La fibrillation auriculaire (FA) figure parmi les arythmies les plus courantes chez les patients âgés et dont l’incidence augmente avec l’âge. La compréhension des mécanismes liant les caractéristiques tissulaires et le risque de la FA demeure centrale pour l’optimisation du traitement. Les alternances de la durée du potentiel d’action (APD) dans le tissu cardiaque ont été depuis peu documentées comme l’un des phénomènes qui facilitent la FA. Généralement, la FA est associée à de courtes périodes de stimulation électrique. Récemment, la FA a été observée aux longues périodes de stimulation chez les patients atteints de la FA chronique (FAc). Les mécanismes sous-jacents aux alternances d’APD aux longues périodes de stimulation ne sont pas totalement déterminés. En partant d’un modèle mathématique avec le remodelage électrophysiologique associé à la FAc d’un myocyte auriculaire humain, notre objectif était de premièrement identifier ces mécanismes ainsi, nous avons réalisé une analyse de la sensibilité des alternances aux changements des paramètres du modèle. Dix-huit (18) paramètres associés au remodelage de la FA ont été mis à l’échelle entre 30% et 200% de leur valeur de base. Ensuite, nous avons stimulé le tissu à partir de l’électrode de stimulation pendant des périodes de stimulation (CL) comprise entre 700 ms et 350 ms. Les alternances de la durée du potentiel d’action et du calcium intracellulaire (Cai) ont été quantifiées par la suite au point d’enregistrement. On a validé que les alternances d’APD et de Cai étaient significatives seulement pour le changement du paramètre kiCa qui représente la constante d’inactivation des récepteurs ryanodines (RyR). Sachant que ce sont les alternances discordantes qui constituent un substrat pour la FA, nous avons en second lieu, validé la formation des alternances spatialement discordantes aux longues périodes de stimulation lorsque les alternances étaient occasionnées par la diminution de kiCa. Lorsque les alternances discordantes étaient entraînées par l’hétérogénéité de l’inactivation des RyR, le motif des alternances dépendait des conditions initiales de cette hétérogénéité. Nous avons par la suite déterminé les facteurs dynamiques qui modulaient l’apparition des alternances d’APD et de Cai aux périodes de stimulation pour lesquelles les alternances se sont manifestées. On a trouvé que pour notre modèle de FAc avec la diminution de kiCa, les alternances étaient pilotées par le cycle calcique alors que pour le modèle FAc de base, les alternances résultaient des interactions entre le cycle membranaire et calcique. Ces expériences nous ont permis de développer un modèle itéré qui prenait en compte les variables des cycles membranaires, calciques ainsi que le couplage entre ces cycles. L’analyse des données a révélé que le modèle itéré devait être constitué des variables dépendantes suivantes : calcium stocké dans le réticulum sarcoplasmique (SR), calcium cytoplasmique et la durée du potentiel d’action. Notre modèle itéré a pu reproduire les caractéristiques de la dynamique du système représenté par le tissu auriculaire humain avec le remodelage du FAc stimulé périodiquement. / Atrial fibrillation (AF) is one of the most common arrhythmias in elderly patients, and its incidence increases with age. Understanding the mechanisms linking tissue characteristics and the risk of AF remains central to optimising treatment. Action potential duration (APD) alternans in cardiac tissue have recently been documented as one of the phenomena that facilitate AF. Typically, AF is associated with short periods of electrical stimulation. Recently, AF has been observed at long pacing periods in patients with chronic AF (AFc). The mechanisms underlying APD alternans at long pacing periods are not fully determined. Using a mathematical model with the electrophysiological remodeling associated with AFc in a human atrial myocyte, our aim was first to identify these mechanisms and then to analyse the sensitivity of the alternans to changes in the model parameters. Eighteen (18) parameters associated with AF remodelling were scaled between 30% and 200% of their baseline value. The tissue was then paced from the stimulation electrode at pacing periods (CL) between 700 ms and 350 ms. Action potential duration and intracellular calcium (Cai) alternans were subsequently quantified at the recording point. APD and Cai alternans were found to be significant only for the change in the kiCa parameter, which represents the ryanodine receptor (RyR) inactivation constant. Knowing that it is the discordant alternans that constitute a substrate for AF, we secondly validated the formation of spatially discordant alternans at long pacing periods when the alternans were caused by the decrease in kiCa. When the discordant alternans were driven by heterogeneity in RyR inactivation, the pattern of alternans depended on the initial conditions of this heterogeneity. We then determined the dynamic factors that modulated the appearance of APD and Cai alternans at the pacing periods for which the alternans occurred. We found that for our AFc model with the decrease in kiCa, the alternans were driven by the calcium cycle, whereas for the basic AFc model, the alternans resulted from interactions between the membrane and calcium cycles. These experiments enabled us to develop an iterated model that considered the variables of the membrane and calcium cycles, as well as the coupling between these cycles. Analysis of the data revealed that the iterated model should consist of the following dependent variables: calcium load in the sarcoplasmic reticulum (SR), cytoplasmic calcium and the duration of the action potential. Our iterated model was able to reproduce the characteristics of the dynamics of the system represented by human atrial tissue with the electrophysiological remodeling associated with AFc paced periodically.

RATIONNEL : La fibrillation auriculaire (FA) est la forme d’arythmie la plus commune rencontrée en clinique. De nombreux facteurs ou comorbidités comme l’insuffisance cardiaque, l’hypertension, l’âge ou le diabète peuvent provoquer et/ou aggraver la FA. La maladie du coeur droit (MCD) fait également partie de ces facteurs de risque. HYPOTHESE : L’inflammation induite par la MCD pourrait être un facteur d’initiation, de maintien et d’aggravation de la FA via la mise en place d’un substrat pro -arythmogène. METHODES : Une ligature du tronc artériel pulmonaire (LTP) a été effectuée sur des rats Wistar pesant 225-275g pour provoquer une MCD marquée par une hypertrophie et une dilatation ventriculaire droite. Les animaux témoins, n’ont pas subi de ligature. Au 21e jour après la chirurgie, des études électrophysiologiques et des échocardiographies ont été réalisés in vivo. De plus, nous avons effectué de la cartographie optique ex vivo sur coeur perfusé et des mesures de contractilité sur des cardiomyocytes (CM) isolés d’oreillette droite (OD), d’oreillette gauche (OG) et de ventricule droit (VD). La fibrose cardiaque et les niveaux de Connexine-43 (Cx-43) ont été quantifiés par analyses histologiques. L’expression des gènes et les niveaux des protéines associées ont été évalués par qPCR et immuno-buvardage. RESULTATS : Les échocardiographies ont révélé une hypertrophie et dilatation de l’oreillette droite. Les rats LTP ont montré significativement plus de susceptibilité à la FA que les témoins. L’activité contractile des CM atriaux était augmentée chez les LTP comparés aux témoins. Les coupes histologiques et les analyses par qPCR et d’immunobuvardage ont démontré une augmentation significative de la fibrose et des marqueurs inflammatoires dans les CM, comme l’interleukine-6, l’interleukine 1β ou encore l’inflammasome NLRP3, suggérant leur implication dans l’élaboration du profil inflammatoire arythmogène. CONCLUSION : Cette étude nous a permis de caractériser le modèle LTP au niveau des CM atriaux et de mettre en évidence un remodelage physiologique, électrophysiologique et inflammatoire, ainsi qu’une augmentation de la susceptibilité à la FA chez les animaux LTP. / RATIONAL: Atrial fibrillation (AF) is the most common type of arrhythmia encountered clinically. Several risk factors such as heart failure, hypertension, age or diabetes can lead to or/worsen AF. Right heart disease (RHD) has also been described among AF risk factors. The mechanisms linking RHD, inflammation and AF are still rarely described in the literature. The main objective of the project is to characterize the proarrhythmogenic cardiomyocyte (CM) remodeling and CM inflammation profile in rat atria affected by RHD. HYPOTHESIS: RHD-induced inflammation could be a factor for AF initiation, sustainability, and aggravation through development of pro-arrhythmogenic substrate. METHODS: Pulmonary artery banding (PAB) is surgically performed on Wistar rats weighing 225- 275g to induce RHD. Sham animals did not receive the PAB surgery. Cardiac echography and electrophysiological studies are performed in vivo on all animals before sacrifice, 21 days postsurgery. Optical mapping was performed ex vivo on Langendorff-perfused hearts. Freshly isolated right ventricular (RV), as well as right and left atrial (RA and LA) CM, underwent contractility recording in vitro. Histological analyses were performed to assess myocardial fibrosis and Connexin-43 levels. Genes and protein levels were obtained by qPCR and Western-blot analyses respectively. RESULTS: Compared to sham, PAB rats developed severe right-sided myocardial hypertrophy accompanied by RA and RV dilation as assessed by echocardiography. PAB rats had a significantly increased AF susceptibility and AF episode duration. CM contractility was enhanced in PAB rats compared to sham. Histology and qPCR analyses revealed increased fibrosis and inflammation in RA. CONCLUSION: This study allowed us to characterize the PAB model in atrial CM and has highlighted physiological, electrophysiological, and inflammatory remodeling, as well as increased AF susceptibility in PAB animals.

La fibrillation auriculaire (FA) est l’arythmie cardiaque la plus répandue. Les maladies du cœur droit (MCD), caractérisées par une hypertrophie et une inflammation myocardique augmentent le risque de FA. La relation tri-factorielle unissant les MCD, l’inflammation et la FA demeure peu décrite. L’hypothèse était qu’une constriction du tronc pulmonaire entraînerait une MCD induisant une inflammation auriculaire et une augmentation du risque de FA. Une ligature du tronc pulmonaire (LTP) fut réalisée chirurgicalement sur des rats Wistar mâles pour mimer une augmentation chronique de la post-charge du ventricule droit. Des rats Sham ont eu une chirurgie sans ligature. Tous les rats ont eu une échocardiographie puis une étude électrophysiologique pour évaluer leur vulnérabilité à la FA avant d’être sacrifiés aux jours 0, 7, 14 et 21 post-chirurgie. Leurs tissus auriculaires ont servi pour la cartographie optique de leur oreillette droite (OD), l’histologie, mais aussi pour la RPCq et l’immunobuvardage de type Western afin de quantifier des marqueurs inflammatoires/fibrotiques/sénescents et des canaux ioniques. Une hypertrophie et dilatation du cœur droit des rats LTP furent observées. Dès le 7e jour, les rats LTP avaient une vitesse de conduction électrique réduite dans leur OD et étaient vulnérables à la FA. De la fibrose s’était accumulée dans l’OD, coïncidant avec une élévation de l’expression de gènes pro-inflammatoires (Nlrp3) et pro-fibrotiques (Tgfβ1) ainsi qu’une diminution de la protéine SERCA2a. Cette étude a démontré qu’une MCD provoque une augmentation de l’inflammation et de la fibrose auriculaire droite associée à une croissance du risque de FA. / Atrial fibrillation (AF) is the most common cardiac arrhythmia. Right heart diseases (RHD), which are characterized by hypertrophy and myocardial inflammation can also increase the risk of AF. The tri-factorial relationship that exists between RHD, inflammation and AF remains poorly described. We hypothesized that a permanent constriction of the pulmonary trunk would provoke a severe RHD associated with atrial inflammation and an enhanced AF vulnerability. A pulmonary artery trunk banding (PAB) was surgically performed on male Wistar rats to mimic a chronic increase in right ventricular afterload. Sham rats had surgery without ligation. All rats underwent echocardiography and electrophysiological studies to measure their AF vulnerability before being euthanized on days 0, 7, 14 and 21 post-surgery. Their atrial tissues were used for the optical mapping of their right atrium, histology, but also qPCR and Western immunoblotting in order to quantify inflammatory/fibrotic/senescent markers and ionic channels. PAB provoked the hypertrophy and dilation of the right heart. Starting at day 7, conduction velocity was significantly reduced in PAB rats compared to Sham. The right atrium (RA) dimension, RA fibrosis and AF vulnerability were significantly increased in PAB rats compared to Sham. The expression of pro-inflammatory (Nlrp3) and pro-fibrotic (Tgfβ1) genes was increased, and the levels of the SERCA2a protein were decreased in PAB rats compared to Sham. Our study demonstrated that a RHD in rats can induce an increase in RA inflammation and fibrosis, which are associated with an increased risk of AF.

La fibrillation auriculaire (FA) est l'arythmie cardiaque la plus répandue dans le monde et est associée à une hausse de morbidité et une mortalité importante. Des progrès substantiels dans notre compréhension de l'étiologie de la maladie ont été réalisés au cours des deux dernières décennies, conduisant à une amélioration du traitement et de la gestion de la maladie. Cependant, le fardeau de la FA continue d'augmenter. De plus, les mécanismes moléculaires et cellulaires sous-jacents à l’initiation et à la progression de la FA restent incomplètement compris. Dans cette thèse, mon objectif était de caractériser de nouveaux déterminants moléculaires et cellulaires de la FA en utilisant une approche multiomique. J'ai d'abord utilisé le séquençage de l'ARN (RNAseq) pour l'ARN total et les micro-ARN (miRNA) afin de dévaluer l'effet de la FA sur l’expression génique dans deux modèles canins de FA. Ces résultats ont impliqué le locus orthologue humain 14q32 et son lien potentiel avec la signalisation du glutamate. Dans le chapitre trois, j'ai démontré les lacunes actuelles des modèles statistiques utilisés pour prédire l'effet régulateur des régions de chromatine ouvertes sur l'expression des gènes dans des essais multiomiques à noyau unique et suggéré des alternatives montrant un meilleur pouvoir prédictif. Dans le chapitre quatre, j'ai utilisé des analyses par locus quantitatifs d'expression (eQTL) pour caractériser les variants génétiques communs associés à la FA. Grâce à des analyses de colocalisation, une cartographie fine et un multiome à noyau unique, j'ai justifié mécaniquement l’effet de variants non-codants et fait la priorisation de gènes candidats, notamment GNB4, MAPT et LINC01629. Enfin, dans le chapitre cinq, j'ai fourni une caractérisation approfondie des gènes persistants de FA différentiellement exprimés au niveau cellulaire et identifié les facteurs de transcription potentiels impliqués dans leur régulation. En résumé, l’utilisation d’une approche multiomique a permis de découvrir de nombreuses nouvelles voies cellulaires et génétiques modifiées au cours de la FA ainsi que des gènes candidats impliqués dans le risque génétique de la FA. Ces résultats fournissent des informations et ressources importantes pour concevoir de nouvelles stratégies thérapeutiques, impliquant à la fois des cibles génétiques et nouvelles voies cellulaires pour lutter contre cette maladie cardiaque commune. / Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia worldwide and is associated with important morbidity and mortality. Substantial advancement in our understanding of the disease etiology have been made in the past two decades leading to improved treatment and management of the disease, however, AF burden continues to increase. Moreover, the molecular and cellular mechanisms underlying AF initiation and progression remain incompletely understood. In this thesis I aimed to characterise novel molecular and cellular determinants of AF using a multiomic approache. In chapter two, I used RNA sequencing (RNAseq) for total RNA and micro-RNAs (miRNA) to decipher the effect of AF in two canine models, which implicated the orthologue human locus 14q32 and its potential role in glutamate signaling regulation. In chapter three, I demonstrated current shortcomings of statistical models used to predict the regulatory effect of open chromatin regions on gene expression in single nuclei multiomic assays and suggested alternatives showing better predictive power. In chapter four, I used expression quantitative loci (eQTL) to characterize AF associated common genetic variants. Through co-localization analyses, fine-mapping and single nuclei multiome, I mechanistically substantiated non-coding variants and prioritized strong candidate genes including GNB4, MAPT and LINC01629. Finally, in chapter five, I provided a deep characterization of persistent AF differentially expressed genes (DEGs) at the cellular level and identified potential transcription factors involved in their regulation. In summary, using a multiomic approach unraveled numerous new cellular and gene pathways altered during AF and candidate genes implicated in AF genetic risk. These findings provide important insights and data resources to design novel therapeutic strategies, targeting both genetically derived candidate genes and cellular pathways to address this pervasive cardiac disease.

Ventricular fibrillation (VF) is a lethal heart rhythm that leads to cardiac arrest. It has been shown that amplitude spectral area (AMSA) in prolonged VF correlates with success of resuscitation. This study will compare traditional resuscitation with a novel resuscitation algorithm using AMSA and end-tidal carbon dioxide (ETCO2) to time defibrillations.VF will be induced in 60 swine. Resuscitation will commence after 10 minutes of untreated VF. Cases will receive defibrillation if AMSA is >19.8 mVHz and ETCO2 >20 mm of Hg, otherwise chest compressions will continue for another 90 seconds. Controls will have standard resuscitation. Sub group analysis will include effect of induced myocardial infarction (MI).End points will include survival, neurologic scores, duration of resuscitation efforts, and number of defibrillations.This experiment will establish whether using AMSA and ETCO2 to time defibrillations results in superior resuscitation compared with standard techniques.

Objective: The primary objective of this study was to estimate the long-term cost-effectiveness of stroke prevention in patients with nonvalvular atrial fibrillation (NVAF) in the United States using new anticoagulant therapies - dabigatran 150 mg, apixaban 5 mg, and rivaroxaban 20 mg - as well as the standard treatment, warfarin. Methods: A Markov decision-analysis model was constructed using data from clinical trials that evaluated the new oral anticoagulants relative to warfarin (apixaban 5 mg & ARISTOTLE, dabigatran 150 mg & RE-LY, and rivaroxaban 20 mg & ROCKET-AF) to compare the lifetime cost and quality-adjusted life expectancy. The Markov model target population was a hypothetical cohort of 70-year old patients with nonvalvular atrial fibrillation, an increased risk for stroke (CHADS₂ ≥ 1, or equivalent), a renal creatinine clearance (CrCl) of 50 or above, and no contraindication to anticoagulant therapy. Using pair-wise comparisons of each therapy, analyses were conducted to evaluate incremental cost-effectiveness ratios (ICERs), net monetary benefits (NMBs), lifetime costs, life-years, and quality-adjusted life-years (QALYs). Results: In the base case, warfarin had the lowest cost of $71,857 (95% confidence interval [CI]: $68,730, $77,452), followed by rivaroxaban 20 mg ($74,023; 95% CI: $70,943, $77,307), dabigatran 150 mg ($78,584; 95% CI: $75,277, $81,968), and apixaban 5 mg ($81,180; 95% CI: $78,642, $83,756). Apixaban 5 mg also yielded the highest QALY estimate, 8.63 (95% CI: 8.52, 8.72), followed by dabigatran 150 mg (8.55; 95% CI: 8.43, 8.67), rivaroxaban 20 mg (8.42; 95% CI: 8.31, 8.54), and warfarin (8.17; 95% CI: 8.1, 8.24). In a Monte Carlo probabilistic sensitivity analysis, apixaban 5 mg, dabigatran 150 mg, rivaroxaban 20 mg, and warfarin were cost effective in 45%, 37%, 19%, 0%, respectively, of the simulations using a willingness-to pay threshold of $50,000 per QALY gained. From the one-way sensitivity analyses, new anticoagulant (apixaban 5 mg, dabigatran 150 mg, rivaroxaban 20 mg) costs and probabilities associated with intracranial hemorrhage and stroke for patients receiving rivaroxaban 20 mg were identified as significant influential variables impacting model results. Conclusion: In patients with NVAF and an increased risk of stroke prophylaxis, apixaban 5 mg, dabigatran 150 mg, and rivaroxaban 20 mg may all be cost-effective alternatives to warfarin depending on pricing in the United States and neurologic events for rivaroxaban 20 mg.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Background: The Framingham Study from 1991 showed a clear correlation between atrial fibrillation (AF) and ischemic stroke, where patients with AF had an almost fivefold increase in risk of stroke compared with patients without AF. Since then, several trials have evaluated different antithrombotic treatments to reduce the risk of stroke in patients with AF. Other trials have investigated factors that increase the risk of stroke in patients with AF and risk score systems have been developed to categorize patients into low or increased risk of stroke to help clinicians to decide which patients benefit from antithrombotic treatment and in whom it can be abstained, not to expose patients with low stroke risk to an increased risk of bleeding conferred by antithrombotic treatment. The aims of this thesis were: [1] to evaluate if a warfarin dosing algorithm can increase hit rate and decrease mean error compared with manually changed doses; [2] to assess the prevalence and net clinical benefit of aspirin as monotherapy for stroke prevention in AF; [3] to investigate the risk of thromboembolic and haemorrhagic complications within 30 days after electrical cardioversion (ECV) of AF in patients with and without oral anticoagulation (OAC) pre-treatment; and [4] to assess the proportion of patients discontinuing OAC after pulmonary vein isolation (PVI), identify factors predicting stroke after PVI and to investigate risk of complications after PVI with and without OAC. Materials and methods: All studies are retrospective and based on data from Swedish national quality registries. In paper I, data from Auricula was used to compare the resulting INR values after algorithmic warfarin dose suggestions and manually changed doses. In paper II data was extracted from the Swedish National Patient Register, the Dispensed Drugs Register and the Cause of Death Register. Patients with aspirin treatment were compared with patients without any antithrombotic treatment regarding risk of thromboembolic and haemorrhagic complications. In paper III data was collected from the Swedish National Patient Register and the Dispensed Drugs Register to examine risk of complications (thromboembolic and haemorrhagic events) within 30 days after cardioversion, comparing patients with and without oral anticoagulation pre-treatment. In paper IV data from six different Swedish national quality registries were used (Swedish Catheter Ablation Register, Auricula, Swedish National Patient Register, Dispensed Drugs Register, Cause of Death Register and Riksstroke). Patients undergoing pulmonary vein isolation (PVI) were investigated for adherence to guidelines regarding oral anticoagulation, predictors for stroke after PVI, as well as risk of ischemic stroke or intracranial haemorrhage after PVI in patients with and without treatment. Results: Paper I showed that a computerized dosing algorithm for warfarin in most cases perform as well or better compared with doses that have been changed manually, with a better hit-rate (0.72 vs. 0.67) and a lower mean error (0.44 vs. 0.48). Paper II showed that 32% of 182.678 patients with a diagnosis of AF were on monotherapy with aspirin for stroke prevention. A total of 115.185 patients were included, 58.671 with aspirin treatment and 56.514 without antithrombotic treatment at baseline. After stratification after CHA2DS2-VASc score and after multivariable adjustment, aspirin treatment did not confer a decrease in thromboembolic events. After propensity score mathcing, rate of ischemic stroke was 7.4%/year (95% CI 7.1-7.6) in aspirin treated patients and 6.6%/year (95% CI 6.4-6.9) in patients without antithrombotic treatment. In paper III 22.874 patients undergoing electrical cardioversion were included, 10.722 with and 12.152 without OAC pre-treatment. In patients with low stroke risk (CHA2DS2-VASc 0-1), no thromboembolic complication was seen within 30 days after cardioversion. In patients with CHA2DS2-VASc ≥2, the risk of thromboembolic complications was increased when no oral anticoagulation pre-treatment was used, results that remained after propensity score matching. No difference regarding haemorrhagic complications was seen. Paper IV included a total of 1585 patients undergoing PVI with a mean follow up of 2.6 years. Adherence to current guidelines regarding oral anticoagulation was good in patients with CHA2DS2-VASc ≥2. Previous ischemic stroke was a predictor for a new stroke after PVI. In patients with CHA2DS2-VASc ≥2 stroke risk was increased in patients discontinuing OAC compared to those continuing OAC (1,60%/year vs. 0.34%/year). Conclusion: Oral anticoagulation is still underutilized for prevention of stroke and systemic embolism in patients with atrial fibrillation. Patients with risk factors for stroke (CHA2DS2-VASc ≥2p) benefit from continuous oral anticoagulation treatment to prevent stroke, also in conjunction with electrical cardioversion and after pulmonary vein isolation. If warfarin is chosen, a computerised dosing algorithm can facilitate and standardize warfarin dosing and lead to better resulting INR values than manually changed doses. Aspirin should not be used for stroke prevention in patients with atrial fibrillation.