Are activated clotting times helpful in the management of anticoagulation with subcutaneous low-molecular-weight heparin?

Intracardiac ultrasound-guided transseptal puncture in horses: Outcome, follow-up, and perioperative anticoagulant treatment

BACKGROUND

Cardiac catheterizations in horses are mainly performed in the right heart, as access to the left heart traditionally requires an arterial approach. Transseptal puncture (TSP) has been adapted for horses but data on follow-up and closure of the iatrogenic atrial septal defect (iASD) are lacking.

HYPOTHESIS/OBJECTIVES

To perform TSP and assess postoperative complications and iASD closure over a minimum of 4 weeks.

ANIMALS

Eleven healthy adult horses.

METHODS

Transseptal puncture was performed under general anesthesia. Serum cardiac troponin I concentrations were measured before and after puncture. Weekly, iASD closure was monitored using transthoracic and intracardiac echocardiography. Relationship between activated clotting time and anti-factor Xa activity during postoperative enoxaparin treatment was assessed in vitro and in vivo.

RESULTS

Transseptal puncture was successfully achieved in all horses within a median duration of 22 (range, 10-104) minutes. Balloon dilatation of the puncture site for sheath advancement was needed in 4 horses. Atrial arrhythmias occurred in 9/11 horses, including atrial premature depolarizations (N = 1), atrial tachycardia (N = 5), and fibrillation (N = 3). Serum cardiac troponin I concentrations increased after TSP, but remained under the reference value in 10/11 horses. Median time to iASD closure was 14 (1-35) days. Activated clotting time correlated with anti-factor Xa activity in vitro but not in vivo.

CONCLUSIONS AND CLINICAL IMPORTANCE

Transseptal puncture was successfully performed in all horses. The technique was safe and spontaneous iASD closure occurred in all horses. Clinical application of TSP will allow characterization and treatment of left-sided arrhythmias in horses.

In vitro thrombogenicity evaluation of rotary blood pumps by thromboelastometry

In vitro thrombogenicity tests for rotary blood pumps (RBPs) could benefit from assessing coagulation kinematics, as RBP design improves. In this feasibility study, we investigated if the method of thromboelastometry (TEM) is able to assess coagulation kinematics under the in vitro conditions of RBP tests. We conducted in vitro thrombogenicity tests (n=4) by placing Deltastream^® DP3 pumps into test loops that were filled with 150 mL of slightly anti-coagulated porcine blood, adjusted to an activated clotting time (ACT) well below clinically recommended levels. Blood samples were taken at certain time points during the experiment until a continuous decrease in pump flow indicated major thrombus formation. Blood samples were analyzed for ACT, platelet count (PLT), and several TEM parameters. While visible thrombus formation was observed in three pumps, ACT indicated an ongoing activation of coagulation, PLT might have indicated platelet consumption. Unexpectedly, most TEM results gave no clear indications. Nonetheless, TEM clotting time obtained by non-anticoagulated and chemically non-activated whole blood (HEPNATEM-CT) appeared to be more sensitive for the activation of coagulation in vitro than ACT, which might be of interest for future pump tests. However, more research regarding standardization of thrombogenicity pump tests is urgently required.

Perioperative thromboprophylaxis in liver transplant patients

Improvements in surgical and anesthetic procedures have increased patient survival after liver transplantation (LT). However, the perioperative period of LT can still be affected by several complications. Among these, thromboembolic complications (intracardiac thrombosis, pulmonary embolism, hepatic artery and portal vein thrombosis) are relatively common causes of increased morbidity and mortality. The benefit of thromboprophylaxis in general surgical patients has already been established, but it is not the standard of care in LT recipients. LT is associated with a high bleeding risk, as it is performed in a setting of already unstable hemostasis. For this reason, the role of routine perioperative prophylactic anticoagulation is usually restricted. However, recent data have shown that the bleeding tendency of cirrhotic patients is not an expression of an acquired bleeding disorder but rather of coexisting factors (portal hypertension, hypervolemia and infections). Furthermore, in cirrhotic patients, the new paradigm of ‘‘rebalanced hemostasis’’ can easily tip towards hypercoagulability because of the recently described enhanced thrombin generation, procoagulant changes in fibrin structure and platelet hyperreactivity. This new coagulation balance, along with improvements in surgical techniques and critical support, has led to a dramatic reduction in transfusion requirements, and the intraoperative thromboembolic-favoring factors (venous stasis, vessels clamping, surgical injury) have increased the awareness of thrombotic complications and led clinicians to reconsider the limited use of anticoagulants or antiplatelets in the postoperative period of LT.

Anticoagulation Monitoring

Optimal management of anticoagulant therapy requires an understanding of the laboratory tests often employed to guide therapy. The activated partial thromboplastin time (aPTT) can detect abnormalities in the intrinsic and common clotting pathways. Despite numerous limitations in the aPTT test, it remains the gold standard for monitoring unfractionated heparin and direct thrombin inhibitor therapy. The aPTT can be performed in the central laboratory or at the bedside (point of care [POC] testing). The activated clotting time (ACT) is a POC test that is routinely employed to monitor high-dose heparin during invasive and surgical procedures. The ACT therapeutic range will depend on the specific procedure or surgery being performed. Heparin levels are becoming more routinely available and are used to establish the aPTT therapeutic range for heparin therapy as well as for direct monitoring of heparin and low-molecular-weight heparin therapy. The international normalized ratio (INR) is the gold standard for monitoring warfarin patients. The target INR depends on the indication for anticoagulation. POC monitoring for warfarin is becoming increasingly used. Clinicians should have a thorough understanding of the benefits as well as the limitations of warfarin POC monitoring.

Monitoring and Reversal of Anticoagulation and Antiplatelets

Since percutaneous transluminal coronary angioplasty was first described and the breakthrough studies of the role of stents were reported, the evolution in anticoagulation and antiplatelet therapy used during percutaneous coronary intervention (PCI) has reduced periprocedural ischemic events and stent thrombosis. Although greater combinations and doses of anticoagulation with antiplatelets seem to provide the best protection against thrombogenic and embolic events, there is a significant trade-off with a higher risk of major and minor bleeding episodes. This review article expands on each of the commonly used antiplatelet and anticoagulants used at time of PCI, focusing on drug monitoring and reversal.

Point-of-care testing in haemostasis

Point-of-care testing (POCT) in haematology has seen a significant increase in both the spectrum of tests available and the number of tests performed annually. POCT is frequently undertaken with the belief that this will reduce the turnaround time for results and so improve patient care. The most obvious example of POCT in haemostasis is the out-of-hospital monitoring of the International Normalized Ratio in patients receiving a vitamin K antagonist, such as warfarin. Other areas include the use of the Activated Clotting Time to monitor anticoagulation for patients on cardio-pulmonary bypass, platelet function testing to identify patients with apparent aspirin or clopidogrel resistance and thrombelastography to guide blood product replacement during cardiac and hepatic surgery. In contrast to laboratory testing, POCT is frequently undertaken by untrained or semi-trained individuals and in many cases is not subject to the same strict quality control programmes that exist in the central laboratory. Although external quality assessment programmes do exist for some POCT assays these are still relatively few. The use of POCT in haematology, particularly in the field of haemostasis, is likely to expand and it is important that systems are in place to ensure that the generated results are accurate and precise.

Administration of dalteparin based on the activated clotting time for prophylaxis of hepatic vessel thrombosis in living donor liver transplantation

Beginning in 2004, dalteparin doses based on activated clotting time (ACT) were administered for hepatic vessel thrombosis prophylaxis in living donor liver transplantation (LDLT). We verified the feasibility of this new therapy by comparing it with the previous one. From 1993 through 2008, 42 metabolic liver patients who underwent LDLT were divided into two groups. Group A (1993-2003, n = 32) was administered a fixed dalteparin dose and a large amount of fresh frozen plasma (FFP); Group B (2004-2008, n = 10) was administered an appropriate dosage of dalteparin to maintain the ACT levels from 140 to 150 seconds and a small amount of FFP. Group B was administered a lesser amount of FFP and more dalteparin. This resulted in longer activated partial thromboplastin time, lower fibrinogen degradation products D-dimer, and lower aspartate aminotransferase levels compared to group A; all differences were significant. Group B showed neither thrombotic nor hemorrhagic complications. Anticoagulation therapy comprising adjustment of the dalteparin dose based on ACT reduces thrombotic complications without increasing hemorrhagic complications. ACT measurement is a simple, reliable method for bedside monitoring of dalteparin anticoagulant effects for LDLT.

Systemic coagulation changes caused by pulmonary artery catheters: laboratory findings and clinical correlation

BACKGROUND

A higher rate of pulmonary embolism has been associated with pulmonary artery (PA) catheters; however, no mechanism has been described. Conventional tests of coagulation reveal no changes related to PA catheterization. The purpose of this study was to determine whether PA catheterization resulted in a hypercoagulable state detectable by thrombelastography (TEG).

METHODS

ANIMAL

Healthy, anesthetized, swine (n = 19) underwent PA catheterization. Samples were drawn from 7F femoral arterial catheters before and two hours after PA catheterization, at 5 mL/min, and analyzed (native whole blood, n = 15, kaolin activated blood, n = 4) by TEG (Hemoscope, Niles, IL) at precisely two minutes. Human: An IRB-approved prospective, observational trial was conducted in critically ill patients (n = 19). Samples were drawn from 22-gauge radial artery catheters, before and three hours after PA catheterization. Kaolin-activated TEG samples were analyzed at precisely five minutes. Data are mean +/- SE; Groups were compared with analysis of variance and significance was assessed at the 95% confidence interval.

RESULTS

In both animals and patients, PA catheterization truncated R times (time to initial fibrin formation). In swine, the R times were 17.6 +/- 1.3 minutes (native) and 3.8 +/- 0.4 (kaolin) before PA catheterization, and decreased to 6.3 +/- 1.0 minutes (p = 0.002) and 1.9 +/- 0.5 minutes (p = 0.010) afterward. There were no changes in pH or temperature during the experiment. In patients, 4 of 19 were excluded for protocol violations. The R time was 6.3 +/- 1.0 minutes (kaolin) before and 3.0 +/- 0.3 minutes after catheterization (p = 0.003). No changes were observed in conventional coagulation parameters, temperature or pH.

CONCLUSION

In healthy swine, and critically ill patients, PA catheters may enhance thrombin formation and fibrin polymerization, indicating a systemic hypercoagulable state. This may explain why PA catheters are associated with an increased risk of pulmonary emboli.

Anticoagulation Monitoring Part 2: Unfractionated Heparin and Low-Molecular-Weight Heparin

OBJECTIVE

To review the availability, mechanisms, limitations, and clinical application of point-of-care (POC) devices used in monitoring anticoagulation with unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs).

DATA SOURCES

Articles were identified through a MEDLINE search (1966–August 2004), device manufacturer Web sites, additional references listed in articles and Web sites, and abstracts from scientific meetings.

STUDY SELECTION AND DATA EXTRACTION

English-language literature from clinical trials was reviewed to evaluate the accuracy, reliability, and clinical application of POC monitoring devices.

DATA SYNTHESIS

The activated partial thromboplastin time (aPTT) and activated clotting time (ACT) are common tests for monitoring anticoagulation with UFH. Multiple devices are available for POC aPTT, ACT, and heparin concentration testing. The aPTT therapeutic range for UFH will vary depending upon the reagent and instrument employed. Although recommended by the American College of Chest Physicians Seventh Conference on Antithrombotic and Thrombolytic Therapy, establishing a heparin concentration–derived therapeutic range for UFH is rarely performed. Additional research evaluating anti-factor Xa monitoring of LMWHs using POC testing is necessary.

CONCLUSIONS

Multiple POC devices are available to monitor anticoagulation with UFH. For each test, there is some variability in results between devices and between reagents used in the same device. Despite these limitations, POC anticoagulation monitoring of UFH using aPTT and, more often, ACT is common in clinical practice, particularly when evaluating anticoagulation associated with interventional cardiology procedures and cardiopulmonary bypass surgery.

Epidural blood patch in a patient taking enoxaparin

A 36-year-old, 204-kg parturient with a past medical history of Factor V Leiden requiring enoxaparin therapy developed a postdural puncture headache. With careful coordination of her enoxaparin dosing, an epidural blood patch was successfully performed. Performance of a blood patch in patients taking enoxaparin involves the withholding of the medication for a specific period.

Factor Xa-activated whole blood clotting time (Xa-ACT) for bedside monitoring of dalteparin anticoagulation during haemodialysis

BACKGROUND

Low molecular weight heparins (LMWH) like dalteparin are increasingly used for anticoagulation during haemodialysis (HD). The available laboratory tests for monitoring LMWH anticoagulation are time-consuming and expensive, and the suitability of the conventional activated clotting time (ACT) is controversial. A simple and cheap bedside test would be useful.

METHODS

We studied the factor Xa-activated whole blood clotting time (Xa-ACT) in vitro and in vivo in nine patients undergoing chronic HD with i.v. dalteparin bolus anticoagulation and compared it with the conventional ACT. Plasma anti-factor Xa (antiXa) activity was determined with a chromogenic assay. Thrombin-antithrombin complexes were measured to detect coagulation activation.

RESULTS

Xa-ACT and ACT were prolonged with rising dalteparin concentration. In vitro, both clotting times were strongly correlated with the antiXa levels (r = 0.94 and 0.89, respectively). Nevertheless, compared with the ACT, the Xa-ACT was considerably more sensitive to the LMWH in vitro (healthy blood: Xa-ACT 90 s/U vs ACT 26 s/U; uraemic blood: Xa-ACT 96 s/U vs ACT 31 s/U) as well as in vivo (Xa-ACT 81 s/U vs ACT 22 s/U) and reflected different intensities of anticoagulation. An initial dalteparin bolus of 80+/-11 U/kg body weight was able to prevent coagulation activation for up to 4 h of HD.

CONCLUSION

For monitoring LMWH anticoagulation the Xa-ACT was superior to the conventional ACT in vitro as well as in vivo during HD. The Xa-ACT can be useful as a LMWH bedside test. The ACT was not sensitive enough to serve as a LMWH monitoring tool.

The activated clotting time can be used to monitor the low molecular weight heparin dalteparin after intravenous administration

OBJECTIVES

This study was designed to compare the dose response of dalteparin versus unfractionated heparin (UFH) on the activated clotting time (ACT), and to determine whether the ACT can be used to monitor intravenous (IV) dalteparin during percutaneous coronary intervention (PCI).

BACKGROUND

The use of low molecular weight heparin (LMWH) during PCI has been limited by the presumed inability to monitor its anticoagulant effect using bedside assays.

METHODS

This study was performed in three phases. In vitro, ACTs were measured on volunteer (n = 10) blood samples spiked with increasing concentrations of dalteparin or UFH. To extend these observations in vivo, ACTs were then measured in patients (n = 15) who were sequentially treated with IV dalteparin and then UFH. Finally, a larger monitoring study was undertaken involving patients (n = 110) who received dalteparin 60 or 80 international U (IU)/kg alone or followed by abciximab. We measured ACT (Hemochron), activated partial thromboplastin time (aPTT), plasma anti-Xa and anti-IIa levels, tissue factor pathway inhibitor (TFPI) concentration, and plasma dalteparin concentration.

RESULTS

Dalteparin induced a significant rise in the ACT with a smaller degree of variance as compared to UFH. Five min after administration of IV dalteparin 80 IU/kg the ACT increased from 125 s (122 s, 129 s) to 184 s (176 s, 191 s) (p < 0.001). The aPTT, anti-Xa and anti-IIa activities, and TFPI concentration also demonstrated significant increases following IV dalteparin.

CONCLUSIONS

The ACT and aPTT are sensitive to IV dalteparin at clinically relevant doses. These data suggest that the ACT may be useful in monitoring the anticoagulant effect of intravenously administered dalteparin during PCI.

Assessment of anticoagulation using activated clotting times in patients receiving intravenous enoxaparin during percutaneous coronary intervention

Enoxaparin is being used more frequently in patients undergoing percutaneous coronary intervention (PCI). In this study, we determined the effect of intravenous enoxaparin on activated clotting time (ACT) measurements in the setting of PCI. In 67 consecutive patients, either 1 mg/kg intravenous enoxaparin alone was given for anticoagulation or 0.75 mg/kg given in patients receiving eptifibatide. ACT was measured before and 5 min following enoxaparin administration. After 1 mg/kg enoxaparin (n = 22), mean ACT increased from 122 +/- 22 to 199 +/- 20 sec. After 0.75 mg/kg enoxaparin and eptifibatide (n = 45), mean ACT increased from 125 +/- 22 to 194 +/- 24 sec. The mean increase in ACT was 77 +/- 26 sec in the 1 mg/kg group and 69 +/- 23 sec in the 0.75 mg/kg group (both P values < 0.0001). Moreover, in a subgroup of 26 patients, there was an excellent correlation (r = 0.86) between ACTs and the ENOX test, a new point-of-care test for assessing enoxaparin anticoagulation. None of the patients had transient abrupt closure, thrombus formation, major bleeding, or required urgent revascularization. Intravenous enoxaparin at clinically relevant doses with and without eptifibatide increases ACT levels at 5 min in patients undergoing PCI. These data suggest the ACT may be useful in the assessment of anticoagulation by enoxaparin.