Gap Junctions May Have A Computational Function In The Cerebellum: A Hypothesis.

In the cerebellum, granule cells make parallel fibre contact on (and excite) Golgi cells and Golgi cells inhibit granule cells, forming an open feedback loop. Parallel fibres excite Golgi cells synaptically, each making a single contact. Golgi cells inhibit granule cells in a structure called a glomerulus almost exclusively by GABA spillover acting through extrasynaptic GABAA receptors. Golgi cells are connected dendritically by gap junctions. It has long been suspected that feedback contributes to homeostatic regulation of parallel fibre signals activity, causing the fraction of the population that are active to be maintained at a low level. We present a detailed neurophysiological and computationally-rendered model of functionally grouped Golgi cells which can infer the density of parallel fibre signals activity and convert it into proportional modulation of inhibition of granule cells. The conversion is unlearned and not actively computed; rather, output is simply the computational effect of cell morphology and network architecture. Unexpectedly, the conversion becomes more precise at low density, suggesting that self-regulation is attracted to sparse code, because it is stable. A computational function of gap junctions may not be confined to the cerebellum.

The Effect of Nucleo-Olivary Stimulation on Climbing Fiber EPSPs in Purkinje Cells.

Climbing fibers, connecting the inferior olive and Purkinje cells, form the nervous system's strongest neural connection. These fibers activate after critical events like motor errors or anticipation of rewards, leading to bursts of excitatory postsynaptic potentials (EPSPs) in Purkinje cells. The number of EPSPs is a crucial variable when the brain is learning a new motor skill. Yet, we do not know what determines the number of EPSPs. Here, we measured the effect of nucleo-olivary stimulation on periorbital elicited climbing fiber responses through in-vivo intracellular Purkinje cell recordings in decerebrated ferrets. The results show that while nucleo-olivary stimulation decreased the probability of a response occurring at all, it did not reduce the number of EPSPs. The results suggest that nucleo-olivary stimulation does not influence the number of EPSPs in climbing fiber bursts.

Predicting COVID-19 Incidence Using Wastewater Surveillance Data, Denmark, October 2021-June 2022.

Analysis of wastewater is used in many settings for surveillance of SARS-CoV-2, but it remains unclear how well wastewater testing results reflect incidence. Denmark has had an extensive wastewater analysis system that conducts 3 weekly tests in ≈200 sites and has 85% population coverage; the country also offers free SARS-CoV-2 PCR tests to all residents. Using time series analysis for modeling, we found that wastewater data, combined with information on circulating variants and the number of human tests performed, closely fitted the incidence curve of persons testing positive. The results were consistent at a regional level and among a subpopulation of frequently tested healthcare personnel. We used wastewater analysis data to estimate incidence after testing was reduced to a minimum after March 2022. These results imply that data from a large-scale wastewater surveillance system can serve as a good proxy for COVID-19 incidence and for epidemic control.

The ability to maintain rhythm is predictive of ADHD diagnosis and profile.

Attention deficit hyperactivity disorder (ADHD) is the most prevalent neuropsychiatric disorder in the world. Currently, the diagnosis is based mainly on interviews, resulting in uncertainties in the clinical assessment. While some neuropsychological tests are used, their specificity and selectivity are low, and more reliable biomarkers are desirable. Previous research indicates that ADHD is associated with morphological changes in the cerebellum, which is essential for motor ability and timing. Here, we compared 29 children diagnosed with ADHD to 96 age-matched controls on prism adaptation, eyeblink conditioning, and timed motor performance in a finger tapping task. Prism adaptation and timing precision in the finger tapping task, but not performance on eyeblink conditioning, differed between the ADHD and control groups, as well as between children with and without Deficits in Attention, Motor control, and Perception (DAMP) - a more severe form of ADHD. The results suggest finger tapping can be used as a cheap, objective, and unbiased biomarker to complement current diagnostic procedures.

Fast tipping point sensitivity analyses in clinical trials with missing continuous outcomes under multiple imputation.

When dealing with missing data in clinical trials, it is often convenient to work under simplifying assumptions, such as missing at random (MAR), and follow up with sensitivity analyses to address unverifiable missing data assumptions. One such sensitivity analysis, routinely requested by regulatory agencies, is the so-called tipping point analysis, in which the treatment effect is re-evaluated after adding a successively more extreme shift parameter to the predicted values among subjects with missing data. If the shift parameter needed to overturn the conclusion is so extreme that it is considered clinically implausible, then this indicates robustness to missing data assumptions. Tipping point analyses are frequently used in the context of continuous outcome data under multiple imputation. While simple to implement, computation can be cumbersome in the two-way setting where both comparator and active arms are shifted, essentially requiring the evaluation of a two-dimensional grid of models. We describe a computationally efficient approach to performing two-way tipping point analysis in the setting of continuous outcome data with multiple imputation. We show how geometric properties can lead to further simplification when exploring the impact of missing data. Lastly, we propose a novel extension to a multi-way setting which yields simple and general sufficient conditions for robustness to missing data assumptions.

An indirect treatment comparison of the efficacy of semaglutide 1.0 mg versus dulaglutide 3.0 and 4.5 mg.

AIM: To compare the effects of semaglutide 1.0 mg versus dulaglutide 3.0 and 4.5 mg on HbA1c and body weight in patients with type 2 diabetes. MATERIALS AND METHODS: A Bucher indirect comparison was conducted to compare efficacy outcomes of semaglutide 1.0 mg versus dulaglutide 3.0 and 4.5 mg using published results from the SUSTAIN 7 and AWARD-11 trials. Sensitivity analyses using individual patient data from SUSTAIN 7 and aggregate data from AWARD-11 were conducted to explore the impact of adjustment for cross-trial imbalances in baseline characteristics. RESULTS: Semaglutide 1.0 mg significantly reduced HbA1c versus dulaglutide 3.0 mg, with an estimated treatment difference (ETD) of -0.24%-points (95% confidence interval [CI] -0.43, -0.05), with comparable reductions in HbA1c versus dulaglutide 4.5 mg with an ETD of -0.07%-points (95% CI -0.26, 0.12). Semaglutide 1.0 mg significantly reduced body weight versus dulaglutide 3.0 and 4.5 mg with an ETD of -2.65 kg (95% CI -3.57, -1.73) and -1.95 kg (95% CI -2.87, -1.03), respectively. Sensitivity analyses supported the primary analysis findings. CONCLUSIONS: This indirect comparison showed significantly greater reductions in HbA1c with semaglutide 1.0 mg versus dulaglutide 3.0 mg and comparable HbA1c reductions versus dulaglutide 4.5 mg. Semaglutide 1.0 mg significantly reduced body weight versus both dulaglutide 3.0 and 4.5 mg. With several glucagon-like peptide-1 receptor agonists available, information regarding their comparative efficacy can be valuable to clinicians.

Feedback from HTC Vive Sensors Results in Transient Performance Enhancements on a Juggling Task in Virtual Reality.

Virtual reality headsets, such as the HTC Vive, can be used to model objects, forces, and interactions between objects with high perceived realism and accuracy. Moreover, they can accurately track movements of the head and the hands. This combination makes it possible to provide subjects with precise quantitative feedback on their performance while they are learning a motor task. Juggling is a challenging motor task that requires precise coordination of both hands. Professional jugglers throw objects so that the arc peaks just above head height, and they time their throws so that the second ball is thrown when the first ball reaches its peak. Here, we examined whether it is possible to learn to juggle in virtual reality and whether the height and the timing of the throws can be improved by providing immediate feedback derived from the motion sensors. Almost all participants became better at juggling in the ~30 min session: the height and timing of their throws improved and they dropped fewer balls. Feedback on height, but not timing, improved performance, albeit only temporarily.

Graded error signals in eyeblink conditioning.

Minimizing errors is an important aspect of learning. However, it is not enough merely to record if an error occurred. For efficient learning, information about the magnitude of errors is critical. Did my tennis swing completely miss the target or did I hit the ball, but not quite in the sweet spot? How can neurons - which have traditionally been thought of as binary units - signal the magnitude of an error? Here I review evidence that eyeblink conditioning - a basic form of motor learning - depends on graded signals from the inferior olive which guides plasticity in the cerebellum and ultimately tunes behavior. Specifically, evidence suggests that: (1) Error signals are conveyed to the cerebellum via the inferior olive; (2) Signals from the inferior olive are graded; (3) The strength of the olivary signal affects learning; (4) Cerebellar feedback influences the strength of the olivary signal. I end the review by exploring how graded error signals might explain some behavioral learning phenomena.

Learned response sequences in cerebellar Purkinje cells.

Associative learning in the cerebellum has previously focused on single movements. In eyeblink conditioning, for instance, a subject learns to blink at the right time in response to a conditional stimulus (CS), such as a tone that is repeatedly followed by an unconditional corneal stimulus (US). During conditioning, the CS and US are transmitted by mossy/parallel fibers and climbing fibers to cerebellar Purkinje cells that acquire a precisely timed pause response that drives the overt blink response. The timing of this conditional Purkinje cell response is determined by the CS-US interval and is independent of temporal patterns in the input signal. In addition to single movements, the cerebellum is also believed to be important for learning complex motor programs that require multiple precisely timed muscle contractions, such as, for example, playing the piano. In the present work, we studied Purkinje cells in decerebrate ferrets that were conditioned using electrical stimulation of mossy fiber and climbing fiber afferents as CS and US, while alternating between short and long interstimulus intervals. We found that Purkinje cells can learn double pause responses, separated by an intermediate excitation, where each pause corresponds to one interstimulus interval. The results show that individual cells can not only learn to time a single response but that they also learn an accurately timed sequential response pattern.

Purkinje cell activity during classical conditioning with different conditional stimuli explains central tenet of Rescorla­Wagner model [corrected].

A central tenet of Rescorla and Wagner's model of associative learning is that the reinforcement value of a paired trial diminishes as the associative strength between the presented stimuli increases. Despite its fundamental importance to behavioral sciences, the neural mechanisms underlying the model have not been fully explored. Here, we present findings that, taken together, can explain why a stronger association leads to a reduced reinforcement value, within the context of eyeblink conditioning. Specifically, we show that learned pause responses in Purkinje cells, which trigger adaptively timed conditioned eyeblinks, suppress the unconditional stimulus (US) signal in a graded manner. Furthermore, by examining how Purkinje cells respond to two distinct conditional stimuli and to a compound stimulus, we provide evidence that could potentially help explain the somewhat counterintuitive overexpectation phenomenon, which was derived from the Rescorla-Wagner model.

Using cell nuclei features to detect colon cancer tissue in hematoxylin and eosin stained slides.

Currently, diagnosis of colon cancer is based on manual examination of histopathological images by a pathologist. This can be time consuming and interpretation of the images is subject to inter- and intra-observer variability. This may be improved by introducing a computer-aided diagnosis (CAD) system for automatic detection of cancer tissue within whole slide hematoxylin and eosin (H&E) stains. Cancer disrupts the normal control mechanisms of cell proliferation and differentiation, affecting the structure and appearance of the cells. Therefore, extracting features from segmented cell nuclei structures may provide useful information to detect cancer tissue. A framework for automatic classification of regions of interest (ROI) containing either benign or cancerous colon tissue extracted from whole slide H&E stained images using cell nuclei features was proposed. A total of 1,596 ROI's were extracted from 87 whole slide H&E stains (44 benign and 43 cancer). A cell nuclei segmentation algorithm consisting of color deconvolution, k-means clustering, local adaptive thresholding, and cell separation was performed within the ROI's to extract cell nuclei features. From the segmented cell nuclei structures a total of 750 texture and intensity-based features were extracted for classification of the ROI's. The nine most discriminative cell nuclei features were used in a random forest classifier to determine if the ROI's contained benign or cancer tissue. The ROI classification obtained an area under the curve (AUC) of 0.96, sensitivity of 0.88, specificity of 0.92, and accuracy of 0.91 using an optimized threshold. The developed framework showed promising results in using cell nuclei features to classify ROIs into containing benign or cancer tissue in H&E stained tissue samples. © 2017 International Society for Advancement of Cytometry.

White Matter Hyperintensities Improve Ischemic Stroke Recurrence Prediction.

BACKGROUND: Nearly one in 5 patients with ischemic stroke will invariably experience a second stroke within 5 years. Stroke risk stratification schemes based solely on clinical variables perform only modestly in non-atrial fibrillation (AF) patients and improvement of these schemes will enhance their clinical utility. Cerebral white matter hyperintensities are associated with an increased risk of incident ischemic stroke in the general population, whereas their association with the risk of ischemic stroke recurrence is more ambiguous. In a non-AF stroke cohort, we investigated the association between cerebral white matter hyperintensities and the risk of recurrent ischemic stroke, and we evaluated the predictive performance of the CHA2DS2VASc score and the Essen Stroke Risk Score (clinical scores) when augmented with information on white matter hyperintensities. METHODS: In a registry-based, observational cohort study, we included 832 patients (mean age 59.6 (SD 13.9); 42.0% females) with incident ischemic stroke and no AF. We assessed the severity of white matter hyperintensities using MRI. Hazard ratios stratified by the white matter hyperintensities score and adjusted for the components of the CHA2DS2VASc score were calculated based on the Cox proportional hazards analysis. Recalibrated clinical scores were calculated by adding one point to the score for the presence of moderate to severe white matter hyperintensities. The discriminatory performance of the scores was assessed with the C-statistic. RESULTS: White matter hyperintensities were significantly associated with the risk of recurrent ischemic stroke after adjusting for clinical risk factors. The hazard ratios ranged from 1.65 (95% CI 0.70-3.86) for mild changes to 5.28 (95% CI 1.98-14.07) for the most severe changes. C-statistics for the prediction of recurrent ischemic stroke were 0.59 (95% CI 0.51-0.65) for the CHA2DS2VASc score and 0.60 (95% CI 0.53-0.68) for the Essen Stroke Risk Score. The recalibrated clinical scores showed improved C-statistics: the recalibrated CHA2DS2VASc score 0.62 (95% CI 0.54-0.70; p = 0.024) and the recalibrated Essen Stroke Risk Score 0.63 (95% CI 0.56-0.71; p = 0.031). C-statistics of the white matter hyperintensities score were 0.62 (95% CI 0.52-0.68) to 0.65 (95% CI 0.58-0.73). CONCLUSIONS: An increasing burden of white matter hyperintensities was independently associated with recurrent ischemic stroke in a cohort of non-AF ischemic stroke patients. Recalibration of the CHA2DS2VASc score and the Essen Stroke Risk Score with one point for the presence of moderate to severe white matter hyperintensities led to improved discriminatory performance in ischemic stroke recurrence prediction. Risk scores based on white matter hyperintensities alone were at least as accurate as the established clinical risk scores in the prediction of ischemic stroke recurrence.

Death and thrombo-embolic risk after ablation of atrial flutter compared with atrial fibrillation: a nationwide cohort study.

AIMS: The aim of this study was to investigate whether there is a similar mortality and thrombo-embolic risk, after an atrial ablation procedure, compared with an atrial fibrillation (AF) procedure. METHODS AND RESULTS: Using data from nationwide Danish health registries, we identified patients aged 18-75 years undergoing a first-time atrial flutter or an AF ablation procedure in the period 2000-13. Cox proportional hazards regression was used to calculate hazard ratios (HRs) after 5 years of follow-up, adjusting for concomitant risk factors. A total of 1096 and 2266 patients underwent an ablation for atrial flutter or AF, respectively. Age distribution was similar in the two, but atrial flutter patients had more co-morbidities. During 5 years of follow-up, we observed 38 and 36 deaths in the atrial flutter and AF groups, corresponding to an almost two-fold higher mortality rate among atrial flutter patients [crude HR 1.92, 95% confidence interval (CI) 1.22-3.03]. The higher mortality rate persisted after adjustment for age, sex, diabetes mellitus, and hypertension (adjusted HR 1.68, 95% CI 1.05-2.69). The rate of thrombo-embolic events was similar in the two groups (crude HR 1.34, 95% CI 0.71-2.56; adjusted HR 1.22, 95% CI 0.62-2.41). CONCLUSION: In this observational study, patients with atrial flutter had a significantly higher all-cause mortality rate compared with those with AF after an ablation procedure, but similar thrombo-embolic event rates. Future studies should elucidate the reason for this difference in mortality.

Memory trace and timing mechanism localized to cerebellar Purkinje cells.

The standard view of the mechanisms underlying learning is that they involve strengthening or weakening synaptic connections. Learned response timing is thought to combine such plasticity with temporally patterned inputs to the neuron. We show here that a cerebellar Purkinje cell in a ferret can learn to respond to a specific input with a temporal pattern of activity consisting of temporally specific increases and decreases in firing over hundreds of milliseconds without a temporally patterned input. Training Purkinje cells with direct stimulation of immediate afferents, the parallel fibers, and pharmacological blocking of interneurons shows that the timing mechanism is intrinsic to the cell itself. Purkinje cells can learn to respond not only with increased or decreased firing but also with an adaptively timed activity pattern.

Restarting Anticoagulant Treatment After Intracranial Hemorrhage in Patients With Atrial Fibrillation and the Impact on Recurrent Stroke, Mortality, and Bleeding: A Nationwide Cohort Study.

BACKGROUND: Intracranial hemorrhage is the most feared complication of oral anticoagulant treatment. The optimal treatment option for patients with atrial fibrillation who survive an intracranial hemorrhage remains unknown. We hypothesized that restarting oral anticoagulant treatment was associated with a lower risk of stroke and mortality in comparison with not restarting. METHODS AND RESULTS: Linkage of 3 Danish nationwide registries in the period between 1997 and 2013 identified patients with atrial fibrillation on oral anticoagulant treatment with incident intracranial hemorrhage. Patients were stratified by treatment regimens (no treatment, oral anticoagulant treatment, or antiplatelet therapy) after the intracranial hemorrhage. Event rates were assessed 6 weeks after hospital discharge and compared with Cox proportional hazard models. In 1752 patients (1 year of follow-up), the rate of ischemic stroke/systemic embolism and all-cause mortality (per 100 person-years) for patients treated with oral anticoagulants was 13.6, in comparison with 27.3 for nontreated patients and 25.7 for patients receiving antiplatelet therapy. The rate of ischemic stroke/systemic embolism and all-cause mortality (per 100 person-years) for recurrent intracranial hemorrhage, the rate of ischemic stroke/systemic embolism, and all-cause mortality (per 100 person-years) patients treated with oral anticoagulants was 8.0, in comparison with 8.6 for nontreated patients and 5.3 for patients receiving antiplatelet therapy. The adjusted hazard ratio of ischemic stroke/systemic embolism and all-cause mortality was 0.55 (95% confidence interval, 0.39-0.78) in patients on oral anticoagulant treatment in comparison with no treatment. For ischemic stroke/systemic embolism and for all-cause mortality, hazard ratios were 0.59 (95% confidence interval, 0.33-1.03) and 0.55 (95% confidence interval, 0.37-0.82), respectively. CONCLUSIONS: Oral anticoagulant treatment was associated with a significant reduction in ischemic stroke/all-cause mortality rates, supporting oral anticoagulant treatment reintroduction after intracranial hemorrhage as feasible. Future trials are encouraged to guide clinical practice in these patients.

Rivaroxaban versus warfarin and dabigatran in atrial fibrillation: comparative effectiveness and safety in Danish routine care.

PURPOSE: To evaluate effectiveness and safety of rivaroxaban versus warfarin or dabigatran etexilate in a prospective cohort of routine care non-valvular atrial fibrillation (AF) patients during February 2012 to August 2014. METHODS: We identified in nationwide health registries a cohort of AF patients who were new-users of rivaroxaban 15 mg (R15) or 20 mg (R20); dabigatran 110 mg (D110) or 150 mg (D150); or warfarin. Propensity-adjusted Cox regression was used to compare outcome rates in four settings: 'R15 vs. warfarin'; 'R15 vs. D110'; 'R20 vs. warfarin'; and 'R20 vs. D150'. RESULTS: Rivaroxaban users (R15: n = 776; R20: n = 1629) were older and with more comorbidities than warfarin (n = 11 045) and dabigatran users (D110: n = 3588; D150: n = 5320). Rivaroxaban 15-mg users had the overall highest crude mortality rate. After propensity adjustment, rivaroxaban had lower stroke rates vs. warfarin (R15: hazard ratio [HR] 0.46, 95% confidence interval [CI]: 0.26-0.82; R20 HR: 0.72, 95%CI: 0.51-1.01), and similar stroke rates vs. dabigatran. The bleeding rate was similar to warfarin and moderately higher vs. dabigatran (R15 vs. D110 HR: 1.28, 95%CI: 0.82-2.01; R20 vs. D150 HR: 1.81, 95%CI: 1.25-2.62). The mortality rate was higher vs. dabigatran (R15 vs. D110 HR: 1.43, 95%CI: 1.13-1.81; R20 vs. D150 HR: 1.52, 95%CI: 1.06-2.19). CONCLUSIONS: Rivaroxaban was associated with similar or lower stroke rates, but higher bleeding and mortality rates. Channeling of rivaroxaban towards elderly and less healthy patients may have generated residual confounding. In particular, our findings cannot stand alone when deciding which oral anticoagulant to prescribe. Copyright © 2016 John Wiley & Sons, Ltd.

Bidirectional plasticity of Purkinje cells matches temporal features of learning.

Many forms of learning require temporally ordered stimuli. In Pavlovian eyeblink conditioning, a conditioned stimulus (CS) must precede the unconditioned stimulus (US) by at least about 100 ms for learning to occur. Conditioned responses are learned and generated by the cerebellum. Recordings from the cerebellar cortex during conditioning have revealed CS-triggered pauses in the firing of Purkinje cells that likely drive the conditioned blinks. The predominant view of the learning mechanism in conditioning is that long-term depression (LTD) at parallel fiber (PF)-Purkinje cell synapses underlies the Purkinje cell pauses. This raises a serious conceptual challenge because LTD is most effectively induced at short CS-US intervals, which do not support acquisition of eyeblinks. To resolve this discrepancy, we recorded Purkinje cells during conditioning with short or long CS-US intervals. Decerebrated ferrets trained with CS-US intervals ≥150 ms reliably developed Purkinje cell pauses, but training with an interval of 50 ms unexpectedly induced increases in CS-evoked spiking. This bidirectional modulation of Purkinje cell activity offers a basis for the requirement of a minimum CS-US interval for conditioning, but we argue that it cannot be fully explained by LTD, even when previous in vitro studies of stimulus-timing-dependent LTD are taken into account.

Recurrent Stroke: The Value of the CHA2DS2VASc Score and the Essen Stroke Risk Score in a Nationwide Stroke Cohort.

BACKGROUND AND PURPOSE: The CHA2DS2VASc score and the Essen Stroke Risk Score are respectively used for risk stratification in patients with atrial fibrillation and in patients with cerebrovascular incidents. We aimed to test the ability of the 2 scores to predict stroke recurrence, death, and cardiovascular events (stroke, transient ischemic attack, myocardial infarction, or arterial thromboembolism) in a nationwide Danish cohort study, among patients with incident ischemic stroke and no atrial fibrillation. METHODS: We conducted a registry-based study in patients with incident ischemic stroke and no atrial fibrillation. Patients were stratified according to the CHA2DS2VASc score and the Essen Stroke Risk Score and were followed up until stroke recurrence or death. We estimated stratified incidence rates and hazard ratios and calculated the cumulative risks. RESULTS: 42 182 patients with incident ischemic stroke with median age 70.1 years were included. The overall 1-year incidence rates of recurrent stroke, death, and cardiovascular events were 3.6%, 10.5%, and 6.7%, respectively. The incidence rates, the hazard ratios, and the cumulative risk of all outcomes increased with increasing risk scores. C-statistics for both risk scores were around 0.55 for 1-year stroke recurrence and cardiovascular events and correspondingly for death around 0.67 for both scores. CONCLUSIONS: In this cohort of non-atrial fibrillation patients with incident ischemic stroke, increasing CHA2DS2VASc score and Essen Stroke Risk Score was associated with increasing risk of recurrent stroke, death, and cardiovascular events. Their discriminatory performance was modest and further refinements are required for clinical application.

Female sex is associated with a lower risk of stroke in patients with heart failure.

BACKGROUND: Stroke in patients with heart failure is associated with poor outcomes. Risk stratification schemes may improve clinical decision making in this patient population. This study investigated whether female sex is a risk factor for stroke in patients with heart failure in sinus rhythm. METHODS: This is a population-based cohort study of patients diagnosed with heart failure during 2000 to 2012, identified by record linkage between nationwide Danish registries. Our primary outcome was stroke, and secondary outcome was thromboembolic event. We used relative risks (RRs) after 1 and 5 years to compare males with females within each of the following age groups: 50 to 59 years, 60 to 69 years, 70 to 79 years, 80 to 89 years, and 90+ years. Analyses took into account the competing risks of death. RESULTS: During the study period, 84,142 patients were diagnosed with heart failure, of which 39,946 (47.5%) were females. At 5-year follow-up, female sex was associated with a lower risk of stroke compared with males (adjusted overall hazard ratio 0.91, 95% CI 0.85-0.96). The observed lower risks of stroke in females were not present in the older age groups, where the competing risk of death was substantial among males in particular. When considering a more broadly defined thromboembolic end point, a decreased risk among females persisted across nearly all age groups after 5-year follow-up (adjusted overall hazard ratio 0.93, 95% CI 0.91-0.96). CONCLUSIONS: We found an association between female sex and decreased stroke risk in patients with heart failure, which persisted after adjustment for concomitant cardiovascular risk factors. The association was attenuated with increasing age, possibly because of competing risks of death.