Lipid-siRNA conjugate accesses a perivascular transport mechanism and achieves widespread and durable knockdown in the central nervous system.

Short-interfering RNA (siRNA) has gained significant interest for treatment of neurological diseases by providing the capacity to achieve sustained inhibition of nearly any gene target. Yet, achieving efficacious drug delivery throughout deep brain structures of the CNS remains a considerable hurdle. We herein describe a lipid-siRNA conjugate that, following delivery into the cerebrospinal fluid (CSF), is transported effectively through perivascular spaces, enabling broad dispersion within CSF compartments and through the CNS parenchyma. We provide a detailed examination of the temporal kinetics of gene silencing, highlighting potent knockdown for up to five months from a single injection without detectable toxicity. Single-cell RNA sequencing further demonstrates gene silencing activity across diverse cell populations in the parenchyma and at brain borders, which may provide new avenues for neurological disease-modifying therapies.

Elevated protease-activated receptor 4 (PAR4) gene expression in Alzheimer's disease predicts cognitive decline.

Platelet activation of protease-activated receptor 4 (PAR4) and thrombin are at the top of a chain of events leading to fibrin deposition, microinfarcts, blood-brain barrier disruption, and inflammation. We evaluated mRNA expression of the PAR4 gene F2RL3 in human brain and global cognitive performance in participants with and without cognitive impairment or dementia. Data were acquired from the Religious Orders Study (ROS) and the Rush Memory and Aging Project (MAP). F2RL3 mRNA was elevated in AD cases and was associated with worse retrospective longitudinal cognitive performance. Moreover, F2RL3 expression interacted with clinical AD diagnosis on longitudinal cognition whereas this relationship was attenuated in individuals without cognitive impairment. Additionally, when adjusting for the effects of AD neuropathology, F2RL3 expression remained a significant predictor of cognitive decline. F2RL3 expression correlated positively with transcript levels of proinflammatory markers including TNFα, IL-1ß, NFκB, and fibrinogen α/ß/γ. Together, these results reveal that F2RL3 mRNA expression is associated with multiple AD-relevant outcomes and its encoded product, PAR4, may play a role in disease pathogenesis.

IQGAP2 regulates blood-brain barrier immune dynamics.

Brain endothelial cells (BECs) play an important role in maintaining central nervous system (CNS) homeostasis through blood-brain barrier (BBB) functions. BECs express low baseline levels of adhesion receptors, which limits entry of leukocytes. However, the molecular mediators governing this phenotype remain mostly unclear. Here, we explored how infiltration of immune cells across the BBB is influenced by the scaffold protein IQ motif containing GTPase activating protein 2 (IQGAP2). In mice and zebrafish, we demonstrate that loss of Iqgap2 increases infiltration of peripheral leukocytes into the CNS under homeostatic and inflammatory conditions. Using single-cell RNA sequencing and immunohistology, we further show that BECs from mice lacking Iqgap2 exhibit a profound inflammatory signature, including extensive upregulation of adhesion receptors and antigen-processing machinery. Human tissue analyses also reveal that Alzheimer's disease is associated with reduced hippocampal IQGAP2. Overall, our results implicate IQGAP2 as an essential regulator of BBB immune privilege and immune cell entry into the CNS.

Arteriolar degeneration and stiffness in cerebral amyloid angiopathy are linked to ß-amyloid deposition and lysyl oxidase.

Cerebral amyloid angiopathy (CAA) is a vasculopathy characterized by vascular ß-amyloid (Aß) deposition on cerebral blood vessels. CAA is closely linked to Alzheimer's disease (AD) and intracerebral hemorrhage. CAA is associated with the loss of autoregulation in the brain, vascular rupture, and cognitive decline. To assess morphological and molecular changes associated with the degeneration of penetrating arterioles in CAA, we analyzed post-mortem human brain tissue from 26 patients with mild, moderate, and severe CAA end neurological controls. The tissue was optically cleared for three-dimensional light sheet microscopy, and morphological features were quantified using surface volume rendering. We stained Aß, vascular smooth muscle (VSM), lysyl oxidase (LOX), and vascular markers to visualize the relationship between degenerative morphological features, including vascular dilation, dolichoectasia (variability in lumenal diameter) and tortuosity, and the volumes of VSM, Aß, and LOX in arterioles. Atomic force microscopy (AFM) was used to assess arteriolar wall stiffness, and we identified a pattern of morphological features associated with degenerating arterioles in the cortex. The volume of VSM associated with the arteriole was reduced by around 80% in arterioles with severe CAA and around 60% in cases with mild/moderate CAA. This loss of VSM correlated with increased arteriolar diameter and variability of diameter, suggesting VSM loss contributes to arteriolar laxity. These vascular morphological features correlated strongly with Aß deposits. At sites of microhemorrhage, Aß was consistently present, although the morphology of the deposits changed from the typical organized ring shape to sharply contoured shards with marked dilation of the vessel. AFM showed that arteriolar walls with CAA were more than 400% stiffer than those without CAA. Finally, we characterized the association of vascular degeneration with LOX, finding strong associations with VSM loss and vascular degeneration. These results show an association between vascular Aß deposition, microvascular degeneration, and increased vascular stiffness, likely due to the combined effects of replacement of VSM by ß-amyloid, cross-linking of extracellular matrices (ECM) by LOX, and possibly fibrosis. This advanced microscopic imaging study clarifies the association between Aß deposition and vascular fragility. Restoration of physiologic ECM properties in penetrating arteries may yield a novel therapeutic strategy for CAA.

Apixaban versus Aspirin for Embolic Stroke of Undetermined Source.

BACKGROUND: Rivaroxaban and dabigatran were not superior to aspirin in trials of patients with embolic stroke of undetermined source (ESUS). It is unknown whether apixaban is superior to aspirin in patients with ESUS and known risk factors for cardioembolism. METHODS: We conducted a multicenter, randomized, open-label, blinded-outcome trial of apixaban (5 mg twice daily) compared with aspirin (100 mg once daily) initiated within 28 days after ESUS in patients with at least one predictive factor for atrial fibrillation or a patent foramen ovale. Cardiac monitoring was mandatory, and aspirin treatment was switched to apixaban in case of atrial fibrillation detection. The primary outcome was any new ischemic lesion on brain magnetic resonance imaging (MRI) during 12-month follow-up. Secondary outcomes included major and clinically relevant nonmajor bleeding. RESULTS: A total of 352 patients were randomly assigned to receive apixaban (178 patients) or aspirin (174 patients) at a median of 8 days after ESUS. At 12-month follow-up, MRI follow-up was available in 325 participants (92.3%). New ischemic lesions occurred in 23 of 169 (13.6%) participants in the apixaban group and in 25 of 156 (16.0%) participants in the aspirin group (adjusted odds ratio, 0.79; 95% confidence interval, 0.42 to 1.48; P=0.57). Major and clinically relevant nonmajor bleeding occurred in five and seven participants, respectively (1-year cumulative incidences, 2.9 and 4.2; hazard ratio, 0.68; 95% confidence interval, 0.22 to 2.16). Serious adverse event rates were 43.9 per 100 person-years in those given apixaban and 45.7 per 100 person-years in those given aspirin. The Apixaban for the Treatment of Embolic Stroke of Undetermined Source trial was terminated after a prespecified interim analysis as a result of futility. CONCLUSIONS: Apixaban treatment was not superior to cardiac monitoring-guided aspirin in preventing new ischemic lesions in an enriched ESUS population. (Funded by Bristol-Myers Squibb and Medtronic Europe; ClinicalTrials.gov number, NCT02427126.)

IV Thrombolysis for central retinal artery occlusion - Real-world experience from a comprehensive stroke center.

OBJECTIVES: Central retinal artery occlusion (CRAO) is a stroke of the retina potentially amenable to intravenous thrombolysis (IVT). We aimed to determine feasibility of an emergency treatment protocol and risk profile of IVT for CRAO in a comprehensive stroke center (CSC). METHODS: We performed a retrospective, observational cohort study including patients with acute CRAO admitted to a CSC over 4 years. Patients are offered IVT if they present with acute vision loss of ≤ 20/200 in the affected eye, have no other cause of vision loss (incorporating a dilated ophthalmologic exam), and meet criteria akin to acute ischemic stroke. We collected socio-demographic data, triage data, time from onset to presentation, IVT candidacy, and rates of symptomatic intracranial hemorrhage (sICH)- or extracranial hemorrhage. RESULTS: 36 patients presented within the study period, mean (standard deviation (SD)) age of 70.7 (10), 52 % female, and median time (Q1, Q3) to ED presentation of 13.5 (4.3, 18.8) h. Patients within 4.5 h from onset presented more commonly directly to our ED (66.6 % vs 37.1 %, p = 0.1). Nine patients (25 %) presented within the 4.5 h window. Of those eligible, 7 (77 %) received IVT. There were no events of intracranial or extracranial hemorrhage. CONCLUSIONS: Our study confirmed that IVT for acute CRAO is feasible. We found a high rate of treatment with IVT of those eligible. However, because 75 % of patients presented outside the treatment window, continued educational efforts are needed to improve rapid triage to emergency departments to facilitate evaluation for possible candidacy with IVT.

Fatal iatrogenic cerebral ß-amyloid-related arteritis in a woman treated with lecanemab for Alzheimer's disease.

We report the case of a 79-year-old woman with Alzheimer's disease who participated in a Phase III randomized controlled trial called CLARITY-AD testing the experimental drug lecanemab. She was randomized to the placebo group and subsequently enrolled in an open-label extension which guaranteed she received the active drug. After the third biweekly infusion, she suffered a seizure characterized by speech arrest and a generalized convulsion. Magnetic resonance imaging revealed she had multifocal swelling and a marked increase in the number of cerebral microhemorrhages. She was treated with an antiepileptic regimen and high-dose intravenous corticosteroids but continued to worsen and died after 5 days. Post-mortem MRI confirmed extensive microhemorrhages in the temporal, parietal and occipital lobes. The autopsy confirmed the presence of two copies of APOE4, a gene associated with a higher risk of Alzheimer's disease, and neuropathological features of moderate severity Alzheimer's disease and severe cerebral amyloid angiopathy with perivascular lymphocytic infiltrates, reactive macrophages and fibrinoid degeneration of vessel walls. There were deposits of ß-amyloid in meningeal vessels and penetrating arterioles with numerous microaneurysms. We conclude that the patient likely died as a result of severe cerebral amyloid-related inflammation.

Atrial fibrillation as a novel risk factor for retinal stroke: A protocol for a population-based retrospective cohort study.

Central retinal artery occlusion (CRAO; retinal stroke or eye stroke) is an under-recognized, disabling form of acute ischemic stroke which causes severe visual loss in one eye. The classical risk factor for CRAO is ipsilateral carotid stenosis; however, nearly half of patients with CRAO do not have high-grade carotid stenosis, suggesting that other cardiovascular risk factors may exist for CRAO. Specifically, prior studies have suggested that cardioembolism, driven by underlying atrial fibrillation, may predispose patients to CRAO. We describe the design of an observational, population-based study in this protocol. We evaluate two specific objectives: 1) To determine if atrial fibrillation is an independent risk factor for CRAO after adjusting for medical and cardiovascular risk; 2) To determine if use of oral anticoagulation can modify the risk of CRAO for patients with atrial fibrillation. This protocol lays out our strategy for cohort definition, case and control definition, comorbidity ascertainment, and statistical methods.

Targeting lysyl-oxidase (LOX) may facilitate intramural periarterial drainage for the treatment of Alzheimer's disease.

Alzheimer's disease is the commonest form of dementia. It is likely that a lack of clearance of amyloid beta (Aß) results in its accumulation in the parenchyma as Aß oligomers and insoluble plaques, and within the walls of blood vessels as cerebral amyloid angiopathy (CAA). The drainage of Aß along the basement membranes of blood vessels as intramural periarterial drainage (IPAD), could be improved if the driving force behind IPAD could be augmented, therefore reducing Aß accumulation. There are alterations in the composition of the vascular basement membrane in Alzheimer's disease. Lysyl oxidase (LOX) is an enzyme involved in the remodelling of the extracellular matrix and its expression and function is altered in various disease states. The expression of LOX is increased in Alzheimer's disease, but it is unclear whether this is a contributory factor in the impairment of IPAD in Alzheimer's disease. The pharmacological inhibition of LOX may be a strategy to improve IPAD and reduce the accumulation of Aß in the parenchyma and within the walls of blood vessels.

Detection, visualization and quantification of protein complexes in human Alzheimer's disease brains using proximity ligation assay.

Examination of healthy and diseased human brain is essential to translational neuroscience. Protein-protein interactions play a pivotal role in physiological and pathological processes, but their detection is difficult, especially in aged and fixed human brain tissue. We used the in-situ proximity ligation assay (PLA) to broaden the range of molecular interactions assessable in-situ in the human neuropathology. We adapted fluorescent in-situ PLA to detect ubiquitin-modified proteins in human brains with Alzheimer's disease (AD), including approaches for the management of autofluorescence and quantification using a high-content image analysis system. We confirmed that phosphorylated microtubule-associated protein tau (Serine202, Threonine205) aggregates were modified by ubiquitin and that phospho-tau-ubiquitin complexes were increased in hippocampal and frontal cortex regions in AD compared to non-AD brains. Overall, we refined PLA for use in human neuropathology, which has revealed a profound change in the distribution of ubiquitin in AD brain and its association with characteristic tau pathologies.

Complications of Intravenous Tenecteplase Versus Alteplase for the Treatment of Acute Ischemic Stroke: A Systematic Review and Meta-Analysis.

BACKGROUND: Prior systematic reviews have compared the efficacy of intravenous tenecteplase and alteplase in acute ischemic stroke, assigning their relative complications as a secondary objective. The objective of the present study is to determine whether the risk of treatment complications differs between patients treated with either agent. METHODS: We performed a systematic review including interventional studies and prospective and retrospective, observational studies enrolling adult patients treated with intravenous tenecteplase for ischemic stroke (both comparative and noncomparative with alteplase). We searched MEDLINE, Embase, the Cochrane Library, Web of Science, and the www. CLINICALTRIALS: gov registry from inception through June 3, 2022. The primary outcome was symptomatic intracranial hemorrhage, and secondary outcomes included any intracranial hemorrhage, angioedema, gastrointestinal hemorrhage, other extracranial hemorrhage, and mortality. We performed random effects meta-analyses where appropriate. Evidence was synthesized as relative risks, comparing risks in patients exposed to tenecteplase versus alteplase and absolute risks in patients treated with tenecteplase. RESULTS: Of 2226 records identified, 25 full-text articles (reporting 26 studies of 7913 patients) were included. Sixteen studies included alteplase as a comparator, and 10 were noncomparative. The relative risk of symptomatic intracranial hemorrhage in patients treated with tenecteplase compared with alteplase in the 16 comparative studies was 0.89 ([95% CI, 0.65-1.23]; I2=0%). Among patients treated with low dose (<0.2 mg/kg; 4 studies), medium dose (0.2-0.39 mg/kg; 13 studies), and high dose (≥0.4 mg/kg; 3 studies) tenecteplase, the RRs of symptomatic intracranial hemorrhage were 0.78 ([95% CI, 0.22-2.82]; I2=0%), 0.77 ([95% CI, 0.53-1.14]; I2=0%), and 2.31 ([95% CI, 0.69-7.75]; I2=40%), respectively. The pooled risk of symptomatic intracranial hemorrhage in tenecteplase-treated patients, including comparative and noncomparative studies, was 0.99% ([95% CI, 0%-3.49%]; I2=0%, 7 studies), 1.69% ([95% CI, 1.14%-2.32%]; I2=1%, 23 studies), and 4.19% ([95% CI, 1.92%-7.11%]; I2=52%, 5 studies) within the low-, medium-, and high-dose groups. The risks of any intracranial hemorrhage, mortality, and other studied outcomes were comparable between the 2 agents. CONCLUSIONS: Across medium- and low-dose tiers, the risks of complications were generally comparable between those treated with tenecteplase versus alteplase for acute ischemic stroke.

Association Between Hospital-Documented Atrial Fibrillation and Central Retinal Artery Occlusion.

BACKGROUND: Carotid stenosis is thought to be the primary risk factor for central retinal artery occlusion (CRAO); however, it is not known whether atrial fibrillation (AF)-a cardiac arrhythmia that underlies over 25% of cerebral ischemic strokes-predisposes patients to CRAO. METHODS: A retrospective, observational, cohort study was performed using data from the State Inpatient Databases and State Emergency Department Databases from New York (2006-2015), California (2003-2011), and Florida (2005-2015) to determine the association between AF and CRAO. The primary exposure was hospital-documented AF. The primary end point was hospital-documented CRAO, defined as having an International Classification of Diseases, Ninth Revision, Clinical Modification, code 362.31 in the primary diagnosis position. Cause-specific hazard models were used to model CRAO-free survival among patients according to hospital-documented AF status. RESULTS: Of 39 834 885 patients included in the study, 2 723 842 (median age, 72.7 years; 48.5% women) had AF documented during the exposure window. The median follow-up duration was 6 years and 1 month. Patients with AF were older, more likely to be of non-Hispanic White race/ethnicity, and had a higher burden of cardiovascular comorbidities compared with patients without AF. The cumulative incidence of CRAO determined prospectively after exclusions was 8.69 per 100 000 at risk in those with AF and 2.39 per 100 000 at risk in those without AF over the study period. Before adjustment, AF was associated with higher risk of CRAO (hazard ratio, 2.55 [95% CI, 2.15-3.03]). However, after adjustment for demographics, state, and cardiovascular comorbidities, there was an inverse association between AF and risk of CRAO (adjusted hazard ratio, 0.72 [95% CI, 0.60-0.87]). These findings were robust in our prespecified sensitivity analyses. By contrast, positive control outcomes of embolic and ischemic stroke showed an expected strong relationship between AF and risk of stroke. CONCLUSIONS: We found an inverse association between AF and CRAO in a large, representative study of hospitalized patients; however, this cohort did not ascertain AF or CRAO occurring outside of hospital or emergency department settings.

Detection, Visualization and Quantification of Protein Complexes in Human Alzheimer's Disease Brains using Proximity Ligation Assay.

Examination of healthy and diseased human brain is essential to translational neuroscience. Protein-protein interactions play a pivotal role in physiological and pathological processes, but their detection is difficult, especially in aged and fixed human brain tissue. We used the proximity ligation assay (PLA) to broaden the range of molecular interactions assessable in-situ in human neuropathology. We adapted fluorescent in-situ PLA to detect ubiquitin-modified proteins in human brains with Alzheimer's disease (AD), including approaches for the management of autofluorescence and quantification using a high-content image analysis system. We confirmed that hyperphosphorylated microtubule-associated protein tau (Serine202, Threonine205) aggregates were modified by ubiquitin and that phospho-tau-ubiquitin complexes were increased in hippocampal and frontal cortex regions in AD compared to non-AD brains. Overall, we refined PLA for use in human neuropathology, which has revealed a profound change in the distribution of ubiquitin in AD brain and its association with characteristic tau pathologies.

Reactive astrocytes transduce inflammation in a blood-brain barrier model through a TNF-STAT3 signaling axis and secretion of alpha 1-antichymotrypsin.

Astrocytes are critical components of the neurovascular unit that support blood-brain barrier (BBB) function. Pathological transformation of astrocytes to reactive states can be protective or harmful to BBB function. Here, using a human induced pluripotent stem cell (iPSC)-derived BBB co-culture model, we show that tumor necrosis factor (TNF) transitions astrocytes to an inflammatory reactive state that causes BBB dysfunction through activation of STAT3 and increased expression of SERPINA3, which encodes alpha 1-antichymotrypsin (α1ACT). To contextualize these findings, we correlated astrocytic STAT3 activation to vascular inflammation in postmortem human tissue. Further, in murine brain organotypic cultures, astrocyte-specific silencing of Serpina3n reduced vascular inflammation after TNF challenge. Last, treatment with recombinant Serpina3n in both ex vivo explant cultures and in vivo was sufficient to induce BBB dysfunction-related molecular changes. Overall, our results define the TNF-STAT3-α1ACT signaling axis as a driver of an inflammatory reactive astrocyte signature that contributes to BBB dysfunction.

CRISPRi screens in human iPSC-derived astrocytes elucidate regulators of distinct inflammatory reactive states.

Astrocytes become reactive in response to insults to the central nervous system by adopting context-specific cellular signatures and outputs, but a systematic understanding of the underlying molecular mechanisms is lacking. In this study, we developed CRISPR interference screening in human induced pluripotent stem cell-derived astrocytes coupled to single-cell transcriptomics to systematically interrogate cytokine-induced inflammatory astrocyte reactivity. We found that autocrine-paracrine IL-6 and interferon signaling downstream of canonical NF-κB activation drove two distinct inflammatory reactive signatures, one promoted by STAT3 and the other inhibited by STAT3. These signatures overlapped with those observed in other experimental contexts, including mouse models, and their markers were upregulated in human brains in Alzheimer's disease and hypoxic-ischemic encephalopathy. Furthermore, we validated that markers of these signatures were regulated by STAT3 in vivo using a mouse model of neuroinflammation. These results and the platform that we established have the potential to guide the development of therapeutics to selectively modulate different aspects of inflammatory astrocyte reactivity.

Physiology and Clinical Relevance of Enlarged Perivascular Spaces in the Aging Brain.

Perivascular spaces (PVS) are fluid-filled compartments that are part of the cerebral blood vessel wall and represent the conduit for fluid transport in and out of the brain. PVS are considered pathologic when sufficiently enlarged to be visible on MRI. Recent studies have demonstrated that enlarged PVS (ePVS) may have clinical consequences related to cognition. Emerging literature points to arterial stiffening and abnormal protein aggregation in vessel walls as 2 possible mechanisms that drive ePVS formation. We describe the clinical consequences, anatomy, fluid dynamics, physiology, risk factors, and in vivo quantification methods of ePVS. Given competing views of PVS physiology, we detail the 2 most prominent theoretical views and review ePVS associations with other common small vessel disease markers. Because ePVS are a marker of small vessel disease and ePVS burden is higher in Alzheimer disease, a comprehensive understanding about ePVS is essential in developing prevention and treatment strategies.

Management of Intracerebral Hemorrhage: Update and Future Therapies.

PURPOSE OF REVIEW: Intracerebral hemorrhage (ICH) represents about 15% of all strokes in the USA, but almost 50% of fatal strokes. There are many causes of ICH, but the most common are hypertension and cerebral amyloid angiopathy. This review will discuss new advances in the treatment of intracerebral hemorrhage. RECENT FINDINGS: The treatment of ICH focuses on management of edema, aggressive blood pressure reduction, and correction of coagulopathy. Early initiation of supportive medical therapies, including blood pressure management, in a neurological intensive care unit reduces mortality, but at present there is no definitive, curative therapy analogous to mechanical thrombectomy for ischemic stroke. Nonetheless, new medical and surgical approaches promise more successful management of ICH patients, especially new approaches to surgical management. In this review, we focus on the current standard of care of acute ICH and discuss emerging therapies that may alter the landscape of this devastating disease.

Ipsilateral internal carotid artery web and acute ischemic stroke: A cohort study, systematic review and meta-analysis.

INTRODUCTION: The carotid web is a compelling potential mechanism of embolic ischemic stroke. In this study, we aim to determine the prevalence of ipsilateral carotid web in a cohort of ischemic stroke patients and to perform a systematic review and meta-analysis of similar cohorts. PATIENTS & METHODS: We performed a retrospective, observational, cohort study of acute ischemic stroke patients admitted to a comprehensive stroke center from June 2012 to September 2017. Carotid web was defined on computed tomography angiography (CTA) as a thin shelf of non-calcified tissue immediately distal to the carotid bifurcation. We described the prevalence of carotid artery webs in our cohort, then performed a systematic review and meta-analysis of similar cohorts in the published literature. RESULTS: We identified 1,435 potentially eligible patients of whom 879 met criteria for inclusion in our analysis. An ipsilateral carotid web was detected in 4 out of 879 (0.45%) patients, of which 4/4 (1.6%) were in 244 patients with cryptogenic stroke and 3/4 were in 66 (4.5%) patients <60 years old with cryptogenic stroke. Our systematic review yielded 3,192 patients. On meta-analysis, the pooled prevalence of ipsilateral carotid web in cryptogenic stroke patients <60 was 13% (95% CI: 7%-22%; I2 = 66.1%). The relative risk (RR) of ipsilateral versus contralateral carotid web in all patients was 2.5 (95% CI 1.5-4.2, p = 0.0009) whereas in patients less than 60 with cryptogenic stroke it was 3.0 (95% CI 1.6-5.8, p = 0.0011). DISCUSSION: Carotid webs are more common in young patients with cryptogenic stroke than in other stroke subtypes. Future studies concerning the diagnosis and secondary prevention of stroke associated with carotid web should focus on this population.

Detection of Atrial Fibrillation After Central Retinal Artery Occlusion.

Background: Central retinal artery occlusion (CRAO) causes sudden, irreversible blindness and is a form of acute ischemic stroke. In this study, we sought to determine the proportion of patients in whom atrial fibrillation (AF) is detected by extended cardiac monitoring after CRAO. Methods: We performed a retrospective, observational cohort study using data from the Optum deidentified electronic health record of 30.8 million people cross-referenced with the Medtronic CareLink database of 2.7 million people with cardiac monitoring devices in situ. We enrolled patients in 3 groups: (1) CRAO, (2) cerebral ischemic stroke, and (3) age-, sex-, and comorbidity-matched controls. The primary end point was the detection of new AF (defined as ≥2 minutes of AF detected on a cardiac monitoring device). Results: We reviewed 884 431 patient records in common between the two databases to identify 100 patients with CRAO, 6559 with ischemic stroke, and 1000 matched controls. After CRAO, the cumulative incidence of new AF at 2 years was 49.6% (95% CI, 37.4%­61.7%). Patients with CRAO had a higher rate of AF than controls (hazard ratio, 1.64 [95% CI, 1.17­2.31]) and a comparable rate to patients with stroke (hazard ratio, 1.01 [95% CI, 0.75­1.36]). CRAO was associated with a higher incidence of new stroke compared with matched controls (hazard ratio, 2.85 [95% CI, 1.29­6.29]). Conclusions: The rate of AF detection after CRAO is higher than that seen in age-, sex-, and comorbidity-matched controls and comparable to that seen after ischemic cerebral stroke. Paroxysmal AF should be considered as part of the differential etiology of CRAO, and those patients may benefit from long-term cardiac monitoring.