Platelet Biomarkers in Patients with Atherosclerotic Extracranial Carotid Artery Stenosis: A Systematic Review.

OBJECTIVE: The aim was to enhance understanding of the role of platelet biomarkers in the pathogenesis of vascular events and risk stratifying patients with asymptomatic or symptomatic atherosclerotic carotid stenosis. DATA SOURCES: Systematic review conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. REVIEW METHODS: A systematic review collated data from 1975 to 2020 on ex vivo platelet activation and platelet function/reactivity in patients with atherosclerotic carotid stenosis. RESULTS: Forty-three studies met the inclusion criteria; the majority included patients on antiplatelet therapy. Five studies showed increased platelet biomarkers in patients with ≥ 30% asymptomatic carotid stenosis (ACS) vs. controls, with one neutral study. Preliminary data from one study suggested that quantification of "coated platelets" in combination with stenosis severity may aid risk stratification in patients with ≥ 50% - 99% ACS. Platelets were excessively activated in patients with ≥ 30% symptomatic carotid stenosis (SCS) vs. controls (≥ 11 positive studies and one neutral study). Antiplatelet-High on Treatment Platelet Reactivity (HTPR), previously called "antiplatelet resistance", was observed in 23% - 57% of patients on aspirin, with clopidogrel-HTPR in 25% - 100% of patients with ≥ 50% - 99% ACS. Aspirin-HTPR was noted in 9.5% - 64% and clopidogrel-HTPR in 0 - 83% of patients with ≥ 50% SCS. However, the data do not currently support the use of ex vivo platelet function/reactivity testing to tailor antiplatelet therapy outside of a research setting. Platelets are excessively activated (n = 5), with increased platelet counts (n = 3) in recently symptomatic vs. asymptomatic patients, including those without micro-emboli on transcranial Doppler (TCD) monitoring (n = 2). Most available studies (n = 7) showed that platelets become more reactive or activated following carotid endarterectomy or stenting, either as an acute phase response to intervention or peri-procedural treatment. CONCLUSION: Platelets are excessively activated in patients with carotid stenosis vs. controls, in recently symptomatic vs. asymptomatic patients, and may become activated/hyper-reactive following carotid interventions despite commonly prescribed antiplatelet regimens. Further prospective multicentre studies are required to determine whether models combining clinical, neurovascular imaging, and platelet biomarker data can facilitate optimised antiplatelet therapy in individual patients with carotid stenosis.

Optimal Antiplatelet Therapy in Moderate to Severe Asymptomatic and Symptomatic Carotid Stenosis: A Comprehensive Review of the Literature.

OBJECTIVES: Carotid stenosis patients are at risk of vascular events despite antiplatelet therapy. Data on prescribed antiplatelet regimens have not been comprehensively collated from trials to guide optimal therapy in this population. METHODS: This review was conducted in line with the current Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Medline, Ovid, Embase, Web of Science, and Google Scholar from 1988 to 2018 were searched using the search terms "carotid stenosis", "asymptomatic", "symptomatic", "antiplatelet", and "anti-platelet" to identify randomised trials in patients with asymptomatic or symptomatic extracranial moderate-severe carotid stenosis on any form of antiplatelet therapy in which vascular events and pre specified composite outcome events were reported. RESULTS: Twenty-five studies were judged eligible for inclusion. Data from one randomised controlled trial showed no significant difference in benefit with aspirin versus placebo in asymptomatic carotid stenosis, but it is still reasonable to recommend aspirin (81-325 mg daily) for prevention of vascular events in these patients. Low to medium dose aspirin (81-325 mg daily) is superior to higher doses (>650 mg daily) at preventing recurrent vascular events in patients undergoing endarterectomy. Data from endovascular treatment (EVT) trials support peri-procedural treatment of asymptomatic and symptomatic patients with 81-325 mg of aspirin daily. The use of peri-procedural aspirin-clopidogrel in patients undergoing EVT is based on one pilot trial, but appears safe. Short-term aspirin-dipyridamole or aspirin-clopidogrel treatments are equally effective at reducing micro-embolic signals on transcranial Doppler ultrasound in patients with ≥50% symptomatic carotid stenosis. There is insufficient evidence to recommend routine aspirin-clopidogrel combination therapy to reduce the risk of recurrent clinical ischaemic events in patients with symptomatic moderate-severe carotid stenosis. CONCLUSIONS: This comprehensive review outlines an evidence based approach to antiplatelet therapy in carotid stenosis patients. Future trials should randomise such patients to receive different antiplatelet regimens to assess their efficacy and safety and to optimise peri-procedural and long-term preventive treatment in this patient cohort.

Platelet function testing in transient ischaemic attack and ischaemic stroke: A comprehensive systematic review of the literature.

The majority of patients with ischaemic cerebrovascular disease (CVD) are not protected from further vascular events with antiplatelet therapy. Measurement of inhibition of platelet function ex vivo on antiplatelet therapy, using laboratory tests that correlate with the clinical effectiveness of these agents, would potentially enable physicians to tailor antiplatelet therapy to suit individuals. A systematic review of the literature was performed to collate all available data on ex vivo platelet function/reactivity in CVD patients, especially those treated with aspirin, dipyridamole or clopidogrel. Particular emphasis was paid to information from commonly available whole blood platelet function analysers (PFA-100®, VerifyNow® and Multiplate®). Data on pharmacogenetic mechanisms potentially influencing high on-treatment platelet reactivity (HTPR) on antiplatelet therapy in CVD were reviewed. Two-hundred forty-nine potentially relevant articles were identified; 93 manuscripts met criteria for inclusion. The prevalence of ex vivo HTPR in CVD varies between 3-62% with aspirin monotherapy, 8-61% with clopidogrel monotherapy and 56-59% when dipyridamole is added to aspirin in the early, subacute or late phases after TIA/stroke onset. The prevalence of HTPR on aspirin was higher on the PFA-100 than on the VerifyNow in one study (p < 0.001). Furthermore, the prevalence of HTPR on aspirin was lower when one used 'novel longitudinal' rather than 'cross-sectional, case-control' definitions of HTPR on the PFA early after TIA or stroke (p = 0.003; 1 study). Studies assessing the influence of genetic polymorphisms on HTPR in CVD patients are limited, and need validation in large multicentre studies. Available data illustrate that an important proportion of CVD patients have ex vivo HTPR on their prescribed antiplatelet regimen, and that the prevalence varies depending on the definition and assay used. Large, adequately-sized, prospective multicentre collaborative studies are urgently needed to determine whether comprehensive assessment of HTPR at high and low shear stress with a range of user-friendly whole blood platelet function testing platforms, in conjunction with pharmacogenetic data, improves our ability to predict the risk of recurrent vascular events in CVD patients, and thus enhance secondary prevention following TIA or ischaemic stroke.

Frequency of inter-specialty consensus decisions and adherence to advice following discussion at a weekly neurovascular multidisciplinary meeting.

BACKGROUND/AIMS: Data are limited on the frequency of 'consensus decisions' between sub-specialists attending a neurovascular multidisciplinary meeting (MDM) regarding management of patients with extracranial carotid/vertebral stenoses and post-MDM 'adherence' to such advice. METHODS: This prospective audit/quality improvement project collated prospectively-recorded data from a weekly Neurovascular/Stroke Centre MDM documenting the proportion of extracranial carotid/vertebral stenosis patients in whom 'consensus management decisions' were reached by neurologists, vascular surgeons, stroke physicians-geriatricians and neuroradiologists. Adherence to MDM advice was analysed in asymptomatic carotid stenosis (ACS), symptomatic carotid stenosis (SCS), 'indeterminate symptomatic status stenosis' (ISS) and vertebral artery stenosis (VAS) patients, including intervals between index event to MDM + / - intervention. RESULTS: One hundred fifteen patients were discussed: 108 with carotid stenosis and 7 with VAS. Consensus regarding management was noted in 96.5% (111/115): 100% with ACS and VAS, 96.2% with SCS and 92.9% with ISS. Adherence to MDM management advice was 96.4% (107/111): 100% in ACS, ISS and VAS patients; 92% (46/50) in SCS patients. The median interval from index symptoms to revascularisation in 50-99% SCS patients was 12.5 days (IQR: 9-18.3 days; N = 26), with a median interval from MDM to revascularisation of 5.5 days (IQR: 1-7 days). Thirty patients underwent revascularisation. Two out of twenty-nine patients (6.9%) with either SCS or ISS had a peri-procedural ipsilateral ischaemic stroke, with no further strokes/deaths during 3-months follow-up. CONCLUSIONS: The high frequency of inter-specialty consensus regarding management and adherence to proposed treatment supports a collaborative/multidisciplinary model of care in patients with extracranial arterial stenoses. Service development should aim to shorten times between MDM discussion-intervention and optimise prevention of stroke/death.

von Willebrand Factor Antigen, von Willebrand Factor Propeptide, and ADAMTS13 in Carotid Stenosis and Their Relationship with Cerebral Microemboli.

BACKGROUND: The relationship between von Willebrand factor antigen (VWF:Ag), VWF propeptide (VWFpp), VWFpp/VWF:Ag ratio, ADAMTS13 activity, and microembolic signal (MES) status in carotid stenosis is unknown. METHODS: This prospective, multicenter study simultaneously assessed plasma VWF:Ag levels, VWFpp levels and ADAMTS13 activity, and their relationship with MES in asymptomatic versus symptomatic moderate-to-severe (≥50-99%) carotid stenosis patients. One-hour transcranial Doppler ultrasound of the middle cerebral arteries classified patients as MES+ve or MES-ve. RESULTS: Data from 34 asymptomatic patients were compared with 43 symptomatic patients in the "early phase" (≤4 weeks) and 37 patients in the "late phase" (≥3 months) after transient ischemic attack (TIA)/ischemic stroke. VWF:Ag levels were higher (p = 0.049) and VWFpp/VWF:Ag ratios lower (p = 0.006) in early symptomatic than in asymptomatic patients overall, and in early symptomatic versus asymptomatic MES-ve subgroups (p ≤0.02). There were no intergroup differences in VWFpp expression or ADAMTS13 activity (p ≥0.05). VWF:Ag levels and ADAMTS13 activity decreased (p ≤ 0.048) and VWFpp/VWF:Ag ratios increased (p = 0.03) in symptomatic patients followed up from the early to late phases after TIA/stroke. Although there were no differences in the proportions of symptomatic and asymptomatic patients with blood group O, a combined analysis of early symptomatic and asymptomatic patients revealed lower median VWF:Ag levels in patients with blood group O versus those without blood group O (9.59 vs. 12.32 µg/mL, p = 0.035). DISCUSSION: VWF:Ag expression, a marker of endothelial ± platelet activation, is enhanced in recently symptomatic versus asymptomatic carotid stenosis patients, including in MES-ve patients, and decreases with ADAMTS13 activity over time following atherosclerotic TIA/ischemic stroke.

Platelet function/reactivity testing and prediction of risk of recurrent vascular events and outcomes after TIA or ischaemic stroke: systematic review and meta-analysis.

BACKGROUND: The prevalence of ex vivo 'high on-treatment platelet reactivity (HTPR)' and its relationship with recurrent vascular events/outcomes in patients with ischaemic cerebrovascular disease (CVD) is unclear. METHODS: A systematic review and meta-analysis was performed in accordance with the PRISMA statement. MEDLINE, EMBASE and Cochrane Library were searched for completed manuscripts until May 2019 on TIA/ischaemic stroke patients, ≥ 18 years, treated with commonly-prescribed antiplatelet therapy, who had platelet function/reactivity testing and prospective follow-up data on recurrent stroke/TIA, myocardial infarction, vascular death or other cerebrovascular outcomes. Data were pooled using random-effects meta-analysis. Primary outcome was the composite risk of recurrent stroke/TIA, myocardial infarction or vascular death. Secondary outcomes were recurrent stroke/TIA, severe stroke (NIHSS > 16) or disability/impairment (modified Rankin scale ≥ 3) during follow-up. RESULTS: Antiplatelet-HTPR prevalence was 3-65% with aspirin, 8-56% with clopidogrel and 1.8-35% with aspirin-clopidogrel therapy. Twenty studies (4989 patients) were included in our meta-analysis. There was a higher risk of the composite primary outcome (OR 2.93, 95% CI 1.90-4.51) and recurrent ischaemic stroke/TIA (OR 2.43, 95% CI 1.51-3.91) in patients with vs. those without 'antiplatelet-HTPR' on any antiplatelet regimen. These risks were also more than twofold higher in patients with vs. those without 'aspirin-HTPR' and 'dual antiplatelet-HTPR', respectively. Clopidogrel-HTPR status did not significantly predict outcomes, but the number of eligible studies was small. The risk of severe stroke was higher in those with vs. without antiplatelet-HTPR (OR 2.65, 95% CI 1.00-7.01). DISCUSSION: Antiplatelet-HTPR may predict risks of recurrent vascular events/outcomes in CVD patients. Given the heterogeneity between studies, further prospective, multi-centre studies are warranted.

Increased Leucocyte-Platelet Complex Formation in Recently Symptomatic versus Asymptomatic Carotid Stenosis Patients and in Micro-emboli Negative Subgroups.

INTRODUCTION: Cerebral micro-embolic signals (MES) predict risk of stroke in carotid stenosis patients. However, MES-negative 'recently symptomatic patients' also have a higher stroke risk than 'asymptomatic patients'. Differences in platelet activation status may contribute to this disparity in risk. METHODS: This prospective, observational study assessed platelet biomarkers and their relationship with MES in asymptomatic versus symptomatic moderate (≥50-69%) or severe (≥70-99%) carotid stenosis patients. Full blood count parameters were measured and whole-blood flow cytometry was used to quantify platelet surface CD62P and CD63 expression and leucocyte-platelet complex formation. Bilateral simultaneous transcranial Doppler ultrasound of the middle cerebral arteries classified patients as 'MES positive' or 'MES negative'. RESULTS: Data from 34 asymptomatic patients were compared with those from 43 symptomatic patients in the 'early phase' (≤ 4 weeks) and 37 of these symptomatic patients in the 'late phase' (≥ 3 months) after transient ischaemic attack/ischaemic stroke. There were no differences in %CD62P or %CD63 expression between early or late symptomatic and asymptomatic patients overall (p > 0.05). The percentage of lymphocyte-platelet complexes was higher in early symptomatic than in asymptomatic patients (2.8 vs. 2.16%; p < 0.001). MES were more commonly observed in early symptomatic (31.4%; p = 0.027) but not in late symptomatic (6.7%; p = 0.996) versus asymptomatic patients (7.1%). The percentage of lymphocyte-platelet complexes was higher in early symptomatic than in asymptomatic MES-negative patients (2.7 vs. 2.17%; p = 0.02). CONCLUSION: These data add to the evidence that leucocyte-platelet complex formation/platelet activation is increased in recently symptomatic versus asymptomatic patients, and may contribute to the pathogenesis of first and subsequent strokes in carotid stenosis patients, including those who are MES negative.

Extracranial and Intracranial Vasculopathy With "Moyamoya Phenomenon" in Association With Alagille Syndrome.

Background: Alagille syndrome (AGS) is an autosomal-dominant, multisystem disorder caused by mutations in the JAG1 gene. Case Description: A 34-year-old man was referred to our service 10 years ago with focal seizures with impaired awareness and transient slurred speech. He had a 5-year history of intermittent left monocular low-flow retinopathy. He has a family history of AGS. General examination revealed mild hypertension, aortic regurgitation, and livedo reticularis. Neurological examination was normal. Investigations: He had mild hyperlipidaemia and persistently-positive lupus anticoagulant consistent with primary anti-phospholipid syndrome. Color Doppler ultrasound revealed low velocity flow in a narrowed extracranial left internal carotid artery (ICA). MR and CT angiography revealed a diffusely narrowed extracranial and intracranial left ICA. Formal cerebral angiography confirmed severe left ICA narrowing consistent with a left ICA "vasculopathy" and moyamoya phenomenon. Transthoracic echocardiogram revealed a bicuspid aortic valve and aortic incompetence. Molecular genetic analysis identified a missense mutation (A211P) in exon 4 of the JAG1 gene, consistent with AGS. Discussion: AGS should be considered in young adults with TIAs/stroke and unexplained extracranial or intracranial vascular abnormalities, and/or moyamoya phenomenon, even in the absence of other typical phenotypic features. Gene panels should include JAG1 gene testing in similar patients.

Clinical outcomes and a high prevalence of abnormalities on comprehensive arterial and venous thrombophilia screening in TIA or ischaemic stroke patients with a patent foramen ovale, an inter-atrial septal aneurysm or both.

INTRODUCTION: Data are limited on the optimal management of cryptogenic TIA/stroke patients with a patent foramen ovale (PFO)±inter-atrial septal aneurysm (IASA), especially with an inherited thrombophilia. METHODS: Prospectively-collected data on TIA/ischaemic stroke patients with PFO, IASA or both who received 'goal-directed secondary-prevention medical treatment' were analysed. All patients had trans-oesophageal echocardiography, anti-nuclear, anti-cardiolipin, anti-beta 2 glycoprotein I antibodies, rheumatoid factor, lupus anticoagulant, protein C&S, anti-thrombin, factor VIII activity, activated protein C resistance, Factor V Leiden, prothrombin gene and MTHFR-c.677C>T mutation screening. ENA and homocysteine were assessed in the latter study period. RESULTS: Eighty-three patients were recruited. Mean follow-up: 48.1months. Forty-seven patients (56.6%) had an isolated PFO, 32 (38.6%) a PFO and an IASA, and 4 (4.8%) an IASA alone. Eighteen (21.7%) had ≥1 abnormality on thrombophilia screening. The most important abnormalities which lead to treatment changes in 11 patients (13.3%) were primary anti-phospholipid syndrome (N=3; 3.6%), protein S deficiency (N=2; 2.4%) hyper-homocysteinaemia (N=6/72 screened, 8.3%). Four patients (4.8%) opted for PFO closure: two with protein S deficiency, and two with no identified thrombophilia. Seven (8.4%) had recurrent TIA/ischaemic stroke during follow-up (overall annualised incidence: 2.1%), of whom five had a PFO alone and two a PFO and IASA. DISCUSSION: Comprehensive arterial and venous thrombophilia screening is warranted in TIA/ischaemic stroke patients with a PFO±IASA, is conclusively abnormal in over a fifth, and informed important decision-making regarding individualised therapy in 13.3% of patients. The incidence of recurrent vascular events in this population is low on optimal, personalised secondary-prevention treatment, even with an underlying thrombophilia.

Continuation and adherence rates on initially-prescribed intensive secondary prevention therapy after Rapid Access Stroke Prevention (RASP) service assessment.

INTRODUCTION: Consistent adherence to treatment is essential for effective secondary prevention following TIA/ischaemic stroke. Representative data on long-term treatment continuation and adherence rates are limited. METHODS: This single centre study recruited patients attending our Rapid Access Stroke Prevention clinic in Ireland from 07/09/2006 → 30/11/2009. Demographic and clinical data, and prescribed medication regimens at initial assessment were recorded. All patients received copies of clinical correspondence containing clear 'goal-directed treatment advice' sent to their general practitioner or referring physician. Patients were subsequently interviewed with a standardised pro-forma to assess continuation and adherence rates; overall adherence rates with secondary prevention therapy were also assessed with a validated self-reporting tool (Morisky Scale). Recurrent vascular events during follow-up were recorded. RESULTS: One hundred and fourteen patients were recruited; mean age: 64.5 ± 13.8 years; median duration of follow-up: 630 days. Patients were prescribed aspirin (69.3%), alone (17.5%) or in combination with dipyridamole MR (51.8%), clopidogrel (18.2%), warfarin (16.7%), statins (76.3%) and anti-hypertensives (51.8%). During follow-up, the percentages of patients continuing treatment prescribed at the initial visit were: Aspirin (93.7%), dipyridamole MR (72.9%), clopidogrel (81%), warfarin (94.7%), statins (87.9%) and anti-hypertensives (89.8%). Overall, 99.1% reported taking their medication the preceding day. Morisky scale scores for all treatments revealed that 41.2% (N=47) were high, 36.8% (N=42) medium, and 12.3% (N=14) low adherers; 9.7% (N=11) had incomplete data. Two patients (1.8%) had recurrent cerebrovascular events, and two (1.8%) had myocardial infarctions. DISCUSSION: This novel study in European TIA/ischaemic stroke patients, who were provided with a goal-directed secondary prevention plan, showed high rates of medication-continuation and self-reported adherence with prescribed treatment, associated with a low incidence of recurrent vascular events during a median follow up of 1.7 years.

Relationship between ADAMTS13 activity, von Willebrand factor antigen levels and platelet function in the early and late phases after TIA or ischaemic stroke.

BACKGROUND: Reduced ADAMTS13 activity is seen in thrombotic thrombocytopenic purpura (TTP), and may lead to accumulation of prothrombotic ultra-large von Willebrand factor (ULVWF) multimers in vivo. ADAMTS13 activity and its relationship with VWF antigen (VWF:Ag) levels and platelet function in 'non-TTP related' TIA or ischaemic stroke has not been comprehensively studied. METHODS: In this prospective pilot observational analytical case-control study, ADAMTS13 activity and VWF:Ag levels were quantified in platelet poor plasma in 53 patients in the early phase (≤ 4 weeks) and 34 of these patients in the late phase (≥ 3 months) after TIA or ischaemic stroke on aspirin. Data were compared with those from 22 controls not on aspirin. The impact of ADAMTS13 on platelet function in whole blood was quantified by measuring Collagen-ADP (C-ADP) and Collagen-Epinephrine closure times on a platelet function analyser (PFA-100(®)). RESULTS: Median ADAMTS13 activity was significantly reduced in the early phase (71.96% vs. 95.5%, P <0.01) but not in the late phase after TIA or stroke compared with controls (86.3% vs. 95.5%, P=0.19). There was a significant inverse relationship between ADAMTS13 activity and VWF:Ag levels in the early phase (r=-0.31; P=0.024), but not in the late phase after TIA or stroke (P=0.74). There was a positive correlation between ADAMTS13 activity and C-ADP closure times in early phase patients only, likely mediated via VWF:Ag levels. DISCUSSION: ADAMTS13 activity is reduced and VWF:Ag expression is increased within 4 weeks of TIA or ischaemic stroke onset, and can promote enhanced platelet adhesion and aggregation in response to stimulation with collagen and ADP via VWF-mediated pathways. These data improve our understanding of the dynamic haemostatic and thrombotic profiles of ischaemic cerebrovascular disease (CVD) patients, and are important in view of the potential future role that ADAMTS13 may have to play as an anti-thrombotic agent in CVD.