The management and prevention of Sudden Cardiac Death remains a great challenge in modern Cardiology. Implantable Cardioverter Defibrillators (ICDs) have been shown to reduce mortality. Despite decades of research, the mechanisms are not fully understood and ICD treatment is crude, palliative and expensive. Nonetheless, outcome studies have helped to inform national and international guidance in the implantation of these devices. Patient selection is crucial to ensure correct patients are identified and appropriately treated. More refined and stringent risk stratification is needed to identify patients at high risk. This thesis examines non-invasive, readily measureable markers to see whether they can be used to assess the risk of ventricular arrhythmia in patients with cardiomyopathy who have indications for ICD implantation. Baseline data in the form of 12 lead electrocardiograms, echocardiography, 24 hour Holter monitoring and venous blood were obtained to analyse QT dispersion, Heart Rate Variability (HRV), QT Variability Index (QTVI), ECG restitution measures and NTproBNP levels in these patients. Patients were followed up for a two year period through the ICD clinic and appropriate therapy was recorded as a surrogate marker for ventricular arrhythmia. Patients with and without appropriate therapy were then compared to look for significant differences in the examined markers. The percentage of beats with a QT/TQ ratio>1 was associated with appropriate shocks when compared with no therapy (p=0.04). However, the result was not significant when all appropriate ICD therapy was compared with no therapy (p=0.06). This possibly reflects the period of time the heart spends on the more ‘unstable portion’ of the restitution slope in patients at highest risk. Median BNP was non-significantly higher in patients with arrhythmia compared to those who were shock free. None of the other examined markers were predictive of appropriate therapy. There is thus promise in the use of some non-invasive markers in the refinement of patient selection with LVSD being considered for ICD therapy.

Stretch is known to result in an electrically less stable ventricular substrate, yet the reported effects of stretch on measured electrophysiological parameters have been inconsistent and even contradictory. The goal of this study was to evaluate the effects of acute mechanical stretch on cardiac electrical features thought to be key in generation of arrhythmia, namely restitution of action potential duration (APD), electrical memory, and onset of alternans. Microelectrodes were used to record intracellular potentials pre, during, and post-stretch from isolated right ventricular tissues from swine. In separate experiments, the effects of two levels of stretch were quantified. Pacing protocols employing explicit diastolic interval (DI) control and cycle length (CL) control were used to obtain measures of restitution of APD, memory, and alternans of APD. Stretching the tissue had varying effects on APD, restitution and memory. Stretch increased APD, restitution slopes and memory by as much as 24, 30 and 53 % in some cases, while it decreased these by up to 18, 37 and 81 % in others. During stretch, alternans of APD were observed in some cases, which occurred at slower rates of activation than before stretch. Histology of tissue samples showed localized changes in orientation of cells relative to the direction of stretch. Our results show that among individual trials, stretch altered the measured electrophysiological properties, sometimes markedly. However, when pooled together, these changes cancelled each other and the averages showed no statistically significant difference after stretch. A potential mechanism that explains this divergent and inconsistent response to stretch is the presence of local, micron level, variation in orientation of myocytes. Upon stretch, these divergent effects likely increase dispersion of repolarization diffusely and might thus be the reason behind the consistently observed increase in arrhythmic substrate after stretch.

Les techniques de traitement du signal numérique prennent une place grandissante en rythmologie clinique. Ces outils offrent de nouvelles perspectives d'amélioration de la détection d'anomalies rythmiques subtiles et d'interprétation des arythmies complexes. Notre travail se focalise sur l'apport des techniques de traitement du signal pour les arythmies ventri­culaires. Il s'intéresse à trois champs complémentaires: les signaux unidimensionnels (ECG et EGM), la cartographie non-invasive, et la cartographie invasive. Concernant les signaux unidimensionnels, nous proposons tout d'abord une méthodologie d'amélio­ration du rapport signal sur bruit des enregistrements ECG par des méthodes de moyennage et de gating respiratoire. Cette méthodologie offre des perspectives intéressantes pour [a détection de si­gnaux anormaux de faible amplitude et pour la mesure non-invasive de l'intervalle HV. Nous détaillons ensuite les liens entre signaux endocardiques et ECG en fibrillation ventriculaire (FV), en montrant notamment que les fréquences dominantes sont fortement corrélées et qu'une fragmentation endocardique se traduit sur l'ECG de surface par une chute de l'amplitude. Enfin, nous démontrons par une analyse fréquentielle de 63épisodes de FV le lien entre les caractéristiques de ces épisodes et les caractéristiques cliniques des patients qui en sont victimes. Notamment, la fréquence dominante est très corrélée à la cardiopathie sous jacente. Le mode et le site d'induc tion ont également un impact important sur l'arythmie, aussi bien sur les fréquences que le degré de fragmentation et la phase de l'ECG de surface. Concernant la cartographie non-invasive, nous présentons une comparaison de différentes méthodes de résolution en potentiel du problème inverse. Cette comparaison démontre que la méthodologie ECGi fait partie des meilleures approches évaluées. Nous proposons ensuite une étude de validation des cartes d'activation ventriculaires par ECGi dans un contexte clinique sur 55 patients. Cette étude retrouve une corrélation médiocre entre les cartes non-invasives et les cartes de référence. Les résultats sont hétérogènes, avec une bonne corrélation sur les rythmes avec QRS larges. Nous proposons ensuite quelques pistes d'amélioration de ces cartes d'activation, par une analyse nouvelle de la solution fondamentale ECGi qui s'intéresse au gradient et au laplacien du potentiel et par un post-traitement des potentiels reconstruits, en combinant une évaluation des délais entre points voisin avec une mesure locale de temps d'activation. Ces deux techniques permettent une amélioration significative de la qualité des cartes reconstruites. Concernant la cartographie invasive, nous nous intéressons aux domaines et aux techniques d'inter­ polation de mesures ponctuelles. Nous montrons l'importance de ces techniques sur le rendu final d'une carte d'activation. Nous utilisons ensuite une de ces méthodologies pour produire des cartes améliorées chez les pa­tients porteurs d'un syndrome de Brugada. Nous montrons qu'il existe chez ces patients des arguments cliniques en faveur d'un bloc partiel de conduction endo-épicardique prédominant au niveau de l'infundibulum et de la partie latérobasale du ventricule droit. Enfin, nous montrons à l'aide d'un modèle in silico les conséquences arythmogènes d'une telle dis­ sociation, qui se traduit par une inductibilité accrue lorsque le nombre de connexions fonctionnelles résiduelles diminue. Au TOTAL, notre travail utilise les techniques de traitement du signal pour différentes applications autour des arythmies ventriculaires. Nous proposons plusieurs innovations méthodologiques per­mettant d'extraire et de traiter de manière nouvelle le signal électrique cardiaque. Les techniques de cartographie non-invasives doivent encore être améliorées pour tenir toutes leurs promesses. L'élec­trocardiographie et la cartographie de contact pourront voir leur champ d'utilisation étendu par ces innovations. / Signal processing tools are increasingly present in the electrophysiologist' s daily practice. These tools have the potential to enhance the detection of small electrical anomalies, and to enable the analysis of complex arrhythmia. Our work focuses on ventricular arrhythmia, and more specifically on how signal processing tech­ niques can help usbetter understand these diseases. lt is made up of three parts,focusing on different topics: uni-dimensional signal analysis (ECG and endocardial electrograms), non-invasive mapping, and invasive contact mapping. Concerning uni-dimensional signal analysis, we first propose a method to enhance the signal to noise ratio of ECG recordings. We use a combination of signal averaging and respiration gating to achieve this goal, and offer interesting perspectives for the detection of abnormal low amplitude potentials and non-invasive measurement of the HV interval. We then analyze the relationship between endocardial and ECG signais during ventricular fibrilla­ tion (VF) episodes. We demonstrate that endocardial and ECG dominant frequencies are similar,and that higher endocardial fragmentation results in a drop of the waveform amplitude on the surface ECG. Finally, we demonstrate through frequency domain analysis of 63 VF episodes a clear correlation between VF characteristics and clinical factors. Dominant frequency is particularly useful to dis­ criminate between different underlying causal substrates. We also demonstrate that VF characteris­ tics depend on the induction mode and induction site, in terms of dominant frequency, amount of fragmentation and ECG phase. Concerning non-invasive mapping, we compare different potential-based inverse problem resolution techniques. ECGi appears as one of the most reliable techniques. A clinical validation study of non-invasive ventricular activation mapping using ECGi isthen carried­ out. Fifty-five patients were included for whom non-invasive maps are compared to contact maps. We show a very poor overall correlation between non-invasive and invasive maps. Results are het­ erogeneous, with good correlation in patients with wide QRS activation patterns. Wethen propose different techniques to improve non-invasive activation mapping. A first study uses the surface laplacian and the gradient of the inverse-computed potential as inputs to activation map­ ping. A second study combines estimated delays between neighboring points and local activation time estimates to create a more globally coherent solution. Both studies demonstrate a significant improvement of activation maps. Concerning contact mapping, we first give an overview of interpolation domains and techniques that can be used to provide dense activation maps from sparse measures. We illustrate the influence of these techniques on the clinician's ability to make a correct diagnosis. We then use one of these interpolation techniques to create epicardial activation maps in Brugada patients. We show that these patients harbor epicardial electrical activity compatible with partial endo-epicardial conduction block. This phenomenon predominates in the right ventricular lateral wall and outflow tract. Finally,using an in silico model, we demonstrate the arrhythmogenic potential of such a dissociation. lnducibility peaks as the number of residual functional connections between endo and epicardium falls. ÜVERALL, our work uses signal processing techniques for different applications conceming ven­ tricular arrhythmia. We propose different methodological innovations that allow us to record and process cardiac electrical activity with increasing precision. Further progress is still required before non-invasive mapping can live up to its promises. The proposed methodological innovations can extend the use of electrocardiography and invasive mapping.

Wnt/β-catenin signaling is activated in the heart after myocardial infarction (MI). This study aims to investigate if β-catenin deletion affects post-MI ion channel gene alterations and ventricular tachycardias (VT). MI was induced by permanent ligation of left anterior descending artery in wild-type (WT) and cardiomyocyte-specific β-catenin knockout (KO) mice. KO mice showed reduced susceptibility to VT (18% vs. 77% in WT) at 8 weeks after MI, associated with reduced scar size and attenuated chamber dilation. qPCR analyses of both myocardial tissues and purified cardiomyocytes demonstrated upregulation of Wnt pathway genes in border and infarct regions after MI, including Wnt ligands (such as Wnt4) and receptors (such as Fzd1 and Fzd2). At 1 week after MI, cardiac sodium channel gene (Scn5a) transcript was reduced in WT but not in KO hearts, consistent with previous studies showing Scn5a inhibition by Wnt/β-catenin signaling. At 8 weeks after MI when Wnt genes have declined, Scn5a returned to near sham levels and K⁺ channel gene downregulations were not different between WT and KO mice. This study demonstrated that VT susceptibility in the chronic phase after MI is reduced in mice with cardiomyocyte-specific β-catenin deletion primarily through attenuated structural remodeling, but not ion channel gene alterations.

Real time spectrum analysis of signals obtained through lasso catheter during radiofrequency ablation of pulmonary vein was performed to determine the channel with dominant frequency. Threshold algorithm was used for signals which could be classified as type I and type II AF. Type III AF Signals which were highly fractionated or differentiated were evaluated for frequency content by performing Fast Fourier Transform. Data from Seven patients was collected and an episode of 180 ± 40 seconds was recorded and analyzed for each pulmonary vein that showed electrical activation. Frequency spectra for one second segment of signal for each channel were determined. The frequencies of channels were then compared to determine the channel with highest or dominant frequency. In most cases the frequency of a single channel varied erratically between 1 to 10 Hz for every subsequent one second segment which made DF detection among the channels unreliable and a single channel with dominant frequency could not be determined. A five second averaging for each channel did not produce a stable DF output and improvement was minimal. The erratic frequency behavior could be attributed to the spatial shift of micro- reentrant circuits or temporal variation in waveform over lap at the point of detection. To determine the DF more precisely either an increase in number of electrode or increase in time segment block for DF calculation is warranted. Increasing the time segment block will defeat the purpose of real time analysis thus an increase in number of electrode mapping the area of interest would be appropriate to resolve the issue.

Cardiovascular disease is the leading cause of mortality in the developed world with up to fifty percent of cases being due to sudden cardiac death. Changes in sympatho-vagal balance underpin many cardiovascular conditions including heart failure and myocardial infarction. Neuraxial modulation of the autonomic nervous system is an emerging therapy to prevent ventricular arrhythmias, the main cause of sudden cardiac death. <b>Chapter One</b> reviews our current understanding of how the cardiac autonomic nervous system influences ventricular arrhythmogenesis. A particular focus was on the controversial role of cholinergic receptors and nitric oxide (NO) in parasympathetic protection from ventricular arrhythmias. Tetrahydrobiopterin (BH₄), a critical cofactor for both tyrosine hydroxylase and NO synthases, and the co-transmitter neuropeptide-Y (NPY) may also influence sympathetic triggering of ventricular arrhythmias. This leads to the specific aims of the thesis which were to determine the mechanisms of the cholinergic antifibrillatory effect, investigate the role of cotransmission in arrhythmogenesis and, the mechanistic role of BH4 in autonomic cardiovascular control. <b>Chapter Two</b> detailed the experimental approach taken to investigate the hypotheses. A novel Langendorff heart preparation was developed with intact autonomic nerves to investigate how the stable analogue of acetylcholine, carbamylcholine (CCh) raises ventricular fibrillation threshold (VFT) and whether exogenous or endogenously released NPY lowers VFT. These actions are further investigated using optical mapping, dye free imaging of ventricular cell monolayers, immunohistochemistry, ELISA assays and measurements of NO metabolite production. To investigate the role of BH4 in the sympathetic control of the heart, an IRES-cre recombinase strategy was used to produce genomic deletion of GCH1 (the gene encoding BH4) in sympathetic neurons. Biopterins and plasma catecholamines were measured using HPLC, and blood pressure and heart rate via tail cuff plethysmography. <b>Chapter 3</b> showed that CCh increased VFT, prolonged action potential duration and flattened the electrical restitution curve. This effect required stimulation of both muscarinic and nicotinic receptors and the generation of nNOS derived NO utilising a cGMP dependent pathway. These observations are in keeping with established evidence demonstrating the obligatory role of the muscarinic receptor and indicate that the role of NO is likely to be via modulation of cholinergic neurotransmission. <b>Chapter 4</b> studied the role of the sympathetic co-transmitter NPY. NPY has been shown to increase ventricular myocyte calcium dynamics. Plasma levels are also increased post myocardial infarction and during heart failure, and correlate with outcomes. Perfusion of NPY decreased VFT via a Y1 receptor dependent mechanism and increased arrhythmic activity in myocyte monolayers. Direct sympathetic stimulation resulted in NPY release and remained pro-arrhythmic despite &beta;-blockade, an effect that could be abolished by combined &beta;-Y₁ receptor blockade. These observations indicated that NPY may be a novel, pro-arrhythmic trigger amenable to therapeutic pharmacological modulation. <b>Chapter 5</b> details the generation and phenotyping of two tissue specific Gch1 knockout mouse models. Whilst one model failed to produce significant lowering of BH₄ in sympatho-adrenal tissue, the other did result in a marked neuro-motor phenotype. A biochemical rescue or alternative genomic modification approach would be required to study the cardiovascular phenotype of sympathetic Gch1 deletion in more detail. <b>Chapter 6</b> is a concluding discussion summarising the main findings of the thesis, placing them in a clinical context and discussing avenues for further research.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19606号 / 医博第4113号 / 新制||医||1015(附属図書館) / 32642 / 京都大学大学院医学研究科医学専攻 / (主査)教授 小池 薫, 教授 YOUSSEFIAN Shohab, 教授 川村 孝 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13232号 / 論医博第2172号 / 新制||医||1036(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 山下 潤, 教授 江藤 浩之, 教授 木村 剛 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

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Identifying factors associated with appropriate and inappropriate therapies in patients with implantable cardioverter-defibrillator (ICD) could help to identify those at risk and reduce the incidence of this emergency situation which has detrimental effect on mortality and morbidity in patients with ICD. These studies were designed to find the prevalence and factors associated with appropriate and inappropriate therapies in patients with ICD.