Levels and value of platelet activity in patients with severe internal carotid artery stenosis

Prospective pilot study of tirofiban in progressive stroke after intravenous thrombolysis

Background

Intravenous thrombolysis (IVT) is a standard procedure for the treatment of patients with acute ischemic stroke (AIS). Improving the therapeutic efficacy of IVT is an important task for neurologists. The aim of this study was to evaluate the efficacy and safety of early low-dose tirofiban treatment in AIS patients with early neurological deterioration (END) after IVT.

Methods

In this prospective and randomized pilot study, 73 AIS patients with END were recruited from a local hospital in China. Of these, 14 patients were treated with regular antiplatelet agents (aspirin plus clopidogrel) and 59 patients were treated with tirofiban within 24 h of IVT, followed by regular antiplatelet therapy. Neurological deficits and functional recovery were assessed with NIHSS and modified Rankin Scale (mRS) at 7 and 90 days. During the 90-day follow-up period, both hemorrhagic (e.g., intracerebral hemorrhage) and non-hemorrhagic (e.g., pneumonia) events were recorded.

Results

Treatment with tirofiban compared with regular antiplatelet therapy: (1) improved functional recovery of AIS patients to mRS (≤2) at both 7 and 90 days (odds ratios [ORs], 1.37 and 1.64; 95% confidence interval [CI], 1.16–1.61 and 1.26–2.12; P = 0.008 and < 0.001, respectively), and (2) reduced NIHSS scores from 11.14 ± 2.38 to 5.95 ± 3.48 at day 7 (P < 0.001) and from 8.14 ± 2.74 to 4.08 ± 3.50 at day 90 (P < 0.001). Tirofiban treatment did not increase the risk of hemorrhagic complications. Multivariate regression analysis showed that tirofiban treatment independently predicted a favorable functional outcome (P ≤ 0.001).

Conclusion

Early treatment with low-dose tirofiban in AIS patients with neurologic deterioration after IVT potentially improved functional recovery and attenuated neurologic deficits as early as 7 days and did not increase the risk of various hemorrhagic complications. However, the therapeutic efficacy of tirofiban treatment in END patients needs to be determined by future randomized clinical trials with a large study population.

Clinical trial registration

http://www.chictr.org.cn/, Identifier ChiCTR2200058513.

Aspirin Resistance in Vascular Disease: A Review Highlighting the Critical Need for Improved Point-of-Care Testing and Personalized Therapy

Aspirin resistance describes a phenomenon where patients receiving aspirin therapy do not respond favorably to treatment, and is categorized by continued incidence of adverse cardiovascular events and/or the lack of reduced platelet reactivity. Studies demonstrate that one in four patients with vascular disease are resistant to aspirin therapy, placing them at an almost four-fold increased risk of major adverse limb and adverse cardiovascular events. Despite the increased cardiovascular risk incurred by aspirin resistant patients, strategies to diagnose or overcome this resistance are yet to be clinically validated and integrated. Currently, five unique laboratory assays have shown promise for aspirin resistance testing: Light transmission aggregometry, Platelet Function Analyzer-100, Thromboelastography, Verify Now, and Platelet Works. Newer antiplatelet therapies such as Plavix and Ticagrelor have been tested as an alternative to overcome aspirin resistance (used both in combination with aspirin and alone) but have not proven to be superior to aspirin alone. A recent breakthrough discovery has demonstrated that rivaroxaban, an anticoagulant which functions by inhibiting active Factor X when taken in combination with aspirin, improves outcomes in patients with vascular disease. Current studies are determining how this new regime may benefit those who are considered aspirin resistant.

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.

High on-clopidogrel platelet reactivity in ischaemic stroke or transient ischaemic attack: Systematic review and meta-analysis

OBJECTIVES

To assess the prevalence of high on-clopidogrel platelet reactivity (HCPR) in patients with ischaemic stroke or transient ischaemic attack (IS/TIA), their outcome and genetic basis of on-treatment response variability in IS/TIA patients.

METHODS

We conducted a comprehensive search of PubMed and EMBASE from their inceptions to March 9, 2019. Studies that reported absolute numbers/percentages of HCRP at any time point after IS/TIA onset evaluated with any type of platelet function tests, clinical outcomes and genotyping data were included.

RESULTS

Among 21 studies of 4312 IS/TIA patients treated with clopidogrel, the pooled prevalence of HCPR was 28% (95%CI: 24-32%; high heterogeneity: I² = 88.2%, p < 0.001). Heterogeneity degree diminished across groups defined by the HCPR testing method. Clopidogrel non-responder IS/TIA patients had poorer outcome compared to responders (RR = 2.09, 95%CI: 1.61-2.70; p = 0.036; low heterogeneity across studies: I² = 27.4%, p = 0.210). IS/TIA carriers of CYP2C19*2 or CYP2C19*3 loss of function alleles had a higher risk of HCPR compared to wild type (RR = 1.69, 95%CI: 1.47-1.95; p < 0.001; I² = 0.01%, p = 0.475).

CONCLUSIONS

This systematic review shows a high prevalence of clopidogrel resistance in IS/TIA and poor outcome in these patients. CYP2C19 polymorphisms may potentially influence clopidogrel resistance.

Blood Biomarkers for Stroke Diagnosis and Management

Biomarkers are objective indicators used to assess normal or pathological processes, evaluate responses to treatment and predict outcomes. Many blood biomarkers already guide decision-making in clinical practice. In stroke, the number of candidate biomarkers is constantly increasing. These biomarkers include proteins, ribonucleic acids, lipids or metabolites. Although biomarkers have the potential to improve the diagnosis and the management of patients with stroke, there is currently no marker that has demonstrated sufficient sensitivity, specificity, rapidity, precision, and cost-effectiveness to be used in the routine management of stroke, thus highlighting the need for additional work. A better standardization of clinical, laboratory and statistical procedures between centers is indispensable to optimize biomarker performance. This review focuses on blood biomarkers that have shown promise for translation into clinical practice and describes some newly reported markers that could add to routine stroke care. Avenues for the discovery of new stroke biomarkers and future research are discussed. The description of the biomarkers is organized according to their expected application in clinical practice: diagnosis, treatment decision, and outcome prediction.

Relationship between 'on-treatment platelet reactivity', shear stress, and micro-embolic signals in asymptomatic and symptomatic carotid stenosis

BACKGROUND

Assessment of 'high on-treatment platelet reactivity (HTPR)' could enhance understanding of the pathophysiology of first or recurrent vascular events in carotid stenosis patients on antiplatelet therapy.

METHODS

This prospective, multi-centre study assessed antiplatelet-HTPR status and its relationship with micro-emboli signals (MES) in asymptomatic vs. symptomatic ≥ 50-99% carotid stenosis. Platelet function/reactivity was assessed under 'moderately high shear stress' with the PFA-100^® and 'low shear stress' with VerifyNow^® and Multiplate^® analysers. Bilateral 1-h 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 TIA/ischaemic stroke. Median daily aspirin doses were higher in early symptomatic (225 mg; P < 0.001), but not late symptomatic (75 mg; P = 0.62) vs. asymptomatic patients (75 mg). There was a lower prevalence of aspirin-HTPR in early (28.6%; P = 0.028), but not late symptomatic (38.9%; P = 0.22) compared with asymptomatic patients (56.7%) on the PFA-100^®, but not on the VerifyNow^® or Multiplate^® (P ≤ 0.53). Early symptomatic patients had a higher prevalence of aspirin-HTPR on the PFA-100^® (28.6%) vs. VerifyNow^® (9.5%; P = 0.049), but not Multiplate^® assays (11.9%, P = 0.10). There was no difference in aspirin-HTPR prevalence between any symptomatic vs. asymptomatic MES + ve or MES - ve subgroup.

DISCUSSION

Recently symptomatic moderate-severe carotid stenosis patients had a lower prevalence of aspirin-HTPR than their asymptomatic counterparts on the PFA-100^®, likely related to higher aspirin doses. The prevalence of antiplatelet-HTPR was positively influenced by higher shear stress levels, but not MES status.

Levels and values of lipoprotein-associated phospholipase A2, galectin-3, RhoA/ROCK, and endothelial progenitor cells in critical limb ischemia: pharmaco-therapeutic role of cilostazol and clopidogrel combination therapy

Objective

We tested the hypothesis that clopidogrel and cilostazol combination therapy could effectively attenuate systemic inflammatory reaction, facilitate proliferation of circulating endothelial progenitor cell (EPC), and improve the clinical outcomes of critical limb ischemia (CLI) in patients unsuitable for surgical revascularization or percutaneous transluminal angioplasty (PTA).

Methods

A total 55 patients (mean age, 72 years; 56% female) were consecutively enrolled. Clopidogrel and cilostazol combination therapy was administered throughout the study period.

Results

As compared with the baseline, circulating endothelial progenitor cell level (as shown by flow cytometry) was significantly increased (p < 0.003), whereas the CLI-related ulcers and painfulness were significantly improved (all p < 0.01) by day 90 after treatment. On the other hand, after clopidogrel and cilostazol combination therapy, galectin-3 level, lipoprotein-associated phospholipase A₂ gene expression, and RhoA/ROCK-related protein expression in peripheral blood mononuclear cells were significantly suppressed (all p < 0.01). Eventually, by day 90, 5 patients (9.1%) died of other etiologies, 3 (5.5%) withdrew from the study, 6 (10.9%) required amputation, and the remaining 41 had satisfactory clinical improvement with complete wound healing in 9 (16.4%) patients.

Conclusion

The results of the present study highlight that clopidogrel and cilostazol combination therapy may be considered to be an alternative method for treating patients with CLI unsuitable for surgical revascularization or PTA.

Biomarkers for stroke

Background

Major stroke clinical trials have failed during the past decades. The failures suggest the presence of heterogeneity among stroke patients. Biomarkers refer to indicators found in the blood, other body fluids or tissues that predicts physiologic or disease states, increased disease risk, or pharmacologic responses to a therapeutic intervention. Stroke biomarkers could be used as a guiding tool for more effective personalized therapy.

Main Contents

Three aspects of stroke biomarkers are explored in detail. First, the possible role of biomarkers in patients with stroke is discussed. Second, the limitations of conventional biomarkers (especially protein biomarkers) in the area of stroke research are presented with the reasons. Lastly, various types of biomarkers including traditional and novel genetic, microvesicle, and metabolomics-associated biomarkers are introduced with their advantages and disadvantages. We especially focus on the importance of comprehensive approaches using a variety of stroke biomarkers.

Conclusion

Although biomarkers are not recommended in practice guidelines for use in the diagnosis or treatment of stroke, many efforts have been made to overcome the limitations of biomarkers. The studies reviewed herein suggest that comprehensive analysis of different types of stroke biomarkers will improve the understanding of individual pathophysiologies and further promote the development of screening tools for of high-risk patients, and predicting models of stroke outcome and rational stroke therapy tailored to the characteristics of each case.

Platelet activation, function, and reactivity in atherosclerotic carotid artery stenosis: a systematic review of the literature

An important proportion of transient ischemic attack or ischemic stroke is attributable to moderate or severe (50-99%) atherosclerotic carotid stenosis or occlusion. Platelet biomarkers have the potential to improve our understanding of the pathogenesis of vascular events in this patient population. A detailed systematic review was performed to collate all available data on ex vivo platelet activation and platelet function/reactivity in patients with carotid stenosis. Two hundred thirteen potentially relevant articles were initially identified; 26 manuscripts met criteria for inclusion in this systematic review. There was no consistent evidence of clinically informative data from urinary or soluble blood markers of platelet activation in patients with symptomatic moderate or severe carotid stenosis who might be considered suitable for carotid intervention. Data from flow cytometry studies revealed evidence of excessive platelet activation in patients in the early, sub-acute, or late phases after transient ischemic attack or stroke in association with moderate or severe carotid stenosis and in asymptomatic moderate or severe carotid stenosis compared with controls. Furthermore, pilot data suggest that platelet activation may be increased in recently symptomatic than in asymptomatic severe carotid stenosis. Excessive platelet activation and platelet hyperreactivity may play a role in the pathogenesis of first or subsequent transient ischemic attack or stroke in patients with moderate or severe carotid stenosis. Larger longitudinal studies assessing platelet activation status with flow cytometry and platelet function/reactivity in symptomatic vs. asymptomatic carotid stenosis are warranted to improve our understanding of the mechanisms responsible for transient ischemic attack or stroke.

Migraine: possible role of shear-induced platelet aggregation with serotonin release

BACKGROUND

Migraine patients are at an increased risk for stroke, as well as other thromboembolic events. This warrants further study of the role of platelets in a proportion of migraine patients.

OBJECTIVE

To extend the "platelet hypothesis" using literature data and observations made in a rat model of shear stress-induced platelet aggregation. Such aggregation causes release of serotonin, leading to vasoconstriction during sufficiently strong aggregation and to long-lasting vasodilation when aggregation diminishes. This vasodilation also depends on nitric oxide and prostaglandin formation.

RESULTS

A role for platelet aggregation in a number of migraineurs is indicated by reports of an increased platelet activity during attacks and favorable effects of antiplatelet medication. We hypothesize that in those patients, a migraine attack with or without aura may both be caused by a rise in platelet-released plasma serotonin, albeit at different concentration. At high concentrations, serotonin may cause vasoconstriction and, consequently, the neuronal signs of aura, whereas at low concentrations, it may already stimulate perivascular pain fibers and cause vasodilation via local formation of nitric oxide, prostaglandins, and neuropeptides. Platelet aggregation may be unilaterally evoked by elevated shear stress in a stenotic cervico-cranial artery, by reversible vasoconstriction or by other cardiovascular abnormality, eg, a symptomatic patent foramen ovale. This most likely occurs when a migraine trigger has further enhanced platelet aggregability; literature shows that many triggers either stimulate platelets directly or reduce endogenous platelet antagonists like prostacyclin.

CONCLUSION

New strategies for migraine medication and risk reduction of stroke are suggested.

Flow visualization techniques in a mock ventricle supported by a nonpulsatile left ventricular assist device

Little is known about flow patterns in ventricles supported by continuous flow left ventricular assist devices (LVADs), and valuable information can be obtained with simple flow visualization experiments. We describe the application of several experimental techniques for the in vitro study of ventricular flow patterns (e.g., unsteadiness, vortical motions, stagnation regions) in the presence of a continuous flow LVAD. We used dye streaks, particle paths, and hydrogen bubble techniques to visualize fluid flow in an idealized, static, transparent mock ventricle attached to a Jarvik 2000 continuous flow LVAD. We recorded ventricular flow behavior at various pump speeds while independently adjusting pump flow (by varying the afterload) to emulate in vivo pump flow at various phases of the cardiac cycle. Changes in ventricular flow behavior at different pump flow rates may be of clinical relevance, because continuous flow pumps are extremely sensitive to inflow and outflow pressures and instantaneous pump flow varies significantly at different points throughout the cardiac cycle. Further work is needed to quantitatively compare the flow behavior of different continuous flow devices in a pulsatile ventricular model.

In vitro Doppler ultrasound investigation of turbulence intensity in pulsatile flow with simulated cardiac variability

An in vitro investigation of turbulence intensity (TI) associated with a severe carotid stenosis in the presence of physiological cardiac variability is described. The objective of this investigation was to determine if fluctuations due to turbulence could be quantified with conventional Doppler ultrasound (DUS) in the presence of normal physiological cycle-to-cycle cardiac variability. An anthropomorphic model of a 70% stenosed carotid bifurcation was used in combination with a programmable flow pump to generate pulsatile flow with a mean flow rate of 6 mL/s. Utilizing the pump, we studied normal, nonrepetitive cycle-to-cycle cardiac variability (+/-3.9%) in flow, as well as waveform shapes with standard deviations equal to 0, 2 and 3 times the normal variation. Eighty cardiac cycles of Doppler data were acquired at two regions within the model, representing either laminar or turbulent flow; each measurement was repeated six times. Turbulence intensity values were found to be 11 times higher (p < 0.001), on average, in the turbulent region than in the laminar region, with a mean difference of 24 cm/s. Twenty cardiac cycles were required for confidence in TI values. In conclusion, these results indicate that it is possible to quantify TI in vitro, even in the presence of normal and exaggerated cycle-to-cycle cardiac variability.