST Genesia, fibrinogen on the Start, anti-thrombin (AT) on the STA R Max and α₂Macroglobulin (α₂M) with an in-house chromogenic assay.

Results

TG was measured using STG-BleedScreen, STG-ThromboScreen and STG-DrugScreen. The TG data was used as an input for TD analysis, in combination with plasma levels of AT, α₂M and fibrinogen that were 113% (108-118%), 2.6 μM (2.2 μM-3.1 μM) and 2.9 g/L (2.6-3.2 g/L), respectively. The maximum rate of the prothrombinase complex (PCmax) and the total amount of prothrombin converted (PCtot) increased with increasing tissue factor (TF) concentration. PC_tot increased from 902 to 988 nM, whereas PC_max increased from 172 to 508 nM/min. Thrombin (T)-AT and T-α₂M complexes also increased with increasing TF concentration (i.e., from 860 to 955 nM and from 28 to 33 nm, respectively). PC_tot, T-AT and T-α₂M complex formation were strongly inhibited by addition of thrombomodulin (-44%, -43%, and -48%, respectively), whereas PC_max was affected less (-24%). PC_tot, PC_max, T-AT, and T-α₂M were higher in women using oral contraceptives (OC) compared to men/women without OC, and inhibition by thrombomodulin was also significantly less in women on OC (p < 0.05).

Conclusions

TG measured on the ST Genesia can be used as an input for TD analysis. The data obtained can be used as reference values for future clinical studies as the balance between prothrombin conversion and thrombin inactivation has shown to be useful in several clinical settings.

Functional changes in hemostasis during asexual and sexual parasitemia in a controlled human malaria infection

Decreased platelet count is an early phenomenon in asexual Plasmodium falciparum parasitemia, but its association with acute or long-term functional changes in platelets and coagulation is unknown. Moreover, the impact of gametocytemia on platelets and coagulation remains unclear. We investigated the changes in platelet number and function during early asexual parasitemia, gametocytemia and convalescence in 16 individuals participating in a controlled human malaria infection study, and studied its relationship with changes in total and active von Willebrand factor levels (VWF) and the coagulation system. Platelet activation and reactivity were determined by flow cytometry, and the coagulation system was assessed using different representative assays including antigen assays, activity assays and global functional assays. Platelet count was decreased during asexual blood stage infection but normalized during gametocytemia. Platelet P-selectin expression was slightly increased during asexual parasitemia, gametocytemia and at day 64. In contrast, platelet reactivity to different agonists remained unchanged, except a marked decrease in reactivity to low dose collagen-related peptide-XL. Thrombin generation and antigen assays did not show a clear activation of the coagulation during asexual parasitemia, whereas total and active VWF levels were markedly increased. During gametocytemia and on day 64, the endogenous thrombin potential, thrombin peak and velocity index were increased and prothrombin conversion and plasma prothrombin levels were decreased. We conclude that the decreased platelet count during asexual parasitemia is associated with increased active VWF levels (i.e. endothelial activation), but not platelet hyperreactivity or hypercoagulability, and that the increased platelet clearance in asexual parasitemia could cause spontaneous VWF-platelet complexes formation.

Tailoring the effect of antithrombin-targeting therapy in haemophilia A using in silico thrombin generation

Factor (F) VIII deficiency causes bleeding in haemophilia A patients because of the reduced formation of procoagulant enzyme thrombin, which is needed to make the blood clot. We measured the dynamics of coagulation in haemophilia A patients by measuring thrombin generation (TG). Additionally, we quantified the procoagulant process of prothrombin conversion and anticoagulant process of thrombin inhibitor complex formation. In haemophilia A, prothrombin conversion is severely reduced, causing TG to be low. Nevertheless, the thrombin inactivation capacity of these patients is comparable to that in healthy subjects, leading to a severe imbalance between procoagulant and anticoagulant processes and a subsequent increased bleeding risk. A novel therapy in haemophilia A is the targeting of anticoagulant pathway, e.g. thrombin inhibitor antithrombin (AT), to restore the haemostatic balance. We simulated the effect of AT reduction on TG in silico. Lowering AT levels restored TG dose-dependently and an AT reduction of 90-95% led to almost normal TG in most patients . However, the variation in response to AT reduction was large between patients, indicating that this approach should be tailored to each individual patients. Ideally, TG and thrombin dynamics simulation could in the future contribute to the management of patients undergoing AT targeting therapy.

Comparison of 4-Factor Prothrombin Complex Concentrate With Frozen Plasma for Management of Hemorrhage During and After Cardiac Surgery: A Randomized Pilot Trial

IMPORTANCE

Approximately 15% of patients undergoing cardiac surgery receive frozen plasma (FP) for bleeding. Four-factor prothrombin complex concentrates (PCCs) have logistical and safety advantages over FP and may be a suitable alternative.

OBJECTIVES

To determine the proportion of patients who received PCC and then required FP, explore hemostatic effects and safety, and assess the feasibility of study procedures.

DESIGN, SETTING, AND PARTICIPANTS

Parallel-group randomized pilot study conducted at 2 Canadian hospitals. Adult patients requiring coagulation factor replacement for bleeding during cardiac surgery (from September 23, 2019, to June 19, 2020; final 28-day follow-up visit, July 17, 2020). Data analysis was initiated on September 15, 2020.

INTERVENTIONS

Prothrombin complex concentrate (1500 IU for patients weighing ≤60 kg and 2000 IU for patients weighing >60 kg) or FP (3 U for patients weighing ≤60 kg and 4 U for patients weighing >60 kg), repeated once as needed within 24 hours (FP used for any subsequent doses in both groups). Patients and outcome assessors were blinded to treatment allocation.

MAIN OUTCOMES AND MEASURES

Hemostatic effectiveness (whether patients received any hemostatic therapies from 60 minutes to 4 and 24 hours after initiation of the intervention, amount of allogeneic blood components administered within 24 hours after start of surgery, and avoidance of red cell transfusions within 24 hours after start of surgery), protocol adherence, and adverse events. The analysis set comprised all randomized patients who had undergone cardiac surgery, received at least 1 dose of either treatment, and provided informed consent after surgery.

RESULTS

Of 169 screened patients, 131 were randomized, and 101 were treated (54 with PCC and 47 with FP), provided consent, and were included in the analysis (median age, 64 years; interquartile range [IQR], 54-73 years; 28 [28%] were female; 82 [81%] underwent complex operations). The PCC group received a median 24.9 IU/kg (IQR, 21.8-27.0 IU/kg) of PCC (2 patients [3.7%; 95% CI, 0.4%-12.7%] required FP). The FP group received a median 12.5 mL/kg (IQR, 10.0-15.0 mL/kg) of FP (4 patients [8.5%; 95% CI, 2.4%-20.4%] required >2 doses of FP). Hemostatic therapy was not required at the 4-hour time point for 43 patients (80%) in the PCC group and for 32 patients (68%) in the FP group (P = .25) nor at the 24-hour time point for 41 patients (76%) in the PCC group and for 31 patients (66%) patients in the FP group (P = .28). The median numbers of units for 24-hour cumulative allogeneic transfusions (red blood cells, platelets, and FP) were 6.0 U (IQR, 4.0-11.0 U) in the PCC group and 14.0 U (IQR, 8.0-20.0 U) in the FP group (ratio, 0.58; 95% CI, 0.45-0.77; P < .001). After exclusion of FP administered as part of the investigational medicinal product, the median numbers of units were 6.0 U (IQR, 4.0-11.0 U) in the PCC group and 10.0 U (IQR, 6.0-16.0 U) in the FP group (ratio, 0.80; 95% CI, 0.59-1.08; P = .15). For red blood cells alone, the median numbers were 1.5 U (IQR, 0.0-4.0 U) in the PCC group and 3.0 U (IQR, 1.0-5.0 U) in the FP group (ratio, 0.69; 95% CI, 0.47-0.99; P = .05). During the first 24 hours after start of surgery, 15 patients in the PCC group (28%) and 8 patients in the FP group (17%) received no red blood cells (P = .24). Adverse event profiles were similar.

CONCLUSIONS AND RELEVANCE

This randomized clinical trial found that the study protocols were feasible. Adequately powered randomized clinical trials are warranted to determine whether PCC is a suitable substitute for FP for mitigation of bleeding in cardiac surgery.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04114643.

Perioperative Factor Concentrate Use is Associated With More Beneficial Outcomes and Reduced Complication Rates Compared With a Pure Blood Product-Based Strategy in Patients Undergoing Elective Cardiac Surgery: A Propensity Score-Matched Cohort Study

OBJECTIVE

The goal of this study was to compare factor concentrate (FC)-based and blood product-based hemostasis management of coagulopathy in cardiac surgical patients in terms of postoperative bleeding, required blood products, and outcome.

DESIGN

Retrospective, propensity score-matched analysis.

SETTING

Single, tertiary, academic medical center.

PARTICIPANTS

One hundred eighteen matched pairs of 433 consecutive patients scheduled for cardiac surgery in two isolated periods with distinct strategies of hemostasis management.

INTERVENTIONS

Patients received either blood product-based (period I) or FC-based (period II) hemostasis management to treat perioperative coagulopathy.

MEASUREMENTS AND MAIN RESULTS

Patients treated with FC management experienced less postoperative blood loss (907 v 1,153 mL, p = 0.014) and required less red blood cell and fresh frozen plasma transfusion (2.3 v 3.7 units p < 0.0001, and 2.0 v 3.4 units p < 0.0001, respectively) compared with subjects in the blood product-based management group. The frequency of Stage 3 acute kidney injury and 30-day mortality rate were significantly higher in the blood product-based group than in the FC management group (6.8% v 0.8%, p = 0.016, and 7.2% v 0.8%, p = 0.022, respectively). FC management-related thromboembolic events were not registered. The FC strategy was associated with a 2.19-fold decrease in the odds of massive postoperative bleeding (p < 0.0001), a 2.56-fold decrease in the odds of polytransfusion (p < 0.0001), and a 13.16-fold decrease in the odds of early postoperative death (p = 0.003).

CONCLUSIONS

FC-based versus blood product-based management is associated with reduced blood product needs and fewer complications, and was not linked to a higher frequency of thromboembolic events or a decrease in long-term survival in cardiac surgical patients developing perioperative coagulopathy and bleeding.

Deciphering the coagulation profile through the dynamics of thrombin activity

Thrombosis has proven to be extremely difficult to predict. Measuring the generation of thrombin is a very sensitive method to detect changes in the hemostatic system. We developed a method based on the generation of thrombin to further fingerprint hemostasis, which we have named thrombin dynamics. Via this method we are able to exactly measure the prothrombin conversion and thrombin inactivation, and any change in the coagulation cascade will be reflected in these two processes. In the current study we analyzed the importance of the members of the prothrombin complex on the dynamics of thrombin activation and inactivation. We show that prothrombin conversion is predominantly influenced by factor X and antithrombin, which will provide essential insights in complex thrombosis-related diseases, such as liver cirrhosis and kidney failure.

Controlled Multifactorial Coagulopathy: Effects of Dilution, Hypothermia, and Acidosis on Thrombin Generation In Vitro

BACKGROUND

Coagulopathy and hemostatic abnormalities remain a challenge in patients following trauma and major surgery. Coagulopathy in this setting has a multifactorial nature due to tissue injury, hemodilution, hypothermia, and acidosis, the severity of which may vary. In this study, we combined computational kinetic modeling and in vitro experimentation to investigate the effects of multifactorial coagulopathy on thrombin, the central enzyme in the coagulation system.

METHODS

We measured thrombin generation in platelet-poor plasma from 10 healthy volunteers using the calibrated automated thrombogram assay (CAT). We considered 3 temperature levels (31°C, 34°C, and 37°C), 3 pH levels (6.9, 7.1, and 7.4), and 3 degrees of dilution with normal saline (no dilution, 3-fold dilution, and 5-fold dilution). We measured thrombin-generation time courses for all possible combinations of these conditions. For each combination, we analyzed 2 scenarios: without and with (15 nM) supplementation of thrombomodulin, a key natural regulator of thrombin generation. For each measured thrombin time course, we recorded 5 quantitative parameters and analyzed them using multivariable regression. Moreover, for multiple combinations of coagulopathic conditions, we performed routine coagulation tests: prothrombin time (PT) and activated partial thromboplastin time (aPTT). We compared the experimental results with simulations using a newly developed version of our computational kinetic model of blood coagulation.

RESULTS

Regression analysis allowed us to identify trends in our data (P < 10). In both model simulations and experiments, dilution progressively reduced the peak of thrombin generation. However, we did not experimentally detect the model-predicted delay in the onset of thrombin generation. In accord with the model predictions, hypothermia delayed the onset of thrombin generation; it also increased the thrombin peak time (up to 1.30-fold). Moreover, as predicted by the kinetic model, the experiments showed that hypothermia increased the area under the thrombin curve (up to 1.97-fold); it also increased the height of the thrombin peak (up to 1.48-fold). Progressive acidosis reduced the velocity index by up to 24%; acidosis-induced changes in other thrombin generation parameters were much smaller or none. Acidosis increased PT by 14% but did not influence aPTT. In contrast, dilution markedly prolonged both PT and aPTT. In our experiments, thrombomodulin affected thrombin-generation parameters mainly in undiluted plasma.

CONCLUSIONS

Dilution with normal saline reduced the amount of generated thrombin, whereas hypothermia increased it and delayed the time of thrombin accumulation. In contrast, acidosis in vitro had little effect on thrombin generation.

Reference values for thrombin dynamics in platelet rich plasma

Thrombin generation (TG) is a better determinant of the overall function of the hemostatic system than routinely used clotting time-based assays and can be studied more in detail by thrombin dynamics analysis. Platelet poor plasma is often used to measure TG, however, measuring the contribution of the platelets is also important as patients with a low platelet count or with dysfunctional platelets have an increased risk of developing bleeding. In this study, platelet rich plasma (PRP) was collected from 117 healthy individuals. PRP was measured undiluted and diluted to a varying platelet concentration of 10*10⁹/L to 400*10⁹/L. Prothrombin conversion and thrombin inactivation were calculated from the data obtained by the TG parameters and coagulation factor levels (antithrombin, α₂Macroglobulin (α₂M) and fibrinogen). Reference ranges of TG and thrombin dynamics in PRP of 117 healthy individuals were established. Peak, velocity index and the maximum rate of prothrombin conversion increased linearly with platelet count, but endogenous thrombin potential reached a maximum at 150*10⁹/L as seen in a subset population (n = 20). More extensive analysis revealed that a platelet count below 50*10⁹/L did not affect TG parameters (except for the ETP). Correlation analysis indicated that the platelet count mainly affected the rate of prothrombin conversion. Inhibition of thrombin by antithrombin and α₂M increased with increasing TG, but the ratio of inhibition by antithrombin or α₂M remained the same independently of the total thrombin formed. In conclusion, TG and thrombin dynamics were assessed in PRP of healthy donors to provide reference values for future TG studies in PRP. Increasing the platelet count mainly affected the rate of prothrombin conversion and TG, rather than the total amount of thrombin formed.

Thrombin generation and bleeding in cardiac surgery: a clinical narrative review

This narrative review discusses the role of thrombin generation in coagulation and bleeding in cardiac surgery, the laboratory methods for clinical detection of impaired thrombin generation, and the available hemostatic interventions that can be used to improve thrombin generation. Coagulopathy after cardiopulmonary bypass (CPB) is associated with excessive blood loss and adverse patient outcomes. Thrombin plays a crucial role in primary hemostasis, and impaired thrombin generation can be an important cause of post-CPB coagulopathy. Existing coagulation assays have significant limitations in assessing thrombin generation, but whole-blood assays designed to measure thrombin generation at the bed-side are under development. Until then, clinicians may need to institute therapy empirically for non-surgical bleeding in the setting of normal coagulation measures. Available therapies for impaired thrombin generation include administration of plasma, prothrombin complex concentrate, and bypassing agents (recombinant activated factor VII and factor eight inhibitor bypassing activity). In vitro experiments have explored the relative potency of these therapies, but clinical studies are lacking. The potential incorporation of thrombin generation assays into clinical practice and treatment algorithms for impaired thrombin generation must await further clinical development.

Prothrombin conversion is accelerated in the antiphospholipid syndrome and insensitive to thrombomodulin

Antiphospholipid syndrome (APS) is a condition in which the presence of antibodies against phospholipid-binding proteins is associated with thrombophilia and/or pregnancy morbidity. Although antiphospholipid antibodies have anticoagulant characteristics in vitro, they are associated with thromboembolic complications. Thrombin generation (TG) is a sensitive global test of coagulation, and elevated TG is associated with thrombosis. Increased TG can be caused by increased prothrombin conversion, decreased thrombin inactivation, or a combination of both. In this study, we measured TG in APS patients and healthy controls with and without vitamin K antagonist (VKA) treatment at 1 and 5 pM tissue factor and with thrombomodulin. Prothrombin conversion and thrombin inactivation were determined by thrombin dynamics analysis. The TG peak was increased in nontreated APS patients at 1 pM TF compared with nontreated controls. Prothrombin conversion was significantly increased in nontreated APS patients. In contrast, prothrombin conversion did not differ in controls and patients that were on VKA therapy. Thrombin inactivation was comparable between controls and APS patients in the presence and absence of VKAs. Both TG (peak and ETP) and prothrombin conversion were significantly higher in APS patients with prior thrombosis compared with patients without a history of thrombosis. In this study, we demonstrate that in APS, the hemostatic balance shifts toward a more prothrombotic phenotype due to elevated prothrombin conversion but unchanged thrombin inactivation rates. Within the group of APS patients, increased TG and prothrombin conversion are associated with a history of thrombosis.