L-band and SHF multiple access schemes for the MSAT system

The first generation of the Canadian Mobile Satellite (MSAT) system, planned to be operational in the early 1990s, will provide voice and data services to land, aeronautical, and maritime mobile terminals within the Canadian land mass and its territorial waters. The system will be managed by a centralized Demand Assignment Multiple Access (DAMA) control system. Users will request a communication channel by communicating with the DAMA Control System (DCS) via the appropriate signalling channels. Several access techniques for both L-band and SHF signalling channels have been investigated. For the L-band, Slotted Aloha (SA) and Reservation Aloha (RA), combined with a token scheme, are discussed here. The results of Telesat studies to date indicate that SA, when combined with token scheme, provides the most efficient access and resource management tool in a mobile propagation environment. For SHF signalling channels, slim time division multiple access (TDMA) and SA have been considered as the most suitable candidate schemes. In view of the operational environment of the SHF links, provision of a very short channel access delay and a relatively high packet success rate are highly desirable. Studies carried out generally favor slim-TDMA as the most suitable approach for SHF signalling channels

Efficacy of antiplatelet therapy in secondary prevention following lacunar stroke:Pooled analysis of randomized trials

Background and Purpose: Lacunar stroke accounts for ≈25% of ischemic stroke, but optimal antiplatelet regimen to prevent stroke recurrence remains unclear. We aimed to evaluate the efficacy of antiplatelet agents in secondary stroke prevention after a lacunar stroke. Methods: We searched MEDLINE, Embase, and the Cochrane library for randomized controlled trials that reported risk of recurrent stroke or death with antiplatelet therapy in patients with lacunar stroke. We used random effects meta-analysis and evaluated heterogeneity with I2. Results: We included 17 trials with 42 234 participants (mean age 64.4 years, 65% male) and follow up ranging from 4 weeks to 3.5 years. Compared with placebo, any single antiplatelet agent was associated with a significant reduction in recurrence of any stroke (risk ratio [RR] 0.77, 0.62–0.97, 2 studies) and ischemic stroke (RR 0.48, 0.30–0.78, 2 studies), but not for the composite outcome of any stroke, myocardial infarction, or death (RR 0.89, 0.75–1.05, 2 studies). When other antiplatelet agents (ticlodipine, cilostazol, and dipyridamole) were compared with aspirin, there was no consistent reduction in stroke recurrence (RR 0.91, 0.75–1.10, 3 studies). Dual antiplatelet therapy did not confer clear benefit over monotherapy (any stroke RR 0.83, 0.68–1.00, 3 studies; ischemic stroke RR 0.80, 0.62–1.02, 3 studies; composite outcome RR 0.90, 0.80–1.02, 3 studies). Conclusions: Our results suggest that any of the single antiplatelet agents compared with placebo in the included trials is adequate for secondary stroke prevention after lacunar stroke. Dual antiplatelet therapy should not be used for long-term stroke prevention in this stroke subtype

Prevalence of Clinical and Neuroimaging Markers in Cerebral Amyloid Angiopathy: A Systematic Review and Meta-Analysis

BACKGROUND: Limited data exist regarding the prevalence of clinical and neuroimaging manifestations among patients diagnosed with cerebral amyloid angiopathy (CAA). We sought to determine the prevalence of clinical phenotypes and radiological markers in patients with CAA. METHODS: Systematic review and meta-analysis of studies including patients with CAA was conducted to primarily assess the prevalence of clinical phenotypes and neuroimaging markers as available in the included studies. Sensitivity analyses were performed based on the (1) retrospective or prospective study design and (2) probable or unspecified CAA status. We pooled the prevalence rates using random-effects models and assessed the heterogeneity using the Cochran Q and I2 statistics. RESULTS: We identified 12 prospective and 34 retrospective studies including 7159 patients with CAA. The pooled prevalence rates were cerebral microbleeds (52% [95% CI, 43%-60%]; I2=93%), cortical superficial siderosis (49% [95% CI, 38%-59%]; I2=95%), dementia or mild cognitive impairment (50% [95% CI, 35%-65%]; I2=97%), intracerebral hemorrhage (ICH; 44% [95% CI, 27%-61%]; I2=98%), transient focal neurological episodes (48%; 10 studies [95% CI, 29%-67%]; I2=97%), lacunar infarcts (30% [95% CI, 25%-36%]; I2=78%), high grades of perivascular spaces located in centrum semiovale (56% [95% CI, 44%-67%]; I2=88%) and basal ganglia (21% [95% CI, 2%-51%]; I2=98%), and white matter hyperintensities with moderate or severe Fazekas score (53% [95% CI, 40%-65%]; I2=91%). The only neuroimaging marker that was associated with higher odds of recurrent ICH was cortical superficial siderosis (odds ratio, 1.57 [95% CI, 1.01-2.46]; I2=47%). Sensitivity analyses demonstrated a higher prevalence of ICH (53% versus 16%; P=0.03) and transient focal neurological episodes (57% versus 17%; P=0.03) among retrospective studies compared with prospective studies. No difference was documented between the prevalence rates based on the CAA status. CONCLUSIONS: Approximately one-half of hospital-based cohort of CAA patients was observed to have cerebral microbleeds, cortical superficial siderosis, mild cognitive impairment, dementia, ICH, or transient focal neurological episodes. Cortical superficial siderosis was the only neuroimaging marker that was associated with higher odds of ICH recurrence. Future population-based studies among well-defined CAA cohorts are warranted to corroborate our findings

Clinical, Neuroimaging, and Genetic Markers in Cerebral Amyloid Angiopathy-Related Inflammation: A Systematic Review and Meta-Analysis

Background: There are limited data regarding the prevalence of distinct clinical, neuroimaging and genetic markers among patients diagnosed with cerebral amyloid angiopathy-related inflammation (CAA-ri). We sought to determine the prevalence of clinical, radiological, genetic and cerebrospinal fluid biomarker findings in patients with CAA-ri. Methods: A systematic review and meta-analysis of published studies including patients with CAA-ri was conducted to determine the prevalence of clinical, neuroimaging, genetic and cerebrospinal fluid biomarker findings. Subgroup analyses were performed based on (1) prospective or retrospective study design and (2) CAA-ri diagnosis with or without available biopsy. We pooled the prevalence rates using random-effects models and assessed the heterogeneity using Cochran-Q and I2-statistics. Results: We identified 4 prospective and 17 retrospective cohort studies comprising 378 patients with CAA-ri (mean age, 71.5 years; women, 52%). The pooled prevalence rates were as follows: cognitive decline at presentation 70% ([95% CI, 54%-84%]; I2=82%), focal neurological deficits 55% ([95% CI, 40%-70%]; I2=82%), encephalopathy 54% ([95% CI, 39%-68%]; I2=43%), seizures 37% ([95% CI, 27%-49%]; I2=65%), headache 31% ([95% CI, 22%-42%]; I2=58%), T2/fluid-attenuated inversion recovery-hyperintense white matter lesions 98% ([95% CI, 93%-100%]; I2=44%), lobar cerebral microbleeds 96% ([95% CI, 92%-99%]; I2=25%), gadolinium enhancing lesions 54% ([95% CI, 42%-66%]; I2=62%), cortical superficial siderosis 51% ([95% CI, 34%-68%]; I2=77%) and lobar macrohemorrhage 40% ([95% CI, 11%-73%]; I2=88%). The prevalence rate of the ApoE (Apolipoprotein E) ϵ4/ϵ4 genotype was 34% ([95% CI, 17%-53%]; I2=76%). Subgroup analyses demonstrated no differences in these prevalence rates based on study design and diagnostic strategy. Conclusions: Cognitive decline was the most common clinical feature. Hyperintense T2/fluid-attenuated inversion recovery white matter lesions and lobar cerebral microbleeds were by far the most prevalent neuroimaging findings. Thirty-four percent of patients with CAA-ri have homozygous ApoE ϵ4/ϵ4 genotype and scarce data exist regarding the cerebrospinal fluid biomarkers and its significance in these patients

Cilostazol for Secondary Stroke Prevention: History, Evidence, Limitations, and Possibilities

Cilostazol is a phosphodiesterase III inhibitor with a long track record of safety that is FDA and EMA approved for the treatment of claudication in patients with peripheral arterial disease. In addition, cilostazol has been approved for secondary stroke prevention in several Asian countries based on trials that have demonstrated a reduction in stroke recurrence among patients with non-cardioembolic stroke. The onset of benefit appears after 60–90 days of treatment, which is consistent with cilostazol’s pleiotropic effects on platelet aggregation, vascular remodeling, blood flow, and plasma lipids. Cilostazol appears safe and does not increase the risk of major bleeding when given alone or in combination with aspirin or clopidogrel. Adverse effects such as headache, gastrointestinal symptoms and palpitations, however, contributed to a 6% increase in drug discontinuation among patients randomized to cilostazol in a large secondary stroke prevention trial (CSPS.com). Due to limitations of prior trials, such as open label design, premature trial termination, large loss to follow-up, lack of functional or cognitive outcome data, and exclusive enrollment in Asia, the existing trials have not led to a change in clinical practice or guidelines in Western countries. These limitations could be addressed by a double-blind placebo-controlled randomized trial conducted in a broader population. If positive, it would increase the evidence in support of long-term treatment with cilostazol for secondary prevention in the millions of patients worldwide who have suffered a non-cardioembolic ischemic stroke

Cognitive performance following stroke, transient ischaemic attack, myocardial infarction, and hospitalisation:an individual participant data meta-analysis of six randomised controlled trials

BACKGROUND: Survivors of stroke are often concerned about cognitive problems, and information on the risk of cognitive problems often comes from small studies. We aimed to estimate years of cognitive ageing associated with stroke compared with transient ischaemic attack, myocardial infarction, and other hospitalisations in a large population.METHODS: Using data from six randomised controlled trials (ORIGIN, ONTARGET, TRANSCEND, COMPASS, HOPE-3, and NAVIGATE ESUS), we completed an individual participant data meta-analysis using data requested from the Public Health Research Institute to estimate the association of stroke (by type and severity), transient ischaemic attack, myocardial infarction, and other hospitalisations with cognitive performance measured at the end of each trial. We included participants in any of these randomised controlled trials with a cognitive assessment at baseline and at least one other timepoint. Cognitive performance was measured with the Mini-Mental State Examination or the Montreal Cognitive Assessment, transformed into Z scores. We estimated Z score differences in end of trial cognitive performance between people with and without events and calculated corresponding years of cognitive ageing in these trials, and additionally calculated using a population representative cohort-the Cognitive Function and Ageing Study.FINDINGS: In 64 106 participants from 55 countries, compared with no event, stroke was associated with 18 years of cognitive ageing (1487 strokes included in the model, 95% CI 10 to 28; p&lt;0·0001) and transient ischaemic attack with 3 years (660 transient ischaemic attacks included in the model, 0 to 6; p=0·021). Myocardial infarction (p=0·60) and other hospitalisations (p=0·26) were not associated with cognitive ageing. The mean difference in SD compared with people without an event was -0·84 (95% CI -0·91 to -0·76; p&lt;0·0001) for disabling stroke, and -0·12 (-0·19 to -0·05; p=0·0012) for non-disabling stroke. Haemorrhagic stroke was associated with worse cognition (-0·75, -0·95 to -0·55; p&lt;0·0001) than ischaemic stroke (-0·42, -0·48 to -0·36; p &lt;0·0001).INTERPRETATION: Stroke has a substantial effect on cognition. The effects of transient ischaemic attack were small, whereas myocardial infarction and hospitalisation had a neutral effect. Prevention of stroke could lead to a reduction in cognitive ageing in those at greatest risk.FUNDING: Population Health Research Institute and Chief Scientist Office of Scotland.</p

Early Anticoagulation in Patients with Acute Ischemic Stroke Due to Atrial Fibrillation: A Systematic Review and Meta-Analysis.

Introduction: There is uncertainty regarding the optimal timing for initiation of oral anticoagulation in patients with acute ischemic stroke (AIS) due to atrial fibrillation (AF). Methods: We performed a systematic review and meta-analysis of randomized-controlled clinical trials (RCTs) and prospective observational studies to assess the efficacy and safety of early anticoagulation in AF-related AIS (within 1 week versus 2 weeks). A second comparison was performed assessing the efficacy and safety of direct oral anticoagulants (DOACs) versus vitamin-K antagonists (VKAs) in the two early time windows. The outcomes of interest were IS recurrence, all-cause mortality, symptomatic intracerebral haemorrhage (sICH) and any ICH. Results: Eight eligible studies (6 observational, 2 RCTs) were identified, including 5616 patients with AF-related AIS who received early anticoagulation. Patients that received anticoagulants within the first week after index stroke had similar rate of recurrent IS, sICH and all-cause mortality compared to patients that received anticoagulation within two weeks (test for subgroup differences p = 0.1677; p = 0.8941; and p = 0.7786, respectively). When DOACs were compared to VKAs, there was a significant decline of IS recurrence in DOAC-treated patients compared to VKAs (RR: 0.65; 95%CI: 0.52-0.82), which was evident in both time windows of treatment initiation. DOACs were also associated with lower likelihood of sICH and all-cause mortality. Conclusions: Early initiation of anticoagulation within the first week may have a similar efficacy and safety profile compared to later anticoagulation (within two weeks), while DOACs seem more effective in terms of IS recurrence and survival compared to VKAs

Key design elements of successful acute ischemic stroke treatment trials

Purpose: We review key design elements of positive randomized controlled trials (RCTs) in acute ischemic stroke (AIS) treatment and summarize their main characteristics. Method: We searched Medline, Pubmed and Cochrane databases for positive RCTs in AIS treatment. Trials were included if (1) they had a randomized controlled design, with (at least partial) blinding for endpoints, (2) they tested against placebo (or on top of standard therapy in a superiority design) or against approved therapy; (3) the protocol was registered and/or published before trial termination and unblinding (if required at study commencement); (4) the primary endpoint was positive in the intention to treat analysis; and (5) the study findings led to approval of the investigational product and/or high ranked recommendations. A topical approach was used, therefore the findings were summarized as a narrative review. Findings: Seventeen positive RCTs met the inclusion criteria. The majority of trials included less than 1000 patients (n=15), had highly selective inclusion criteria (n=16), used the modified Rankin score as a primary endpoint (n=15) and had a frequentist design (n=16). Trials tended to be national (n=12), investigator-initiated and performed with public funding (n=11).Discussion: Smaller but selective trials are useful to identify efficacy in a particular subgroup of stroke patients. It may also be of advantage to limit the number of participating countries and centers to avoid heterogeneity in stroke management and bureaucratic burden.Conclusion: The key characteristics of positive RCTs in AIS treatment described here may assist in the design of further trials investigating a single intervention with a potentially high effect size

Characteristics of Recurrent Ischemic Stroke after Embolic Stroke of Undetermined Source: Secondary Analysis of a Randomized Clinical Trial

Importance: The concept of embolic stroke of undetermined source (ESUS) unifies a subgroup of cryptogenic strokes based on neuroimaging, a defined minimum set of diagnostic tests, and exclusion of certain causes. Despite an annual stroke recurrence rate of 5%, little is known about the etiology underlying recurrent stroke after ESUS. Objective: To identify the stroke subtype of recurrent ischemic strokes after ESUS, to explore the interaction with treatment assignment in each category, and to examine the consistency of cerebral location of qualifying ESUS and recurrent ischemic stroke. Design, Setting, and Participants: The NAVIGATE-ESUS trial was a randomized clinical trial conducted from December 23, 2014, to October 5, 2017. The trial compared the efficacy and safety of rivaroxaban and aspirin in patients with recent ESUS (n = 7213). Ischemic stroke was validated in 309 of the 7213 patients by adjudicators blinded to treatment assignment and classified by local investigators into the categories ESUS or non-ESUS (ie, cardioembolic, atherosclerotic, lacunar, other determined cause, or insufficient testing). Five patients with recurrent strokes that could not be defined as ischemic or hemorrhagic in absence of neuroimaging or autopsy were excluded. Data for this secondary post hoc analysis were analyzed from March to June 2019. Interventions: Patients were randomly assigned to receive rivaroxaban, 15 mg/d, or aspirin, 100 mg/d. Main Outcomes and Measures: Association of recurrent ESUS with stroke characteristics. Results: A total of 309 patients (205 men [66%]; mean [SD] age, 68 [10] years) had ischemic stroke identified during the median follow-up of 11 (interquartile range [IQR], 12) months (annualized rate, 4.6%). Diagnostic testing was insufficient for etiological classification in 39 patients (13%). Of 270 classifiable ischemic strokes, 156 (58%) were ESUS and 114 (42%) were non-ESUS (37 [32%] cardioembolic, 26 [23%] atherosclerotic, 35 [31%] lacunar, and 16 [14%] other determined cause). Atrial fibrillation was found in 27 patients (9%) with recurrent ischemic stroke and was associated with higher morbidity (median change in modified Rankin scale score 2 [IQR, 3] vs 0 (IQR, 1]) and mortality (15% vs 1%) than other causes. Risk of recurrence did not differ significantly by subtype between treatment groups. For both the qualifying and recurrent strokes, location of infarct was more often in the left (46% and 54%, respectively) than right hemisphere (40% and 37%, respectively) or brainstem or cerebellum (14% and 9%, respectively). Conclusions and Relevance: In this secondary analysis of randomized clinical trial data, most recurrent strokes after ESUS were embolic and of undetermined source. Recurrences associated with atrial fibrillation were a minority but were more often disabling and fatal. More extensive investigation to identify the embolic source is important toward an effective antithrombotic strategy. Trial Registration: ClinicalTrials.gov Identifier: NCT02313909