<p>The role of cardiac tissue structure in both normal and abnormal impulse conduction has been extensively studied by researchers in cardiac electrophysiology. However, much is left unknown on how specific micro- and macroscopic structural features affect conduction and conduction block. Progress in this field is constrained by the inability to simultaneously assess intramural cardiac structure and function, as well as the intrinsic complexity and variability of intact tissue preparations. Cultured monolayers of cardiac cells, on the other hand, present a well-controlled in vitro model system that provides the necessary structural and functional simplifications to enable well-defined studies of electrical phenomena. In this thesis, I developed a novel, reproducible cell culture system that accurately replicates the realistic microstructure of cardiac tissues. This system was then applied to systematically explore the influence of natural structure (e.g. tissue boundaries, expansions, local fiber directions) on normal and arrhythmogenic electrical conduction.</p><p>Specifically, soft lithography techniques were used to design cell cultures based on microscopic DTMRI (diffusion tensor magnetic resonance imaging) measurements of fiber directions in murine ventricles. Protein micropatterns comprised of mosaics of square pixels with angled lines that followed in-plane cardiac fiber directions were created to control the adhesion and alignment of cardiac cells on a two-dimensional substrate. The high accuracy of cell alignment in the resulting micropatterned monolayers relative to the original DTMRI-measured fiber directions was validated using immunofluorescence and image processing techniques.</p><p>Using this novel model system, I first examined how specific structural features of murine ventricles influence basic electrical conduction. (1) Realistic ventricular tissue boundaries, either alone or with (2) microscopic fiber directions were micropatterned to distinguish their individual functional roles in action potential propagation. By optically mapping membrane potentials and applying low-rate pacing from multiple sites in culture, I found that ventricular tissue boundaries and fiber directions each shaped unique spatial patterns of impulse propagation and additively increased the spatial dispersion of conduction velocity.</p><p>To elucidate the roles that natural tissue structure play in arrhythmogenesis, I applied rapid-rate pacing from multiple sites in culture in an attempt to induce unidirectional conduction block remote from the pacing site--a precursor to reentry. The incidence of remote block was found to be highly dependent on the direction of wave propagation relative to the underlying tissue structure, and with a susceptibility that was synergistically increased by both realistic tissue boundaries and fiber directions. Furthermore, all instances of remote block in these micropatterned cultures occurred at the anterior and posterior junctions of the septum and right ventricular free wall. At these sites, rapid excitation yielded more abrupt conduction slowing and promoted wavefront-waveback interactions that ultimately evolved into transmural lines of conduction block. The location and shape of these lines of block was found to strongly correlate with the spatial distribution of the electrotonic source-load mismatches introduced by ventricular structures, such as tissue expansions and sharp turns in fiber direction.</p><p>In summary, the overall objective of the work described in this thesis was to reveal the distinct influences of realistic cardiac tissue structure on action potential conduction and conduction block by engineering neonatal rat cardiomyocyte monolayers that reproducibly replicated the anatomical details of murine ventricular cross-sections. In the future, this novel model system is expected to further our understanding of structure-function relationships in normal and structurally diseased hearts, and possibly enable the development of novel gene, cell, and ablation therapies for cardiac arrhythmias.</p> / Dissertation

A neuropatia motora multifocal (NMM) é uma neuropatia inflamatória de baixa prevalência, 0,6/100.000 pacientes, caracterizada por uma fraqueza muscular progressiva, assimétrica e distal, sem comprometimento sensitivo. A NMM pode mimetizar a esclerose lateral amiotrófica (ELA), outras variantes da doença do neurônio motor e outras polineuropatias inflamatórias desmielinizantes crônicas, com início assimétrico. A diferenciação é importante, tendo em vista as especificidades da evolução e do tratamento das referidas neuropatias. O principal achado eletrofisiológico é o bloqueio de condução nervosa na ausência de anormalidades sensitivas. A fisiopatogenia da NMM é pouco conhecida. O frequente achado de anticorpos circulantes contra o monoassialogangliosídeo (GM1) é sugestivo de que possa haver seu comprometimento em alterações estruturais nodais e perinodais, com comprometimento multifocal da condução nervosa. O corolário desses distúrbios são paresias e paralisias, também de distribuição multifocal. A Imunoglobulina humana por via endovenosa em altas doses constitui o tratamento de escolha. Novas estratégias de tratamento alternativas são necessárias para prevenir fraqueza muscular permanente e incapacidade. Poucos estudos e revisões bibliográficas têm elucidado as características clínicas da NMM, com a ausência na literatura de publicações de série de casos nacionais. No presente estudo, a partir de uma revisão retrospectiva, serão avaliados os aspectos clínicos- eletrofisiológicos da NMM, a fim de se obter um maior entendimento da evolução da doença. / The multifocal motor neuropathy (MMN) is an inflammatory neuropathy that has low prevalence (0.6 / 100,000 patients). It is characterized by progressive, asymmetric and distal muscle weakness without sensory impairment. The MMN can mimic amyotrophic lateral sclerosis (ALS), other motor neuron disease variants and other chronic inflammatory demyelinating polyneuropathy, with asymmetric start. Differentiation is important, given the specificities of the development and treatment of these neuropathies. The main electrophysiological finding is the nerve conduction block in the absence of sensory abnormalities. The pathophysiology of MMN is little known. The frequent finding of circulating antibodies against monoassialogangliosides (GM1) is suggestive that there may be their involvement in nodal and perinodal structural changes with multifocal impairment of nerve conduction. The corollary of these disorders is paresis and paralysis, with also multifocal distribution. The human immunoglobulin intravenously in high doses constitutes the treatment of choice. New alternative treatment strategies are needed to prevent permanent muscle weakness and disability. Few studies and literature reviews have elucidated the clinical features of MMN and there are no case series publications in the national literature. In this study, from a retrospective review, will be assessed clinic and electrophysiological features of MMN in order to obtain a greater understanding of disease progression.

A neuropatia motora multifocal (NMM) é uma neuropatia inflamatória de baixa prevalência, 0,6/100.000 pacientes, caracterizada por uma fraqueza muscular progressiva, assimétrica e distal, sem comprometimento sensitivo. A NMM pode mimetizar a esclerose lateral amiotrófica (ELA), outras variantes da doença do neurônio motor e outras polineuropatias inflamatórias desmielinizantes crônicas, com início assimétrico. A diferenciação é importante, tendo em vista as especificidades da evolução e do tratamento das referidas neuropatias. O principal achado eletrofisiológico é o bloqueio de condução nervosa na ausência de anormalidades sensitivas. A fisiopatogenia da NMM é pouco conhecida. O frequente achado de anticorpos circulantes contra o monoassialogangliosídeo (GM1) é sugestivo de que possa haver seu comprometimento em alterações estruturais nodais e perinodais, com comprometimento multifocal da condução nervosa. O corolário desses distúrbios são paresias e paralisias, também de distribuição multifocal. A Imunoglobulina humana por via endovenosa em altas doses constitui o tratamento de escolha. Novas estratégias de tratamento alternativas são necessárias para prevenir fraqueza muscular permanente e incapacidade. Poucos estudos e revisões bibliográficas têm elucidado as características clínicas da NMM, com a ausência na literatura de publicações de série de casos nacionais. No presente estudo, a partir de uma revisão retrospectiva, serão avaliados os aspectos clínicos- eletrofisiológicos da NMM, a fim de se obter um maior entendimento da evolução da doença. / The multifocal motor neuropathy (MMN) is an inflammatory neuropathy that has low prevalence (0.6 / 100,000 patients). It is characterized by progressive, asymmetric and distal muscle weakness without sensory impairment. The MMN can mimic amyotrophic lateral sclerosis (ALS), other motor neuron disease variants and other chronic inflammatory demyelinating polyneuropathy, with asymmetric start. Differentiation is important, given the specificities of the development and treatment of these neuropathies. The main electrophysiological finding is the nerve conduction block in the absence of sensory abnormalities. The pathophysiology of MMN is little known. The frequent finding of circulating antibodies against monoassialogangliosides (GM1) is suggestive that there may be their involvement in nodal and perinodal structural changes with multifocal impairment of nerve conduction. The corollary of these disorders is paresis and paralysis, with also multifocal distribution. The human immunoglobulin intravenously in high doses constitutes the treatment of choice. New alternative treatment strategies are needed to prevent permanent muscle weakness and disability. Few studies and literature reviews have elucidated the clinical features of MMN and there are no case series publications in the national literature. In this study, from a retrospective review, will be assessed clinic and electrophysiological features of MMN in order to obtain a greater understanding of disease progression.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis describes a novel method to reversibly and safely block nerve conduction using a low frequency alternating current (LFAC) waveform at 1 Hz applied through a bipolar extrafascicular electrode. This work follows up on observations made on excised mammalian peripheral nerves and earthworm nerve cords. An in-situ electrophysiology setup was used to assess the LFAC waveform on propagating action potentials (APs) within the cervical vagus nerve in anaesthetized Sprague-Dawley rats (n = 12). Two sets of bipolar cuff or hook electrodes were applied unilaterally to the cervical vagus nerve, which was crushed rostral to the electrodes to exclude reflex effects on the animal. Pulse stimulation was applied to the rostral electrode, while the LFAC conditioning waveform was applied to the caudal electrode. The efferent volley, if unblocked, elicits acute bradycardia and hypotension. The degree of block of the vagal stimulation induced bradycardia was used as a biomarker. Block was assessed by the ability to reduce the bradycardic drive by monitoring the heart rate (HR) and blood pressure (BP) during LFAC alone, LFAC with vagal stimulation, and vagal stimulation alone. LFAC applied via a hook electrode (n = 7) achieved 86.6 +/- 11% block at current levels 95 +/- 38 uAp (current to peak). When applied via a cuff electrode (n = 5) 85.3 +/- 4.60% block was achieved using current levels of 110+/-65 uAp. Furthermore, LFAC was explored on larger vagal afferent fibers in larger human sized nerve bundles projecting to effects mediated by a reflex. The effectiveness of LFAC was assessed in an in-situ electrophysiological setup on the left cervical vagus in anaesthetized domestic swine (n = 5). Two bipolar cuff electrodes were applied unilaterally to the cervical vagus nerve, which was crushed caudal to the electrodes to eliminate cardiac effects. A tripolar extrafascicular cuff electrode was placed most rostral on the nerve for recording of propagating APs induced by electrical stimulation and blocked via the LFAC waveform. Standard pulse stimulation was applied to the left cervical vagus to induce the Hering-Breuer reflex. If unblocked, the activation of the Hering-Breuer reflex would cause breathing to slow down and potentially cease. Block was quantified by the ability to reduce the effect of the Hering-Breuer reflex by monitoring the breathing rate during LFAC alone, LFAC and vagal stimulation, and vagal stimulation alone. LFAC achieved 87.2 +/- 8.8% (n = 5) block at current levels of 0.8 +/- 0.3 mAp. Compound nerve action potentials (CNAP) were monitored directly. They show changes in nerve activity during LFAC, which manifests itself as the slowing and amplitude reduction of components of the CNAPs. Since the waveform is balanced, all forward reactions are reversed, leading to a blocking method that is similar in nature to DC block without the potential issues of toxic byproduct production. These results suggest that LFAC can achieve a high degree of nerve block in both small and large nerve bundles, resulting in the change in behavior of a biomarker, in-vivo in the mammalian nervous system at low amplitudes of electrical stimulation that are within the water window of the electrode.

En utilisant la méthode de génétique inverse, la mutation causale d'un bloc de conduction cardiaque familial a été localisée sur le bras long du chromosome 19 en 13.3 dans une grande famille libanaise. Après avoir testé 12 gènes candidats, nous avons trouvé 3 mutations différentes dans trois familles indépendantes de bloc de conduction cardiaque isolé. Les conséquences des 3 mutations ont été explorées par des études électrophysiologiques. Il s'agit dans les 3 cas d'un gain de fonction. Puis, une cohorte de 248 patients atteints de syndrome de Brugada a été étudiée. Onze mutations du gène TRPM4 ont été trouvées chez 20 patients. Les conséquences électrophysiologiques des mutations étaient diverses. Ensuite, des cohortes de patients atteints de syndrome du QT long, de fibrillation auriculaire ou de cardiomyopathie dilaté ont été étudiées. Nous avons également trouvé des mutations ou des variants prédisposants du gène TRPM4 chez ces patients. Une étude électrophysiologique doit être réalisée pour comprendre le rôle de TRPM4 dans ces autres pathologies. Enfin, notre étude immunohistochimique a démontré que TRPM4 est fortement exprimé dans le système de conduction cardiaque mais aussi plus faiblement dans les cardiomyocytes auriculaires et ventriculaires communs. Ce travail a permis d'impliquer pour la première fois le gène TRPM4 dans des maladies humaines. Ce travail donne les bases pour comprendre le rôle du canal TRPM4 dans le fonctionnement cardiaque. C'est le préalable nécessaire avant de pouvoir développer de nouvelles thérapeutiques dans le futur / By using reverse genetics, the causal mutation of a familial cardiac conduction block was localized to the long arm of chromosome 19 in 13.3. After screening 12 candidate genes, we found 3 different mutations in three independent families with isolated cardiac conduction block. The consequences of these 3 mutations were explored by electrophysiological studies. In all 3 mutations it was a gain of function. Then, a cohort of 248 patients with a Brugada syndrome was studied. Eleven mutations were found in the TRPM4 gene in 20 patients. The electrophysiological consequences of these mutations were diverse. Then, cohorts of patients with long QT syndrome, atrial fibrillation, and dilated cardiomyopathy were studied. We found also mutations or predisposing variants in these patients. An electrophysiology study should be conducted to understand the role of TRPM4 in these other pathologies. Finally, our immunohistochemical study showed that TRPM4 is highly expressed in the cardiac conduction system but also although with less intensity in common auricular and ventricular cardiomyocytes. This work implied for the first time the TRPM4 gene in human diseases. This work provides the basis to understand the role of the TRPM4 channel in cardiac function. This is a prerequisite to be able to develop novel therapies in the future

5 Abstract: Aims: The main objective of this work was to analyze in detail the effects of acute temperature changes on the function of isolated chick embryonic heart in vitro in comparison with natural conditions in ovo. Methods: The effects of temperature change (34 řC, 37 řC and 40 řC - hypo-, normo- and hyperthermia, respectively) on calcium dynamics in four days old isolated chick hearts in vitro were investigated by high-speed calcium optical imaging. For comparison and validation of in vitro measurements, experiments were also performed in ovo using videomicroscopy. Artificial electrical stimulation experiments were performed in vitro and in ovo to uncover conduction limits of different heart segments. Results: We observed almost linear dependence of sinus frequency on temperature in our temperature range. Sinus frequency during hypothermia and hyperthermia in vitro and in ovo changed about 20% in comparison with normothermia. We observed no significant changes in amplitude of calcium transients during temperature change to hypothermia but hyperthermia caused a significant decrease in amplitude of calcium transients (atria 35%, ventricles 38%). We observed a wide spectrum of arrhythmias, which occurred spontaneously even during normothermia in vitro. Occurrence of arrhythmias in vitro significantly...

This thesis describes a novel method to reversibly and safely block nerve conduction using a low frequency alternating current (LFAC) waveform at 1 Hz applied through a bipolar extrafascicular electrode. This work follows up on observations made on excised mammalian peripheral nerves and earthworm nerve cords. An<i> in-situ</i> electrophysiology setup was used to assess the LFAC<br>waveform on propagating action potentials (APs) within the cervical vagus nerve in anaesthetized Sprague-Dawley rats (n = 12). Two sets of bipolar cuff or hook electrodes were applied unilaterally to the cervical vagus nerve, which was crushed rostral to the electrodes to exclude reflex effects<br>on the animal. Pulse stimulation was applied to the rostral electrode, while the LFAC conditioning waveform was applied to the caudal electrode. The efferent volley, if unblocked, elicits acute bradycardia and hypotension. The degree of block of the vagal stimulation induced bradycardia<br>was used as a biomarker. Block was assessed by the ability to reduce the bradycardic drive by monitoring the heart rate (HR) and blood pressure (BP) during LFAC alone, LFAC with vagal stimulation, and vagal stimulation alone. LFAC applied via a hook electrode (n = 7) achieved 86.6 +/- 11% block at current levels 95 +/- 38 uAp (current to peak). When applied via a cuff electrode (n = 5) 85.3 +/- 4.60% block was achieved using current levels of 110 +/- 65 uAp. Furthermore, LFAC was explored on larger vagal afferent fibers in larger human sized nerve bundles projecting to effects mediated by a reflex. The effectiveness of LFAC was assessed in an <i>in-situ</i> electrophysiological setup on the left cervical vagus in anaesthetized domestic swine (n = 5). Two bipolar cuff electrodes were applied unilaterally to the cervical vagus nerve, which was crushed caudal to the electrodes to eliminate cardiac effects. A tripolar extrafascicular cuff electrode was placed most rostral on the nerve for recording of propagating APs induced by<br>electrical stimulation and blocked via the LFAC waveform.<br>Standard pulse stimulation was applied to the left cervical vagus to induce the Hering-Breuer reflex. If unblocked, the activation of the Hering-Breuer reflex would cause breathing to slow down and potentially cease. Block was quantified by the ability to reduce the effect of the Hering-Breuer<br>reflex by monitoring the breathing rate during LFAC alone, LFAC and vagal stimulation, and vagal stimulation alone. LFAC achieved 87.2 +/- 8.8% (n = 5) block at current levels of 0.8 +/- 0.3 mAp. Compound nerve action potentials (CNAP) were monitored directly. They show changes<br>in nerve activity during LFAC, which manifests itself as the slowing and amplitude reduction of components of the CNAPs. Since the waveform is balanced, all forward reactions are reversed, leading to a blocking method that is similar in nature to DC block without the potential issues of<br>toxic byproduct production. These results suggest that LFAC can achieve a high degree of nerve block in both small and large nerve bundles, resulting in the change in behavior of a biomarker, <i>in-vivo </i>in the mammalian nervous system at low amplitudes of electrical stimulation that are within the water window of the electrode.<br>