Development of High Resolution Tools for Investigating Cardiac Arrhythmia Dynamics

Every year 300,000 Americans die due to sudden cardiac death. There are many pathologies, acquired and genetic, that can lead to sudden cardiac death. Regardless of the underlying pathology, death is frequently the result of ventricular tachycardia and/or fibrillation (VT/VF). Despite decades of research, the mechanisms of ventricular arrhythmia initiation and maintenance are still incompletely understood. A contributing factor to this lack of understanding is the limitations of the investigative tools used to study VT/VF. Arrhythmias are organ level phenomena that are governed by cellular interactions and as such, near cellular levels of resolution are needed to tease out their intricacies. They are also behaviors that are not limited by region, but dynamically affect the entirety of the heart. For these reasons, high-resolution methodologies capable of measuring electrophysiology of the whole entirety of the ventricles will play an important role in gaining a complete understanding of the principles that govern ventricular arrhythmia dynamics. They will also be essential in the development of novel therapies for arrhythmia management. In this dissertation, I first present the validation and characterization of a novel capacitive electrode design that overcomes the key limitations faced by modern implantable cardiac devices. I then outline the construction, methodologies, and open-source tools of an improved optical panoramic mapping system for small mammalian cardiac electrophysiology studies. I conclude with a small mammal study of the relationship between action potential duration restitution dynamics and the mechanisms of maintenance in ventricular arrhythmias

Quantification of the transmural dynamics of atrial fibrillation by simultaneous endocardial and epicardial optical mapping in an acute sheep model

BACKGROUND: Therapy strategies for atrial fibrillation based on electrical characterization are becoming viable personalized medicine approaches to treat a notoriously difficult disease. In light of these approaches that rely on high-density surface mapping, this study aims to evaluate the presence of three-dimensional electrical substrate variations within the transmural wall during acute episodes of atrial fibrillation. METHODS AND RESULTS: Optical signals were simultaneously acquired from the epicardial and endocardial tissue during acute fibrillation in ovine isolated left atria. Dominant frequency, regularity index, propagation angles and phase dynamics were assessed and correlated across imaging planes to gauge the synchrony of the activation patterns compared to paced rhythms. Static frequency parameters were well correlated spatially between the endocardium and the epicardium (dominant frequency, 0.79+/-0.06 and regularity index, 0.93+/-0.009). However, dynamic tracking of propagation vectors and phase singularity trajectories revealed discordant activity across the transmural wall. The absolute value of the difference in the number, spatial stability, and temporal stability of phase singularities between the epicardial and endocardial planes was significantly greater than 0 with a median difference of 1.0, 9.27%, and 19.75%, respectively. The number of wavefronts with respect to time was significantly less correlated and the difference in propagation angle was significantly larger in fibrillation compared to paced rhythms. CONCLUSIONS: Atrial fibrillation substrates are dynamic three-dimensional structures with a range of discordance between the epicardial and endocardial tissue. The results of this study suggest that transmural propagation may play a role in AF maintenance mechanisms

Influence of cardiac tissue anisotropy on re-entrant activation in computational models of ventricular fibrillation

The aim of this study was to establish the role played by anisotropic diffusion in (i) the number of filaments and epicardial phase singularities that sustain ventricular fibrillation in the heart, (ii) the lifetimes of filaments and phase singularities, and (iii) the creation and annihilation dynamics of filaments and phase singularities. A simplified monodomain model of cardiac tissue was used, with membrane excitation described by a simplified 3-variable model. The model was configured so that a single re-entrant wave was unstable, and fragmented into multiple re-entrant waves. Re-entry was then initiated in tissue slabs with varying anisotropy ratio. The main findings of this computational study are: (i) anisotropy ratio influenced the number of filaments Sustaining simulated ventricular fibrillation, with more filaments present in simulations with smaller values of transverse diffusion coefficient, (ii) each re-entrant filament was associated with around 0.9 phase singularities on the surface of the slab geometry, (iii) phase singularities were longer lived than filaments, and (iv) the creation and annihilation of filaments and phase singularities were linear functions of the number of filaments and phase singularities, and these relationships were independent of the anisotropy ratio. This study underscores the important role played by tissue anisotropy in cardiac ventricular fibrillation

High Resolution Multi-parametric Diagnostics and Therapy of Atrial Fibrillation: Chasing Arrhythmia Vulnerabilities in the Spatial Domain

After a century of research, atrial fibrillation (AF) remains a challenging disease to study and exceptionally resilient to treatment. Unfortunately, AF is becoming a massive burden on the health care system with an increasing population of susceptible elderly patients and expensive unreliable treatment options. Pharmacological therapies continue to be disappointingly ineffective or are hampered by side effects due to the ubiquitous nature of ion channel targets throughout the body. Ablative therapy for atrial tachyarrhythmias is growing in acceptance. However, ablation procedures can be complex, leading to varying levels of recurrence, and have a number of serious risks. The high recurrence rate could be due to the difficulty of accurately predicting where to draw the ablation lines in order to target the pathophysiology that initiates and maintains the arrhythmia or an inability to distinguish sub-populations of patients who would respond well to such treatments. There are electrical cardioversion options but there is not a practical implanted deployment of this strategy. Under the current bioelectric therapy paradigm there is a trade-off between efficacy and the pain and risk of myocardial damage, all of which are positively correlated with shock strength. Contrary to ventricular fibrillation, pain becomes a significant concern for electrical defibrillation of AF due to the fact that a patient is conscious when experiencing the arrhythmia. Limiting the risk of myocardial injury is key for both forms of fibrillation. In this project we aim to address the limitations of current electrotherapy by diverging from traditional single shock protocols. We seek to further clarify the dynamics of arrhythmia drivers in space and to target therapy in both the temporal and spatial domain; ultimately culminating in the design of physiologically guided applied energy protocols. In an effort to provide further characterization of the organization of AF, we used transillumination optical mapping to evaluate the presence of three-dimensional electrical substrate variations within the transmural wall during acutely induced episodes of AF. The results of this study suggest that transmural propagation may play a role in AF maintenance mechanisms, with a demonstrated range of discordance between the epicardial and endocardial dynamic propagation patterns. After confirming the presence of epi-endo dyssynchrony in multiple animal models, we further investigated the anatomical structure to look for regional trends in transmural fiber orientation that could help explain the spectrum of observed patterns. Simultaneously, we designed and optimized a multi-stage, multi-path defibrillation paradigm that can be tailored to individual AF frequency content in the spatial and temporal domain. These studies continue to drive down the defibrillation threshold of electrotherapies in an attempt to achieve a pain-free AF defibrillation solution. Finally, we designed and characterized a novel platform of stretchable electronics that provide instrumented membranes across the epicardial surface or implanted within the transmural wall to provide physiological feedback during electrotherapy beyond just the electrical state of the tissue. By combining a spatial analysis of the arrhythmia drivers, the energy delivered and the resulting damage, we hope to enhance the biophysical understanding of AF electrical cardioversion and xiii design an ideal targeted energy delivery protocol to improve upon all limitations of current electrotherapy

Cardiac Remodeling Of Conduction, Repolarization and Excitation-Contraction Coupling: From Animal Model to Failing Human Heart

Heart failure is one of the leading causes of death worldwide, with rising impact with the increasing ageing population. This is in sharp contrast with the limited and non-ideal therapies available. Approximately 50% of deaths from heart failure are sudden and unexpected, and presumably the consequence of lethal ventricular arrhythmias. Despite significant reduction of mortality from sudden cardiac death achieved by ICDs and drugs such as beta-blockers, there remains a large room for improving the survivability of heart failure patients by advancing our understanding of arrhythmogenesis from molecular level to multi-cellular tissue level. Another important aspect of heart failure is abnormal excitation-contraction: EC) coupling and calcium handling, functional changes of which exert great impact on both arrhythmia vulnerability and pump failure. Advancing the understanding the remodeling of EC coupling and calcium handling might provide potential molecular and anatomical targets for clinical intervention. In this dissertation, I first developed two optical imaging systems: both hardware and software) for quantifying the conduction, repolarization and excitation-contraction coupling. The first one is the panoramic imaging system for mapping the entire ventricular epicardium of a rabbit heart. The second one is the dual imaging system for simultaneous measurement of action potential and calcium transient. Using the systems I developed, I conducted two rabbit studies to investigate the role electrical instability and structural heterogeneity in the induction and maintenance of arrhythmias. We first identified the importance of both dynamic instability and effective tissue size in the spontaneous termination of arrhythmia in the normal rabbit heart. We then identified novel mechanism of how healed myocardial infarction promotes the induction of ventricular arrhythmia. Finally, guided by the knowledge from the animal studies, I studied the failing human heart with the aim to advance our understanding of cardiac electrophysiology in human heart failure. We first demonstrated the transmural heterogeneity of EC coupling in nonfailing heart and identified potential mechanisms of electrical and mechanical dysfunction by quantifying the remodeling of EC coupling. We then studied the remodeling of conduction and repolarization with the aim to determine of the role of dispersion of repolarization and electrical instability in the induction of arrhythmia in human heart failure

Instantaneous Amplitude and Frequency Modulations Detect the Footprint of Rotational Activity and Reveal Stable Driver Regions as Targets for Persistent Atrial Fibrillation Ablation

RATIONALE: Costly proprietary panoramic multielectrode (64-256) acquisition systems are being increasingly used together with conventional electroanatomical mapping systems for persistent atrial fibrillation (PersAF) ablation. However, such approaches target alleged drivers (rotational/focal) regardless of their activation frequency dynamics. OBJECTIVES: To test the hypothesis that stable regions of higher than surrounding instantaneous frequency modulation (iFM) drive PersAF and determine whether rotational activity is specific for such regions. METHODS AND RESULTS: First, novel single-signal algorithms based on instantaneous amplitude modulation (iAM) and iFM to detect rotational-footprints without panoramic multielectrode acquisition systems were tested in 125 optical movies from 5 ex vivo Langendorff-perfused PersAF sheep hearts (sensitivity/specificity, 92.6/97.5%; accuracy, 2.5-mm) and in computer simulations. Then, 16 pigs underwent high-rate atrial pacing to develop PersAF. After a median (interquartile range [IQR]) of 4.4 (IQR, 2.5-9.9) months of high-rate atrial pacing followed by 4.1 (IQR, 2.7-5.4) months of self-sustained PersAF, pigs underwent in vivo high-density electroanatomical atrial mapping (4920 [IQR, 4435-5855] 8-second unipolar signals per map). The first 4 out of 16 pigs were used to adapt ex vivo optical proccessing of iFM/iAM to in vivo electrical signals. In the remaining 12 out of 16 pigs, regions of higher than surrounding average iFM were considered leading-drivers. Two leading-driver + rotational-footprint maps were generated 2.6 (IQR, 2.4-2.9) hours apart to test leading-driver spatiotemporal stability and guide ablation. Leading-driver regions (2.5 [IQR, 2.0-4.0] regions/map) exactly colocalized (95.7%) in the 2 maps, and their ablation terminated PersAF in 92.3% of procedures (radiofrequency until termination, 16.9 [IQR, 9.2-35.8] minutes; until nonsustainability, 20.4 [IQR, 12.8-44.0] minutes). Rotational-footprints were found at every leading-driver region, albeit most (76.8% [IQR, 70.5%-83.6%]) were located outside. Finally, the translational ability of this approach was tested in 3 PersAF redo patients. CONCLUSIONS: Both rotational-footprints and spatiotemporally stable leading-driver regions can be located using iFM/iAM algorithms without panoramic multielectrode acquisition systems. In pigs, ablation of leading-driver regions usually terminates PersAF and prevents its sustainability. Rotational activations are sensitive but not specific to such regions. Single-signal iFM/iAM algorithms could be integrated into conventional electroanatomical mapping systems to improve driver detection accuracy and reduce the cost of patient-tailored/mechanistic approaches.This study was supported by the European Regional Development Fund and the Spanish Ministry of Science, Innovation and Universities (SAF2016-80324-R). The CNIC is supported by the Spanish Ministry of Science, Innovation and Universities and the Pro-CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505).S

Spatiotemporal Control of Human Cardiac Tissue Through Optogenetics

Cardiac arrhythmias are caused by disordered propagation of electrical activity. Progress in understanding and controlling arrhythmias requires novel methods to characterize and control the spatiotemporal propagation of electrical activity. We used patterned illumination of cardiomyocytes derived from optogenetic human induced pluripotent stem cells to create dynamic conduction blocks, and to test spatially extended control schemes. Using this model, we demonstrated the ability to initiate, circumscribe, relocate, and terminate pathologic spiral waves that drive many arrhythmias. When cells were derived from patients with long QT syndrome, longer action potential durations made spiral waves more resistant to termination. This work lays the foundation for personalized models of cardiac injury and disease, and the development of tailored approaches to the management of arrhythmias

EFFECTS OF SPATIAL RESOLUTION ON ARRHYTHMIA DRIVERS’ DETECTION AND LOCALIZATION: INTER-ELECTRODE RECOMMENDATIONS FOR CARDIAC ELECTROPHYSIOLOGICAL MAPPING DEVICES

Arrhythmia is a cardiac rhythm disorder that can be fatal. Its treatment includes ablation of the cardiac tissue and/or defibrillation. Advances are being made for both treatment options to localize the culprit region and apply therapy directly where it is needed. However, success rates have been inconsistent, with frequent arrhythmia recurrence. A likely reason is the limited current resolution of mapping devices, that averages 4 mm. Higher resolution may improve localization of arrhythmia drivers, termed rotors, and consequently improve efficacy of treatment. This study evaluates the effects of spatial resolution on arrhythmia dynamics, rotor tracking, and rotor localization. Optical data from ex vivo human hearts was used, being clinically relevant and with ultra-high spatial resolution. To simulate different resolutions, original data was downsampled bymultiple factors and upsampled back to full resolution. Rotors were tracked for each sub-resolution and compared to the rotors in the original data. Further comparisons were made according to arrhythmia type, sex, anatomical region, and mapped surface. Accuracy profiles were created for both rotor detection and localization, describing how accuracy changed with spatial resolution and spatial accuracy. Rotor detection accuracy for currently used mapping devices was found to be 57±4%. Localization accuracy is 61±7%. Detection accuracy was above 80% only for a resolution of 1.4 mm. Moreover, the detection and localization accuracies were affected by arrhythmia type, and rotor incidence was found to be higher in the endocardium. Therefore, current clinical rotor detection and localization accuracies can be expected to fall within a confidence interval of 47-67% and 46-75%, respectively. This means that a higher spatial resolution is needed in cardiac mapping devices than what is currently available. For high accuracy, a resolution of at least 1.4 mm is required. The accuracy profiles provided in this thesis may serve as a guideline for future mapping device developmentArritmia é um distúrbio do ritmo cardíaco que pode ser fatal. O seu tratamento passa por ablação do tecido cardíaco e/ou desfibrilhação. Tem havido progressos em ambas as opções para localizar a região afetada e aplicar a terapia diretamente onde é requerida. Contudo, a taxa de sucesso tem sido inconsistente, com frequente recorrência das arritmias. Uma razão provável é a limitada resolução atual dos dispositivos de mapeamento, sendo, em média, de 4 mm. Uma maior resolução poderá melhorar a localização de catalisadores de arritmias, designados por rotores, e, consequentemente, melhorar a eficácia do tratamento. Este estudo avalia os efeitos da resolução espacial na dinâmica de arritmias e na localização e deteção de rotores. Dados óticos de corações humanos ex vivo foram usados, tendo alta resolução espacial e sendo clinicamente relevantes. De modo a simular diferentes resoluções, os dados recolhidos foram downsampled por vários fatores e upsampled de volta para a resolução original. Os rotores foram monitorizados para cada sub-resolução e comparados com os rotores dos dados originais. Outras comparações foram feitas em consideração com tipo de arritmia, sexo, região anatómica e superfície mapeada. Perfis de exatidão foram criados para a deteção e localização de rotores, de forma a descrever as alterações na exatidão face à resolução especial e exatidão espacial. A exatidão da deteção de rotores para os atuais dispositivos de mapeamento é de 57±4%. A exatidão da localização é de 61±7%. A precisão da deteção foi acima de 80% apenas para uma resolução de 1,4 mm. Adicionalmente, as exatidões de deteção e localização foram afetadas pelo tipo de arritmia e a incidência de rotores é maior no endocárdio. Portanto, as atuais exatidões clínicas de deteção e localização de rotores encontram-se num intervalo de confiança de 47-67% e 46-75%, respetivamente. Ou seja, é necessária uma maior resolução espacial nos dispositivos cardíacos de mapeamento do que existe atualmente. Para uma alta precisão, é necessária uma resolução de pelo menos 1.4 mm. Os perfis de exatidão disponibilizados nesta tese poderão servir como diretriz para o futuro desenvolvimento de dispositivos médicos de mapeamento cardíaco

Effects of Bepridil on Spiral Reentry

Bepridil is effective for conversion of atrial fibrillation to sinus rhythm and in the treatment of drug-refractory ventricular tachyarrhythmias. We investigated the effects of bepridil on electrophysiological properties and spiral-wave (SW) reentry in a 2-dimensional ventricular muscle layer of isolated rabbit hearts by optical mapping. Ventricular tachycardia (VT) induced in the presence of bepridil (1 μM) terminated earlier than in the control. Bepridil increased action potential duration (APD) by 5% – 8% under constant pacing and significantly increased the space constant. There was a linear relationship between the wavefront curvature (κ) and local conduction velocity: LCV = LCV0 − D·κ (D, diffusion coefficient; LCV0, LCV at κ = 0). Bepridil significantly increased D and LCV0. The regression lines with and without bepridil crossed at κ = 20 – 40 cm−1, resulting in a paradoxical decrease of LCV at κ > 40 cm−1. Dye transfer assay in cultured rat cardiomyocytes confirmed that bepridil increased intercellular coupling. SW reentry in the presence of bepridil was characterized by decremental conduction near the rotation center, prominent drift, and self-termination by collision with boundaries. These results indicate that bepridil causes an increase of intercellular coupling and a moderate APD prolongation, and this combination compromises wavefront propagation near the rotation center of SW reentry, leading to its drift and early termination