Structural and electro-anatomical characterization of the equine pulmonary veins: implications for atrial fibrillation

INTRODUCTION/OBJECTIVES

Spontaneous pulmonary vein (PV) activity triggers atrial fibrillation (AF) in humans. Although AF frequently occurs in horses, the origin remains unknown. This study investigated the structural and electro-anatomical properties of equine PVs to determine the potential presence of an arrhythmogenic substrate.

ANIMALS, MATERIALS AND METHODS

Endocardial three-dimensional electro-anatomical mapping (EnSite Precision) using high-density (HD) catheters was performed in 13 sedated horses in sinus rhythm. Left atrium (LA) access was obtained retrogradely through the carotid artery. Post-mortem, tissue was harvested from the LA, right atrium (RA), and PVs for histological characterization and quantification of ion channel expression using immunohistochemical analysis.

RESULTS

Geometry, activation maps, and voltage maps of the PVs were created and a median of four ostia were identified. Areas of reduced conduction were found at the veno-atrial junction. The mean myocardial sleeve length varied from 28 ± 13 to 49 ± 22 mm. The PV voltage was 1.2 ± 1.4 mV and lower than the LA (3.4 ± 0.9 mV, P < 0.001). The fibrosis percentage was higher in PV myocardium (26.1 ± 6.6 %) than LA (14.5 ± 5.0 %, P = 0.003). L-type calcium channel (CaV1.2) expression was higher in PVs than LA (P = 0.001). T-type calcium channels (CaV3.3), connexin-43, ryanodine receptor-2, and small conductance calcium-activated potassium channel-3 was expressed in PVs.

CONCLUSIONS

The veno-atrial junction had lower voltages, increased structural heterogeneity and areas of slower conduction. Myocardial sleeves had variable lengths, and a different ion channel expression compared to the atria. Heterogeneous properties of the PVs interacting with the adjacent LA likely provide the milieu for re-entry and AF initiation.

Proteostasis governs differential temperature sensitivity across embryonic cell types

Embryonic development is remarkably robust, but temperature stress can degrade its ability to generate animals with invariant anatomy. Phenotypes associated with environmental stress suggest that some cell types are more sensitive to stress than others, but the basis of this sensitivity is unknown. Here, we characterize hundreds of individual zebrafish embryos under temperature stress using whole-animal single-cell RNA sequencing (RNA-seq) to identify cell types and molecular programs driving phenotypic variability. We find that temperature perturbs the normal proportions and gene expression programs of numerous cell types and also introduces asynchrony in developmental timing. The notochord is particularly sensitive to temperature, which we map to a specialized cell type: sheath cells. These cells accumulate misfolded protein at elevated temperature, leading to a cascading structural failure of the notochord and anatomic defects. Our study demonstrates that whole-animal single-cell RNA-seq can identify mechanisms for developmental robustness and pinpoint cell types that constitute key failure points.

MS4A4A modifies the risk of Alzheimer disease by regulating lipid metabolism and immune response in a unique microglia state

Genome-wide association studies (GWAS) have identified many modifiers of Alzheimer disease (AD) risk enriched in microglia. Two of these modifiers are common variants in the MS4A locus (rs1582763: protective and rs6591561: risk) and serve as major regulators of CSF sTREM2 levels. To understand their functional impact on AD, we used single nucleus transcriptomics to profile brains from carriers of these variants. We discovered a "chemokine" microglial subpopulation that is altered in MS4A variant carriers and for which MS4A4A is the major regulator. The protective variant increases MS4A4A expression and shifts the chemokine microglia subpopulation to an interferon state, while the risk variant suppresses MS4A4A expression and reduces this subpopulation of microglia. Our findings provide a mechanistic explanation for the AD variants in the MS4A locus. Further, they pave the way for future mechanistic studies of AD variants and potential therapeutic strategies for enhancing microglia resilience in AD pathogenesis.

Functional regulatory variants implicate distinct transcriptional networks in dementia

Predicting the function of noncoding variation is a major challenge in modern genetics. In this study, we used massively parallel reporter assays to screen 5706 variants identified from genome-wide association studies for both Alzheimer's disease (AD) and progressive supranuclear palsy (PSP), identifying 320 functional regulatory variants (frVars) across 27 loci, including the complex 17q21.31 region. We identified and validated multiple risk loci using CRISPR interference or excision, including complement 4 (C4A) and APOC1 in AD and PLEKHM1 and KANSL1 in PSP. Functional variants disrupt transcription factor binding sites converging on enhancers with cell type-specific activity in PSP and AD, implicating a neuronal SP1-driven regulatory network in PSP pathogenesis. These analyses suggest that noncoding genetic risk is driven by common genetic variants through their aggregate activity on specific transcriptional programs.

A CRISPRi/a platform in human iPSC-derived microglia uncovers regulators of disease states

Microglia are emerging as key drivers of neurological diseases. However, we lack a systematic understanding of the underlying mechanisms. Here, we present a screening platform to systematically elucidate functional consequences of genetic perturbations in human induced pluripotent stem cell-derived microglia. We developed an efficient 8-day protocol for the generation of microglia-like cells based on the inducible expression of six transcription factors. We established inducible CRISPR interference and activation in this system and conducted three screens targeting the ‘druggable genome’. These screens uncovered genes controlling microglia survival, activation and phagocytosis, including neurodegeneration-associated genes. A screen with single-cell RNA sequencing as the readout revealed that these microglia adopt a spectrum of states mirroring those observed in human brains and identified regulators of these states. A disease-associated state characterized by osteopontin (SPP1) expression was selectively depleted by colony-stimulating factor-1 (CSF1R) inhibition. Thus, our platform can systematically uncover regulators of microglial states, enabling their functional characterization and therapeutic targeting.

Dräger et al. establish a rapid, scalable platform for iPSC-derived microglia. CRISPRi/a screens uncover roles of disease-associated genes in phagocytosis, and regulators of disease-relevant microglial states that can be targeted pharmacologically.

Trajectory of cognitive impairments over 1 year after COVID-19 hospitalisation: Pattern, severity, and functional implications

The ongoing Coronavirus Disease (COVID-19) pandemic has so far affected more than 500 million people. Lingering fatigue and cognitive difficulties are key concerns because they impede productivity and quality of life. However, the prevalence and duration of neurocognitive sequelae and association with functional outcomes after COVID-19 are unclear. This longitudinal study explored the frequency, severity and pattern of cognitive impairment and functional implications 1 year after hospitalisation with COVID-19 and its trajectory from 3 months after hospitalisation. Patients who had been hospitalised with COVID-19 from our previously published 3-months study at the Copenhagen University Hospital were re-invited for a 1-year follow-up assessment of cognitive function, functioning and depression symptoms. Twenty-five of the 29 previously assessed patients (86%) were re-assessed after 1 year (11±2 months). Clinically significant cognitive impairments were identified in 48-56 % of patients depending on the cut-off, with verbal learning and executive function being most severely affected. This was comparable to the frequency of impairments observed after 3 months. Objectively measured cognitive impairments scaled with subjective cognitive difficulties, reduced work capacity and poorer quality of life. Further, cognitive impairments after 3 months were associated with the severity of subsequent depressive symptoms after 1 year. In conclusion, the stable cognitive impairments in approximately half of patients hospitalized with COVID-19 and negative implications for work functioning, quality of life and mood symptoms underline the importance of screening for and addressing cognitive sequelae after severe COVID-19.

Sympatho-vagal activation during obstructive respiratory events in pigs and blunted atrial arrhythmogenic effects by pharmacological IKACh-inhibition

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Novo nordisk foundation

Background

Obstructive sleep apnea (OSA) is associated with a sympatho-vagal activation which is suspected to create a complex substrate for atrial fibrillation (AF).

Purpose

In pigs, we investigated atrial arrhythmogenic consequences of simulated obstructive respiratory events by intermittent negative upper airway pressure (INAP) application and tested antiarrhythmic properties of an atria-specific IK,ACh-inhibitor.

Methods

In spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds, every 10 minutes, three times before (vehicle) and two times following infusion of an IK,ACh-inhibitor. P-wave, PQ-duration, atrial effective refractory periods (AERP) and left ventricular hemodynamic parameters (maximum upstroke velocity, minimal downslope velocity and systole duration) were acquired before (Pre-INAP), during (INAP) and after (Post-) INAP. AF-inducibility was determined by a S1S2 atrial pacing protocol.

Results

During vehicle infusion, INAP transiently shortened AERP (Pre-INAP: 147±8ms vs. Post-INAP 105±12 ms; p=0.021) and increased AF-inducibility (Pre-INAP: 10±6% vs. Post-INAP 57±15%; p=0.018). Whereas p-wave duration remained stable, PQ-duration prolonged (Pre-INAP: 130±6ms vs. Post-INAP 142±7ms; p=0.03). Left ventricular maximum upstroke velocity increased (Pre-INAP: 1990±118 mmHg/s vs. Post-INAP 3980±704 mmHg/s; p=0.04), minimal downslope velocity decreased and systole duration shortened (Pre-INAP: 236±6 ms vs. Post-INAP 202±12 ms; p=0.04).

The IK,ACh-inhibitor increased AERP (vehicle 147±8ms vs. IK,ACh-inhibitor 171±9ms; p=0.05) and sufficiently prevented INAP-associated AERP-shortening (Pre-INAP: 171±9ms vs. Post-INAP 180±9ms; p=0.219) and PQ-duration prolongation (Pre-INAP: 116±8ms vs. Post-INAP 113±7ms; p=0.76). INAP-induced changes of left ventricular maximum upstroke/minimal downslope velocity and systole duration remained unaffected in the presence of the IK,ACh-inhibitor.

Conclusion

During obstructive respiratory events simulated by INAP in pigs, left ventricular hemodynamic changes demonstrated elevated sympathetic tone, while atrial electrophysiological parameters resemble elevated parasympathetic tone at the same time. This was associated with increased AF-susceptibility. Pharmacological IK,ACh-inhibition blunted INAP-induced impairment of atrial electrophysiology without affecting left ventricular hemodynamic changes. Hence, pharmacological IKACh-inhibition may constitute a promising treatment strategy in AF-patients with OSA.

Pharmacological inhibition of SK-channels with AP14145 prevents atrial arrhythmogenic changes in a porcine model for obstructive respiratory events

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): This work was supported by the Novo Nordisk Foundation (Tandem Programme; #31634).

Background

Obstructive sleep apnea (OSA) creates a complex substrate for atrial fibrillation (AF), which is refractory to many clinically available pharmacological interventions.

Purpose

To investigate atrial antiarrhythmogenic properties and ventricular electrophysiological safety of small-conductance Ca2+ -activated K+ (SK)- channel inhibition in a porcine model for obstructive respiratory events.

Methods

In spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds, every 10 minutes, three times before and three times during infusion of the SK-channel inhibitor AP14145. Atrial effective refractory periods (AERP) were acquired before (Pre-INAP), during (INAP) and after (Post-) INAP. AF-inducibility was determined by a S1S2 atrial pacing protocol. For the purpose of drug safety, ventricular arrhythmicity was evaluated by heart rate adjusted QT-interval duration (QT-paced) and electromechanical window (EMW) calculation.

Results

During vehicle infusion, INAP transiently shortened AERP (Pre-INAP: 135±10 ms vs. Post-INAP 101±11 ms; p=0.008) and increased AF-inducibility. QT-paced prolonged during INAP (Pre-INAP 270±7 ms vs. INAP 275±7 ms; p=0.04) and EMW shortened progressively throughout INAP and Post-INAP (Pre-INAP 80±4 ms; INAP 59±6 ms, Post-INAP 46±10 ms). AP14145 prolonged baseline AERP, partially prevented INAP-induced AERP-shortening and reduced AF-susceptibility. AP14145 did neither alter QT-paced (Pre-AP14145 270±7 ms vs. AP14145 268±6 ms, p=0.83) nor INAP-induced QT-paced prolongation, but blunted Post-INAP associated EMW-shortening.

Conclusion

In a pig model for obstructive respiratory events, the SK-channel-inhibitor AP14145 prevented INAP-associated AERP-shortening and AF-susceptibility without impairing ventricular electrophysiology. Hence, SK-channels may represent a promising target for OSA-related AF.

Left ventricular mass quantification by echocardiography; a novel accurate and more reproducible 2D-method validated by cardiac magnetic resonance in humans and cardiac autopsy in pigs

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): The research fund of The Heart Center at Rigshospitalet, Denmark

Background

Left ventricular mass (LVM) is a strong independent risk factor for adverse cardiovascular events, but conventional echocardiographic methods used to assess and monitor individuals are currently limited by poor reproducibility and accuracy.

Purpose

We aimed to develop and validate an echocardiographic method for LVM-quantification that is simple, reproducible and accurate.

Methods

Our ‘novel method’ (Figure) adds the left ventricular wall thickness (t) to the left ventricular end-diastolic volume acquired by endocardial tracings using the biplane method of discs. For development of the novel method, cardiac assessment was performed using echocardiography followed immediately by gold standard cardiac magnetic resonance (CMR) in 85 humans with different left ventricular geometries, ranging from patients with various cardiac disorders (n = 41) to individuals without known cardiac disorders (n = 44). We compared the novel two-dimensional (2D) method to various conventional one-dimensional (1D) and 2D methods as well as three-dimensional (3D) echocardiography. Validation against anatomical LVM by cardiac autopsy was performed in thirty-four Danish Landrace pigs, weight 47-59 kg. Echocardiography was performed during anaesthesia, the pigs were euthanised, the heart explanted, and cardiac autopsy was performed where the left ventricle was trimmed and weighed for autopsy LVM.

Results

In humans, the novel method had better reproducibility in intra-examiner (coefficients of variation (CV) 8.6% vs. 11.0-14.5%) and inter-examiner analysis (CV 9.0% vs. 10.2-19.6%) than any other method, including 3D (CV intra-examiner 14.3%, inter-examiner 16.6%). Accuracy of the novel method against CMR was similar to 3D (mean difference ± 95% limits of agreement, CV): Novel: 2 ± 50g, 15.4% vs. 3D: 2 ± 51g, 15.6%; and better than the 1D-method by Devereux (7 ± 76g, 23.0%). Feasibility for the novel method was 95%. Autopsy validation in pigs confirmed high reproducibility; intra-examiner (CV 8.7% vs. 9.1-11.4%) and inter-examiner-analysis (CV 8.7% vs. 8.8-10.0%). Accuracy of the novel method against autopsy LVM was better than for the conventional echocardiographic methods: Novel -1 ± 20g, 7.8% vs. Devereux 26 ± 37g, 11.3%. 3D-validation was not available in pigs.

Conclusions

The novel 2D-based method for LVM-quantification had better reproducibility than any other echocardiographic method. Accuracy was similar to 3D and better than any conventional method. Autopsy validation in pigs supported our findings amongst the human population. As endocardial tracings using the biplane method forms part of the standard echocardiographic protocol, the novel method can easily be integrated into any echocardiographic software without substantially increasing analysis time, and provides an equivalent yet simpler alternative to 3D echocardiography. Abstract Figure.

Glucagon-like peptide-1 directly increases heart rate and shortens atrial refractoriness: an in vivo and ex vivo study in pigs

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Novo Nordisk Foundation Synergy program Novo Nordisk Foundation Center for Basic Metabolic Research

Background

 Treatment with glucagon-like peptide-1 receptor agonists (GLP-1 RAs) in patients with type 2 diabetes not only reduces hyperglycaemia, but also improves cardiovascular outcomes. However, GLP-1 RA treatment also increases heart rate: an apparent paradox.

Purpose

 Whether the heart rate increase is a direct effect, and whether GLP-1 affects other aspects of cardiac electrophysiology, remain unclear. To answer these questions we investigated the effect of GLP-1 infusion on cardiac electrophysiology in vivo and ex vivo in pigs and pig hearts, respectively, during sinus rhythm and pacing.

Methods

 Anaesthetised pigs (n = 8) received infusions of GLP-1 (10 pmol/kg/min). Electrocardiogram, atrial monophasic action potentials and atrial conduction velocity data were collected and atrial and ventricular effective refractory periods (ERP) were measured. For the ex vivo studies, pig hearts (n = 7) were excised, retrogradely perfused and exposed to consecutive bolus perfusions of 2 and 4 nmol GLP-1, 100 nmol of the GLP-1 receptor antagonist exendin-9-39 and a final 4 nmol bolus of GLP-1. The same electrophysiological parameters were measured.

Results

 In anaesthetised pigs, GLP-1 increased heart rate, cardiac output and diastolic pressure, while systemic vascular resistance was decreased. Infusion of GLP-1 decreased PQ interval in sinus rhythm (P = 0.019, n = 8) and during atrial pacing (P = 0.027, n = 6) with 8 ± 3 % and 12 ± 3 %, respectively. Additionally, GLP-1 decreased atrial ERP at all pacing cycle lengths (P = 0.04, n = 7), while ventricular ERP was unaffected (P = 0.29, n = 7). In the isolated perfused heart, GLP-1 increased heart rate with 13 ± 2 bpm (P = 0.001, n = 7). This increase in heart rate was completely abolished by pre-administration of exendin-9-39. Atrial ERP shortened after GLP-1 perfusion (P = 0.01, n = 7) comparable to the in vivo studies, with an average decrease of 11 ± 2 %. This effect was also abolished by exendin-9-39.

Conclusion

 GLP-1 increases heart rate through activation of the GLP-1 receptor in the isolated perfused heart, suggesting a direct effect of GLP-1 rather than activation through the central nervous system. Additionally, GLP-1 affects atrial electrophysiology, but not ventricular electrophysiology, in vivo and ex vivo independent of the increase in heart rate.

Cognitive impairments four months after COVID-19 hospital discharge: Pattern, severity and association with illness variables

The ongoing Coronavirus Disease 2019 (COVID-19) pandemic has affected more than 100 million people and clinics are being established for diagnosing and treating lingering symptoms, so called long-COVID. A key concern are neurological and long-term cognitive complications. At the same time, the prevalence and nature of the cognitive sequalae of COVID-19 are unclear. The present study aimed to investigate the frequency, pattern and severity of cognitive impairments 3-4 months after COVID-19 hospital discharge, their relation to subjective cognitive complaints, quality of life and illness variables. We recruited patients at their follow-up visit at the respiratory outpatient clinic, Copenhagen University Hospital, Bispebjerg, approximately four months after hospitalisation with COVID-19. Patients underwent pulmonary, functional and cognitive assessments. Twenty-nine patients were included. The percentage of patients with clinically significant cognitive impairment ranged from 59% to 65% depending on the applied cut-off for clinical relevance of cognitive impairment, with verbal learning and executive functions being most affected. Objective cognitive impairment scaled with subjective cognitive complaints, lower work function and poorer quality of life. Cognitive impairments were associated with d-dimer levels during acute illness and residual pulmonary dysfunction. In conclusion, these findings provide new evidence for frequent cognitive sequelae of COVID-19 and indicate an association with the severity of the lung affection and potentially restricted cerebral oxygen delivery. Further, the associations with quality of life and functioning call for systematic cognitive screening of patients after recovery from severe COVID-19 illness and implementation of targeted treatments for patients with persistent cognitive impairments.

High-density Mapping Guided Pulmonary Vein Isolation for Treatment of Atrial Fibrillation - Two-year clinical outcome of a single center experience

Pulmonary vein isolation (PVI) as interventional treatment for atrial fibrillation (AF) aims to eliminate arrhythmogenic triggers from the PVs. Improved signal detection facilitating a more robust electrical isolation might be associated with a better outcome. This retrospective cohort study compared PVI procedures using a novel high-density mapping system (HDM) with improved signal detection vs. age- and sex-matched PVIs using a conventional 3D mapping system (COM). Endpoints comprised freedom from AF and procedural parameters. In total, 108 patients (mean age 63.9 ± 11.2 years, 56.5% male, 50.9% paroxysmal AF) were included (n = 54 patients/group). Our analysis revealed that HDM was not superior regarding freedom from AF (mean follow-up of 494.7 ± 26.2 days), with one- and two-year AF recurrence rates of 38.9%/46.5% (HDM) and 38.9%/42.2% (COM), respectively. HDM was associated with reduction in fluoroscopy times (18.8 ± 10.6 vs. 29.8 ± 13.4 min; p < 0.01) and total radiation dose (866.0 ± 1003.3 vs. 1731.2 ± 1978.4 cGy; p < 0.01) compared to the COM group. HDM was equivalent but not superior to COM with respect to clinical outcome after PVI and resulted in reduced fluoroscopy time and radiation exposure. These results suggest that HDM-guided PVI is effective and safe for AF ablation. Potential benefits in comparison to conventional mapping systems, e.g. arrhythmia recurrence rates, have to be addressed in randomized trials.