Antithrombin activity during the period of percutaneous coronary revascularization: relation to heparin use, thrombotic complications and restenosis

Finding a common definition of heparin resistance in adult cardiac surgery: communication from the ISTH SSC subcommittee on perioperative and critical care thrombosis and hemostasis

Ensuring adequate anticoagulation for patients requiring cardiac surgery and cardiopulmonary bypass (CPB) is important due to the adverse consequences of inadequate anticoagulation with respect to bleeding and thrombosis. When target anticoagulation is not achieved with typical doses, the term heparin resistance is routinely used despite the lack of uniform diagnostic criteria. Prior reports and guidance documents that define heparin resistance in patients requiring CPB and guidance documents remain variable based on the lack of standardized criteria. As a result, we conducted a review of clinical trials and reports to evaluate the various heparin resistance definitions employed in this clinical setting and to identify potential standards for future clinical trials and clinical management. In addition, we also aimed to characterize the differences in the reported incidence of heparin resistance in the adult cardiac surgical literature based on the variability of both target-activated clotting (ACT) values and unfractionated heparin doses. Our findings suggest that the most extensively reported ACT target for CPB is 480 seconds or higher. Although most publications define heparin resistance as a failure to achieve this target after a weight-based dose of either 400 U/kg or 500 U/kg of heparin, a standardized definition would be useful to guide future clinical trials and help improve clinical management. We propose the inability to obtain an ACT target for CPB of 480 seconds or more after 500 U/kg as a standardized definition for heparin resistance in this setting.

The effect of perioperative antithrombin supplementation on blood conservation and postoperative complications after cardiopulmonary bypass surgery: A systematic review, meta-analysis and trial sequential analysis

Study objective

Antithrombin (AT) activity is reduced during cardiopulmonary bypass (CPB) surgery. Guidelines has demonstrated that perioperative AT supplementation contributed to blood conservation and prevent perioperative thrombotic complications and target organ injury owing to its role in reducing thrombin generation. But these recommends is lack of support of meta-analysis in the guidelines. This meta-analysis aims to include all the relevant randomized controlled trails (RCT) on patients who experienced cardiac surgeries with CPB and investigate the effect of perioperative AT on blood conservation and complications after cardiac surgery.

Methods

Standard published RCTs were searched from bibliographic databases to identify all evidence reporting perioperative AT supplementation for patients undergoing cardiovascular surgeries. The primary outcome was postoperative blood loss, the secondary outcomes were blood component transfusion (red blood cell (RBC), fresh frozen plasma (FFP), platelet and autologous blood), postoperative morbidity and in hospital mortality. The relative risk (RR) for dichotomous outcomes and the standardized mean difference (SMD) for continuous outcomes were estimated using a random-effects model. Trial sequential analysis (TSA) was performed using TSA software 0.9.5.10.

Results

13 RCTs with 996 participants undergoing different cardiovascular surgeries were included. Meta-analysis showed AT did not decrease postoperative blood loss (SMD -0.01, 95%CI -0.2 to 0.19). Subgroup analysis showed the effect of AT on postoperative blood loss was not associated with age, RCT type, surgery type, injection time of AT and AT deficiency. TSA further suggested that no additional studies were required for the stable result. Perioperative AT also did not reduce RBC ((SMD 0.10, 95%CI -0.66 to 0.85), (RR 0.99, 95%CI 0.83 to 1.19)), FFP ((SMD 0.11, 95%CI -0.19 to 0.41), (RR 1.30, 95%CI 0.90 to 1.87)), platelet (RR 1.10, 95%CI 0.83 to 1.46) and autologous blood (SMD 0.46, 95%CI -0.12 to 1.8504) transfusions. Perioperative AT significantly increased in hospital mortality (RR 2.53, 95%CI 1.02 to 6.28) and acute kidney injury (AKI) (RR 3.72, 95%CI 1.73 to 8.04) incidence. There was no significant difference in postoperative reexploration, thromboembolism, ECMO/IABP support, and stroke incidence between AT and non-AT group.

Conclusions

With the improvement of AT level and heparin sensitivity, perioperative AT has no significant effect on blood conservation. And it is noteworthy that the treatment increased in hospital mortality and the incidence of AKI after cardiac surgery.

Heparin Resistance During Cardiopulmonary Bypass in Adult Cardiac Surgery

The use of heparin for anticoagulation has changed the face of cardiac surgery by allowing a bloodless and motionless surgical field throughout the introduction of cardiopulmonary bypass (CPB). However, heparin is a drug with complex pharmacologic properties that can cause significant interpatient differences in terms of responsiveness. Heparin resistance during CPB is a weighty issue due to the catastrophic consequences stemming from inadequate anticoagulation, and the treatment of it necessitates a rationalized stepwise approach due to the multifactorial contributions toward this entity. The widespread use of activated clotting time (ACT) as a measurement of anticoagulation during CPB is examined, as it may be a false indicator of heparin resistance. Heparin resistance also has been repeatedly reported in patients infected with COVID-19, which deserves further exploration in this pandemic era. This review aims to examine the variability in heparin potency, underlying mechanisms, and limitations of using ACT for monitoring, as well as provide a framework towards the current management of heparin resistance.

The role of SERPIN citrullination in thrombosis

Aberrant protein citrullination is associated with many pathologies; however, the specific effects of this modification remain unknown. We have previously demonstrated that serine protease inhibitors (SERPINs) are highly citrullinated in rheumatoid arthritis (RA) patients. These citrullinated SERPINs include antithrombin, antiplasmin, and t-PAI, which regulate the coagulation and fibrinolysis cascades. Notably, citrullination eliminates their inhibitory activity. Here, we demonstrate that citrullination of antithrombin and t-PAI impairs their binding to their cognate proteases. By contrast, citrullination converts antiplasmin into a substrate. We recapitulate the effects of SERPIN citrullination using in vitro plasma clotting and fibrinolysis assays. Moreover, we show that citrullinated antithrombin and antiplasmin are increased and decreased in a deep vein thrombosis (DVT) model, accounting for how SERPIN citrullination shifts the equilibrium toward thrombus formation. These data provide a direct link between increased citrullination and the risk of thrombosis in autoimmunity and indicate that aberrant SERPIN citrullination promotes pathological thrombus formation.

Continuous intravenous infusion of enoxaparin controls thrombin formation more than standard subcutaneous administration in critically ill patients. A sub-study of the ENOKSI thromboprophylaxis RCT

INTRODUCTION

Standard subcutaneous low-molecular-weight heparin (LMWH) thromboprophylaxis yields low anti-factor Xa activity in patients in the intensive care unit (ICU). The aim of the study was to assess coagulation status in ICU patients randomized to receive enoxaparin thromboprophylaxis either as a standard subcutaneous bolus (SCB) or continuous intravenous infusion (CII) for 3 consecutive days after the initiation of LMWH thromboprophylaxis.

MATERIALS AND METHODS

Thirty-eight patients were studied by conventional coagulation variables: prothrombin fragment F 1+2 (F 1+2) representing FXa inhibition and antithrombin (AT). Additionally, 18 patients were analyzed by the thrombin generation assay-calibrated automated thrombogram (TGA-CAT). Blood samples were collected before the initiation of the LMWH thromboprophylaxis (ie, baseline), at 51 h, and at 72 h.

RESULTS

At beginning, no differences in coagulation biomarkers were observed. The levels of F 1+2 were significantly lower at 51 and 72 h in the CII group than in the SCB group. AT levels increased during the follow-up in the CII group, unlike in the SCB group. TGA-CAT was poor in some patients overall. In a subset of patients at 51 h lag time (4.3 vs 7.5 min, respectively, P < 0.05) and time to peak (7.7 vs 14.3 min, respectively, P < 0.05) were prolonged in the SCB group. At 72 h, however, peak thrombin was lower in the CII than in the SCB group: 271 vs 356 nM, respectively (P < 0.05).

CONCLUSIONS

Enoxaparin thromboprophylaxis administered by CII inhibited more prominently FXa and preserved better the AT level, compared with standard subcutaneous care.

Antithrombin and Protein C in Systemic Inflammatory Response Syndrome

Coronary artery bypass grafting with cardiopulmonary bypass can induce systemic inflammatory response syndrome. To assess the prevalence of preoperative antithrombin and protein C deficiencies in relation to the incidence of this syndrome, antithrombin and protein C levels were measured in 130 patients undergoing coronary artery bypass grafting with cardiopulmonary bypass. Systemic inflammatory response syndrome developed in 36 (27.7%) patients who were predominantly male, had a lower EuroSCORE, longer cardiopulmonary bypass time, higher pre-bypass temperature, and shorter activated coagulation time. Logistic regression showed that predictive factors included bypass duration and pre-bypass temperature; however, low antithrombin levels appeared to be a negative predictive factor. Antithrombin levels were < 80% in 33.8% of patients, and 11.6% had protein C levels < 80%. Postoperative antithrombin and protein C deficiencies are not uncommon in adults undergoing cardiac surgery with cardiopulmonary bypass, but detection of these deficits did not identify patients at increased risk of systemic inflammatory response syndrome.

Review article: heparin sensitivity and resistance: management during cardiopulmonary bypass

Heparin resistance during cardiac surgery is defined as the inability of an adequate heparin dose to increase the activated clotting time (ACT) to the desired level. Failure to attain the target ACT raises concerns that the patient is not fully anticoagulated and initiating cardiopulmonary bypass may result in excessive activation of the hemostatic system. Although antithrombin deficiency has generally been thought to be the primary mechanism of heparin resistance, the reasons for heparin resistance are both complex and multifactorial. Furthermore, the ACT is not specific to heparin's anticoagulant effect and is affected by multiple variables that are commonly present during cardiac surgery. Due to these many variables, it remains unclear whether decreased heparin responsiveness as measured by the ACT represents inadequate anticoagulation. Nevertheless, many clinicians choose a target ACT to assess anticoagulation, and interventions aimed at achieving the target ACT are routinely performed in the setting of heparin resistance. Treatments for heparin resistance/alterations in heparin responsiveness include additional heparin or antithrombin supplementation. In this review, we discuss the variability of heparin potency, heparin responsiveness as measured by the ACT, and the current management of heparin resistance.

2011 update to the Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesiologists blood conservation clinical practice guidelines

BACKGROUND

Practice guidelines reflect published literature. Because of the ever changing literature base, it is necessary to update and revise guideline recommendations from time to time. The Society of Thoracic Surgeons recommends review and possible update of previously published guidelines at least every three years. This summary is an update of the blood conservation guideline published in 2007.

METHODS

The search methods used in the current version differ compared to the previously published guideline. Literature searches were conducted using standardized MeSH terms from the National Library of Medicine PUBMED database list of search terms. The following terms comprised the standard baseline search terms for all topics and were connected with the logical 'OR' connector--Extracorporeal circulation (MeSH number E04.292), cardiovascular surgical procedures (MeSH number E04.100), and vascular diseases (MeSH number C14.907). Use of these broad search terms allowed specific topics to be added to the search with the logical 'AND' connector.

RESULTS

In this 2011 guideline update, areas of major revision include: 1) management of dual anti-platelet therapy before operation, 2) use of drugs that augment red blood cell volume or limit blood loss, 3) use of blood derivatives including fresh frozen plasma, Factor XIII, leukoreduced red blood cells, platelet plasmapheresis, recombinant Factor VII, antithrombin III, and Factor IX concentrates, 4) changes in management of blood salvage, 5) use of minimally invasive procedures to limit perioperative bleeding and blood transfusion, 6) recommendations for blood conservation related to extracorporeal membrane oxygenation and cardiopulmonary perfusion, 7) use of topical hemostatic agents, and 8) new insights into the value of team interventions in blood management.

CONCLUSIONS

Much has changed since the previously published 2007 STS blood management guidelines and this document contains new and revised recommendations.

Heparin responsiveness during off-pump coronary artery bypass graft surgery: predictors and clinical implications

AIM

To evaluate the clinical impact of reduced heparin responsiveness (HR(reduced)) on the incidence of myocardial infarction (MI) following off-pump coronary artery bypass graft surgery (OPCAB), and to identify the predictors of HR(reduced).

METHODS

A total of 199 patients scheduled for elective OPCAB were prospectively enrolled. During anastomosis, 150 U/kg of heparin was injected to achieve an activated clotting time (ACT) of ≥ 300 s, and the heparin sensitivity index (HSI) was calculated. HSIs below 1.0 were considered reduced (HR(reduced)). The relationships between the HSI and postoperative MI, cardiac enzyme levels and preoperative risk factors of HR(reduced) were investigated.

RESULTS

There was no significant relationship between the HSI and cardiac enzyme levels after OPCAB. The incidence of MI after OPCAB was not higher in HR(reduced) patients. HR(reduced) occurred more frequently in patients with low plasma albumin concentrations and high platelet counts.

CONCLUSION

HR(reduced) was not associated with adverse ischemic outcomes during the perioperative period in OPCAB patients, which seemed to be attributable to a tight prospective protocol for obtaining a target ACT regardless of the presence of HR(reduced).

Genetics of coagulation: considerations for cardiac surgery

Genetic variants in the coagulation system have been known since antiquity. Today, because of modern improvements in diagnosis and medical management, the clinician is likely to encounter a spectrum of coagulation factor deficiencies and identified polymorphic variants in the surgical population. Because perioperative hemorrhagic and thrombotic complications are potentially serious, it is important to understand the role that these defects and variants may play in predicting risk and optimizing patient management. The implications of coagulation genetics on the perioperative management of the cardiac surgery patient are reviewed.

Elective percutaneous coronary intervention using broad-spectrum antiplatelet therapy (eptifibatide, clopidogrel, and aspirin) alone, without scheduled unfractionated heparin or other antithrombin therapy

BACKGROUND

Adjunctive pharmacotherapy during percutaneous coronary intervention (PCI) has historically consisted of a regimen of antiplatelet agents accompanied by an antithrombin agent, typically unfractionated heparin. Paradoxically, unfractionated heparin may activate platelets, induce other pro-thrombotic activities, increase bleeding complications, and cause thrombocytopenia. To optimize patient care and avoid the potential risks of unfractionated heparin in patients undergoing elective PCI, one of the authors began to use adjunctive pharmacotherapy consisting of broad-spectrum antiplatelet therapy alone, without scheduled unfractionated heparin or other antithrombin therapy.

METHODS

Five hundred consecutive patients undergoing scheduled, elective PCI (stent deployment, cutting balloon atherotomy, conventional balloon angioplasty, or high-speed rotational atherectomy) received adjunctive pharmacotherapy consisting of eptifibatide, clopidogrel, and aspirin.

RESULTS

The technical success rate was 100%. During the first 24 hours, there were no major adverse clinical events. Non-Q-wave myocardial infarction occurred in 1.6% of patients, major and minor bleeding complications in 0.2% and 0.6%, respectively, and thrombocytopenia in 0.6%. During the first 30 days, there was 1 (0.2%) major adverse clinical event.

CONCLUSIONS

For elective PCI, adjunctive pharmacotherapy consisting of broad-spectrum antiplatelet therapy alone, without scheduled unfractionated heparin or other antithrombin therapy, appears to be safe and may prove to be efficacious.

Efficacy and safety of minimal dose (< or =1,000 units) unfractionated heparin with abciximab in percutaneous coronary intervention

Abciximab decreases adverse cardiac ischemic events, and in some subgroups, decreases the need for revascularization after percutaneous coronary intervention (PCI). However, abciximab may cause bleeding complications and thrombocytopenia after PCI. We hypothesized that the efficacy and safety of PCI would be maintained, if not improved, when performed using abciximab accompanied by only minimal doses (< or =1,000 U) of unfractionated heparin. In this prospectively designed observational study, we assessed 500 consecutive patients who underwent PCI, consisting of either stent deployment or high-speed rotational atherectomy, and who received abciximab accompanied by only a minimal dose of unfractionated heparin, as directed by a novel dosing strategy: (1) if the patient was previously receiving an infusion of heparin, then it was terminated upon arrival to the cardiac catheterization laboratory, and no further heparin was administered; or (2) if the patient was not receiving an infusion of heparin, then a single bolus infusion of 1,000 U was administered after establishment of vascular access. The median activated clotting time for the patients during PCI was 168 seconds (25% quartiles, 153 to 185). The technical success rate was 99.8%. There were no major adverse clinical events during the 24 hours after PCI. The incidence of non-Q-wave myocardial infarction was 1.6%. The incidences of major and minor bleeding complications were 0.2% and 3.6%, respectively, and the incidence of thrombocytopenia was 2.2%. During the 30 days after PCI, there was 1 major adverse clinical event (0.2%). During the 1 year after PCI, among the remaining patients, there were 92 adverse events (18.4%). We conclude that, in the context of historical data, the efficacy and safety of PCI using either stent deployment or high-speed rotational atherectomy is maintained, if not improved, when performed using abciximab accompanied by only minimal doses of unfractionated heparin.

Low preoperative antithrombin activity causes reduced response to heparin in adult but not in infant cardiac-surgical patients

We evaluated the interaction of preoperative antithrombin (AT) activity and intraoperative response to heparin in cardiac surgery. Heparin anticoagulation is essential during cardiopulmonary bypass (CPB). Heparin itself has no anticoagulant properties, however it causes a conformational change of the physiologic plasma inhibitor AT that converts this slow-acting serine protease inhibitor into a fast acting one. Thus, adequate AT activity is a prerequisite for sufficient heparin anticoagulation. AT activity is reduced by long-term heparin therapy. This prospective, observational study investigated 1516 consecutive cardiac-surgical patients (1304 patients >1 yr (Group A) and 212 patients < or = 1 yr (Group I)). AT activity was measured the day before surgery by a chromogenic substrate assay. The celite-activated activated clotting time (ACT) was used to guide intraoperative heparin administration. Heparin sensitivity was calculated and the postoperative blood loss and perioperative blood requirement was recorded. Infant patients had significantly less preoperative AT activity compared with older patients: 84 (33)% vs 97 (17)%, median (interquartile range) (P < 0. 05). The subgroup of patients aged <1 mo (n = 64) demonstrated a preoperative AT activity of 56 (27)% as compared with 90 (23)% in infant patients between one month and one year (n = 148). In adult patients, preoperative AT activity depended predominantly on preoperative heparin treatment: 62% of the patients with an AT activity <80% were pretreated with heparin. Five minutes after heparin but before CPB the ACT was 587 (334) s in Group A patients with AT activity > or = 80%, and 516 (232) in patients with AT activity < or = 80% (P < 0.05). The target ACT of 480 s was achieved in 70% of patients with normal AT activity in Group A compared with only 54% of patients with AT activity <80% (P < 0.05). In Group A patients with decreased AT activity, 18% demonstrated an inadequate ACT response-defined as ACT <400 s-to the first bolus injection of heparin. In Group I, preoperative AT activity did not influence the ACT response (ACT 5 min after heparin: 846 [447] s in patients with AT activity > or = 80% vs 1000 [364] s in patients with decreased AT activity). The heparin sensitivity was 2.4 (1.1) s/unit heparin/kg compared with 1.5 (0.8) s/unit heparin/KG in group A (P < 0.05). These results suggest that preoperative diminished AT activity causes reduced response to heparin in adult but not in infant patients. Infant patients demonstrate a higher heparin sensitivity despite lower preoperative AT activity. Measurement of preoperative AT activity identifies adult patients at risk of reduced sensitivity to heparin.

IMPLICATIONS

In patients less than one year of age, low antithrombin (AT) activity is caused by the immature coagulation system. Despite low AT activity, these young patients demonstrate a normal or increased response to heparin anticoagulation before cardiopulmonary bypass (CPB). In contrast, in patients older than one year of age and adult patients decreased preoperative AT activity is mainly caused by preoperative heparin therapy and causes insufficient response to heparin anticoagulation with a standard heparin dosage. Measurement of preoperative AT activity identifies patients at risk of inadequate anticoagulation during CPB.