Antithrombin III During Cardiac Surgery

A retrospective investigation of varied dose of heparin for cardiopulmonary bypass for repair of cardiac myxomas

INTRODUCTION

There is no consensus on the dose of heparin to be used intraoperatively in cardiac myxomas, so the goal of this study was to look into the differences in the clinical effects on the perioperative period of patients with cardiac myxomas when different doses of heparin were used intraoperatively.

METHODS AND ANALYSIS

70 patients who had cardiac myxomas excision via cardiopulmonary bypass between January 2024 and July 2024. The 70 patients were separated into two groups based on the heparin dose administered prior to cardiopulmonary bypass heparinization. 42 patients in group A had a dose of ≤400 U/kg, while 28 patients in group B received a dose of >400 U/kg.

RESULT

PT, INR, and APTT were significantly prolonged in patients with cardiac myxomas in group A in the postoperative period 24 h after surgery, which was statistically significant (P < .05) compared with that in group B. Intraoperative heparin dose appeared to influence changes in coagulation at 24 h postoperatively, but was mainly dominated by APTT. Also, heparinized doses showed a weak positive correlation with 24-h postoperative drainage volume. In addition, the dimension of the cardiac myxomas appeared to have some correlation with the patient's preoperative APTT and age.

CONCLUSION

When patients with cardiac myxomas were heparinized intraoperatively with varying doses of heparin, the enhancement of coagulation in the 24 h after surgery was more pronounced in the group given higher doses of heparin, and endogenous coagulation pathways were activated much more than exogenous coagulation pathways in the 24 h after surgery.

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.

Unfractionated heparin and the activated clotting time in non-cardiac arterial procedures

INTRODUCTION

Unfractionated heparin is administered during non-cardiac arterial procedures (NCAP) to prevent thromboembolic complications. In order to achieve a safe level of anticoagulation, the effect of heparin can be measured. The aim of this review was to provide an overview on what is known about heparin, suggested tests to monitor the effect of heparin, including the activated clotting time (ACT), and the factors that could influence that ACT.

EVIDENCE ACQUISITION

A literature search in PubMed was performed. Articles reporting on heparin, clotting time tests (including thrombin time, activated partial thromboplastin time, anti-activated factor X and ACT), and ACT measurement devices were selected.

EVIDENCE SYNTHESIS

Heparin has a non-predictable effect in the individual patient, which could be measured using the ACT. However, ACT values can be influenced by many factors, such as hemodilution, hypothermia and thrombocytopenia. In addition, a high variation in ACT outcomes is found between measurement devices of different brands. In the sparse literature on the role of ACT during NCAP, no consensus has been reached on optimal target ACT values. An ACT >250 seconds leads to more bleeding complications. Females have a longer ACT after heparin administration, with a higher risk of bleeding complications.

CONCLUSIONS

The effect of heparin is unpredictable. ACT can be used to monitor the effect of heparin and achieve individualized anticoagulation, tailored to the patient and the specifics of the operative procedure. However, the ACT itself can be affected by several factors and caution must be present, as measured ACT values differ between measurement devices.

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.

A Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial of Preoperative Antithrombin Supplementation in Patients at Risk for Antithrombin Deficiency After Cardiac Surgery

BACKGROUND

Antithrombin (AT) activity is reduced during cardiac operations with cardiopulmonary bypass (CPB), which is associated with adverse outcomes. Preoperative AT supplementation, to achieve >58% and <100% AT activity, may potentially reduce postoperative morbidity and mortality in cardiac operations with CPB. This prospective, multicenter, randomized, double-blind, placebo-controlled study was designed to evaluate the safety and efficacy of preoperative treatment with AT supplementation in patients at risk for low AT activity after undergoing cardiac surgery with CPB.

METHODS

A total of 425 adult patients were randomized (1:1) to receive either a single dose of AT (n = 213) to achieve an absolute increase of 20% above pretreatment AT activity or placebo (n = 212) before surgery. The study duration was approximately 7 weeks. The primary efficacy end point was the percentage of patients with any component of a major morbidity composite (postoperative mortality, stroke, acute kidney injury [AKI], surgical reexploration, arterial or venous thromboembolic events, prolonged mechanical ventilation, and infection) in the 2 groups. Secondary end points included AT activity, blood loss, transfusion requirements, duration of intensive care unit (ICU), and hospital stays. Safety was also assessed.

RESULTS

Overall, 399 patients (men, n = 300, 75.2%) with a mean (standard deviation [SD]) age of 66.1 (11.7) years, with the majority undergoing complex surgical procedures (n = 266, 67.9%), were analyzed. No differences in the percentage of patients experiencing morbidity composite outcomes between groups were observed (AT-treated 68/198 [34.3%] versus placebo 58/194 [29.9%]; P = .332; relative risk, 1.15). After AT infusion, AT activity was significantly higher in the AT group (108% [42-143]) versus placebo group (76% [40-110]), and lasted up to postoperative day 2. At ICU, the frequency of patients with AT activity ≥58% in the AT group (81.5%) was significantly higher (P < .001) versus placebo group (43.2%). Secondary end point analysis did not show any advantage of AT over placebo group. There were significantly more patients with AKI (P < .001) in the AT group (23/198; 11.6%) than in the placebo group (5/194, 2.6%). Safety results showed no differences in treatment-emergent adverse events nor bleeding events between groups.

CONCLUSIONS

AT supplementation did not attenuate adverse postoperative outcomes in our cohort of patients undergoing cardiac surgery with CPB.

A Prospective Pilot Trial to Assess the Efficacy of Argatroban (Argatra®) in Critically Ill Patients with Heparin Resistance

The current study aims to evaluate whether prophylactic anticoagulation using argatroban or an increased dose of unfractionated heparin (UFH) is effective in achieving the targeted activated partial thromboplastin time (aPTT) of more than 45 s in critically ill heparin-resistant (HR) patients. Patients were randomized either to continue receiving an increased dose of UFH, or to be treated with argatroban. The endpoints were defined as achieving an aPTT target of more than 45 s at 7 h and 24 h. This clinical trial was registered on clinicaltrials.gov (NCT01734252) and on EudraCT (2012-000487-23). A total of 42 patients, 20 patients in the heparin and 22 in the argatroban group, were included. Of the patients with continued heparin treatment 55% achieved the target aPTT at 7 h, while only 40% of this group maintained the target aPTT after 24 h. Of the argatroban group 59% reached the target aPTT at 7 h, while at 24 h 86% of these patients maintained the targeted aPTT. Treatment success at 7 h did not differ between the groups (p = 0.1000), whereas at 24 h argatroban showed significantly greater efficacy (p = 0.0021) than did heparin. Argatroban also worked better in maintaining adequate anticoagulation in the further course of the study. There was no significant difference in the occurrence of bleeding or thromboembolic complications between the treatment groups. In the case of heparin-resistant critically ill patients, argatroban showed greater efficacy than did an increased dose of heparin in achieving adequate anticoagulation at 24 h and in maintaining the targeted aPTT goal throughout the treatment phase.

Society of Cardiovascular Anesthesiologists Clinical Practice Improvement Advisory for Management of Perioperative Bleeding and Hemostasis in Cardiac Surgery Patients

Bleeding after cardiac surgery is a common and serious complication leading to transfusion of multiple blood products and resulting in increased morbidity and mortality. Despite the publication of numerous guidelines and consensus statements for patient blood management in cardiac surgery, research has revealed that adherence to these guidelines is poor, and as a result, a significant variability in patient transfusion practices among practitioners still remains. In addition, although utilization of point-of-care (POC) coagulation monitors and the use of novel therapeutic strategies for perioperative hemostasis, such as the use of coagulation factor concentrates, have increased significantly over the last decade, they are still not widely available in every institution. Therefore, despite continuous efforts, blood transfusion in cardiac surgery has only modestly declined over the last decade, remaining at ≥50% in high-risk patients. Given these limitations, and in response to new regulatory and legislature requirements, the Society of Cardiovascular Anesthesiologists (SCA) has formed the Blood Conservation in Cardiac Surgery Working Group to organize, summarize, and disseminate the available best-practice knowledge in patient blood management in cardiac surgery. The current publication includes the summary statements and algorithms designed by the working group, after collection and review of the existing guidelines, consensus statements, and recommendations for patient blood management practices in cardiac surgery patients. The overall goal is creating a dynamic resource of easily accessible educational material that will help to increase and improve compliance with the existing evidence-based best practices of patient blood management by cardiac surgery care teams.

Identification of Cost-Saving Opportunities for the Use of Antithrombin III in Adult and Pediatric Patients

Thrombate III is a human plasma-derived antithrombin III (AT-III) often utilized in patients on extracorporeal membrane oxygenation (ECMO) with suspected AT-III-mediated heparin resistance. It is supplied as 500-U and 1000-U vials, costing US$4.66 per unit. Literature is limited in describing the clinical value of AT-III in relation to its high cost. The primary objective was to determine conditions of use and associated cost of potentially unnecessary utilization of AT-III at The Johns Hopkins Hospital. Secondary objectives included evaluating the effect of AT-III on anticoagulation parameters and the overall cost utilized and wasted on AT-III. A retrospective cohort study was performed. The primary end point was the total cost associated with potentially unnecessary utilization of AT-III. There were 326 doses of AT-III administered to 65 patients in 2014. There were 177 (54%) potentially unnecessary doses associated with a cost of US$541 634. Antithrombin III repletion significantly increased median AT-III levels in non-ECMO and ECMO patients compared to baseline (non-ECMO: 62% vs 81%, P < .01; ECMO: 63% vs 81%, P < .01); however, 37.3% of ECMO and 49% of non-ECMO patients had therapeutic anticoagulation monitoring parameters prior to administration. A total cost of US$688 478 was spent on administered AT-III and US$417 194 (38%) was wasted. Utilizing restriction criteria and a new dosing strategy potentially results in estimated annual savings of US$556 000. Utilizing restriction criteria and alternative dosing strategies to mitigate waste and unnecessary use has the potential to result in significant cost savings.

A Pilot Study of Antithrombin Replacement Prior to Cardiopulmonary Bypass in Neonates

Neonates have low levels of antithrombin. Inadequate anticoagulation during cardiopulmonary bypass (CPB) due to low antithrombin activity may result in a poor preservation of the coagulation system during bypass. We hypothesize that antithrombin replacement to neonates prior to CPB will preserve the hemostatic system and result in less postoperative bleeding. A randomized, double-blinded, placebo-controlled pilot study of antithrombin replacement to neonates prior to CPB was conducted. Preoperative antithrombin levels determined the dose of recombinant antithrombin or placebo to be given. Antithrombin levels were measured following the dosing of the antithrombin/placebo, after initiation of bypass, near the completion of bypass, and upon intensive care unit admission. Eight subjects were enrolled. No subject had safety concerns. Mediastinal exploration occurred in two antithrombin subjects and one placebo subject. Antithrombin activity levels were significantly higher in the treated group following drug administration; levels continued to be higher than preoperatively but not different from the placebo group at all other time points. Total heparin administration was less in the antithrombin group; measurements of blood loss were similar in both groups. A single dose of recombinant antithrombin did not maintain 100% activity levels throughout the entire operation. Although no safety concerns were identified in this pilot study, a larger trial is necessary to determine clinical efficacy.

Prothrombotic SERPINC1 Gene Polymorphism may Affect Heparin Sensitivity Among Different Ethnicities of Chinese Patients Receiving Heart Surgery

The purpose of this study was to investigate a possible correlation between single-nucleotide polymorphisms (SNPs) of the antithrombin (gene, SERPINC1, and perioperative sensitivity to heparin in patients receiving heart surgery. The SERPINC1 genotype and allele frequency, coagulation parameters 24 hours before and after surgery, and clinical findings were compared among 3 ethnic groups, Han, Uighur, and Kazakh, patientswho received heart surgery. In Han patients, longer coagulation time as well as higher heparin and protamine dosage was observed. SERPINC1 gene sequencing identified 2 mutations in exon 5, g.981A>G (rs5877) and g.1011A>G (rs5878). The minor allele frequency of allele (A>G) for rs5877 and rs5878 was higher in the Han patients and was significantly different among the ethnic groups ( P = .004 and P = .006, respectively). The increased SERPINC1 SNP frequency among Han patients receiving heart surgery might contribute to the differences in their perioperative sensitivity to heparin.

A polyadenosine-coralyne complex as a novel fluorescent probe for the sensitive and selective detection of heparin in plasma

This study presents the development of a simple, label-free, sensitive, and selective detection system for heparin based on the use of a complex of 20-repeat adenosine (A20) and coralyne. Coralyne emits relatively weak fluorescence in an aqueous solution. In the presence of A20, coralyne molecules complexed with A20 through A2-coralyne-A2 coordination. An increase in the fluorescence of coralyne was observed because coralyne remained separate from water in the hydrophobic environment of the folded A20. The presence of heparin and the formation of the coralyne-heparin complex caused coralyne to be removed from the A20-corlayne complex. Because heparin promoted coralyne dimerization, the fluorescence of coralyne decreased as a function of the concentration of added heparin. This detection method is effective because the electrostatic attraction between heparin and coralyne is substantially stronger than the coordination between A20 and coralyne in a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer at pH 7.0. Under optimal conditions (5 μM coralyne, 1 μM poly A20, and 10mM HEPES), this probe exhibited high selectivity (>90-fold) toward heparin over hyaluronic acid and chondroitin sulfate. The probe׳s detection limit for heparin was determined to be 4 nM (75 ng/mL) at a signal-to-noise ratio of 3. This study validates the practicality of using the A20-corlayne complex to determine the concentration of heparin in plasma.

[Role of antithrombin iii in cardiac surgery]

Coagulation of blood is of multidisciplinary interest. Cardiac surgery produces major changes in the delicate balance between pro-and anti-coagulant serum factors. The role of antithrombin iii has been analysed after finding evidence that associated decreased levels of protein activity to postoperative morbidity and mortality. Supplementing exogenous antithrombin is considered with the aim of optimising outcomes. Its intrinsic anticoagulant and anti-inflammatory properties have stimulated a growing interest, and suggests new lines of research.

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 dose response is independent of preoperative antithrombin activity in patients undergoing coronary artery bypass graft surgery using low heparin concentrations

BACKGROUND

Unfractionated heparin's primary mechanism of action is to enhance the enzymatic activity of antithrombin (AT). We hypothesized that there would be a direct association between preoperative AT activity and both heparin dose response (HDR) and heparin sensitivity index (HSI) in patients undergoing coronary artery bypass graft surgery.

METHODS

Demographic and perioperative data were collected from 304 patients undergoing primary coronary artery bypass graft surgery. AT activity was measured after induction of general anesthesia using a colorimetric method (Siemens Healthcare Diagnostics, Tarrytown, NY). Activated coagulation time (ACT), HDR, and HSI were measured using the Hepcon HMS Plus system (Medtronic, Minneapolis, MN). Heparin dose was calculated for a target ACT using measured HDR by the same system. Multivariate linear regression was performed to identify independent predictors of HDR. Subgroup analysis of patients with low AT activity (<80% normal; <0.813 U/mL) who may be at risk for heparin resistance was also performed.

RESULTS

Mean baseline ACT was 135 ± 18 seconds. Mean calculated HDR was 98 ± 21 s/U/mL. Mean baseline AT activity was 0.93 ± 0.13 U/mL. Baseline AT activity was not significantly associated with baseline or postheparin ACT, HDR, or HSI. Addition of AT activity to multivariable linear regression models of both HDR and HSI did not significantly improve model performance. Subgroup analysis of 49 patients with baseline AT <80% of normal levels did not reveal a relationship between low AT activity and HDR or HSI. Preoperative AT activity, HDR, and HSI were not associated with cardiac troponin I levels on the first postoperative day, intensive care unit duration, or hospital length of stay.

CONCLUSION

Although enhancing AT activity is the primary mechanism by which heparin facilitates cardiopulmonary bypass anticoagulation, low preoperative AT activity is not associated with impaired response to heparin or to clinical outcomes when using target ACTs of 300 to 350 seconds.

Postoperative activity, but not preoperative activity, of antithrombin is associated with major adverse cardiac events after coronary artery bypass graft surgery

BACKGROUND

Low levels of antithrombin (AT) have been independently associated with prolonged intensive care unit stay and an increased incidence of neurologic and thromboembolic events after cardiac surgery. We hypothesized that perioperative AT activity is independently associated with postoperative major adverse cardiac events (MACEs) in patients undergoing coronary artery bypass graft (CABG) surgery.

METHODS

We prospectively studied 1403 patients undergoing primary CABG surgery with cardiopulmonary bypass (CPB) (http://clinicaltrials.gov/show/NCT00281164). The primary clinical end point was occurrence of MACE, defined as a composite outcome of any one or more of the following: postoperative death, reoperation for coronary graft occlusion, myocardial infarction, stroke, pulmonary embolism, or cardiac arrest until first hospital discharge. Plasma AT activity was measured before surgery, after post-CPB protamine, and on postoperative days (PODs) 1-5. Multivariate logistic regression modeling was performed to estimate the independent effect of perioperative AT activity upon MACE.

RESULTS

MACE occurred in 146 patients (10.4%), consisting of postoperative mortality (n = 12), myocardial infarction (n = 108), stroke (n = 17), pulmonary embolism (n = 8), cardiac arrest (n = 16), or a subsequent postoperative or catheter-based treatment for graft occlusion (n = 6). AT activity at baseline did not differ between patients with (0.91 ± 0.13 IU/mL; n = 146) and without (0.92 ± 0.13 IU/mL; n = 1257) (P = 0.18) MACE. AT activity in both groups was markedly reduced immediately after CPB and recovered to baseline values over the ensuing 5 PODs. Postoperative AT activity was significantly lower in patients with MACE than those without MACE. After adjustment for clinical predictors of MACE, AT activity on PODs 2 and 3 was associated with MACE.

CONCLUSIONS

Preoperative AT activity is not associated with MACE after CABG surgery. MACE is independently associated with postoperative AT activity but only at time points occurring predominantly after the MACE.

[Heparin resistance and antithrombin deficiency]

The phenomenon of heparin resistance (HR) is characterized by high doses of unfractionated heparin (UFH) being required to bring activated partial thromboplastin time (aPTT) and activated coagulation time (ACT) within therapeutically desired ranges, or by the impossibility of reaching these ranges. At UFH dosages > 35,000 IU/d, HR should be considered a factor. The most frequent cause of HR is deficiency of antithrombin (AT), the presence of which is essential for UFH to exert its anticoagulatory effect. AT in concentrate form may be applied to overcome AT-dependent HR. The main clinically relevant situations in which AT-dependent HR occurs, with possible indication of AT substitution, are congenital AT deficiency, asparaginase therapy, disseminated intravascular coagulation (DIC) and administration of high doses of heparin during extracorporeal circulation, where it is significant, due to the need to maintain a very high ACT (> 400 s), that use of heart-lung machines is associated with an HR incidence of approximately 20%. The following procedure is recommended when there is no DIC and when extracorporeal circulation is not used: if HR is suspected and AT activity is < or = 60%, UFH should first be reduced to 500 IU/h (to prevent bleeding complications), before AT is substituted. AT activity should then exceed 80%. Under normalized and stable AT activity, the UFH dose should be adjusted such that aPTT is within a range of 60-100 s. If anticoagulation over a longer term is indicated, then overlapping anticoagulation with a vitamin K antagonist should be started as quickly as possible.

Acquired deficit of antithrombin and role of supplementation in septic patients during continuous veno-venous hemofiltration

Continuous renal replacement therapy (CRRT) is widely used in the management of septic patients with acute renal failure (ARF). Short filter lifespan (<24 hours) is a major concern and may result of a procoagulating state. The aim of this study was to investigate the relationship between antithrombin (AT) deficit and early filter clotting, and whether supplementation of AT could increase filter lifespan. Two different methods for supplementation, bolus and continuous infusion were also compared. We conducted a two-center prospective study from March 2003 to May 2004. Twenty-seven patients with septic shock and ARF were included and treated by CRRT. Unfractionated heparin (UHF) was used for anticoagulation. The initial level of AT was low with a median level at 45.4% (16%-69%). Low AT activity was associated with shorter filter lifespan. Supplementation led to a longer filter lifespan (15.2-33.2 hours) (p < 0.05). Continuous infusion provided better results: 48.5 vs. 27.8 hours for bolus method. This study suggests that AT measurement should be considered in continuous veno-venous hemofiltration with clotting problems as supplementation could increase filter lifespan by more than 100%. Continuous infusion is preferable. Cost effectiveness should be evaluated shortly.

Aortic Valve Replacement in a Patient With the Prothrombin 20210A Mutation

Patients presenting for cardiac surgery with hypercoagulable states pose a challenge. Although preoperative functional and genetic screening for hypercoagulable disorders may provide pathophysiologic information, it is difficult to make preoperative hematologic management plans in the absence of consensus guidelines, prospective studies, or case reports. We document the first case of prothrombin 20210A mutation in a patient undergoing elective aortic valve replacement. Peri-procedural bridging with heparin and avoidance of antifibrinolytic agents represent salient features of our successful perioperative management.

Antithrombin levels, morbidity, and mortality in a surgical intensive care unit

BACKGROUND

Antithrombin (AT) levels have been suggested as being predictive of outcome in intensive care unit (ICU) patients with septic shock. We investigated the time course of AT levels in a surgical ICU and tested the hypothesis that AT levels may be associated with morbidity and increased mortality rates in a cohort of surgical ICU patients.

METHODS

Three-hundred-twenty-seven consecutive patients admitted to the ICU with an estimated length of stay more than 48 h were included. AT levels were measured daily.

RESULTS

On admission to the ICU, AT levels were below the lower limit of normal in 84.1% (n = 275) of patients and increased significantly by 48 h after admission to reach normal values by the 7th ICU day in patients who never had sepsis (n = 208). This increase in AT levels was delayed in patients with sepsis. Patients with severe sepsis (n = 55) had consistently lower AT levels compared with other patients. Patients with lower AT levels were more likely to need blood products and had a greater maximum degree of organ dysfunction in the ICU than did other patients. The ICU length of stay was similar, regardless of the AT level on admission. Admission AT levels were not associated with increased ICU mortality in a multivariable analysis.

CONCLUSIONS

AT levels are low on admission to the ICU, regardless of the presence of sepsis. Although associated with the degree of organ dysfunction and the severity of sepsis, AT levels were not independently associated with worse outcome in this group of surgical ICU patients.

Kaolin-Based Activated Coagulation Time Measured by Sonoclot in Patients Undergoing Cardiopulmonary Bypass

OBJECTIVES

In vivo data for the kaolin-based ACT test from the Sonoclot Analyzer (SkACT, Sienco Inc, Arvada, CO) are lacking. The aim of this study was to compare SkACT with an established kaolin-based ACT from Hemochron (HkACT) and anti-Xa activity in patients undergoing cardiopulmonary bypass (CPB).

DESIGN

Prospective observational study.

SETTING

Community hospital.

PARTICIPANTS

Fifty patients scheduled for elective cardiac surgery.

INTERVENTIONS

Blood samples were taken before CPB at baseline (T0) and after heparinization (T1 and T2), on CPB after administration of aprotinin (5, 15, 30, 60 minutes; T3-T6), and at the end after protamine infusion (T7).

MEASUREMENTS AND MAIN RESULTS

A total of 375 blood samples were analyzed. ACT measurements were comparable for SkACT and HkACT at each measurement time point. Overall bias +/- standard deviation between SkACT and HkACT was -19 +/- 75 seconds (-2.4% +/- 11.7%). Mean bias between SkACT and HkACT at each time point ranged from -35 to 3 seconds (-4.5% to 2.6%) and showed no statistical significance over time. Heparin sensitivity of SkACT and HkACT, defined as (ACT(Tx)-ACT(T0))/(anti-Xa(Tx)-anti-Xa(T0)), significantly increased for measurements during CPB (p < 0.001) but without significant difference between the 2 methods. Test variability was comparable for both ACT measurement techniques. Overall test variability was 7.5% +/- 7.4% for SkACT and 7.8% +/- 11% for HkACT.

CONCLUSIONS

Accuracy and performance of SkACT and HkACT were comparable for heparin monitoring in patients undergoing CPB for elective cardiac surgery. However, both tests were affected significantly after initiating CPB and aprotinin infusion.

Preoperative low molecular weight heparin reduces heparin responsiveness during cardiac surgery

PURPOSE

Cardiac surgery with cardiopulmonary bypass requires systemic anticoagulation, defined by an activated clotting time (ACT) of 400-480 sec. Patients with altered heparin responsiveness require disproportionately higher doses of heparin to achieve this target ACT. A common risk factor for heparin resistance is preoperative heparin therapy. Recently, therapy with low molecular weight heparin (LMWH) has become an acceptable substitute for prolonged heparin therapy. The current study examines the effect of preoperative LMWH therapy on subsequent heparin responsiveness during cardiac surgery.

METHODS

Records of patients undergoing cardiac surgery with cardiopulmonary bypass over a period of four months were reviewed. We identified patients who, during the week preceding surgery, had received prolonged (>24 hr) therapy with either sc LMWH (LMWH group) or continuous iv unfractionated heparin (Heparin group). A Control group consisted of patients who received neither heparin nor LMWH preoperatively. The heparin sensitivity index (calculated as the first change in ACT from baseline divided by the first intraoperative heparin dose, normalized to body weight), was compared among groups using ANOVA.

RESULTS

One hundred and thirty-nine patients were included in the analysis. The heparin sensitivity index was 33-45% higher in the Control group (1.6+/-0.7 sec.IU-1.kg-1; P<0.0001) compared to the LMWH (1.2+/-0.4 sec.IU-1.kg-1) and Heparin (1.1+/-0.5 sec.IU-1.kg-1) groups. In a multivariable model, the use of preoperative LMWH remained a significant predictor of reduced intraoperative heparin responsiveness (P=0.002).

CONCLUSION

Prolonged preoperative LMWH therapy, similar to the known effect of prolonged unfractionated heparin infusion, reduces subsequent intraoperative response to heparin.

Clinical Measures of Heparin’s Effect and Thrombin Inhibitor Levels in Pediatric Patients with Congenital Heart Disease

In this investigation, we examined the relationship among three thrombin inhibitors, antithrombin III (ATIII), heparin cofactor II (HCII), and alpha-2-macroglobulin (alpha2M), and several clinical tests of heparin's effect in pediatric patients with congenital heart disease undergoing cardiopulmonary bypass. One hundred eighteen children were stratified into six age groups: <1 mo, 1-3 mo, 3-6 mo, 6-12 mo, 12-24 mo, and >10 yr. Baseline ATIII, HCII, and alpha2M values were measured. Baseline celite- and kaolin-activated clotting times (ACT) were also measured and repeated 3 min after a standard heparin dose of 400 U/kg. Differences in ACT values before and after heparin administration and a heparin dose-response relationship were calculated for each patient. Kaolin-activated ACT tests showed less variation after heparin administration than celite-activated tests. In contrast to what has been demonstrated in adults, ATIII showed no positive correlation with the clinical tests of heparin's effect nor did the other thrombin inhibitors. Additionally, patients <1 mo old had unexpectedly low levels of alpha2M accompanying their expected low levels of ATIII and HCII. Our findings raise concerns about the ability of heparin to adequately anticoagulate these neonates during cardiopulmonary bypass and, consequently, challenge the accuracy of ACT prolongation to truly reflect the extent of their anticoagulation.

Antithrombotic therapy in cardiac surgery

PURPOSE

To review the perioperative management of antithrombotic therapy in cardiac surgery, including the management of cardiopulmonary bypass (CPB) and off-pump surgery.

METHODS

A review of the relevant English literature over the period 1975-2005 was undertaken, in addition to a review of international practices in antithrombotic therapy in cardiac surgery.

PRINCIPAL FINDINGS

Cardiopulmonary bypass is required in most procedures and makes anticoagulation mandatory. Anticoagulation is, usually, achieved with unfractionnated heparin (UFH). Unfractionated heparin is monitored by point-of-care (POC) testing, such as the activated clotting time or the determination of heparin concentration. The target values of both tests remain empirical, with no clearly validated thresholds. The target value needs to be adjusted according to the POC test, given significant variations between devices and activators. After CABG, the need for antiplatelet therapy is well demonstrated, in order to limit the risk of postoperative death or ischemic events, and improve venous graft patency. Immediately after valvular surgery, antithrombotic therapy should take into account the specific risk carried by each patient and by each prosthetic device. The risk of venous thromboembolism, though poorly defined, is also present in the postoperative period and may require additional attention. Given the frequent exposure to UFH, occurrence of heparin-induced thrombocytopenia is not infrequent in these patients and requires careful individual management.

CONCLUSIONS

Antithrombotic therapy is an essential component of cardiac surgery. Yet, with the exception of antiplatelet agents in CABG patients, antithrombotic therapy is often based on the clinical experience of medical teams more than on an evidence-based assessment of the literature.

Postoperative treatment with low molecular weight heparin after right heart assist for coronary artery bypass grafting

Right heart assist (RHA) was used for coronary artery bypass grafting (CABG). We explored the affection of the coagulation system during surgery and evaluated two different antithrombotic treatments postoperatively. The pilot study comprised 14 patients. During surgery activated clotting time (ACT) was kept > 200 sec. By random the patients were selected to different postoperative treatments. The control group received acetyl salicylic acid (ASA) 150 mg daily, the intervention group received ASA 150 mg daily and Low Molecular Weight Heparin (LMWH) 5000 IU x2 for three days. Serum levels of prothrombin fragment 1 and 2 (F 1 + 2), plasmin-antiplasmin product (PAP), anti-Xa activity and functional antithrombin (ATIII) were measured. During surgery there was no increase of F 1 + 2 or PAP. After protamin was administered there was a significant increase of F 1 + 2 but not in PAP during the next 6 hours. Postoperative antithrombotic treatment with LMWH seems to normalise F1 + 2 while ASA does not. ACT level > 200 sec. seems sufficient for RHA-CABG surgery. Fibrinolytic agents are not necessary. It seems that postoperative LMWH treatment prevents increased thrombin formation. General recommendations with respect to antithrombotic treatment beyond ASA can not be made based on study.

Recombinant human antithrombin III restores heparin responsiveness and decreases activation of coagulation in heparin-resistant patients during cardiopulmonary bypass

OBJECTIVES

We sought to evaluate the efficacy of recombinant human antithrombin III for restoration of heparin responsiveness in heparin-resistant patients scheduled for cardiac surgery.

METHODS

This was a multicenter, randomized, double-blind, placebo-controlled study in heparin-resistant patients undergoing elective cardiac surgery. Patients were considered heparin resistant if the activated clotting time was less than 480 seconds after 400 U/kg heparin. Fifty-two heparin-resistant patients were randomized into 2 cohorts. One cohort received a single bolus (75 U/kg) of recombinant human antithrombin III (n = 28), and the other, the placebo group (n = 24), received a normal saline bolus. If the activated clotting time remained less than 480 seconds, this was defined as treatment failure, and 2 units of fresh frozen plasma were transfused. Patients were monitored for adverse events during hospitalization.

RESULTS

Six (21%) of the patients in the recombinant human antithrombin III group received fresh frozen plasma transfusions compared with 22 (92%) of the placebo-treated patients ( P < .001). Two units of fresh frozen plasma did not restore heparin responsiveness. There was no increased incidence of adverse events associated with recombinant human antithrombin III administration. Postoperative 24-hour chest tube bleeding was not different in the 2 groups. Surrogate measures of hemostatic activation suggested that there was less activation of the hemostatic system during cardiopulmonary bypass in the recombinant human antithrombin III group.

CONCLUSION

Treatment with recombinant human antithrombin III in a dose of 75 U/kg is effective in restoring heparin responsiveness and promoting therapeutic anticoagulation for cardiopulmonary bypass in the majority of heparin-resistant patients. Two units of fresh frozen plasma were insufficient to restore heparin responsiveness. There was no apparent increase in bleeding associated with recombinant human antithrombin III.

An Evaluation of the Effects of a Standard Heparin Dose on Thrombin Inhibition During Cardiopulmonary Bypass in Neonates

We compared the adequacy of heparinization in neonates and older children undergoing cardiopulmonary bypass (CPB) by measuring heparin activity, thrombin formation, and thrombin activity. Ten neonates and 10 older children were administered 400 U/kg of heparin before CPB. Heparin anti-Xa activity, prothrombin fragment 1.2 (F1.2), and fibrinopeptide A (FPA) were measured at baseline, after 30 min on CPB, immediately post-CPB, and 3 and 24 h post-CPB. Heparin anti-Xa activity was significantly decreased during and immediately post-CPB in the neonatal group. F1.2 and FPA levels in neonates were significantly higher at baseline, decreased with the commencement of CPB, and increased to levels higher than those in older children after CPB. Our data show that with standard heparin doses, neonates exhibit less heparin anti-Xa activity during CPB. Higher baseline levels of F1.2 and FPA present in neonates indicate preoperative activation of their coagulation systems as compared with older children. Although F1.2 and FPA levels initially decrease with the commencement of CPB, probably representing hemodilution, the subsequent increase in these markers indicates significantly more thrombin formation and activity during and after CPB. These results raise the concern that 400 U/kg of heparin may not adequately suppress thrombin formation and activity in neonates undergoing CPB.

Postoperative antithrombin levels and outcome in cardiac operations

OBJECTIVE

During cardiac operations with cardiopulmonary bypass surgery, antithrombin is consumed and low levels of antithrombin activity are commonly observed at admission to the intensive care unit (ICU). This study investigates the association between antithrombin activity at admission to the ICU (ICU-antithrombin activity) and various outcome variables.

DESIGN

The authors conducted a prospective, observational cohort study.

SETTING

The study was conducted at a university hospital.

PATIENTS

The study consisted of 647 consecutive patients who had undergone cardiac surgery with cardiopulmonary bypass.

MEASUREMENTS AND MAIN RESULTS

ICU-antithrombin activity significantly (p < .001) decreased with respect to preoperative values. As seen with univariate analysis, low levels of ICU-antithrombin activity were significantly associated with higher blood loss, prolonged mechanical ventilation time and ICU stay, a higher incidence of allogeneic blood products use, surgical reexploration, low cardiac output syndrome, adverse neurologic events, thromboembolic events, renal dysfunction, and hospital mortality. When corrected for the other explanatory variables, low levels of ICU-antithrombin activity remained independently associated with a prolonged ICU stay (p = .003) and with a higher incidence of surgical reexploration (p = .023), adverse neurologic events (p = .001), and thromboembolic events (p = .036). An ICU-antithrombin activity value of <58% was found to be predictive of prolonged ICU stay, with a sensitivity of 67% and a specificity of 83%.

CONCLUSIONS

Low levels of ICU-antithrombin activity are associated with a poor outcome in cardiac surgery; ICU-antithrombin activity is predictive of prolonged ICU stay.

Factor V Leiden and perioperative risk

Factor V Leiden (FVL) is the most common known inherited cause of thrombophilia; it is present in approximately 5% of the Caucasian population. Although the risk of venous thrombosis associated with this polymorphism in various medical settings is well described, its effect on perioperative risk is only beginning to be explored. Specifically, there are few studies addressing the potential risks of FVL in the surgical population, in which both hemorrhagic and thrombotic complications convey substantial clinical and economic significance. There are speculations and unproven hypotheses regarding FVL in this population, and these therefore highlight the need to comprehensively address this issue. This review will describe the physiology of the FVL mutation, briefly clarify its risk in the nonsurgical setting, and assess current data regarding FVL in noncardiac and cardiac surgery. Finally, a summary of current clinical evidence and a plan for more detailed investigation of this potentially significant risk factor will be proposed.

Effects of tirofiban on haemostatic activation in vitro

BACKGROUND

Thrombin plays a critical role in normal haemostasis and pathological thrombosis. Heparin has long been a mainstay choice of antithrombotic regimen in cardiac patients, but persistent thrombin generation seems to occur during heparin therapy. Because platelets are integral to primary haemostasis and clot formation, we evaluated the use of tirofiban (Aggrastat),a platelet inhibitor, as a therapy to improve heparin sensitivity and delay thrombin formation.

METHODS

Blood samples were obtained from healthy subjects (n=8) and cardiac surgical patients (n=34). Thrombin formation was measured in platelet-rich plasma with a Thrombogram-Ascent fluorescent plate reader system. Platelet inhibition by tirofiban was evaluated with Plateletworks, and the interaction of tirofiban and heparin (>1.5 U ml(-1)) on clot formation was evaluated with Sonoclot Analyzer or kaolin activated clotting times (ACTs).

RESULTS

Addition of tirofiban (70-280 ng ml(-1)) progressively delayed onset of thrombin generation triggered by adenosine diphosphate (ADP). Plateletworks showed platelet inhibition with tirofiban (>35 ng ml(-1)), whereas heparin per se failed to produce platelet inhibition at 7 U ml(-1). Heparin (1.5 U ml(-1)) slowed the onset and rate of fibrin formation on Sonoclot analyses, and this was further slowed after addition of tirofiban (70 ng ml(-1)) to heparin-containing blood samples. Significant increases in ACT at all heparin concentrations were observed with the addition of tirofiban (70 ng ml(-1)). The addition of antithrombin (0.2 units/ml) to heparinized blood samples further prolonged ACTs, but the difference was not statistically significant when compared with heparin alone.

CONCLUSION

Tirofiban delays platelet activation-mediated thrombin generation and prolongs ACT in heparinized blood.

Surveillance de l'anticoagulation des circulations extracorporelles par l'héparine non fractionnée : quels sont les problèmes non résolus ?

Cardiac surgery with extracorporeal circulation induces major alterations of haemostasis and requires high level of anticoagulation, usually achieved by unfractionated heparin infusion. Optimization of anticoagulant regimen, through adapted biological monitoring, can probably improve postoperative course, at least for postoperative haemostatic status. Despite increasing knowledge on extracorporeal circulation-induced haemostatic abnormalities and the development of new biological devices for heparin monitoring, the optimal level of anticoagulation remains matter of debate, as well as the monitoring procedures. This critical review presents the current available data on heparin anticoagulation and monitoring in this specific context, and underlines the pending issues about anticoagulation management during extracorporeal bypass.

Devices for Monitoring Heparin and Protamine in the Operating Room

Ongoing monitoring of heparin anticoagulation is an essential component of many cardiothoracic and vascular surgical procedures in order to prevent significant thrombotic and hemorrhagic complications. The classic test to assess high-dose (>1 unitlmL) heparin anticoagulation is the activated clotting time. Although simple to perform, the activated clotting time has many variations and can be affected by a number of nonanalytical and patient-related factors. Correlation with the heparin concentration may be poor. Alternatively, other test systems assess the individual patient's responsiveness to heparin in order to customize the heparin administration and subsequent protamine neutralization. The choice of test and system depends on the clinical application and the desired outcome. Regulatory and accreditation standards govern this type of testing; modern instrumentation can facilitate compliance with these standards. Understanding of the nature of the test and its performance under a variety of conditions is critical for proper interpretation.

Antithrombin III concentrate to treat heparin resistance in patients undergoing cardiac surgery

OBJECTIVE

The purpose of this report is to describe the clinical use of antithrombin III concentrate in 53 patients who were found, in the operating room before cardiopulmonary bypass, to be heparin resistant.

METHOD

Resistance to heparin was determined to be present when greater than 600 U/kg body weight of heparin failed to prolong the kaolin-activated clotting time to more than 600 seconds in 53 aprotinin-treated patients. Blood samples were obtained for subsequent antithrombin III activity determination. Patients were then administered 500 U of antithrombin III concentrate, and the activated clotting time was remeasured. If the activated clotting time remained less than 600 seconds, a second 500-U dose was given.

RESULTS

Of the 53 patients, 45 (85%) had subnormal measured antithrombin III activity, and the mean plasma antithrombin III activity level for the entire group was 67% (normal 80%-120%). Administration of antithrombin III concentrate (500 U in 45 patients and 1000 U in 8 patients) resulted in prolongation of the mean activated clotting time from 492 to 789 seconds without additional heparin. The mean heparin dose response increased from 36.5 to 69.3 s x U(-1) x mL(-1) with antithrombin III treatment. Only one patient did not achieve the target activated clotting time, despite administration of greater than 600 U/kg heparin and 1000 U of antithrombin III concentrate, and was treated with fresh-frozen plasma.

CONCLUSIONS

On the basis of the criterion used in this report, most of the patients defined as being heparin resistant had subnormal plasma antithrombin III activity. Treatment with antithrombin III concentrate resulted in potentiation of the heparin effect to meet predetermined activated clotting time thresholds and allow for cardiopulmonary bypass.

Pharmacologic preservation of the hemostatic system during cardiac surgery

Bleeding after cardiac surgery remains a major potential problem. Numerous pharmacologic approaches to attenuating hemostatic system activation in cardiac surgery patients have been studied to further improve patient management. Therapeutic approaches studied include inhibiting thrombin generation or activation, preserving platelet function, and decreasing the need for transfusion of allogeneic blood products. Pharmacologic approaches to reduce bleeding and transfusion requirements in cardiac surgery patients are based on either preventing or reversing the defects associated with the CPB-induced coagulopathy. The increasing use of platelet inhibitors (clopidogrel and IIb/IIIa receptor antagonists) and new anticoagulants (low-molecular weight heparins, pentasaccharide, recombinant hirudin, bivalirudin, and argatroban) also pose interesting problems in managing cardiac surgery patients. Aprotinin and lysine analogues (epsilon-aminocaproic acid and tranexamic acid) have become mainstay therapeutic agents to prevent bleeding and the potential need for allogeneic transfusion. Newer therapies that are important to consider include the potential of recombinant activated factor VIIa as a therapy for refractory bleeding after cardiac surgery.

An investigation of a new activated clotting time "MAX-ACT" in patients undergoing extracorporeal circulation

Activated clotting time (ACT) is a test used in the operating room for monitoring heparin effect. However, ACT does not correlate with heparin levels because of its lack of specificity for heparin and its variability during hypothermia and hemodilution on cardiopulmonary bypass (CPB). A modified ACT using maximal activation of Factor XII, MAX-ACT (Actalyke MAX-ACT; Array Medical, Somerville, NJ), may be less variable and more closely related to heparin levels. We compared MAX-ACT with ACT in 27 patients undergoing CPB. We measured ACT, MAX-ACT, temperature, and hematocrit at six time points: baseline; postheparin; on CPB 30, 60, and 90 min; and postprotamine. Additionally, we assessed anti-Factor Xa heparin activity and antithrombin III activity at four of these six time points. With institution of CPB and hemodilution, MAX-ACT and ACT did not change significantly but had a tendency to increase, whereas concomitant heparin levels decreased (P = 0.065). Neither test correlated with heparin levels. ACT and MAX-ACT did not differ during normothermia but did during hypothermia, and ACT was significantly longer than MAX-ACT (P = 0.009). At the postheparin time point, ACT-heparin sensitivity (defined as [ACT postheparin - ACT baseline]/[heparin concentration postheparin - heparin concentration baseline]) was greater than MAX-ACT-heparin sensitivity (analogous calculation for MAX-ACT; 520 [266 - 9366] s. U(-1). mL(-1) vs 468 [203 - 8833] s. U(-1). mL(-1); P = 0.022).

IMPLICATIONS

MAX-ACT (a new activated clotting time [ACT] test) uses more maximal clotting activation in vitro and, although it is less susceptible to increase because of hypothermia and hemodilution than ACT, lack of correlation with heparin levels remains a persistent limitation.