Desmopressin antagonizes the in vitro platelet dysfunction induced by GPIIb/IIIa inhibitors and aspirin

Anticoagulation and bleeding in the cancer patient

Cancer patients have an increased risk of bleeding compared to non-cancer patients with anticoagulant therapy. A bleeding risk assessment before initiation of anticoagulation is recommended. Currently low molecular weight heparin (LMWH) and direct oral anticoagulants (DOACs) are the mainstays of treatment for cancer-associated venous thromboembolism (VTE). Since DOACs are administered orally, they offer some convenience and ease of administration; however, LMWH may be preferred in certain cancers. Given the prevalence of anticoagulant therapies in cancer patients, clinical providers must be able to recognize potentially critical bleeding sites and modalities to reverse major hemorrhage. Reversal agents or antidotes to bleeding may be required when bleeding is persistent or life-threatening. These include vitamin K, fresh frozen plasma (FFP), protamine, prothrombin complex concentrate (PCC) or andexanet alfa, and idarucizumab. Inferior vena cava (IVC) filter insertion can be also considered in those with major bleeding. Evidence for timing and need for re-initiation of anticoagulant therapy after a major bleeding remains sparse, but a multi-disciplinary approach and shared decision-making can be implemented in the interim.

Clinical pharmacology of antiplatelet drugs

INTRODUCTION

Platelets play a key role in arterial thrombosis and antiplatelet therapy is pivotal in the treatment of cardiovascular disease. Current antiplatelet drugs target different pathways of platelet activation and show specific pharmacodynamic and pharmacokinetic characteristics, implicating clinically relevant drug-drug interactions.

AREAS COVERED

This article reviews the role of platelets in hemostasis and cardiovascular thrombosis, and discusses the key pharmacodynamics, drug-drug interactions and reversal strategies of clinically used antiplatelet drugs.

EXPERT OPINION

Antiplatelet therapies target distinct pathways of platelet activation: thromboxane A₂ synthesis, adenosine diphosphate-mediated signaling, integrin α_IIbβ₃ (GPIIb/IIIa), thrombin-mediated platelet activation via the PAR1 receptor and phosphodiesterases. Key clinical drug-drug interactions of antiplatelet agents involve acetylsalicylic acid - ibuprofen, clopidogrel - omeprazole, and morphine - oral P2Y₁₂ inhibitors, all of which lead to an attenuated antiplatelet effect. Platelet function and genetic testing and the use of scores (ARC-HBR, PRECISE-DAPT, ESC ischemic risk definition) may contribute to a more tailored antiplatelet therapy. High on-treatment platelet reactivity presents a key problem in the acute management of ST-elevation myocardial infarction (STEMI). A treatment strategy involving early initiation of an intravenous antiplatelet agent may be able to bridge the gap of insufficient platelet inhibition in high ischemic risk patients with STEMI.

Phase 1/2a Trial of ISPASM

BACKGROUND AND PURPOSE

Microthrombosis could play a role in delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage. Tirofiban has shown promising results in reducing delayed cerebral ischemia in retrospective studies. However, the safety of using tirofiban in aneurysmal subarachnoid hemorrhage is not rigorously established.

METHODS

A phase 1/2a double-blinded randomized controlled trial (2:1 randomization) to assess the safety of a 7-day intravenous infusion of tirofiban compared with placebo, in patients with aneurysmal subarachnoid hemorrhage treated with ventriculostomy placed in the operative room and coiling was conducted. The primary end point was any intracranial hemorrhage during the hospital stay. The secondary end points were: incidence of radiographic and clinical vasospasm, incidence of delayed cerebral ischemia, and incidence of cerebral ischemic changes noted on magnetic resonance imaging or computed tomography.

RESULTS

Eighteen patients received intravenous tirofiban and 12 received placebo. There was no difference in baseline characteristics except for higher male proportions in the tirofiban group. There was no difference in death, in development of new or change in existing intracranial hemorrhages, in thrombocytopenia, and need for shunts in the two arms. However, the tirofiban arm had a lower incidence of delayed cerebral ischemia compared with placebo (6% [1/18] versus 33% [4/12]; P=0.04), and less radiographic vasospasm as detected by catheter angiogram or computed tomography angiography (P=0.01) and computed tomography perfusion (P=0.01).

CONCLUSIONS

The above preliminary results support proceeding with further testing of the safety and efficacy of 7-day intravenous infusion of tirofiban in a pragmatic (placing external ventricular drain by the bedside), multicenter setting, and using a larger population. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03691727.

The use of impedance aggregometry to evaluate platelet function after the administration of DDAVP in healthy dogs treated with aspirin or clopidogrel

OBJECTIVE

To evaluate the effect of 1-Desamino-8-d-arginine vasopressin (DDAVP; desmopressin acetate) on platelet aggregation in healthy dogs receiving aspirin or clopidogrel.

ANIMALS

7 healthy staff-owned dogs.

PROCEDURES

In this randomized double-blinded crossover study, impedance aggregometry was performed on samples of lithium-heparinized whole blood samples from dogs before (T0) treatment with aspirin (1 mg/kg, PO, q 24 h for 4 days; ASP group) or clopidogrel (1 mg/kg, PO, q 24 h for 4 days; CLP group) and then before (T1) and after (T2) treatment with DDAVP (0.3 μg/kg, IV, once). There was a 14-day washout period before the crossover component. Aggregometry was performed with 4 different assays, each of which involved a different agonist reagent to stimulate platelet function: ADP, thrombin receptor activating peptide-6, arachidonic acid, or collagen type 1.

RESULTS

Median results for platelet aggregometry with agonist reagents ADP, arachidonic acid, or thrombin receptor activating peptide-6 significantly decreased between T0 and T1 for the CLP group; however, no meaningful difference in platelet aggregation was detected in the ASP group. Results for platelet aggregometry did not differ substantially between T1 and T2 regardless of treatment group or assay.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that administration of DDAVP may have no effect on platelet aggregation (measured with platelet aggregometry) in healthy dogs treated with clopidogrel. Because no inhibition of platelet aggregation was detected for dogs in the ASP group, no conclusion could be made regarding the effects of DDAVP administered to dogs treated with aspirin.

The aptamer BT200 blocks von Willebrand factor and platelet function in blood of stroke patients

The effect of conventional anti-platelet agents is limited in secondary stroke prevention, and their effects are blunted under high shear stress in the presence of increased levels of circulating von Willebrand factor (VWF). VWF is critically involved in thrombus formation at sites of stenotic extracranial/intracranial arteries. A third generation anti-VWF aptamer (BT200) has been generated which could be useful for secondary stroke prevention. To characterize the effects of BT200 in blood of patients with large artery atherosclerosis stroke (LAA). Blood samples were obtained from 33 patients with acute stroke or transient ischemic attack to measure inhibition of VWF activity and VWF-dependent platelet function. Patients who received clopidogrel or dual antiplatelet therapy did not differ in VWF dependent platelet function tests from aspirin treated patients. Of 18 patients receiving clopidogrel with or without aspirin, only 3 had a prolonged collagen adenosine diphosphate closure time, and none of the patients had ristocetin induced aggregation in the target range. BT200 concentration-dependently reduced median VWF activity from 178 to < 3%, ristocetin induced platelet aggregation from 40U to < 10U and prolonged collagen adenosine diphosphate closure times from 93 s to > 300 s. Baseline VWF activity correlated (r = 0.86, p < 0.001) with concentrations needed to reduce VWF activity to < 20% of normal, indicating that BT200 acts in a target concentration-dependent manner. Together with a long half-life supporting once weekly administration, the safety and tolerability observed in an ongoing phase I trial, and the existence of a reversal agent, BT200 is an interesting drug candidate.

Multiple trauma management in mountain environments - a scoping review : Evidence based guidelines of the International Commission for Mountain Emergency Medicine (ICAR MedCom). Intended for physicians and other advanced life support personnel

Background

Multiple trauma in mountain environments may be associated with increased morbidity and mortality compared to urban environments.

Objective

To provide evidence based guidance to assist rescuers in multiple trauma management in mountain environments.

Eligibility criteria

All articles published on or before September 30th 2019, in all languages, were included. Articles were searched with predefined search terms.

Sources of evidence

PubMed, Cochrane Database of Systematic Reviews and hand searching of relevant studies from the reference list of included articles.

Charting methods

Evidence was searched according to clinically relevant topics and PICO questions.

Results

Two-hundred forty-seven articles met the inclusion criteria. Recommendations were developed and graded according to the evidence-grading system of the American College of Chest Physicians. The manuscript was initially written and discussed by the coauthors. Then it was presented to ICAR MedCom in draft and again in final form for discussion and internal peer review. Finally, in a face-to-face discussion within ICAR MedCom consensus was reached on October 11th 2019, at the ICAR fall meeting in Zakopane, Poland.

Conclusions

Multiple trauma management in mountain environments can be demanding. Safety of the rescuers and the victim has priority. A crABCDE approach, with haemorrhage control first, is central, followed by basic first aid, splinting, immobilisation, analgesia, and insulation. Time for on-site medical treatment must be balanced against the need for rapid transfer to a trauma centre and should be as short as possible. Reduced on-scene times may be achieved with helicopter rescue. Advanced diagnostics (e.g. ultrasound) may be used and treatment continued during transport.

Effect of Desmopressin on Platelet Dysfunction During Antiplatelet Therapy: A Systematic Review

BACKGROUND AND OBJECTIVE

An increasing number of patients receive antiplatelet therapy. Patients exposed to surgery while receiving platelet inhibitors hold an increased bleeding risk. Especially in neurosurgery and neurocritical care patients, bleeding and hematoma expansion are feared complications as even minor bleedings may be hazardous. The objective of this systematic review was to investigate the effect of desmopressin (1-deamino-8-D-arginine vasopressin, DDAVP) on platelet function during antiplatelet therapy in patients undergoing non-cardiac surgery, patients who experience spontaneous or traumatic hemorrhage, healthy individuals and in animals.

METHODS

Studies were identified through a systematic literature search in PubMed and EMBASE on August 19, 2019, with an update on May 2, 2020, and from reference lists of the included studies. Data on clinical and biochemical effect of DDAVP were extracted from included studies for a qualitative data synthesis.

RESULTS

In total, 22 studies were included: 18 human studies and four animal studies. Overall, DDAVP improved bleeding time and increased platelet aggregation in patients undergoing non-cardiac surgery, patients suffering intracerebral or subarachnoid hemorrhage while receiving antiplatelet therapy as well as in healthy individuals and animals exposed to antiplatelet therapy. Observational data indicate that DDAVP may mitigate hematoma expansion in patients with intracerebral hemorrhage or traumatic brain injury.

CONCLUSIONS

The present data hold biochemical evidence that DDAVP improves platelet function during antiplatelet therapy in humans and animals. The need for randomized trials is evident in order to evaluate the potential clinical effect of DDAVP in management of patients with spontaneous or traumatic hemorrhage, or undergoing neurosurgery, while receiving antiplatelet therapy.

von Willebrand Factor Predicts Mortality in ACS Patients Treated with Potent P2Y12 Antagonists and is Inhibited by Aptamer BT200 Ex Vivo

BACKGROUND

 von Willebrand factor (VWF) is crucial for arterial thrombosis and its plasma levels are increased in acute coronary syndromes (ACSs). The effects of conventional platelet inhibitors are compromised by elevated VWF under high shear rates. BT200 is a third-generation aptamer that binds and inhibits the A1 domain of human VWF. This article aims to study whether VWF is a predictor of mortality in ACS patients under potent P2Y12 blocker therapy and to examine the effects of a VWF inhibiting aptamer BT200 and its concentrations required to inhibit VWF in plasma samples of patients with ACS.

METHODS

 VWF activity was measured in 320 patients with ACS, and concentration effect curves of BT200 were established in plasma pools containing different VWF concentrations.

RESULTS

 Median VWF activity in patients was 170% (interquartile range % confidence interval [CI]: 85-255) and 44% of patients had elevated (> 180%) VWF activity. Plasma levels of VWF activity predicted 1-year (hazard ratio [HR]: 2.68; 95% CI: 1.14-6.31; p < 0.024) and long-term (HR: 2.59; 95% CI: 1.10-6.09) mortality despite treatment with potent platelet inhibitors (dual-antiplatelet therapy with aspirin and prasugrel or ticagrelor). Although half-maximal concentrations were 0.1 to 0.2 µg/mL irrespective of baseline VWF levels, increasing concentrations (0.42-2.13 µg/mL) of BT200 were needed to lower VWF activity to < 20% of normal in plasma pools containing increasing VWF activity (p < 0.001).

CONCLUSION

 VWF is a predictor of all-cause mortality in ACS patients under contemporary potent P2Y12 inhibitor therapy. BT200 effectively inhibited VWF activity in a target concentration-dependent manner.

The aptamer BT200 effectively inhibits von Willebrand factor (VWF) dependent platelet function after stimulated VWF release by desmopressin or endotoxin

Von Willebrand factor (VWF) plays a major role in arterial thrombosis. Antiplatelet drugs induce only a moderate relative risk reduction after atherothrombosis, and their inhibitory effects are compromised under high shear rates when VWF levels are increased. Therefore, we investigated the ex vivo effects of a third-generation anti-VWF aptamer (BT200) before/after stimulated VWF release. We studied the concentration-effect curves BT200 had on VWF activity, platelet plug formation under high shear rates (PFA), and ristocetin-induced platelet aggregation (Multiplate) before and after desmopressin or endotoxin infusions in healthy volunteers. VWF levels increased > 2.5-fold after desmopressin or endotoxin infusion (p < 0.001) and both agents elevated circulating VWF activity. At baseline, 0.51 µg/ml BT200 reduced VWF activity to 20% of normal, but 2.5-fold higher BT200 levels were required after desmopressin administration (p < 0.001). Similarly, twofold higher BT200 concentrations were needed after endotoxin infusion compared to baseline (p < 0.011). BT200 levels of 0.49 µg/ml prolonged collagen-ADP closure times to > 300 s at baseline, whereas 1.35 µg/ml BT200 were needed 2 h after desmopressin infusion. Similarly, twofold higher BT200 concentrations were necessary to inhibit ristocetin induced aggregation after desmopressin infusion compared to baseline (p < 0.001). Both stimuli elevated plasma VWF levels in a manner representative of thrombotic or pro-inflammatory conditions such as arterial thrombosis. Even under these conditions, BT200 potently inhibited VWF activity and VWF-dependent platelet function, but higher BT200 concentrations were required for comparable effects relative to the unstimulated state.

Tirofiban Protocol Protects Against Delayed Cerebral Ischemia: A Case-Series Study

BACKGROUND

There has not been any effective prophylaxis for delayed cerebral ischemia delayed cerebral ischemia (DCI) since the introduction of nimodipine. Platelet inhibition may reduce the risk by preventing the formation of microthrombi. Tirofiban has been used as a single monotherapy bridge given its safety profile and controlled platelet inhibition.

OBJECTIVE

To assess the risk of DCI in aneurysmal subarachnoid hemorrhages (aSAH) patients treated with the tirofiban protocol.

METHODS

aSAH patients between December 2010 and March 2019 who were treated with stent assisted coiling or flow-diverting device were started on a continuous tirofiban infusion protocol and were compared with patients who underwent coil embolization without antiplatelet therapy. Safety analysis was performed to assess DCI, hemorrhagic, and ischemic events.

RESULTS

A total of 21 patients were included in the tirofiban series and 81 in the control group. There was no statistical difference in age, gender, Hunt-Hess grade, and Fisher scale between the 2 groups except for a higher Fisher grade II in the tirofiban group. Multivariate analysis revealed tirofiban to reduce the risk of vasospasm by 72 percent (OR .28, P = .03), without affecting the risk of hemorrhagic complications (OR = 0.50, P = .26). Tirofiban reduced the risk of symptomatic stroke endovascular procedure but it did not reach significance (P = .06). DCI, older age, and postprocedural symptomatic stroke were significant predictors of mortality. Tirofiban reduced the mortality risk, but this association was not statistically significant.

CONCLUSION

The tirofiban protocol in aSAH patients reduces the risk of DCI without conferring additional risks. This supports previous findings were antiplatelet therapy reduced DCI in human and animal models.

Clinical practice for antiplatelet and anticoagulant therapy in neurosurgery: data from an Italian survey and summary of current recommendations - part I, antiplatelet therapy

The use of antiplatelet medication is widespread as reducing risk of death, myocardial infarction, and occlusive stroke. Currently, the management of neurosurgical patients receiving this type of therapy continues to be a problem of special importance. In this paper, we present the results of an Italian survey focused on the management neurosurgical patient under antiplatelet therapy and, for any item of the investigation, the relative advices coming from literature. This survey was conducted including 129 neurosurgery units in Italy. The present paper was designed by following each question posed in the survey by a brief discussion on literature data. There is a considerable lack of consensus regarding management of antiplatelet therapy in neurosurgery, with critical impact on patient's treatment. What is clearly evident from the present survey is the considerable variability in neurosurgical care for antiplatelet patients; it is reasonable to assume that this scenario reflects the paucity of evidence regarding this issue.

Glycoprotein IIb/IIIa Inhibitors in Prevention and Rescue Treatment of Thromboembolic Complications During Endovascular Embolization of Intracranial Aneurysms

Thromboembolic complications remain a major risk of endovascular neurosurgery during the treatment of intracranial aneurysms, despite the use of therapeutic heparinization and oral antiplatelet therapy when indicated. Glycoprotein (GP) IIb/IIIa inhibitors target a nonredundant pathway of platelet aggregation following adhesion and activation. Initially established and implemented in the cardiovascular arena, this drug class has provided a new tool in the neurovascular armamentarium as well. Numerous case reports, case series, and retrospective reviews have evaluated the safety and efficacy of abciximab, eptifibatide, and tirofiban in the treatment of acute thromboembolic complications during the endovascular treatment of intracranial aneurysms. The use of this drug class has also been found to be beneficial as a prophylactic agent, providing ischemia protection during the placement of intracranial stents, flow diverters, and thrombogenic coils in the setting of subarachnoid hemorrhage and during elective aneurysmal embolization. While the current published literature clearly establishes efficacy and safety of GP IIb/IIIa inhibitors in the prevention of thromboembolic complications, there does not yet exist an established protocol for their administration in endovascular neurosurgery. This review provides a comprehensive evaluation of the current published literature pertaining to the use of all available GP IIb/IIIa inhibitors for thromboembolic complications, providing recommendations for dosing and administration of abciximab, eptifibatide, and tirofiban based on previously published rates of efficacy and intracranial hemorrhage.

Cohort analysis of desmopressin effect on hematoma expansion in patients with spontaneous intracerebral hemorrhage and documented pre-ictus antiplatelet use

Antiplatelet therapy at the time of spontaneous intracerebral hemorrhage (sICH) may increase risk for hemorrhage expansion and mortality. Current guidelines recommend considering a single dose of desmopressin in sICH associated with cyclooxygenase-1 inhibitors or adenosine diphosphate receptor inhibitors. Adult subjects with sICH and concomitant antiplatelet therapy admitted to a large, tertiary care center were included. We sought to compare the risk of hematoma expansion in patients that received desmopressin for antiplatelet reversal in the setting of sICH to similar patients that did not receive desmopressin. The primary outcomes were the incidence of relative and absolute hematoma expansion. In total, 71 patients (29 received desmopressin, 42 did not receive desmopressin) were analyzed. All patients in the desmopressin group received a 0.3 mcg/kg intravenous dose prior to hematoma expansion assessment. Relative hematoma expansion occurred in 5/29 (17%) with desmopressin compared to 11/42 (26%) without desmopressin (OR 0.59 [95% CI 0.18-1.92]). Absolute hematoma expansion occurred in 9/29 (30%) with desmopressin compared to 12/42 (28%) without desmopressin (OR 1.13 [95% CI 0.40-3.16]). Multiple logistic regression controlling for significant covariates did not reveal a significant effect of desmopressin on relative or absolute hematoma expansion (OR 0.65 [95% CI 0.18-2.43] and OR 1.55 [0.48-4.99], respectively). We failed to find evidence that desmopressin administration for antiplatelet reversal in sICH reduces the incidence of hematoma expansion. Larger studies, focusing on the early phase of sICH, are needed to characterize the clinical efficacy and safety of desmopressin for antiplatelet reversal before widespread implementation.

Perioperative management of the bleeding patient

Perioperative bleeding remains a major complication during and after surgery, resulting in increased morbidity and mortality. The principal causes of non-vascular sources of haemostatic perioperative bleeding are a preexisting undetected bleeding disorder, the nature of the operation itself, or acquired coagulation abnormalities secondary to haemorrhage, haemodilution, or haemostatic factor consumption. In the bleeding patient, standard therapeutic approaches include allogeneic blood product administration, concomitant pharmacologic agents, and increasing application of purified and recombinant haemostatic factors. Multiple haemostatic changes occur perioperatively after trauma and complex surgical procedures including cardiac surgery and liver transplantation. Novel strategies for both prophylaxis and therapy of perioperative bleeding include tranexamic acid, desmopressin, fibrinogen and prothrombin complex concentrates. Point-of-care patient testing using thromboelastography, rotational thromboelastometry, and platelet function assays has allowed for more detailed assessment of specific targeted therapy for haemostasis. Strategic multimodal management is needed to improve management, reduce allogeneic blood product administration, and minimize associated risks related to transfusion.

Targeting von Willebrand Factor in Ischaemic Stroke: Focus on Clinical Evidence

Despite great efforts in stroke research, disability and recurrence rates in ischaemic stroke remain unacceptably high. To address this issue, one potential target for novel therapeutics is the glycoprotein von Willebrand factor (vWF), which increases in thrombogenicity especially under high shear rates as it bridges between vascular sub-endothelial collagen and platelets. The rationale for vWF as a potential target in stroke comes from four bodies of evidence. (1) Animal models which recapitulate the pathogenesis of stroke and validate the concept of targeting vWF for stroke prevention and the use of the vWF cleavage enzyme ADAMTS13 in acute stroke treatment. (2) Extensive epidemiologic data establishing the prognostic role of vWF in the clinical setting showing that high vWF levels are associated with an increased risk of first stroke, stroke recurrence or stroke-associated mortality. As such, vWF levels may be a suitable marker for further risk stratification to potentially fine-tune current risk prediction models which are mainly based on clinical and imaging data. (3) Genetic studies showing an association between vWF levels and stroke risk on genomic levels. Finally, (4) studies of patients with primary disorders of excess or deficiency of function in the vWF axis (e.g. thrombotic thrombocytopenic purpura and von Willebrand disease, respectively) which demonstrate the crucial role of vWF in atherothrombosis. Therapeutic inhibition of VWF by novel agents appears particularly promising for secondary prevention of stroke recurrence in specific sub-groups of patients such as those suffering from large artery atherosclerosis, as designated according to the TOAST classification.

The European guideline on management of major bleeding and coagulopathy following trauma: fourth edition

BACKGROUND

Severe trauma continues to represent a global public health issue and mortality and morbidity in trauma patients remains substantial. A number of initiatives have aimed to provide guidance on the management of trauma patients. This document focuses on the management of major bleeding and coagulopathy following trauma and encourages adaptation of the guiding principles to each local situation and implementation within each institution.

METHODS

The pan-European, multidisciplinary Task Force for Advanced Bleeding Care in Trauma was founded in 2004 and included representatives of six relevant European professional societies. The group used a structured, evidence-based consensus approach to address scientific queries that served as the basis for each recommendation and supporting rationale. Expert opinion and current clinical practice were also considered, particularly in areas in which randomised clinical trials have not or cannot be performed. Existing recommendations were reconsidered and revised based on new scientific evidence and observed shifts in clinical practice; new recommendations were formulated to reflect current clinical concerns and areas in which new research data have been generated. This guideline represents the fourth edition of a document first published in 2007 and updated in 2010 and 2013.

RESULTS

The guideline now recommends that patients be transferred directly to an appropriate trauma treatment centre and encourages use of a restricted volume replacement strategy during initial resuscitation. Best-practice use of blood products during further resuscitation continues to evolve and should be guided by a goal-directed strategy. The identification and management of patients pre-treated with anticoagulant agents continues to pose a real challenge, despite accumulating experience and awareness. The present guideline should be viewed as an educational aid to improve and standardise the care of the bleeding trauma patients across Europe and beyond. This document may also serve as a basis for local implementation. Furthermore, local quality and safety management systems need to be established to specifically assess key measures of bleeding control and outcome.

CONCLUSIONS

A multidisciplinary approach and adherence to evidence-based guidance are key to improving patient outcomes. The implementation of locally adapted treatment algorithms should strive to achieve measureable improvements in patient outcome.

Desmopressin treatment improves platelet function under flow in patients with postoperative bleeding

BACKGROUND

Patients undergoing major cardiothoracic surgery are subjected to dilution, owing to massive fluid infusion and blood component transfusion. These patients may experience bleeding perioperatively, and are frequently treated with the endothelium-activating agent desmopressin.

OBJECTIVES

To investigate the effect of desmopressin administration on von Willebrand factor (VWF)-dependent coagulant and platelet functions under flow conditions.

PATIENTS/METHODS

Blood from 16 patients with postoperative bleeding was obtained before and after desmopressin treatment (0.3 μg kg(-1) body weight), and assessed for coagulant properties and platelet function. Furthermore, VWF antigen levels and multimer composition were determined in both samples.

RESULTS

Desmopressin treatment did not change thrombin generation in plasma or whole blood thromboelasticity. Also coagulation factor levels (other than factor VIII) and coagulation times were unchanged, suggesting that desmopressin treatment did not have a major effect on the coagulant activity. On the other hand, desmopressin treatment raised the already high plasma levels of VWF from a median of 116 IU mL(-1) (interquartile range [IQR] 102-154 IU mL(-1) ) to a median of 160 IU mL(-1) (IQR 126-187 IU mL(-1) ) (P = 0.007), owing to accumulation of the high molecular weight VWF multimers. Furthermore, desmopressin treatment caused an increase in collagen-dependent thrombus formation and platelet phosphatidylserine exposure. Markers of thrombus formation correlated with the plasma levels of VWF. In vitro control experiments confirmed a major contribution of VWF to thrombus formation and procoagulant activity under conditions of blood dilution.

CONCLUSIONS

Desmopressin treatment of patients with bleeding complications after cardiothoracic surgery induces the release of high molecular weight VWF multimers, which enhance platelet activation and thrombus formation under flow conditions.

Desmopressin acetate in intracranial haemorrhage

Introduction. The secondary increase in the size of intracranial haematomas as a result of spontaneous haemorrhage or trauma is of particular relevance in the event of prior intake of platelet aggregation inhibitors. We describe the effect of desmopressin acetate as a means of temporarily stabilising the platelet function. Patients and Methods. The platelet function was analysed in 10 patients who had received single (N = 4) or multiple (N = 6) doses of acetylsalicylic acid and 3 patients (control group) who had not taken acetylsalicylic acid. All subjects had suffered intracranial haemorrhage. Analysis was performed before, half an hour and three hours after administration of desmopressin acetate. Statistical analysis was performed by applying a level of significance of P ≤ 0.05. Results. (1) Platelet function returned to normal 30 minutes after administration of desmopressin acetate. (2) The platelet function worsened again after three hours. (3) There were no complications related to electrolytes or fluid balance. Conclusion. Desmopressin acetate can stabilise the platelet function in neurosurgical patients who have received acetylsalicylic acid prior to surgery without causing transfusion-related side effects or a loss of time. The effect is, however, limited and influenced by the frequency of drug intake. Further controls are needed in neurosurgical patients.

Desmopressin improves platelet activity in acute intracerebral hemorrhage

BACKGROUND AND PURPOSE

Minimizing hematoma growth in high-risk patients is an attractive strategy to improve outcomes after intracerebral hemorrhage. We tested the hypothesis that desmopressin (DDAVP), which improves hemostasis through the release of von Willebrand factor, improves platelet activity after intracerebral hemorrhage.

METHODS

Patients with reduced platelet activity on point-of-care testing alone (5), known aspirin use alone (1), or both (8) received desmopressin 0.4 μg/kg IV. We measured Platelet Function Analyzer-epinephrine (Siemens AG, Germany) and von Willebrand factor antigen from baseline to 1 hour after infusion start and hematoma volume from the diagnostic to a follow-up computed tomographic scan.

RESULTS

We enrolled 14 patients with of mean age 66.8±14.6 years, 11 (85%) of whom were white and 8 (57%) were men. Mean Platelet Function Analyzer-epinephrine results shortened from 192±18 seconds pretreatment to 124±15 seconds (P=0.01) 1 hour later, indicating improved plate activity. von Willebrand factor antigen increased from 242±96% to 289±103% activity (P=0.004), indicating the expected increase in von Willebrand factor. Of 7 (50%) patients who received desmopressin within 12 hours of intracerebral hemorrhage symptom onset, changes in hematoma volume were modest, -0.5 (-1.4 to 8.4) mL and only 2 had hematoma growth. One patient had low blood pressure and another had a new fever within 6 hours of desmopressin administration.

CONCLUSIONS

Intravenous desmopressin was well tolerated and improved platelet activity after acute intracerebral hemorrhage. Larger studies are needed to determine its potential effects on reducing hematoma growth versus platelet transfusion or placebo.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT00961532.

The platelet-function analyzer (PFA-100 ® ) for evaluating primary hemostasis

The platelet-function analyzer, PFA-100, is a relatively novel method for rapid in vitro global evaluation of primary hemostasis. The aim of this review is to summarize the published studies reporting on the utility of the PFA-100 device as a screening tool for primary hemostasis. Data were identified by searches of the published literature, including PubMed, references from reviews and abstracts from the most important meetings on this topic. The literature data support the use of the PFA-100 as a useful screening tool for the investigation of von Willebrand's disease and other acquired and congenital intrinsic platelet function disorders. Moreover, it is useful for evaluating primary hemostasis before surgical procedures and for monitoring desmopressin therapy in both von Willebrand's disease and platelet function disorders. Given its high sensitivity, speed and simplicity of use, we conclude that the PFA-100 could replace the in vivo bleeding time as a screening test for primary hemostasis in routine clinical practice.

Alternatives to blood transfusion

The use of alternatives to allogeneic blood continues to rest on the principles that blood transfusions have inherent risks, associated costs, and affect the blood inventory available for health-care delivery. Increasing evidence exists of a fall in the use of blood because of associated costs and adverse outcomes, and suggests that the challenge for the use of alternatives to blood components will similarly be driven by costs and patient outcomes. Additionally, the risk-benefit profiles of alternatives to blood transfusion such as autologous blood procurement, erythropoiesis-stimulating agents, and haemostatic agents are under investigation. Nevertheless, the inherent risks of blood, along with the continued rise in blood costs are likely to favour the continued development and use of alternatives to blood transfusion. We summarise the current roles of alternatives to blood in the management of medical and surgical anaemias.

Markers of endothelial and platelet activation are associated with high on-aspirin platelet reactivity in patients with stable coronary artery disease

INTRODUCTION

Aspirin inhibits the cyclooxygenase-1 (COX-1) mediated thromboxane A2 synthesis. Despite COX-1 inhibition, in patients with coronary artery disease (CAD), platelets can be activated through other mechanisms, like activation by thrombin.

MATERIALS AND METHODS

At baseline in this cross-sectional substudy of the ASCET trial, 1001 stable CAD patients, all on single aspirin treatment, were classified by the PFA100® method, as having high on-aspirin residual platelet reactivity (RPR) or not. Markers of hypercoagulability, endothelial and platelet activation as related to RPR, were evaluated to explore the potential mechanisms behind high on-aspirin RPR.

RESULTS

Altogether, 25.9% (n=259) of the patients were found to have high on-aspirin RPR. S-thromboxane B(2) levels were very low and did not differ between patients having high on-aspirin RPR or not. Patients with high on-aspirin RPR had significantly higher levels of von Willebrand Factor (vWF) (124 vs 100%, p<0.001, platelet count (236 vs 224 × 10(9)/l, p=0.008), total TFPI (68.4 vs 65.5 ng/ml, p=0.005) and ß-thromboglobulin (ß-TG) (33.3 vs 31.3 IU/ml, p=0.041) compared to patients with low on-aspirin RPR. No significant differences between the groups were observed in levels of endogenous thrombin generation (ETP), pro-thrombin fragment 1+2 (F1+2), D-dimer, soluble TF (sTF) or P-selectin (all p>0.05).

CONCLUSIONS

The high on-aspirin RPR as defined by PFA100® seems not to be due to increased thrombin activity as evaluated with ETP, sTF, F1+2 or D-dimer. The elevated levels of platelet count, ß-TG, TFPI and especially vWF might be explained by increased endothelial and platelet activation in these patients.

The anti-von Willebrand factor aptamer ARC1779 increases von Willebrand factor levels and platelet counts in patients with type 2B von Willebrand disease

Blockade of hyperactive von Willebrand factor (VWF) by ARC1779 blunted the platelet drop induced by desmopressin in patients with type 2B von Willebrand disease (VWD). Thus, we hypothesised that ARC1779 may increase VWF levels and correct thrombocytopenia. Three thrombocytopenic patients suffering from type 2B VWD received a loading dose of 0.23 mg/kg ARC1779 followed by 4 μg/kg/min intravenously for 72 hours in a prospective clinical trial. ARC1779 was well tolerated and safe. Plasma concentrations of ARC1779 increased to 76 μg/ml (59-130) leading to an immediate decrease of free VWF A1 domains. VWF/FVIII levels increased as early as 12 h after start of infusion, peaked near the end of infusion, and returned to baseline at follow-up. VWF ristocetin cofactor activity (VWF:RCo) showed a median 10-fold increase 8 hours after end of infusion, while the median VWF-antigen and FVIII increase was less (5-fold and 4-fold, respectively). Most importantly inhibition of hyperactive VWF rapidly increased platelet counts from 40 x 10(9)/l (38-58 x 10(9)//l) to a maximum of 146 x 10(9)//l (107-248 x 10(9)//l). In conclusion, ARC1779 markedly increases VWF/FVIII levels and most importantly improves or even corrects thrombocytopenia in VWD type 2B patients. This underscores the in vivo potency of ARC1779.

Clinical Significance of Baseline Platelet Reactivity in Patients With Acute Coronary Syndrome

The aim of this study was to assess the baseline platelet hyperactivity in patients with acute coronary syndrome (ACS) and correlate it with the disease severity and clinical outcome.

Participants and Methods:

This study was conducted on 60 patients with the first attack of non-ST-segment elevation ACS and 30 healthy controls. Patients were subdivided into 2 groups: group I: 40 patients with non-ST-segment elevation myocardial infarction (NSTEMI) and group II: 20 patients with unstable angina. All the studied patients were subjected to baseline platelet function analysis using platelet function analyzer 100 (PFA-100).

Results:

Group I patients showed significantly lower PFA-100 closure time (CT) than group II ( P = .04) and control group ( P = .03). The occurrence of complications in NSTEMI patients was associated with older age, hypertension, and shorter baseline collagen adenosine diphosphate PFA-100 CT ( P < .05).

Conclusion:

NSTEMI patients proved to have enhanced platelet function that can be used as a predictor of the outcome.

Illustration of the impact of antiplatelet drugs on the genesis and management of chronic subdural hematoma

The case of a 76-year-old male with a large chronic subdural hematoma that showed total regression with the mere suspension of aspirin, its only apparent causal factor, and that of an 81 year-old male on aspirin and clopidogrel with a chronic subdural hematoma who succumbed after burr holes due to two simultaneous severe hemorrhagic complications (cerebellar hemorrhage and ipsilateral acute subdural hematoma) are presented. The cases may provide support for the following management strategies: (i) if conservative management and drug suspension are feasible, they may well be worth trying and lead to a favorable outcome; (ii) if a patient is at risk of developing a chronic subdural hematoma, namely because of a minor acute subdural hematoma, withdrawal of antiplatelet agents should be considered; (iii) if surgery is necessary, its delay allows for the metabolization of the drug and platelet renewal, thereby minimizing the risk of hemorrhage; (iv) if urgent burr holes are indicated, measures to improve platelet function should be undertaken.

Percutaneous interventions in the coagulopathic patient

Interventional procedures in patients with coagulopathies carry a perceived risk of increased bleeding and complications. Acquired and inherited deficiencies of blood-clotting factors, thrombocytopenia and platelet dysfunction, and effect of anticoagulation are common problems encountered by practicing clinical interventional radiologists. In this article we review common coagulopathies, available data on percutaneous procedures in coagulopathic patients, and recommendations for periprocedure treatment.

Patients with severe aortic valve stenosis and impaired platelet function benefit from preoperative desmopressin infusion

BACKGROUND

Patients with severe aortic valve stenosis have a markedly reduced platelet function as measured by a prolonged collagen adenosine diphosphate closure time (CADP-CT) determined by the platelet function analyzer PFA-100. We hypothesized that such patients may benefit from desmopressin when they present with prolonged CADP-CT due to the specific action of desmopressin on von Willebrand factor (VWF) and CADP-CT.

METHODS

In this double-blind, randomized placebo controlled trial, 43 patients undergoing aortic valve replacement (due to severe aortic valve stenosis with CADP-CT>170 seconds) were given desmopressin 0.3 μg/kg or saline intravenously after induction of anesthesia. Measurement of CADP-CT, factor VIII activity, von Willebrand factor antigen, GpIb binding activity, ristocetin cofactor activity, collagen-binding activity, and multimers were performed after induction of anesthesia, one hour after desmopressin infusion, and 24 hours postoperatively.

RESULTS

In the majority of patients, baseline values of von Willebrand factor related indices were normal, but increased one hour after infusion of desmopressin by 73% to 90% as compared with placebo. Selective loss of high molecular weight multimers was seen only in a minority of patients. The CADP-CT was greater than 170 seconds in 92% of screened patients, and desmopressin shortened CADP-CT by 48% versus baseline and reduced postoperative blood loss by 42% (p<0.001).

CONCLUSIONS

Prolonged CADP-CT indicates platelet dysfunction in severe aortic valve stenosis, and can guide the use of desmopressin as an effective prohemostatic agent in patients with severe aortic valve stenosis.

Incomplete inhibition of platelet function as assessed by the platelet function analyzer (PFA-100) identifies a subset of cardiovascular patients with high residual platelet response while on aspirin

Sixty-six patients with a history of ischemic events (myocardial infarction, unstable angina, or stroke) on chronic aspirin therapy were studied by different platelet function tests: 37 patients had suffered a recurrent event while on aspirin and 29 were without recurrences. Based on results from light transmission aggregometry (LTA) induced by arachidonic acid (AA) and serum TxB(2) both COX-1-dependent methods, only one patient could be identified as aspirin "resistant". However, when methods only partially-dependent on platelet COX-1 activity were considered, the prevalence of aspirin non-responders ranged, according to the different tests, from 0 to 52%. No difference was observed between patients with recurrences and those without. Among patients with recurrent events, those with an incomplete inhibition of platelet function, as assessed by the PFA-100, had significantly higher residual serum TxB(2) (2.4 ± 2.4 ng/mL vs 0.4 ± 0.1 ng/mL, p = 0.03), residual LTA-AA (9.2 ± 10.6% vs 2.0 ± 1.6%, p = 0.008), LTA-Coll (49.3 ± 14.6% vs 10.2 ± 8.3%, p = 0.007) and LTA-ADP (50.9 ± 16.2% vs 34.3 ± 11.0%, p = 0.04). In conclusion, laboratory tests solely exploring the AA-mediated pathway of platelet function, while being the most appropriate to detect the effect of aspirin on its pharmacologic target (platelet COX-1), may fail to reveal the functional interactions between minimal residual TxA(2) and additional stimuli or primers potentially leading to aspirin-insensitive platelet aggregation. High residual platelet response in platelet function tests only partially dependent on COX-1 may reveal a condition of persistent platelet reactivity in a subset of aspirin-treated patients characterizing them as a subgroup at higher vascular risk.

Single dose granulocyte colony-stimulating factor markedly enhances shear-dependent platelet function in humans

Granulocyte colony-stimulating factor (G-CSF) has been associated with the induction of a hypercoagulable state in patients as well as peripheral blood stem donors. Interestingly, sparse data exist on the kinetics of platelet and coagulation activation in response to G-CSF and it is unknown if G-CSF augments shear-dependent platelet function. These two issues are addressed in the current trial. Thirty-six healthy volunteers were enrolled into this study. All subjects received a single-dose of 5 microg/kg filgrastim intravenously. The effects of recombinant G-CSF on platelet and coagulation function were assessed by the platelet function analyzer PFA-100 (collagen/epinephrine (CEPI-CT), collagen/ADP (CADP-CT) closure times), von Willebrand factor activity (vWF : RiCO) ELISA, tissue factor (TF)-mRNA expression on circulating leukocytes and rotation thrombelastography (ROTEM). G-CSF time-dependently enhanced shear dependent platelet function measured by the PFA-100: CEPI-CT declined by 48% and CADP-CT by 31% with nadir values after 24 h (p < 0.001 as compared to baseline) and returned to near-baseline values after 72 hours. In accordance, VWF : RiCO increased by 59% after 24 h (p < 0.001) and returned to baseline 48 h later. TF-mRNA peaked after 4 hours (>6 fold increase p < 0.001) and reached near-baseline values after 24 hours. Nadir closure times were seen after 24 hours (-15%; p < 0.001). Single-dose administration of 5 microg/kg G-CSF significantly enhances shear-dependent platelet function and strongly induces leukocyte TF-mRNA, which translates into shortened clotting times ex vivo.