The Relationship of Antiphospholipid Antibodies to Thromboembolic Disease in Systemic Lupus Erythematosus: A Cross-Sectional Study

In order to determine whether an association exists between antiphospholipid antibodies (APLA) and thromboembolic events in patients with systemic lupus erythematosus (SLE), we performed a cross-sectional study of consecutive unselected SLE patients. The occurrence of previous thromboembolic events was determined by investigators blinded to the APLA status of the patients by critical review of objective tests that had been performed at the time of symptomatic presentation and by performing venous Doppler ultrasound of the legs to elicit venous reflux as an indication of previous venous thrombosis. The presence of APLA was determined by coagulation assays for the lupus anticoagulant (LA) using five tests with well-defined control ranges and by ELISA assay for anticardiolipin antibodies (ACLA). These tests were measured on two separate occasions. The results of the study demonstrate a statistically significant association between persistently abnormal ACLA assays and thromboembolic events and a non-significant trend between persistently abnormal LA and thromboembolic events. Transient abnormalities of LA and ACLA were less strongly associated with thromboembolic events. We conclude that in patients with SLE, there is a significant association between thromboembolism and APLA.

Heparin Effect on Bone Density

In order to provide estimates of the risks of symptomatic osteoporosis and reduced bone density in premenopausal women treated with long-term (greater than 1 month) heparin therapy, we evaluated a cohort of 61 consecutive premenopausal women previously treated with long-term heparin (cases) and a group of controls matched for age, parity and duration between the last pregnancy and evaluation. All patients underwent dual photon absorptiometry of the lumbar spine and single photon absorptiometry of the wrist and most cases underwent plain lateral radiography of the thoracolumbar spine in order to exclude silent fractures. Although none of the cases suffered symptomatic fractures (0 of 61, 95% confidence intervals 0.0 to 5.9%), there was a significantly greater proportion of cases than controls with bone density below our pre-defined levels. The long-term implications of our findings are uncertain but because it is possible that the reduction in bone density predisposes women to fractures, this potential risk should be considered when treating women with long-term heparin.

A Low Molecular Weight Heparin Alters the Fetal Coagulation System in the Pregnant Sheep

Standard heparin and a LMWH, CY222 do not cross the placenta nor alter fetal coagulation when injected into the pregnant ewe. We found that another LMWH, Pharmuka-10169 (PK-10169) alters fetal coagulation without crossing the placenta in the pregnant sheep. To characterize this anticoagulant we measured the in vitro and in vivo effects of 125I-PK-10169 in maternal and fetal plasmas following administration of PK-10169 to the mother or fetus. The fetal anticoagulant activity was not neutralizable by protamine sulphate and was attributable to the inhibition of thrombin but not factor Xa. In vitro, the fetal anticoagulant activity had properties similar to dermatan sulphate : both catalyzed the inhibition of thrombin but not factor Xa by sheep plasma; and neither was neutralizable by protamine sulphate. These effects were due to the enhanced neutralization of thrombin by heparin cofactor II. We conclude that PK-10169 does not cross the placenta, but does induce the release of an endogenous dermatan sulphate-like substance which alters fetal coagulation.

Endothelial Cells Produce a Lipoxygenase Derived Chemo-Repellent which Influences Platelet/Endothelial Cell Interactions – Effect of Aspirin and Salicylate

We performed experiments to determine whether endothelial cells synthesize phospholipid metabolites via the lipoxygenase pathway and whether these metabolites influence platelet/vessel wall interactions. Monolayers of cultured human endothelial cells were incubated with 14C-arachidonic acid and their cyclo-oxygenase and lipoxygenase metabolites were extracted and identified by radioimmunoassay, thin layer chromatography and high performance liquid chromatography. We found that in addition to the membrane-associated production of PGI2, endothelial cells synthesized a cytosol-associated metabolite, LOX, which was presumably derived through the lipoxygenase pathway. Inhibition of LOX was associated with an increase in PGI2 production and inhibition of PGI2 with an increase in LOX production. Under either condition, platelet adhesion to cultured endothelial cells was significantly decreased. In contrast, when both PGI2 and LOX production were inhibited, platelet adhesion to endothelial cells was enhanced. Furthermore, when LOX was bound to a thrombogenic surface, platelet adhesion was significantly decreased whereas when arachidonic acid or 12-HETE was bound to the surface, platelet adhesion was increased. We conclude that endothelial cells produce not only a cyclo-oxygenase metabolite, but also a lipoxygenase metabolite, both of which influence platelet/endothelial cell interactions.

Effects on Thrombin Generation of Single Injections of Hirulog™ in Patients with Calf Vein Thrombosis

1. Study objective: To determine whether single injections of Hirulog, a direct thrombin inhibitor, can inhibit thrombin generation in patients with calf vein thrombosis and, if so, if the inhibition is sustained.

2. Design: Phase II open label cohort study.

3. Setting: Tertiary-care referral centres, university affiliated hospitals.

4. Patients: 10 patients with venographically-demonstrated calf vein thrombosis.

5. Intervention: Patients received a single injection of Hirulog, either 1.0 mg/kg subcutaneously or 0.6 mg/kg as a 15 min intravenous infusion. Prothrombin fragment (F1+2) levels, as an index of thrombin generation, were measured before as well as 6 h post- and 24 h post-Hirulog administration. Patients were followed with non-invasive tests to detect thrombus extension into the proximal veins.

6. Results: There was a significant reduction in the levels of F1+2 with both regimens, 6 h after Hirulog. The Fl+2 levels 24 h post-Hirulog showed a significant increase relative to the 6 h post-Hirulog results. One patient developed thrombus extension into the popliteal vein and was treated with conventional anticoagulants.

7. Conclusion: The single injections of Hirulog used in the study produced incomplete and temporary suppression of F1+2. Complete and permanent inhibition of thrombin generation with Hirulog in patients with calf vein thrombosis may require higher doses, multiple subcutaneous injections and/or prolonged intravenous infusion.

Catalysis of Thrombin Inhibition Provides an Index for Estimating the Antithrombotic Potential of Glycosaminoglycans in Rabbits

Previous studies have demonstrated that standard anticoagulant tests are poor indices of the antithrombotic potential of glycosaminoglycans which are weak catalysts of the thrombinantithrombin III reaction. In this study we investigated whether the catalysis of thrombin inhibition by plasma could serve as a reliable index for assessing the antithrombotic effectiveness of glycosaminoglycans. Equal volumes of 125I-thrombin and control or test plasma were incubated for up to 10 min at 37° C. Inactivation of thrombin was then determined after 7.9% SDS-polyacrylamide gel electrophoresis and subsequent autoradiography. Increasing concentrations of heparin (>0.066 μg/mL or 0.01 USP units/mL) and dermatan sulfate (>0.1 μg/mL) could be readily demonstrated in undiluted plasma by enhanced formation of complexes of thrombin with antithrombin III and heparin cofactor II respectively. However, the detection of any catalytic effect of the two glycosaminoglycans decreased significantly with increasing plasma dilutions. When ex vivo plasmas obtained from rabbits that had been injected with the minimum dose of any one of seven glycosaminoglycans required to achieve their optimal antithrombotic effect were assessed for their ability to catalyse thrombin inhibition, there was approximately a 2-fold increase in the amount of thrombin inactivated 30 s after the thrombin had been added to the plasma. The enhanced inhibition of thrombin was achieved by catalysis of antithrombin III and/or heparin cofactor II activities. These results suggest that measurement of the catalysis of thrombin inactivation in undiluted plasma is a sensitive and reliable index for estimating the antithrombotic potential of glycosaminoglycans in rabbits.

Multicentric Evaluation of a New PT Reagent Based on Recombinant Human Tissue Factor and Synthetic Phospholipids

A new PT reagent based on recombinant human tissue factor and synthetic phospholipids (phosphatidyl choline and phosphatidyl serine) with defined fatty acid side chains was calibrated against BCT/253 and CRM 149R. A small but consistent bias in the International Sensitivity Index (ISI) value was obtained using either the human or rabbit brain reference material. ISI values were around 1.0 or slightly lower depending on the respective instrument. Mixing studies with factor deficient plasmas showed a high factor sensitivity especially for factor VII as compared to commercial rabbit brain or human placenta thromboplastin. In an international field trial the reagent was tested using fully or semi automated Electra™ coagulometers in 4 different laboratories. Results with normal samples were in excellent agreement among the different laboratories. Mean values were 10.9, 10.9, 11.0, 11,7 s with a range of 9.5 to 12.5 s. Results of males and females were not different. In patients with liver disease very similar PT activities were found as compared to sensitive rabbit brain or human placental thromboplastins. In normals and patients with oral anticoagulation INR values correlated very well against BCT (r = 0.98, regression line y =-0.07 + 0.9 x). The distribution of samples was linear over the whole range. In the comparison against sensitive rabbit brain thromboplastin or human placental thromboplastin similar correlations were found. In a few cases higher INR values were observed for the recombinant reagent especially in patients with intensive treatment. Factor assays in those patients showed at least the strong reduction of one vitamin Independent coagulation factor. Over all the linearity was better against the rabbit brain reagent than against the human placental reagent which is slightly less factor VII sensitive as shown in mixing studies with normal and factor VII deficient plasma. Precision studies in the 4 laboratories showed excellent reproducibility of lyophilised controls or local patient plasma pools for all reagents with a better performance of the recombinant reagent. C. V. values from day to day ranged from 1.3% to 5% for normal and abnormal controls.

These results show that the recombinant PT reagent, especially in conjunction with a precise automated instrument, may improve the results of PT testing and thus may lead to better patient care.

Neutralization of Enoxaparine-lnduced Bleeding by Protamine Sulfate

It has been suggested that protamine sulfate is a poor antidote for the bleeding side-effeets of low molecular weight heparins (LMWHs) in vivo, since protamine sulfate does not completely neutralize the anti-factor Xa activity of LMWHs in vitro or ex vivo. Therefore, we performed experiments to compare directly the abilities of protamine sulfate to neutralize the anticoagulant activities of the LMWH, enoxaparine, and unfractionated heparin ex vivo, with its ability to neutralize the bleeding side-effeets of both compounds in vivo. Bleeding was measured as the amount of blood lost from 5 cuts made in rabbits ears before and after treatment with enoxaparine or unfractionated heparin ± protamine sulfate. Plasma anti-factor Xa and anti-thrombin activities ex vivo, were measured chromogenically. Doses of 400 and 1,500 anti-factor Xa U/kg of heparin and enoxaparine, respectively, were required to enhance blood loss to the same extent. Protamine sulfate completely neutralized blood loss induced by both compounds, but did not neutralize the anti-factor Xa nor antithrombin activities ex vivo. We conclude that protamine sulfate is an effective antidote for the bleeding side-effeets of enoxaparine and unfractionated heparin, despite its inability to completely neutralize their anticoagulant activities.

Effects of Thrombolytic Therapy on Hemorrhage from Post-operative Wounds

Hemorrhage from post-operative wounds in different organs and structures during thrombolytic therapy was investigated in relation to the time after surgical trauma and to the results of laboratory tests of coagulation and fibrinolysis. Streptokinase was given to rabbits at different times following the production of standardized wounds in different organs. Bleeding was frequent and severe when streptokinase was given between one and five days after surgery and was most marked from artery, followed in order by kidney, vein, liver, muscle, gut and skin. Bleeding appeared to be associated with the in vitro demonstration of an active systemic fibrinolytic state together with elevated levels of fibrin degradation products.

An Evaluation of Impedance Plethysmography and 125I-Fibrinogen Leg Scanning in Patients following Hip Surgery

Venous thromboembolism is a common post-operative complication in patients following hip surgery. 125I-fibrinogen leg scanning and impedance plethysmography (IPG), are often used in the detection of venous thrombi in such patients. Information on the sensitivity and specificity of these non-invasive tests for the diagnosis of venous thrombosis following hip surgery is relevant for both patient management and for choosing the appropriate outcome measure for clinical trials evaluating new prophylactic regimens.

We determined the sensitivity and specificity of the IPG alone, the 125I-fibrinogen leg scan alone, as well as the combined use of the two tests from a retrospective analysis of 685 hip surgery patients who participated in clinical trials of anti-thrombotic prophylaxis. These patients were followed prospectively with non-invasive tests. Bilateral venography was attempted either when one or both screening tests became positive or on day 10-14 post-operatively if both screening tests remained negative. Adequate venography was obtained in 1,010 (73.7%) legs and thrombi were identified in 198 (19.6%) legs.

The sensitivities of the IPG and leg scanning were 12.9% and 44.6% respectively; the corresponding specificities were 98.1% and 95.0%. The sensitivity of a positive result on one or both screening tests was 49.6% with a specificity of 93.9%.

Therefore, leg scanning and IPG, even in combination, are not sufficiently accurate to be recommended as the only strategy for the diagnosis of venous thrombosis following hip surgery. Venography should be considered in all patients undergoing surveillance testing either when one or both of the screening tests become positive or on day 10-14 if the screening tests remain negative.

The Relationship between Anti-Factor Xa Level and Clinical Outcome in Patients Receiving Enoxaparine Low Molecular Weight Heparin to Prevent Deep Vein Thrombosis after Hip Replacement

Studies in experimental animals have demonstrated that there is a relationship between levels of low molecular weight (LMW) heparin and both bleeding and inhibition of thrombosis. The relationship between these outcomes and ex vivo anti-factor Xa levels has been examined in 163 patients undergoing total hip replacement who were given prophylaxis once daily with a LMW heparin (enoxaparine). Fifty patients received 60 mg of enoxaparine and 113 received 40 mg, both regimens being administered subcutaneously once daily. Blood samples for anti-factor Xa levels were collected 12 hours after the injection on the day of surgery and on days 1, 3 and 6, postoperatively. The incidence of wound hematoma was 5.3% when the maximum anti-factor Xa level was ≤0.2 units per ml, but increased to 24.5% when the anti-factor Xa level exceeded 0.2 units per ml, P = 0.0008. The incidence of postoperative thrombosis was low (6.3%) if the minimum anti-factor Xa level exceeded 0.1 units per ml, but increased to 14.6% when ≤0.1 units per ml, and to 18.8% if the anti-factor Xa level was ≤0.05 units per ml. Regression analysis revealed that there was a statistically significant relationship between anti-factor Xa level and wound hematoma, P = 0.002 and anti-factor Xa level and thrombosis, P = 0.03. These findings suggest that when enoxaparine is administered as a once daily subcutaneous injection, the 12 hour anti-factor Xa level should not exceed 0.2 units per ml to minimize bleeding and levels >0.05 units per ml should be obtained to optimize efficacy.

Antithrombotic Properties of Heparin in a Neonatal Piglet Model of Thrombin-Induced Thrombosis

The relative deficiency of antithrombin III (AT III) in neonatal plasma results in lower recovery of heparin in some assay systems. It is uncertain whether low AT III levels also limit the antithrombotic effects of heparin in this age group. We therefore compared the antithrombotic properties of heparin in mature pigs and newborn piglets, whose coagulation and inhibitor system closely resembles that of the human neonate. Animals were pretreated with saline, 10 or 25 U/kg heparin (n ≥16 per age group and dose). Following an injection of 100 U/kg thrombin, systemic 125I-fibrinogen consumption and local 125I-fibrinogen incorporation into jugular venous stasis thrombi were measured. Significantly more 125I-fibrinogen was consumed in piglets than in pigs systemically (p <0.0001), as well as within the occluded vein segment (p = 0.0112), largely because heparin was less effective in piglets than in pigs. This neonatal resistance to heparin could not be explained by lower heparin levels in the newborn animals. However, pretreatment with AT III concentrate significantly improved the antithrombotic properties of heparin in this age group (p <0.0001). We conclude that physiologically low AT III levels reduce the efficacy of heparin in neutralizing thrombin activity in newborn piglets. We speculate that AT III deficiency may also limit the antithrombotic properties of heparin in newborn infants with thrombotic disease.

The Basement Membrane Underlying the Vascular Endothelium Is Not Thrombogenic: In Vivo and In Vitro Studies with Rabbit and Human Tissue

Studies examining the interaction of platelets with exposed subendothelium in vivo have reported conflicting results, lo examine possible explanations for the apparently discrepant findings, we measured the platelet reactivity of subendothelium prepared by a number of methods both in vivo and in vitro. In addition, we examined the possibility that 13-hydroxyoc-tadecadinoic acid (13-HODE), an endothelial cell-derived chemorepellant, modulates the reactivity of the subendothelium to platelets. In vivo, the subendothelium of segments of rabbit carotid arteries was exposed by removing the endothelial cells by air perfusion or by balloon catheter stripping. Platelet accumulation onto the dc-cndothelialized segments was assessed by 3H-radioaclivily uptake, using 3H-adenine-labelled platelets, and by scanning electron microscopy. In vitro, 3H-adenine-labelled platelet adhesion was measured onto plain plastic discs and onto plastic discs coated with the following purified basement membrane components: collagens type I, III, IV, V, laminin, or fibronectin. In addition, 3H-adenine-labelled platelet adhesion was measured onto plastic discs coveredwith human endothelial cells or onto the basement membrane underlying the endothelial cells.

In vivo, there was marked 3H-platelet accumulation onto the ballon catheter carotid arteries one hour after injury. In contrast, there was no platelet accumulation onto the subendothelium of carotid arteries de-endothelialized by air perfusion. These differences were confirmed by scanning electron microscopy. Transmission electron microscopic examination demonstrated that the extracellular matrix was intact following the air perfusion injury whereas the majority of it was removed by the balloon catheter injury.

In vitro, the accumulation of 3H-platelets onto plain discs and onto discs coated with any of the four collagens, fibronectin or laminin was significantly greater than the adhesion of 3H-platelets onto intact endothelial cells or the basement membrane prepared by cellulose acetate stripping. In contrast, 3H-platelet adhesion onto the basement membrane prepared by ammonium hydroxide treatment was significantly increased. An HPLC analysis of methanol extracts obtained from the two basement membranes and the cultured endothelial in vitro demonstrated that there was significant amounts of 13-HODE present in the endothelial cells and in the basement membrane prepared by the mechanical stripping, but there was no detectable 13-HODE in the basement membrane prepared by ammonium hydroxide treatment.

We conclude that platelets do not adhere to subendothelium immediately beneath the endothelium and that this thromboresistance is contributed to by 13-HODE. We also suggest that the observed thrombogeneicity of subendothelium following balloon-induced injury is due to the mechanical removal of sub-endothelial structures including 13-HODE, exposing deeper more thrombogenic vascular wall structures.

Radioimmunoassay of Fibrinogen and Its Proteolysis Products

The solid-phase radioimmunoassay method has been applied to the measurement of fibrinogen. The method is extremely sensitive, being able to detect fibrinogen concentrations as low as 10 ng/ml. The immunoreactivity of fibrinogen proteolysis products differs from that of native fibrinogen, early proteolysis products showing enhanced immunoreactivity which decreases progressively with further digestion.

Platelet Adhesiveness: A Comparison of the Rotating Bulb and Glass-Bead Column Methods

A comparison was made of the rotating bulb and glass bead column methods of measuring platelet adhesiveness. Closely correlated results were obtained which suggest that the two methods measure the same aspect of platelet behaviour.

Once versus twice daily aspirin after coronary bypass surgery: a randomized trial

Essentials Coronary artery bypass graft (CABG) failure is associated with myocardial infarction and death. We tested whether more frequent dosing improves aspirin (ASA) response following CABG surgery. Twice-daily compared with once-daily dosing reduces ASA hyporesponsiveness after CABG surgery. The efficacy of twice-daily ASA needs to be tested in a trial powered for clinical outcomes.

SUMMARY

Background Acetyl-salicylic acid (ASA) hyporesponsiveness occurs transiently after coronary artery bypass graft (CABG) surgery and may compromise the effectiveness of ASA in reducing thrombotic graft failure. A reduced response to ASA 81 mg once-daily after CABG surgery is overcome by four times daily ASA dosing. Objectives To determine whether ASA 325 mg once-daily or 162 mg twice-daily overcomes a reduced response to ASA 81 mg once-daily after CABG surgery. Methods Adults undergoing CABG surgery were randomized to ASA 81 mg once-daily, 325 mg once-daily or 162 mg twice-daily. The primary outcome was median serum thromboxane B2 (TXB2 ) level on postoperative day 4. We pooled the results with those of our earlier study to obtain better estimates of the effect of ASA 325 mg once-daily or in divided doses over 24 h. Results We randomized 68 patients undergoing CABG surgery. On postoperative day 4, patients randomized to receive ASA 81 mg once-daily had a median day 4 TXB2 level of 4.2 ng mL-1 (Q1, Q3: 1.5, 7.5 ng mL-1 ), which was higher than in those randomized to ASA 162 mg twice-daily (1.1 ng mL-1 ; Q1, Q3: 0.7, 2.7 ng mL-1 ) and similar to those randomized to ASA 325 mg once-daily (1.9 ng mL-1 ; Q1, Q3: 0.9, 4.7 ng mL-1 ). Pooled data showed that the median TXB2 level on day 4 in groups receiving ASA 162 mg twice-daily or 81 mg four times daily was 1.1 ng mL-1 compared with 2.2 ng mL-1 in those receiving ASA 325 mg once-daily. Conclusions Multiple daily dosing of ASA is more effective than ASA 81 mg once-daily or 325 mg once-daily at suppressing serum TXB2 formation after CABG surgery. A twice-daily treatment regimen needs to be tested in a clinical outcome study.

Differential sympathetic outflow to adipose depots is required for visceral fat loss in response to calorie restriction

The sympathetic nervous system (SNS) regulates energy homeostasis in part by governing fatty acid liberation from adipose tissue. We first examined whether SNS activity toward discrete adipose depots changes in response to a weight loss diet in mice. We found that SNS activity toward each adipose depot is unique in timing, pattern of activation, and habituation with the most dramatic contrast between visceral and subcutaneous adipose depots. Sympathetic drive toward visceral epididymal adipose is more than doubled early in weight loss and then suppressed later in the diet when weight loss plateaued. Coincident with the decline in SNS activity toward visceral adipose is an increase in activity toward subcutaneous depots indicating a switch in lipolytic sources. In response to calorie restriction, SNS activity toward retroperitoneal and brown adipose depots is unaffected. Finally, pharmacological blockage of sympathetic activity on adipose tissue using the β3-adrenergic receptor antagonist, SR59230a, suppressed loss of visceral adipose mass in response to diet. These findings indicate that SNS activity toward discrete adipose depots is dynamic and potentially hierarchical. This pattern of sympathetic activation is required for energy liberation and loss of adipose tissue in response to calorie-restricted diet.

A new brain dopamine-deficient Drosophila and its pharmacological and genetic rescue

Dopamine (DA) is a neurotransmitter with conserved behavioral roles between invertebrate and vertebrate animals. In addition to its neural functions, in insects DA is a critical substrate for cuticle pigmentation and hardening. Drosophila tyrosine hydroxylase (DTH) is the rate limiting enzyme for DA biosynthesis. Viable brain DA-deficient flies were previously generated using tissue-selective GAL4-UAS binary expression rescue of a DTH null mutation and these flies show specific behavioral impairments. To circumvent the limitations of rescue via binary expression, here we achieve rescue utilizing genomically integrated mutant DTH. As expected, our DA-deficient flies have no detectable DTH or DA in the brain, and show reduced locomotor activity. This deficit can be rescued by l-DOPA/carbidopa feeding, similar to human Parkinson's disease treatment. Genetic rescue via GAL4/UAS-DTH was also successful, although this required the generation of a new UAS-DTH1 transgene devoid of most untranslated regions, as existing UAS-DTH transgenes express in the brain without a Gal4 driver via endogenous regulatory elements. A surprising finding of our newly constructed UAS-DTH1m is that it expresses DTH at an undetectable level when regulated by dopaminergic GAL4 drivers even when fully rescuing DA, indicating that DTH immunostaining is not necessarily a valid marker for DA expression. This finding necessitated optimizing DA immunohistochemistry, showing details of DA innervation to the mushroom body and the central complex. When DA rescue is limited to specific DA neurons, DA does not diffuse beyond the DTH-expressing terminals, such that DA signaling can be limited to very specific brain regions.

Medical device-induced thrombosis: what causes it and how can we prevent it?

Blood-contacting medical devices, such as vascular grafts, stents, heart valves, and catheters, are often used to treat cardiovascular diseases. Thrombus formation is a common cause of failure of these devices. This study (i) examines the interface between devices and blood, (ii) reviews the pathogenesis of clotting on blood-contacting medical devices, (iii) describes contemporary methods to prevent thrombosis on blood-contacting medical devices, (iv) explains why some anticoagulants are better than others for prevention of thrombosis on medical devices, and (v) identifies future directions in biomaterial research for prevention of thrombosis on blood-contacting medical devices.

Real-world variability in dabigatran levels in patients with atrial fibrillation

BACKGROUND

In clinical practice, physicians are given the choice of selecting one of two dabigatran doses based on patient characteristics, with the lower dose typically used in patients at a higher risk of bleeding.

OBJECTIVES

The objectives of the study were to (i) estimate the inter- and intra-patient variability in dabigatran levels with 110 mg (DE110) and 150 mg (DE150) doses, (ii) examine the effect of physicians' dose selection on levels in DE110 and DE150 subgroups, and (iii) explore whether a single trough measurement identifies patients with extreme levels on subsequent visits.

METHODS

In this prospective observational study of 100 patients with atrial fibrillation (AF), peak and trough levels of dabigatran were measured with the Hemoclot(®) assay at baseline and every 2 months thereafter (maximum four visits).

RESULTS

Inter-patient variability in dabigatran levels (geometric coefficient of variation [gCV], 51-64%) was greater than intra-patient variability (gCV, 32-40%). Similar medians and distributions of levels were observed in DE110 and DE150 subgroups. Patients receiving DE110 were older, had lower renal function and weighed less than those receiving DE150. Up to 40% of patients whose trough levels were in the upper extremes, and up to 80% of patients whose trough levels were in the lower extremes at baseline, showed subsequent levels that fell in the middle quartiles.

CONCLUSIONS

Our data support the practice of selecting the dabigatran dose based upon clinical characteristics because it results in similar levels of drug exposure in patients given DE110 or DE150. They do not support the concept that a single Hemoclot(®) measurement reliably identifies patients with consistently high or low values.

Multiple daily doses of acetyl-salicylic acid (ASA) overcome reduced platelet response to once-daily ASA after coronary artery bypass graft surgery: a pilot randomized controlled trial

BACKGROUND

The efficacy of ASA for prevention of graft failure following CABG surgery may be limited by incomplete platelet inhibition due to increased post-operative platelet turnover.

OBJECTIVES

To determine whether acetyl-salicylic acid (ASA) 325 mg once-daily or 81 mg four-times daily overcomes the impaired response to ASA 81 mg once-daily in post-operative coronary artery bypass graft (CABG) patients.

METHODS

We randomized 110 patients undergoing CABG surgery to either ASA 81 mg once-daily, 81 mg four times daily or 325 mg once-daily and compared their effects on serum thromboxane B2 (TXB2 ) suppression and arachidonate-induced platelet aggregation.

RESULTS

One hundred patients were included in the final analysis. Platelet counts fell after surgery, reached a nadir on day 2, and then gradually increased. Although there was near complete suppression of TXB2 on the second or third post-operative day, TXB2 levels increased in parallel with the rise in platelet count on subsequent days. This increase was most marked in patients receiving ASA 81 mg once-daily and less evident in those receiving ASA four times daily. On post-operative day 4, (i) median TXB2 levels were lower with four times daily ASA than with either ASA 81 mg once-daily (1.1 ng/mL; Quartile(Q) Q1,Q3: 0.5, 2.4 and 13.3 ng/mL; Q1,Q3: 7.8, 30.8 ng/mL, respectively; P < 0.0001) or ASA 325 mg once-daily (3.4 ng/mL; Q1,Q3: 2.0, 8.2 ng/mL; P = 0.002), and (ii) ASA given four times daily was more effective than ASA 81 mg once-daily and 325 mg once-daily at suppressing platelet aggregation.

CONCLUSIONS

Four times daily ASA is more effective than ASA 81 and 325 mg once-daily at suppressing serum TXB2 formation and platelet aggregation immediately following CABG surgery.

Active metabolite concentration of clopidogrel in patients taking different doses of aspirin: results of the interaction trial

BACKGROUND

The CURRENT-OASIS-7 and PLATO trials suggest that the benefit of clopidogrel is influenced by the dose of aspirin.

OBJECTIVE

To explore a potential pharmacokinetic interaction between aspirin and clopidogrel, and determinants of clopidogrel active metabolite (AM) levels.

METHODS

In part 1, using a 2 × 2 factorial design, we randomized patients to clopidogrel 600 mg loading dose (LD) followed by 150 mg day(-1) for 6 days and 75 mg day(-1) thereafter, or clopidogrel 300 mg LD followed by 75 mg day(-1) thereafter, and compared aspirin at 325 mg or 81 mg day(-1) . In part 2, patients were given a 600-mg clopidogrel LD, and were randomly allocated to aspirin 325 mg or 81 mg day(-1) . We combine the data from the two parts. Blood samples were collected 1 h after administration of the study drug.

RESULTS

We randomized 302 patients (mean age 60.4 ± 9.9 years). Clopidogrel AM levels were similar in patients randomized to aspirin 325 or 81 mg (geometric mean, 12.70 ng mL(-1) ; 95% CI, 10.96-14.72 ng mL(-1) ; and geometric mean, 12.55 ng mL(-1) ; 95% CI, 10.80-14.58 ng mL(-1) ; P = 0.91). Blood levels of clopidogrel were lower in CYP2C19*2 loss-of-function (LOF) carriers compared with non-carriers (10.72 ng mL(-1) ; 95% CI, 8.83-13.01 ng mL(-1) ; and 15.21 ng mL(-1) ; 95% CI, 13.30-17.40 ng mL(-1) , respectively; P = 0.003) whereas levels in gain of function carriers and non-carriers were similar (13.31 ng mL(-1) ; 95% CI, 11.53-15.35 ng mL(-1) ; and 14.07 ng mL(-1) ; 95% CI, 11.74-16.87 ng mL(-1) , respectively; P = 0.4). Independent baseline predictors of clopidogrel AM levels were LOF genotype, body mass index, diabetes, proton pump inhibitor use and creatinine clearance, but accounted for only 20% of the variability in levels.

CONCLUSION

Aspirin dose does not predict clopidogrel AM levels 1 h post-LD. Most of the variability in clopidogrel AM levels is not explained by patient characteristics or CYP2C19 metabolizer status.

Comparison of the effects of apixaban and rivaroxaban on prothrombin and activated partial thromboplastin times using various reagents

BACKGROUND

Clinical situations occur where expedient assessment of the anticoagulant activity of the direct factor Xa (FXa) inhibitors is required. Although quantitative anti-FXa (FXa) assays can be used to measure plasma levels of apixaban or rivaroxaban, turnaround is often slow and many laboratories do not perform these assays.

OBJECTIVE

We compared the in vitro effects of apixaban and rivaroxaban on two readily available laboratory tests, the prothrombin time (PT) and activated partial thromboplastin time (APTT), performed with different reagents. We aimed to identify the most sensitive reagents.

METHODS

Rivaroxaban or apixaban was added to human plasma at a range of concentrations covering expected peak and trough levels, and concentrations were confirmed using calibrated anti-FXa assays. Samples were assayed with six PT and seven APTT reagents using different coagulometers.

RESULTS AND CONCLUSIONS

TriniCLOT PT Excel S was the only reagent to demonstrate sensitivity to apixaban. All of the PT reagents were sensitive to rivaroxaban with TriniCLOT PT Excel S and HemosIL HS PLUS being the most sensitive. Sensitivity to rivaroxaban varied among APTT reagents; four reagents exhibited the greatest responsiveness, and of these, Actin FSL was the most responsive. Commonly used coagulation tests may be useful for assessing the anticoagulant effect of rivaroxaban but not of apixaban. The reason for the different effects of apixaban and rivaroxaban on the PT and APTT is unknown.

A guide to GRADE guidelines for the readers of JTH

More than 70 organizations worldwide have adopted the GRADE methodology for guideline development. The ninth iteration of the American Collage of Chest Physicians guidelines (AT9) adopted structural and policy changes that resulted in a greater adherence to GRADE guidance than previous iterations. The most important of these changes include minimizing the impact of financial and intellectual conflict of interest, increasing the rigor of evidence evaluation, acknowledging uncertainty in estimates of typical values and preferences, and awareness of the large variability in values and preferences. One of the consequences of the greater adherence to GRADE methodology is an increase in weak vs. strong recommendations in AT9. The result of the GRADE process highlights the desirability of higher-quality evidence both regarding the outcomes of alternative management strategies and regarding the distribution of values and preferences in patients considering those alternatives. It also encourages shared decision making in encounters between physicians and patients. Although some physicians might find the uncertainty underlying medical practice discouraging or unsettling, relative to denying or obscuring the uncertainty, acknowledging and addressing the uncertainty will lead to more credible, realistic, and useful recommendations.

Reversal of the anti-platelet effects of aspirin and clopidogrel

BACKGROUND

Guidelines recommend stopping aspirin and clopidogrel 7 to 10 days before surgery to allow time for replacement of permanently inhibited platelets by newly released uninhibited platelets.

OBJECTIVES

The purpose of the present study was to determine the rate of offset of the anti-platelet effects of aspirin and clopidogrel after stopping treatment and the proportion of untreated donor platelets that are required to reverse their anti-platelet effects.

METHODS

Cohort 1 consisted of 15 healthy subjects who received aspirin 81 mg day(-1) or clopidogrel 75 mg day(-1) for 7 days and underwent serial blood sampling until platelet function testing results normalized. Cohort 2 consisted of 36 healthy subjects who received aspirin 325 mg day(-1), clopidogrel 75 mg day(-1), aspirin 81 mg day(-1) plus clopidogrel 75 mg day(-1) or no treatment for 7 days and underwent a single blood sampling.

RESULTS

In cohort 1, arachidonic acid (AA)-induced light transmission aggregation (LTA) returned to baseline levels in all subjects within 4 days of stopping aspirin, coinciding with the partial recovery of plasma thromboxane B(2) concentrations. ADP-induced LTA did not return to baseline levels until 10 days after stopping clopidogrel. In cohort 2, AA-induced LTA in patient treated with aspirin reached control levels after mixing with 30% untreated donor platelets whereas ADP-induced LTA in patients treated with clopidogrel reached control levels only after the addition of 90% or more donor platelets.

CONCLUSIONS

Platelet aggregation recovers within 4 days of stopping aspirin but clopidogrel must be stopped for 10 days to achieve a normal aggregatory response.

Randomized controlled trial of a new portable calf compression device (Venowave) for prevention of venous thrombosis in high-risk neurosurgical patients

BACKGROUND

Patients undergoing neurosurgical procedures are at risk of venous thromboembolism (VTE), but often have contraindications for anticoagulant prophylaxis.

OBJECTIVES

To assess the efficacy and tolerability of a new, lightweight, portable, battery-powered, intermittent calf compression device, Venowave, for the prevention of VTE in neurosurgical inpatients.

PATIENTS/METHODS

We performed an open randomized controlled trial comparing Venowave with control for the prevention of VTE in patients undergoing neurosurgery. The primary outcome was the composite of asymptomatic deep vein thrombosis (DVT) detected by screening venography or compression ultrasound performed on day 9 (± 2 days) and symptomatic VTE.

RESULTS

We randomized 75 patients to receive Venowave devices and 75 to the control group. All patients were prescribed graduated compression stockings and physiotherapy. VTE occurred in three patients randomized to Venowave and in 14 patients randomized to control (4.0% vs. 18.7%, relative risk 0.21; 95% confidence interval 0.05-0.75, P = 0.008). Similar reductions were seen for proximal DVT (2.7% vs. 8.0%) and symptomatic VTE (0% vs. 2.7%), and the results were consistent in all subgroups examined.

CONCLUSIONS

Venowave devices are effective in preventing VTE in high-risk neurosurgical patients.

Comparison of the anticoagulant intensities of fondaparinux and enoxaparin in the Organization to Assess Strategies in Acute Ischemic Syndromes (OASIS)-5 trial

BACKGROUND

In the OASIS-5 trial, fondaparinux reduced major bleeding with similar short-term efficacy as enoxaparin but lowered death and stroke during long-term follow-up. The mechanism of lower bleeding and improved efficacy with fondaparinux is uncertain.

METHODS AND RESULTS

We compared the anti-Xa concentration (reflecting drug levels), Xa clot time (reflecting anticoagulant effect) and endogenous thrombin potential (ETP; a global test of hemostatic function) in plasma samples collected 6, 24 and 72 h after the first dose of the study drug in 48 patients randomly assigned fondaparinux 2.5 mg day(-1) and 42 patients assigned enoxaparin 1 mg kg(-1) twice daily in the OASIS-5 trial. Patients assigned to fondaparinux compared with enoxaparin had a significantly lower mean anti-Xa level [0.52 IU mL(-1) (SD 0.22 IU mL(-1)) vs. 1.2 IU mL(-1) (SD 0.45 IU mL(-1)), P<0.0001] and Xa clot time [64.9 s (SD 17.7 s) vs. 111.8 s (SD 29.6 s), P<0.0001], and significantly higher ETP area under the curve (AUC) [386.7 mA (SD 51.5 mA) vs. 206.4 mA (SD 90.6 mA), P<0.001] at 6 h, and these differences remained evident at 24 and 72 h. There was significantly less variability of the results of anti-Xa levels, Xa clot time and ETP AUC for fondaparinux compared with enoxaparin at 6 h (P<0.001 for each comparison).

CONCLUSION

Fondaparinux 2.5 mg day(-1) compared with enoxaparin 1 mg kg(-1) twice daily produces less variable anticoagulant effect and lower mean anticoagulant intensity. These results most likely explain the reduced risk of bleeding seen with fondaparinux compared with enoxaparin in the OASIS-5 trial and suggest that a lower intensity of anticoagulation than used in the past may be sufficient to prevent recurrent ischemic events and death in patients with ACS who are concurrently treated with aspirin and clopidogrel.

Combined antiplatelet and anticoagulant therapy: clinical benefits and risks

The combination of anticoagulant and antiplatelet therapy is more effective than antiplatelet therapy alone for the initial and long-term management of acute coronary syndromes but increases the risk of bleeding. Antiplatelet therapy is often combined with oral anticoagulants in patients with an indication for warfarin therapy (e.g. atrial fibrillation) who also have an indication for antiplatelet therapy (e.g. coronary artery disease) but the appropriateness of such an approach is unresolved. Anticoagulation appears to be as effective as antiplatelet therapy for long-term management of acute coronary syndrome and stroke, and possibly peripheral artery disease, but causes more bleeding. Therefore, in such patients who develop atrial fibrillation, switching from antiplatelet therapy to anticoagulants might be all that is required. The combination of anticoagulant and antiplatelet therapy has only been proven to provide additional benefit over anticoagulants alone in patients with prosthetic heart valves. The combination of aspirin and clopidogrel is not as effective as oral anticoagulants in patients with atrial fibrillation, whereas the combination of aspirin and clopidogrel is more effective than oral anticoagulants in patients with coronary stents. Whether the benefits of triple therapy outweigh the risks in patients with atrial fibrillation and coronary stents requires evaluation in randomized trials.

Combined antiplatelet and anticoagulant therapy: clinical benefits and risks

The combination of anticoagulant and antiplatelet therapy is more effective than antiplatelet therapy alone for the initial and long-term management of acute coronary syndromes but increases the risk of bleeding. Antiplatelet therapy is often combined with oral anticoagulants in patients with an indication for warfarin therapy (e.g. atrial fibrillation) who also have an indication for antiplatelet therapy (e.g. coronary artery disease) but the appropriateness of such an approach is unresolved. Anticoagulation appears to be as effective as antiplatelet therapy for long-term management of acute coronary syndrome and stroke, and possibly peripheral artery disease, but causes more bleeding. Therefore, in such patients who develop atrial fibrillation, switching from antiplatelet therapy to anticoagulants might be all that is required. The combination of anticoagulant and antiplatelet therapy has only been proven to provide additional benefit over anticoagulants alone in patients with prosthetic heart valves. The combination of aspirin and clopidogrel is not as effective as oral anticoagulants in patients with atrial fibrillation, whereas the combination of aspirin and clopidogrel is more effective than oral anticoagulants in patients with coronary stents. Whether the benefits of triple therapy outweigh the risks in patients with atrial fibrillation and coronary stents requires evaluation in randomized trials.

Association between asymptomatic deep vein thrombosis detected by venography and symptomatic venous thromboembolism in patients undergoing elective hip or knee surgery

BACKGROUND

Venography is commonly used to compare the efficacy of different thromboprophylaxis strategies for preventing deep vein thrombosis (DVT) in patients undergoing total hip replacement (THR) or total knee replacement (TKR).

METHODS

We explored the relation between asymptomatic DVT and symptomatic venous thromboembolism (VTE) in patients undergoing THR or TKR treated with standard doses of enoxaparin (30 mg b.i.d. or 40 mg o.d.) by comparing the incidence of asymptomatic DVT in venographic studies with the incidence of symptomatic VTE in studies where venography was not performed.

RESULTS

In 10 venographic studies involving 5796 patients, the incidence of asymptomatic DVT after THR was 13.2% [95% CI, 12.2-14.2%] and after TKR was 38.1% (95% CI, 35.5-40.8%). In two studies involving 3500 patients who did not undergo venography, the 90-day incidence of symptomatic VTE after THR was 2.7% (95% CI, 2.1-3.4%) and after TKR was 1.8% (95% CI, 0.9-2.7%). For every symptomatic VTE in THR studies where venography was not performed there were five asymptomatic DVTs in the venographic studies; for TKR, the ratio was 1:21. The incidence of asymptomatic DVT and the symptomatic VTE/asymptomatic DVT ratio was influenced by the venogram reading committee (Gothenburg vs. Hamilton: total DVT after THR, 19.5% vs. 8.7%, P < 0.0001; for TKR, 42.7% vs. 27.2%, P < 0.0001).

CONCLUSIONS

Comparisons across trials show a consistent relation between asymptomatic venographic DVT in patients undergoing elective THR or TKR surgery and symptomatic VTE in patients not undergoing venography. Differences exist in the strength of the relation depending on the type of surgery and the venogram reading committee.

Combined antiplatelet and anticoagulant therapy: clinical benefits and risks

The combination of anticoagulant and antiplatelet therapy is more effective than antiplatelet therapy alone for the initial and long-term management of acute coronary syndromes but increases the risk of bleeding. Antiplatelet therapy is often combined with oral anticoagulants in patients with an indication for warfarin therapy (e.g. atrial fibrillation) who also have an indication for antiplatelet therapy (e.g. coronary artery disease) but the appropriateness of such an approach is unresolved. Anticoagulation appears to be as effective as antiplatelet therapy for long-term management of acute coronary syndrome and stroke, and possibly peripheral artery disease, but causes more bleeding. Therefore, in such patients who develop atrial fibrillation, switching from antiplatelet therapy to anticoagulants might be all that is required. The combination of anticoagulant and antiplatelet therapy has only been proven to provide additional benefit over anticoagulants alone in patients with prosthetic heart valves. The combination of aspirin and clopidogrel is not as effective as oral anticoagulants in patients with atrial fibrillation, whereas the combination of aspirin and clopidogrel is more effective than oral anticoagulants in patients with coronary stents. Whether the benefits of triple therapy outweigh the risks in patients with atrial fibrillation and coronary stents requires evaluation in randomized trials.

Comparison of 1 month with 3 months of anticoagulation for a first episode of venous thromboembolism associated with a transient risk factor

BACKGROUND

The risk of recurrence is lower after treatment of an episode of venous thromboembolism associated with a transient risk factor, such as recent surgery, than after an episode associated with a permanent, or no, risk factor. Retrospective analyses suggest that 1 month of anticoagulation is adequate for patients whose venous thromboembolic event was provoked by a transient risk factor.

METHODS

In this double-blind study, patients who had completed 1 month of anticoagulant therapy for a first episode of venous thromboembolism provoked by a transient risk factor were randomly assigned to continue warfarin or to placebo for an additional 2 months. Our goal was to determine if the duration of treatment could be reduced without increasing the rate of recurrent venous thromboembolism during 11 months of follow-up.

RESULTS

Of 84 patients assigned to placebo, five (6.0%) had recurrent venous thromboembolism, compared with three of 81 (3.7%) assigned to warfarin, resulting in an absolute risk difference of 2.3%[95% confidence interval (CI) - 5.2, 10.0]. The incidence of recurrent venous thromboembolism after discontinuation of warfarin was 6.8% per patient-year in those who received warfarin for 1 month and 3.2% per patient-year in those who received warfarin for 3 months (rate difference of 3.6% per patient-year; 95% CI - 3.8, 11.0). There were no major bleeds in either group.

CONCLUSION

Duration of anticoagulant therapy for venous thromboembolism provoked by a transient risk factor should not be reduced from 3 months to 1 month as this is likely to increase recurrent venous thromboembolism without achieving a clinically important decrease in bleeding.