Ventricular fibrillation is one of the leading causes for Sudden Cardiac Death and is characterized by multiple activation wavefronts. Multiple activation wavefronts originate from a reentrant circuit which requires the presence of a unidirectional block in the path of a propagating excitation wave. It has been proposed that at the cellular level beat to beat alternation in the action potential duration at rapid pacing rates can result in a conduction block. Various mechanisms have been postulated to show the mechanisms of alternans. We use simulated activation in a one dimensional tissue fiber to show the existence of a new mechanism via which alternans can result. We used a new pacing protocol to eliminate alternans at the pacing site, and thus eliminating restitution of action potential duration at this site to reveal existence of alternans down the fiber. Effects on alternans of manipulations of specific ionic currents such as the sodium current (INa), calcium current (ICaL), potassium current (Ikr) and of the diffusion co-efficient (Dx) which simulates reduced expression of connexin 43 were determined. Decrease in sodium conductance, i.e. in excitability by half caused the alternans to occur at the pacing site itself even though APD restitution was eliminated. An increase or decrease in calcium current (ICaL) eliminated alternans throughout the fiber. The use of a novel pacing approach in investigation of alternans, as in this study, furthers our understanding of the mechanism of alternans and may prove helpful in the development of better anti-arrhythmic drugs in the future.

Heart Failure is a common long term progressive and serious medical condition with high mortality and costly health services in the UK. By the year of 2010, there were around 90,000 people in the UK suffered from heart failure and in 2008, 10,000 heart failure patients were recorded death. Treatments of heart failure cost the National Health Service around £625 million every year. Although heart failure is highly pro-arrhythmic, the underlying mechanisms of the pro-arrhythmic effects of heart failure are not completely understood. Heart failure is associated with electrical remodelling of the properties and kinetics of some ionic channels responsible for the action potential of cardiac cells. However, it is still unclear whether this ionic channel remodelling can account for the pro-arrhythmic effects of heart failure as the complexity of the heart impedes a detailed experimental analysis. Biophysically detailed computational models have been developed in the last two decades, enabling the evaluation of experimental data. The aim of this thesis is to use arrhythmic mechanisms to investigate the pro-arrhythmic effects of heart failure-induced remodelling on the cardiac action potentials and Purkinje-ventricular junction. Single canine Purkinje fibre and ventricular cell models were developed to investigate the effects of heart failure-remodelled ionic channel currents on cell action potentials and identify optimal options for the potential clinical treatments. One-dimensional strand tissue model and three-dimensional wedge model were developed to further explore the effects of heart failure-induced remodelling in propagation of the canine Purkinje fibre, ventricle and Purkinje-ventricular junction. It was found that heart failure-induced remodelling on the Purkinje fibre and ventricle reduced the conduction safety and increased tissue’s vulnerability to the genesis of the unidirectional conduction block, especially at the Purkinje-ventricular junction, which may cause conduction failure, re-entry or both.

Long QT syndrome (LQTS) is an inherited arrhythmic disorder associated with sudden cardiac death (SCD). This study aimed to identify the clinical and molecular genetic risk factors that contribute to major arrhythmic events (MAEs) in patients with genetically confirmed childhood onset LQTS 1–3. This study was a retrospective double-center study. An MAE was defined as the occurrence of SCD, aborted SCD, appropriate implantable cardioverter defibrillator discharge, or sustained ventricular tachycardia. During a median follow-up of 4.6 years (range 0.1–24.3 years), MAEs occurred in 18 (17.8%) of 101 patients diagnosed with LQTS at a median of 7.7 years (range 0.0–18.0 years) despite the use of beta-blockers in 91.6% of patients at the last follow-up. A multivariate analysis identified a genetic diagnosis of LQTS2 and LQTS3 and variants within the KCNH2 S5-loop-S6 pore region as independent risk factors for MAEs, independent of the QTc value or a history of syncope detected from a univariate analysis. MAEs occur frequently in childhood onset LQTS despite beta-blocker treatment. A detailed molecular genetic diagnosis can contribute to the arrhythmia risk stratification and optimize the use of preventive measures in this vulnerable patient population

Mehrfach ungesättigte omega-3 Fettsäuren (n-3 PUFAs), wie Eicosapentaensäure (EPA) und Docosahexaensäure (DHA), schützen vor kardiovaskulären Erkrankungen, wie tödlichen Arrhythmien. In vitro Untersuchungen belegen, dass rekombinante Cytochrom P450 (CYP) Enzyme nicht nur die n-6 PUFA Arachidonsäure (AA), sondern auch die n-3 PUFAs EPA und DHA als alternative Substrate verwenden. Dabei entstehen bioaktive regio- und stereoisomere Epoxy- und Hydroxymetaboliten, CYP-Eicosanoide, die als sekundäre Botenstoffe bei der Regulation von Gefäß-, Nieren- und Herzfunktionen fungieren. Die genauen molekularen Mechanismen dieser Metabolite sind noch weitgehend unerforscht. In der vorliegenden Arbeit wurde zunächst der ernährungsbedingte Einfluss auf das endogene CYP-Eicosanoidprofil im Menschen untersucht. Die Ergebnisse der klinischen Studie zeigten, dass n-3 PUFAs auch in vivo alternative Substrate von CYP-Enzymen darstellen und wenn verfügbar sogar effektiver zu ihren Metaboliten umgesetzt wurden als AA. Als ein wichtiger Metabolit entsteht nach EPA/DHA-Supplementation 17,18-EEQ, welcher womöglich der eigentliche Vermittler der kardioprotektiven Effekte von n-3 PUFAs ist. Unter Verwendung eines etablierten Zellmodells mit spontan schlagenden neonatalen Rattenkardiomyozyten (NRKMs) wurde der anti-arrhythmische Effekte von 17,18-EEQ genauer untersucht. Der negativ chronotrope Effekt von EPA auf NRKMs wurde tatsächlich durch 17,18-EEQ vermittelt, insbesondere dem R,S-Enantiomer. Mittels Strukturfunktionsanalyse wurden synthetische Analoga mit gleicher Wirksamkeit wie dem 7,18-EEQ gefunden, wobei strikte strukturelle Merkmale für die biologische Funktion identifiziert wurden. Die Suche nach einem molekularen Ziel für CYP-Epoxyeicosanoide führte zu einem möglichen Rezeptorkandidaten, der hinsichtlich seiner Ligandenspezifität untersucht wurde. Dieser oder zukünftige andere Rezeptorkandidaten stellen ein mögliches neues zelluläres Ziel zur Behandlung kardialer Arrhythmien dar. / The n-3 polyunsaturated fatty acids (n-3 PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), protect from cardiovascular disease, especially from fetal arrhythmia. Moreover, in vitro studies proved that recombinant cytochrome P450 (CYP) enzymes not only accept the physiologically most important n-6 PUFA arachidonic acid (AA), but also EPA and DHA as alternative substrates, thereby generating regio- and stereospecific biologically active epoxy- and hydroxymetabolites, CYP-eicosanoids. These metabolites serve as second messengers regulating vascular, renal and cardiac function. The precise underlying molecular mechanisms are only partially understood and need further investigation. The first aim of the thesis was to show that the endogenous CYP-eicosanoid profile depends on the availability of the precursor fatty acids. The results of a clinical trial with 20 volunteers, show that n-3 PUFAs serve also in vivo as alternative CYP-dependent substrates and are even preferentially metabolized compared to AA. After EPA/DHA-supplementation 17,18 EEQ was generated as a major metabolite, potentially an important mediator of cardiovascular effects originally attributed to n-3 PUFAs. To test the anti-arrhythmic effect of EPA and 17,18-EEQ, an established cell model with neonatal rat cardiomyocytes (NRKMs) was used. The negative chronotropic effect of EPA was mimicked by 17,18-EEQ, attributed only to the R,S-enantiomer. A structure activity relationship study revealed synthetic analogs, exerting the same biological effect as 17,18-EEQ. Strict structural requirements were found for agonistic function, hinting at a specific interaction with cellular targets, like GPCRs. The search of a molecular target of CYP-eicosanoids led to a putative receptor, which was tested for ligand binding specificity. If the preliminary results on the ligand binding are confirmed in future experiments this receptor might be a novel target for the treatment of cardiac arrhythmia.

Les arythmies ventriculaires conduisant à la mort subite ont été précédemment associées àun type de cellules spécialisées, les fibres de Purkinje (FP). Elles font partie du systèmede conduction cardiaque, et possèdent un rôle majeur dans l’impulsion électrique et l’activationsynchrone des ventricules. Néanmoins, elles peuvent être impliquées dans des phénomènespro-arythmogéniques à l’origine de l’initiation ou du maintien de la fibrillation ventriculaire(FV) au sein de structures normales ou dans le cas d’un large spectre de maladies cardiaques.Cependant, les caractéristiques électrophysiologiques et structurelles des FP etles mécanismes sous-jacents des arythmies liées au Purkinje restent inconnus. Le systèmePurkinje semblerait jouer un rôle important de substrat de l’arythmie en raison de son impactsur l’hétérogénéité transmurale de repolarisation.Six études décrivant les propriétés électrophysiologiques et les propriétés macro/microstructurellesde ventricules gauches de brebis et de ventricules gauches humains ont étédéveloppées en utilisant une combinaison de méthodes classiques et innovantes.Les résultats ont permis de montrer que les FP, à travers leurs jonctions avec le myocarde,modulaient localement la durée du potentiel d'action et jouaient un rôle dans la dispersionde la repolarisation, révélant ainsi le rôle potentiel des FP dans le déclenchement etle maintien de la FV.Ce travail ouvre de nouvelles perspectives thérapeutiques dans le traitement préventifde l'arythmie ventriculaire afin de lutter contre la mort subite d'origine cardiaque. / Arrhythmias that lead to sudden death have previously been associated with a specializedcell type, the Purkinje fibers (PF). They form the cardiac conduction system, and have a majorrole in the electrical impulse and synchronous activation of the ventricles. However, they maybe involved in pro-arrhythmic phenomena causing the initiation or maintenance of ventricularfibrillation (VF) in structurally normal and a broad spectrum of cardiac diseases.Nevertheless, electrophysiological and structural characteristics of PF and mechanismsunderlying Purkinje-related arrhythmias are poorly understood. It is hypothesized thatthe Purkinje system plays an important role as a substrate for arrhythmias due to, in part,its impact on transmural repolarization heterogeneity.Here within are six studies describing electrophysiological and macro/micro structuralproperties of sheep and human left ventricles using a combination of conventional andinnovative methods.Results showed that PF, through junctions with the myocardium, locally modulatedthe action potential duration and played a role in the dispersion of repolarization. Therefore,revealing a potential role for PF in both, trigger and maintenance of VF.This work opens new therapeutic perspectives in preventive treatment of ventriculararrhythmia to fight against sudden cardiac death.

Le trouble comportemental en sommeil paradoxal idiopathique (TCSPi) précède de plusieurs années le diagnostic d’une maladie synucléinopathique. Dans cette étude, nous cherchions à déterminer si la puissance spectrale relative, les composantes rythmiques et arythmiques des spectres de puissance, ainsi que la connectivité fonctionnelle permettaient d’identifier à un temps de base les patients ayant un TCSPi qui développerait une synucléinopathie lors des suivis cliniques annuels. Un enregistrement EEG au repos et une évaluation neuropsychologique ont été conduits auprès de quatre-vingt-un participants atteints d’un TCSPi (66.89 ± 6.91 ans, 20 femmes) et des évaluations neurologiques annuelles étaient menées afin de définir si les patients montraient des symptômes d’une maladie synucléinopathique. La puissance spectrale standard ainsi qu’une estimation spectrale des composantes rythmiques et arythmiques ont été calculées. Ensuite, la connectivité fonctionnelle globale et entre chaque paire d’électrodes ont été estimée par le weighted Phase Lag Index. Après une durée de suivi de 5.01 ± 2.76 ans, 34 participants ont été diagnostiqués avec une synucléinopathie et 47 sont restés exempts de maladie. Comparativement aux participants avec un TCSPi n’ayant pas converti, ceux ayant converti montraient, lors de l’évaluation de base, une puissance spectrale relative plus élevée dans la bande thêta, une pente de la composante arythmique plus abrupte ainsi qu'une puissance rythmique plus élevée en thêta dans les régions occipitales et temporales ainsi qu’en en bêta1 dans les régions frontales. De plus, les patients TCSPi ayant converti présentaient une hyperconnectivité globale dans la bande bêta, mais une hypoconnectivité dans la bande alpha entre les régions temporo-occipitales gauches lors de l’évaluation de base comparativement à ceux n’ayant pas converti. Les altérations mesurables en EEG au repos lors de l’évaluation de base chez les participants avec TCSPi ayant converti vers une maladie synucléinopathique suggèrent une perturbation des réseaux à grande échelle affectés par la neurodégénérescence précoce des structures sous-corticales. / Idiopathic REM sleep behavior disorder (iRBD) precedes the diagnosis of synucleinopathies by several years. In this study, we aimed to determine whether relative spectral power, rhythmic and arrhythmic components of power spectra, and functional connectivity at baseline could identify patients with iRBD who will develop a synucleinopathy at follow-up. Resting-state EEG recordings and neuropsychological evaluations were conducted on eighty-one participants with iRBD (66.89 ± 6.91 years; 20 women), and annual neurological assessments were performed to define the emergence of synucleinopathy symptoms. Standard spectral power and spectral estimates of rhythmic and arrhythmic components were calculated. Additionally, global and pairwise functional connectivity were estimated using the weighted Phase Lag Index. After a follow-up period of 5.01 ± 2.76 years, 34 participants were diagnosed with a synucleinopathic disorder, while 47 remained disease-free. Compared to patients who did not convert, patients who converted at follow-up exhibited higher relative spectral power in the theta band, steeper slopes of the arrhythmic component, and increased rhythmic power in theta in posterior regions and beta1 in frontal regions at baseline evaluation. Furthermore, participants who converted showed hyperconnectivity in the beta band and hypoconnectivity in the alpha band between left temporo-occipital regions at baseline compared to participants who did not convert. The measurable alterations in resting-state EEG at baseline in participants with iRBD who phenoconverted towards a synucleinopathy suggest disruption of large-scale networks affected by early neurodegeneration of subcortical structures.