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Electrical and Computer Engineering / A high performance, wireless bio-impedance measurement system has been designed for the purpose of monitoring essential electrical properties of the heart during cardiac ablation. The system is broken into three parts: a spring-loaded device to house a tetrapolar surface probe and sensors, a wireless bio-impedance measurement system, and a desktop base station for graphical data display and acquisition. The system is specifically designed for a tetrapolar-electrode configuration where the two outer electrodes served as a current source operating at 20 kHz with an amplitude of 100 µArms and the two inner electrodes served as voltage sensing electrodes. In addition, the system also has a dedicated channel for current sense. The system is designed to be modular and reconfigurable for different measurement needs. Epochs of both discrete voltage and current samples generated by the voltage-controlled current source are processed using a digital signal processing algorithms to generate admittance measurements. In addition to the admittance’s magnitude and phase, pressure, electrocardiogram (EKG), and temperature (two channels) data are also acquired. The measurements are then wirelessly transmitted from the bio-impedance measurement system to a base station where data are processed and viewed graphically. The final system updates the admittance, pressure, EKG, and two temperature channels at 320 Hz, consumes less than 3 W, and has percent of measurement errors of 7 % and 2 % for capacitive and resistive measurements in the range of 100 pF to 10000 pF and 300 Ω to 1600 Ω, respectively. Instrument design, calibration, verification, and modeling are at the heart of this thesis. In the future, the instrument will be deployed for various bio-impedance measurements that require a high degree of linearity, precision, and a wide input range. / text

Atrioventricular nodal reentrant tachycardia (AVNRT) is an abnormal heart rhythm caused by aberrant electrical conduction within the AV node. AVNRT is the most common type of paroxysmal supraventricular tachycardia (PSVT), with approximately 50,000 new cases per year in the United States. Catheter ablation of AV node tissue has become the first-line definitive treatment for AVNRT, owing to its high efficacy, tolerability, and safety. Two modalities of ablation, radiofrequency (RF) and cryoablation are commonly utilized in clinical practice with high levels of success in treating AVNRT. To date, studies on the two modalities have compared metrics such as acute success rate, procedure time, fluoroscopy time, and recurrence of AVNRT. Recurrence of AVNRT has been observed as far as 10 years after RF ablation. In patients with a history of RF ablation for AVNRT, rates of atrial fibrillation are higher than that of the general population. However, long-term studies directly comparing RF and cryoablation outcomes do not exist. This retrospective cohort study is designed to examine the rates of AVNRT recurrence and new arrythmias in patients 10 to 15 years after receiving either RF or cryoablation. To accomplish this, eligible participants will have their medical records reviewed for documentation of AVNRT recurrence, atrial fibrillation, atrial flutter, and complete AV block requiring pacemaker implantation. In doing so, we hope to give providers more insight into the risk profiles for each modality.

<p>This thesis explores the implementation of an electromagnetic positioning system to track medical instruments used in minimally invasive surgeries. The end application is for catheter cardiac ablation. Cardiac ablation is a low-risk procedure that can correct arrhythmia. In the procedure, a diagnostic mapping catheter is inserted into the heart to identify locations causing incorrect heartbeat, and an ablation catheter applies radiofrequency (RF) thermal energy, which burns tissue that emits abnormal heart rhythm. Current techniques which determine the mapping catheter’s tip position while a patient is undergoing heart surgery are usually invasive, often inaccurate, and require some forms of imaging. </p><p><br></p> <p>Most existing electromagnetic (EM) tracking systems track a tiny sensing coil on the catheter tip by placing planar magnetic transmitters in reference locations around a patient. However, the tracking speed of these systems is extremely limited apart from deficiency in positioning accuracy due to poor sensitivity of the small sensor. In this study, we develop a unique real-time tracking system which can track the position and orientation of a medical catheter tip inside a human heart. A configuration of a small transmitting coil on the catheter tip with multiple larger receiving coils placed at reference locations is investigated. </p><p><br></p> <p>We propose a novel tracking system based on a single uniaxial transmitter (1.5 mm diameter) placed on a medical catheter tip and two triaxial receivers placed in reference locations. The electromagnetic field generated by the uniaxial transmitter is controlled by an operational amplifier LC tank driver with a unique active feedback sensing system in the form of a digital phased lock loop (DPLL), which <a>generates a low noise low distortion</a> AC signal for the LC circuit. Such control is vital because the small transmitting coil has a relatively large DC resistance, resulting in copious amounts of heat. This unique transmitter driver active feedback system is optimized to ensure a stable magnetic field transmitted with minimal noise and distortion.</p><p><br></p> <p>Precise and efficient calibration and compensation techniques are developed for the proposed system. The calibration techniques include mutual coupling correction, which rectifies one of the main limitations of a triaxial coil-based implementation. In addition, a novel divergence mitigation method for the position algorithm is developed in the form of a software-based reference sensing coil distance offset. This is advantageous compared to a hardware-based solution, which involves adding more coils to the system, in turn, leading to decreased tracking speed and higher risk of interference among coils. Because of its simplicity, the proposed EM tracking system also has the advantage of supporting a wide dynamic range, multiple catheters, and can be applied to other medical systems in need of real-time positioning.</p><p><br></p> <p>This EM tracking system is demonstrated on a test bench in a research lab and in a pre-clinical environment with a 3D-printed heart inside a phantom. The tested system features a fast update rate of 200 Hz and an average position error of 1.6 mm, which indicates that the proposed system can successfully track a catheter RF tip with millimeter precision. </p><p><br></p> <p> This dissertation presents the proposed EM tracking system. First, the motivation of this research and a review of existing tracking methodologies used in the medical field are presented. Then, the hardware design of individual modules and magnetic positioning firmware are described, which is followed by discussions of full system integration and calibration, as well as system test results. A summary, highlighting novelties of the tracking system, and discussion of future research directions are included in the final chapter.</p>

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abstract: Atrial fibrillation (AF) is the most common abnormal heart rhythm, affecting nearly 2% of the world’s population at a cost of $26 Billion in the United States annually, and incalculable costs worldwide. AF causes no symptoms for some people. However, others with AF experience uncomfortable symptoms including palpitations, breathlessness, dizziness, and fatigue. AF can severely diminish quality of life for both AF sufferers and their loved ones. Beyond uncomfortable symptoms, AF is also linked to congestive heart failure and stroke, both of which can cause premature death. Medications often fail to control AF, leading patients and healthcare providers to seek other cures, including catheter ablation. To date, catheter ablation has yielded uneven results, but garners much attention in research and innovation in pursuit of a cure for AF. This dissertation examines the historical development and contemporary practices of AF ablation to identify opportunities to improve the innovation system for the disease. First, I trace the history of AF and AF ablation knowledge from the 2nd century B.C.E. through the present. This historical look identifies patterns of knowledge co-development between science, technology, and technique, as well as publication patterns impacting knowledge dissemination. Second, I examine the current practices of AF ablation knowledge translation from the perspective of clinical practitioners to characterize the demand-side of knowledge translation in real-world practice. Demand-side knowledge translation occurs in nested patterns, and requires data, experience, and trust in order to incorporate knowledge into a practice paradigm. Third, I use social network mapping and analysis to represent the full AF ablation knowledge-practice system and identify opportunities to modify research and innovation practice in AF ablation based on i measures of centrality and power. Finally, I outline six linked recommendations using raw data capture during ablation procedures and open big data analytics, coupled with multi-stakeholder social networking approaches, to maximize innovation potential in AF ablation research and practice. / Dissertation/Thesis / Doctoral Dissertation Human and Social Dimensions of Science and Technology 2016

Las técnicas ablativas basadas en energía por radiofrecuencia (RF) se emplean con el fin de lograr un calentamiento seguro y localizado en el tejido biológico. En los últimos años ha habido un rápido crecimiento en el número de nuevos procedimientos médicos que hacen uso de dichas técnicas, lo cual ha ido acompañado de la aparición de nuevos diseños de electrodos y protocolos de aplicación de energía. Sin embargo, existen todavía muchas incógnitas sobre el verdadero comportamiento electro-térmico de los aplicadores de energía, así como de la interacción energía-tejido en aplicaciones concretas. El principal propósito de esta Tesis Doctoral es adquirir un mejor conocimiento de los fenómenos eléctricos y térmicos involucrados en los procesos de calentamiento de tejidos biológicos mediante corrientes de RF. Esto permitirá, por un lado, mejorar la eficacia y seguridad de las técnicas actualmente empleadas en la clínica en campos tan diferentes como la cirugía cardiaca, oncológica o dermatológica; y por otro, sugerir mejoras tecnológicas para el diseño de nuevos aplicadores. La Tesis Doctoral combina dos metodologías ampliamente utilizadas en el campo de la Ingeniería Biomédica, como son el modelado computacional (matemático) y la experimentación (ex vivo e in vivo). En cuanto al área cardiaca, la investigación se ha centrado, por una parte, en mejorar la ablación intraoperatoria de la fibrilación auricular por aproximación epicárdica, es decir, susceptible de ser realizada de forma mínimamente invasiva. Para ello, se ha estudiado mediante modelos matemáticos un sistema de medida de la impedancia epicárdica como método de valoración de la cantidad de grasa previo a la ablación. Por otra parte, se ha estudiado cómo mejorar la ablación de la pared ventricular por aproximación endocárdica-endocárdica (septo interventricular) y endocárdica-epicárdica (pared libre del ventrículo). Con este objetivo, se han comparado mediante modelado por computador la eficacia de los modos de ablación bipolar y unipolar en términos de la transmuralidad de la lesión en la pared ventricular. En lo que respecta al área de cirugía oncológica, la investigación se ha centrado en la resección hepática asistida por RF. Las técnicas de calentamiento por RF deberían ser capaces de minimizar el sangrado intraoperatorio y sellar vasos y ductos mediante la creación de una necrosis coagulativa por calentamiento. Si este calentamiento se produce en las cercanías de grandes vasos, existe un problema potencial de daño a la pared de dicho vaso. En este sentido, se ha evaluado con modelos matemáticos y experimentación in vivo si el efecto del flujo de sangre dentro de un gran vaso es capaz de proteger térmicamente su pared cuando se realiza una resección asistida por RF en sus cercanías. Además, se ha realizado un estudio computacional y experimental ex vivo e in vivo del comportamiento electro-térmico de aplicadores de RF bipolares internamente refrigerados, puesto que representan una opción más segura frente a los monopolares en la medida en que las corrientes de RF fluyen casi exclusivamente por el tejido biológico situado entre ambos electrodos. Respecto al área dermatológica, la investigación se ha centrado en mejorar el tratamiento de enfermedades o desórdenes del tejido subcutáneo (tales como lipomatosis, lipedema, enfermedad de Madelung y celulitis) mediante el estudio teórico de la dosimetría correcta en cada caso. Para ello, se han evaluado los efectos eléctricos, térmicos y termo-elásticos de dos estructuras diferentes de tejido subcutáneo durante el calentamiento por RF, y se ha cuantificado el daño térmico producido en ambas estructuras tras dicho calentamiento / González Suárez, A. (2014). Computational Models and Experimentation for Radiofrequency-based Ablative Techniques [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36502 / TESIS