Mark D. Blostein

Oral vitamin K versus placebo to correct excessive anticoagulation in patients receiving warfarin: a randomized trial.

Context Vitamin K decreases the international normalized ratio (INR) in overanticoagulated patients who receive warfarin therapy, but its effect on clinical outcomes is less clear. Contribution Trial investigators detected no differences in the frequency of bleeding, thromboembolism, or death among overanticoagulated patients who received warfarin therapy and were randomly assigned to receive low-dose vitamin K or placebo. Caution The study was underpowered to detect differences in major bleeding. Implication Low-dose vitamin K corrects the INR in overanticoagulated patients who received warfarin therapy, but it has little effect on clinical outcomes. Withdrawal of warfarin may be all that is necessary to manage elevated INRs. The Editors Warfarin is a remarkably effective drug for primary and secondary prevention of arterial and venous thromboembolism. Among commonly used medications, warfarin is unique because its doseresponse characteristics are highly unpredictable, varying both among and within individuals over time. As a result, warfarin therapy requires ongoing monitoring using the international normalized ratio (INR), a value that reflects the degree to which warfarin has reduced coagulation factor levels and the coagulant potential of blood (1). For most indications, an INR range of 2.0 to 3.0 is targeted; INR values less than 2.0 are associated with an increased risk for thromboembolism, and INR values greater than 4.0 are associated with an increase in bleeding complications. The risk for bleeding, particularly intracranial bleeding, increases markedly as the INR exceeds 4.5 (13). Even in clinics dedicated to warfarin management, INRs are outside the therapeutic range one third to one half the time (4). When managing a patient with an INR greater than 4.5 who is not bleeding, clinicians generally either withhold warfarin treatment and allow the INR to decrease to the desired value or administer vitamin K (orally or intravenously) to more rapidly reduce the INR (1, 510). Small randomized trials have shown that a single dose of low-dose oral vitamin K (for example, 1 to 2.5 mg) effectively reduces the INR in otherwise-stable overanticoagulated patients within 24 hours of its administration; however, these studies were not large enough to determine whether low-dose vitamin K reduces bleeding without increasing the risk for thromboembolism (1115). A recent systematic review (16) supported this observation. To determine whether oral vitamin K is indicated in overanticoagulated patients who are not bleeding, we did a randomized trial in which we allocated oral vitamin K or placebo, 1.25 mg, to patients who presented with an INR of 4.5 to 10.0. The primary outcome measure was the frequency of all forms of bleeding events during the first 90 days. Our hypothesis that bleeding events would be reduced was based on our previously published, smaller studies of low-dose oral vitamin K administered to various patient groups. In these studies, we found a consistent and rapid decrease in the INR after low-dose vitamin K was administered (13, 15, 1722). Methods Study Patients We identified patients with INRs of 4.5 to 10.0 in participating outpatient anticoagulant therapy clinics. We screened patients as they presented for routine INR assessment and considered them for eligibility if they were receiving warfarin therapy with a target INR of 2.0 to 3.5, their most recent INR was between 4.5 and 10.0 in the past 24 hours, and they were not bleeding. We excluded patients if discontinuation of warfarin therapy was scheduled and if they were younger than 18 years, had a life expectancy less than 10 days, had an indication for acute normalization of their INR (such as imminent surgery), had a known severe liver disease, had a history of a major bleeding event within 1 month, had a known bleeding disorder, had received thrombolytic therapy within 48 hours, had a platelet count less than 50109 cells/L, could not take oral medications, had a known allergy to vitamin K, or could not return for laboratory or clinical monitoring. Study staff at each participating anticoagulant therapy clinic approached patients who met inclusion criteria for consent to participate. This study ran in parallel with a cohort study in which patients with INRs greater than 10.0 received oral vitamin K, 2.5 mg. Patients were otherwise identical to those enrolled in this study, and we followed them for similar outcome events. The results of the concurrent cohort study will be presented in a subsequent paper. Randomization and Treatment We instructed all eligible, consenting patients to withhold warfarin for 1 day and randomly assigned them to receive a capsule containing either vitamin K, 1.25 mg, or placebo. Randomization was done by using a computer-generated random-number table at the coordinating and methods center and was stratified by clinical center. Vitamin K capsules were compounded from 5-mg vitamin K tablets (Merck & Co., Whitehouse Station, New Jersey) by a commercial pharmacy with Health Canada approval (Clinical Trials Application control number 092635). Placebo capsules contained inert filler and were indistinguishable from the capsules that contained vitamin K. Random allocation of patients was accomplished when site-specific study personnel dispensed the next numbered study drug container at each clinical center; thus, patients, treating clinicians, and research coordinators were unaware of treatment allocation. In 2 centers, we monitored the INR of outpatients in clinics or laboratories outside the clinical center. In such centers, we obtained consent for the study by telephone, and the study drug was shipped within hours to the patients home by using a courier service. In all cases, we confirmed receipt and consumption of the study drug on the day of randomization by telephone. In the remaining centers, in which patients were seen in person, consent and study drug administration occurred at the same time that the elevated INR was detected. Follow-up and Outcome Measures At enrollment, we advised patients to promptly seek medical evaluation if they developed signs or symptoms of bleeding or thromboembolism. At minimum, we assessed patients by telephone or in person on days 1, 3, 7, 14, 28, and 90 after randomization. Additional contact and INR sampling necessary to manage the patients anticoagulant therapy were done at the discretion of the patients physician. At each follow-up, we sought signs and symptoms of bleeding and thromboembolism and collected details about all such events. We asked patients a focused series of questions to help them recall these events. We reviewed and abstracted medical records of all suspected bleeding episodes, thromboembolism, and deaths. Our primary outcome measure was the frequency of bleeding events during the 90 days after randomization. We defined major bleeding as fatal bleeding, bleeding requiring transfusion of 2 or more units of packed red blood cells, bleeding resulting in a therapeutic intervention (such as endoscopy), or objectively confirmed bleeding into an enclosed space. We defined minor bleeding as bleeding resulting in a medical assessment that did not meet criteria as a major bleeding event. We defined trivial bleeding as all patient-reported bleeding events that did not result in a medical assessment. We combined all reported bleeding events (major, minor, and trivial) for this analysis. We chose to combine these events because our clinical experience suggested that reducing medically unimportant but bothersome bleeding, such as epistaxis, bruising, and menorrhagia, was a clinically important goal for our patients; patients with a minor or trivial bleeding event may be at greater risk for subsequent major bleeding; and the frequency of major bleeding was likely to be very low, calling into question the feasibility of a study powered to detect differences in major bleeding events. Secondary outcome measures included the frequency of major bleeding events, objectively confirmed venous or arterial thromboembolism, and death during the 90 days after randomization. We chose the 90-day period on the basis of our previous studies wherein we found a significant reduction in bleeding events (90 days) after the administration of similar doses of oral vitamin K (13). We hypothesized that low-dose oral vitamin K might influence a bleeding event during this extended period, because even small doses of this highly lipophilic drug might have an extended influence on INR control (and thus the risk for bleeding and thrombosis). In post hoc analyses, we examined the frequency of all bleeding and major bleeding events in the first 7 days and the number of clinical events in patients who were older than 70 years at enrollment. An independent adjudication committee, blinded to treatment allocation and not otherwise involved in the study, reviewed all bleeding events, thromboembolism, and deaths. Confirmation of venous thromboembolism required a nononcompressible venous segment on ultrasonography, an intraluminal filling defect on venography or computed tomographic pulmonary angiography, or a segmental (or larger) mismatch defect on ventilationperfusion lung scan. Arterial thromboembolism required either direct surgical visualization of thrombus; an intraluminal filling defect on angiography; or clear evidence of a new ischemic event on an objective test, such as electrocardiography, computed tomography, or magnetic resonance imaging. We advised clinics to reinstitute warfarin therapy once the INR was within the therapeutic reference interval after administration of the study drug. The clinicians who cared for the patients determined the warfarin dose when the drug was readministered. Target INR ranges for individual patients did not change as a result of the elevated INR that led to enrollment. Statistical Analysis Our primary analysis was an intention-to-treat comparison of the proportions of patien

Post-thrombotic syndrome, functional disability and quality of life after upper extremity deep venous thrombosis in adults

The post-thrombotic syndrome (PTS) after upper extremity deep venous thrombosis (UEDVT) has not been well characterized. The objective of our study was to describe and quantify residual symptoms, functional disability and quality of life associated with PTS after UEDVT in adults. Twenty-four patients with objectively diagnosed UEDVT (bilateral in 1 patient) at least 6 months previously were recruited from two Canadian thrombosis clinics. Data were collected on demographic characteristics, DVT risk factors and affected venous segments. The Villalta PTS scale, modified for the upper extremity, was used to diagnose PTS. Patients completed questionnaires on degree of functional disability (DASH questionnaire), and generic (SF-36) and disease-specific (VEINES-QOL) quality of life. Results were compared in patients with and without PTS. Patients were assessed a median of 13 months after the diagnosis of UEDVT. Daily ipsilateral arm or hand swelling was reported by 52% of patients and daily ipsilateral arm pain by 20% of study patients, compared with 0% and 0%, respectively, in the contralateral arm. PTS was present in 11/25 (44%) limbs (11/24 patients). One patient had severe PTS. Patients with PTS, compared with those without PTS, had significantly more functional disability (mean DASH score 20.9 vs. 3.7, p=0.009) and poorer quality of life (mean VEINES-QOL score 45.6 vs. 53.6; p=0.001; mean SF-36 Physical Component Score (PCS) 40.8 vs. 50.2; p=0.12). PTS scores were higher and quality of life was poorer when PTS involved the dominant arm. In conclusion, PTS occurs frequently after UEDVT and is associated with significant functional disability and reduced quality of life. Patients with dominant arm PTS appear to fare worse than those with non-dominant arm PTS. Larger, prospective studies to identify prognostic factors that lead to PTS after UEDVT are warranted.

Perioperative Management of Dabigatran: A Prospective Cohort Study

Background— The perioperative management of dabigatran in clinical practice is heterogeneous. We performed this study to evaluate the safety of perioperative management of dabigatran using a specified protocol. Methods and Results— Patients treated with dabigatran and planned for an invasive procedure were eligible for inclusion. The timing of the last dose of dabigatran before the procedure was based on the creatinine clearance and procedure-related bleeding risk. Resumption of dabigatran was prespecified according to the complexity of the surgery and consequences of a bleeding complication. Patients were followed up for 30 days for major bleeding (primary outcome), minor bleeding, arterial thromboembolism, and death. We included 541 cases: 324 procedures (60%) with standard risk of bleeding and 217 procedures (40%) with increased risk of bleeding. The last dose of dabigatran was at 24, 48, or 96 hours before surgery according to the protocol in 46%, 37%, and 6%, respectively, of the patients. Resumption was timed according to protocol in 77% with 75 mg as the first dose on the day of procedure in 40% of the patients. Ten patients (1.8%; 95% confidence interval, 0.7–3.0) had major bleeding, and 28 patients (5.2%; 95% confidence interval, 3.3–7.0) had minor bleeding events. The only thromboembolic complication was transient ischemic attack in 1 patient (0.2%; 95% confidence interval, 0–0.5), and there were 4 deaths unrelated to bleeding or thrombosis. Bridging was not used preoperatively but was administered in 9 patients (1.7%) postoperatively. Conclusion— Our protocol for perioperative management of dabigatran appears to be effective and feasible. # CLINICAL PERSPECTIVE {#article-title-21}Background— The perioperative management of dabigatran in clinical practice is heterogeneous. We performed this study to evaluate the safety of perioperative management of dabigatran using a specified protocol. Methods and Results— Patients treated with dabigatran and planned for an invasive procedure were eligible for inclusion. The timing of the last dose of dabigatran before the procedure was based on the creatinine clearance and procedure-related bleeding risk. Resumption of dabigatran was prespecified according to the complexity of the surgery and consequences of a bleeding complication. Patients were followed up for 30 days for major bleeding (primary outcome), minor bleeding, arterial thromboembolism, and death. We included 541 cases: 324 procedures (60%) with standard risk of bleeding and 217 procedures (40%) with increased risk of bleeding. The last dose of dabigatran was at 24, 48, or 96 hours before surgery according to the protocol in 46%, 37%, and 6%, respectively, of the patients. Resumption was timed according to protocol in 77% with 75 mg as the first dose on the day of procedure in 40% of the patients. Ten patients (1.8%; 95% confidence interval, 0.7–3.0) had major bleeding, and 28 patients (5.2%; 95% confidence interval, 3.3–7.0) had minor bleeding events. The only thromboembolic complication was transient ischemic attack in 1 patient (0.2%; 95% confidence interval, 0–0.5), and there were 4 deaths unrelated to bleeding or thrombosis. Bridging was not used preoperatively but was administered in 9 patients (1.7%) postoperatively. Conclusion— Our protocol for perioperative management of dabigatran appears to be effective and feasible.

The role of gamma-carboxylation in the anti-apoptotic function of gas6.

Summary.  Gas6 is a novel member of the vitamin K‐dependent family of γ‐carboxylated proteins and is a ligand for the receptor tyrosine kinase Axl. Gas6–Axl interactions have been shown to mediate cell survival in vascular endothelium. Although the receptor‐binding portion of gas6 lies in the C‐terminus, the significance of the N‐terminal γ‐carboxylated residues (Gla domain) is not clear. To address this question, this study examines the role of the Gla domain in phospholipid binding as well as in the promotion of cell survival, especially in endothelial cells. The results show that carboxylated gas6 binds to phosphatidylserine‐containing phospholipid membranes in an analogous manner to other γ‐carboxylated proteins whereas decarboxylated gas6 does not. The γ‐carboxylation inhibitor warfarin abrogates gas6‐mediated protection of NIH3T3 fibroblasts from serum starvation‐induced apoptosis. Furthermore, the role of γ‐carboxylation in gas6s survival effect on endothelium is demonstrated directly in that only carboxylated, but not decarboxylated, gas6 protects endothelial cells from serum starvation‐induced apoptosis. γ‐carboxylation is also required for both Axl phosphorylation and PI3 kinase activation. Taken together, these findings demonstrate that γ‐carboxylation is necessary not only for gas6 binding to phospholipid membranes, but also for gas6‐mediated endothelial cell survival.

Growth Arrest-Specific Gene 6 (gas6) and Vascular Hemostasis

Gas6 (growth arrest-specific 6) belongs structurally to the family of plasma vitamin K-dependent proteins. Gas6 has a high structural homology with the natural anticoagulant protein S, sharing the same modular composition. Interestingly, despite the presence of a γ-carboxyglutamic acid domain in its structure, no role in the coagulation cascade has been identified for gas6. Gas6 has been shown to be involved in vascular homeostasis and more precisely is involved in proliferation, apoptosis, efferocytosis, leukocyte migration, and sequestration and platelet aggregation. It is also involved in the activation of different cell types, from platelets to endothelial and vascular smooth muscle cells. Thus, it has been shown to play a role in several pathophysiological processes such as atherosclerosis, cancer, and thrombosis. Interestingly, studies using gas6 null mice highlighted that gas6 may represent a novel potential target for anticoagulant therapy, because these animals are protected from lethal venous thromboembolism without excessive bleeding. However, the mechanism in thrombus occurrence remains to be further explored. In the present review, we will focus on the role of gas6 in innate immunity, atherosclerosis, thrombosis, and cancer-related events.

Vascular Gas6 contributes to thrombogenesis and promotes tissue factor up-regulation after vessel injury in mice

Gas6 (growth-arrest specific gene 6) plays a role in thrombus stabilization. Gas6 null (-/-) mice are protected from lethal venous and arterial thromboembolism through platelet signaling defects induced only by 5 μM ADP and 10 μM of the thromboxane analog, U46619. This subtle platelet defect, despite a dramatic clinical phenotype, raises the possibility that Gas6 from a source other than platelets contributes to thrombus formation. Thus, we hypothesize that Gas6 derived from the vascular wall plays a role in venous thrombus formation. Bone marrow transplantation and platelet depletion/reconstitution experiments generating mice with selective ablations of Gas6 from either the hematopoietic or nonhematopoietic compartments demonstrate an approximately equal contribution by Gas6 from both compartments to thrombus formation. Tissue factor expression was significantly reduced in the vascular wall of Gas6(-/-) mice compared with WT. In vitro, thrombin-induced tissue factor expression was reduced in Gas6(-/-) endothelial cells compared with wild-type endothelium. Taken together, these results demonstrate that vascular Gas6 contributes to thrombus formation in vivo and can be explained by the ability of Gas6 to promote tissue factor expression and activity. These findings support the notion that vascular wall-derived Gas6 may play a pathophysiologic role in venous thromboembolism.

Mthfr deficiency induces endothelial progenitor cell senescence via uncoupling of eNOS and downregulation of SIRT1

Hyperhomocysteinemia (HHcy) has been shown to induce endothelial dysfunction in part as a result of enhanced oxidative stress. Function and survival of endothelial progenitor cells (EPCs, defined as sca1(+) c-kit(+) flk-1(+) bone marrow-derived cells), which significantly contribute to neovascularization and endothelial regeneration, depend on controlled production of reactive oxygen species (ROS). Mice heterozygous for the gene deletion of methylenetetrahydrofolate reductase (Mthfr(+/-)) have a 1.5- to 2-fold elevation in plasma homocysteine. This mild HHcy significantly reduced the number of circulating EPCs as well as their differentiation. Mthfr deficiency was also associated with increased ROS production and reduced nitric oxide (NO) generation in Mthfr(+/-) EPCs. Treatment of EPCs with sepiapterin, a precursor of tetrahydrobiopterin (BH(4)), a cofactor of endothelial nitric oxide synthase (eNOS), significantly reduced ROS and improved NO production. mRNA and protein expression of eNOS and the relative amount of eNOS dimer compared with monomer were decreased by Mthfr deficiency. Impaired differentiation of EPCs induced by Mthfr deficiency correlated with increased senescence, decreased telomere length, and reduced expression of SIRT1. Addition of sepiapterin maintained cell senescence and SIRT1 expression at levels comparable to the wild type. Taken together, these results demonstrate that Mthfr deficiency impairs EPC formation and increases EPC senescence by eNOS uncoupling and downregulation of SIRT1.

Fondaparinux in acute heparin‐induced thrombocytopenia: a case series

See also Greinacher A. Immunogenic but effective: the HIT‐fondaparinux brain puzzler. This issue, pp 2386–8; Warkentin TE, Pai M, Sheppard JI, Schulman S, Spyropoulos AC, Eikelboom JW. Fondaparinux treatment of acute heparin‐induced thrombocytopenia: confirmed by the serotonin‐release assay: a 30‐month, 16‐patient case series. This issue, pp 2389–96.

Oral vitamin K effectively treats international normalised ratio (INR) values in excess of 10: results of a prospective cohort study.

Unanticipated elevation of the INR is common in patients receiving warfarin. We performed a prospective cohort study of 107 warfarin-treated patients with INR values of more than 10 who received a single 2.5 mg dose of oral vitamin K. During the first week, one patient experienced major bleeding, and one died. In the first 90 days after enrolment four patients had major bleeding (3.7%, 1.0% to 9.3%), eight patients (7.5%, 3.3% to 14.2%) died and two had objectively confirmed thromboembolism. Based on our low rate of observed major bleeding we conclude that 2.5 mg of oral vitamin K is a reasonable treatment for patients with INR values of more than 10 who are not actively bleeding.

Management and adherence to VTE treatment guidelines in a national prospective cohort study in the Canadian outpatient setting. The Recovery Study.

Documenting patterns and outcomes of venous thromboembolism (VTE) management and degree of adherence by clinicians to treatment guidelines could help identify remediable gaps in patient care. Prospective, clinical practice-based data from Canadian outpatient settings on management of VTE, degree of adherence with treatment guidelines and frequency of recurrent VTE and bleeding during follow-up was obtained in a multicentre, prospective observational study. From 12 Canadian centres, we assessed 868 outpatients with acute symptomatic VTE who received the low-molecular-weight heparin (LMWH) enoxaparin alone or with vitamin K antagonists (VKA), at baseline and at six months (or at the end of treatment, whichever came first). Index VTE was limb deep venous thrombosis (DVT) in 583 (67.2%) patients, pulmonary embolism (PE) with or without DVT in 262 (30.2%) patients, and unusual site DVT in 23 (2.6%) patients. VTE was unprovoked in 399 (46.0%) patients, associated with cancer in 74 (8.5%) patients, transient risk factors in 327 (37.7%) patients and hormonal factors in 68 (7.8%) patients.With regard to guideline adherence, 58 (7.3%) patients received <5 days LMWH and 114 (14.5%) had overlap <1 day. Among patients with cancer-related VTE, 59.5% were prescribed LMWH monotherapy and 43.2% received such treatment for >3 months. Only 38.1% of patients with transient VTE risk factors had received thromboprophylaxis. Our study provides useful information on clinical presentation, management and related outcomes in Canadian outpatients with VTE. Our results suggest there may be important gaps in use of thromboprophylaxis to prevent VTE and use of LMWH monotherapy to treat cancer-related VTE.