Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biomedical Engineering

Supervisor

Drangova, Maria

Abstract

Atrial fibrillation (AF), the most common and clinically significant heart rhythm disorder, is characterized by rapid and irregular electrical activity in the upper chambers resulting in abnormal contractions. Radiofrequency (RF) cardiac catheter ablation is a minimally invasive curative treatment that aims to electrically correct signal pathways inside the atria to restore normal sinus rhythm. Successful catheter ablation requires the complete and permanent elimination of arrhythmogenic signals by delivering transmural RF ablation lesions contiguously near and around key cardiac structures. These procedures are complex and technically challenging and, even when performed by the most skilled physician, nearly half of patients undergo repeat procedures due to incomplete elimination of the arrhythmogenic pathways. This thesis aims to incorporate innovative design to improve catheter stability and maneuverability through the development of robotic platforms that enable precise placement of reproducibly durable ablation lesions.

The first part of this thesis deals with the challenges to lesion delivery imposed by cardiorespiratory motion. One of the main determinants of the delivery of durable and transmural RF lesions is the ability to define and maintain a constant contact force between the catheter tip electrode and cardiac tissue, which is hampered by the presence of cardiorespiratory motion. To address this need, I developed and evaluated a novel catheter contact-force control device. The compact electromechanical add-on tool monitors catheter-tissue contact force in real-time and simultaneously adjusts the position of a force-sensing ablation catheter within a steerable sheath to compensate for the change in contact force. In a series of in vitro and in vivo experiments, the contact-force control device demonstrated an ability to: a) maintain an average force to within 1 gram of a set level; b) reduce contact-force variation to below 5 grams (2-8-fold improvement over manual catheter intervention); c) ensure the catheter tip never lost contact with the tissue and never approached dangerous force levels; and importantly, d) deliver reproducible RF ablation lesions regardless of cardiac tissue motion, which were of the same depth and volume as lesions delivered in the absence of tissue motion.

In the second part of the thesis, I describe a novel steerable sheath and catheter robotic navigation system, which incorporates the catheter contact-force controller. The robotic platform enables precise and accurate manipulation of a remote conventional steerable sheath and permits catheter-tissue contact-force control. The robotic navigation system was evaluated in vitro using a phantom that combines stationary and moving targets within an in vitro model representing a beating heart. An electrophysiologist used the robotic system to remotely navigate the sheath and catheter tip to select targets and compared the accuracy of reaching these targets performing the same tasks manually. Robotic intervention resulted in significantly higher accuracy and significantly improved the contact-force profile between the catheter tip and moving tissue-mimicking material.

Our studies demonstrate that using available contact-force information within a robotic system can ensure precise and accurate placement of reliably transmural RF ablation lesions. These robotic systems can be valuable tools used to optimize RF lesion delivery techniques and ultimately improve clinical outcomes for AF ablation therapy.

Summary for Lay Audience

Atrial Fibrillation (AF) is a common heart rhythm disorder often treated using catheters inserted in the heart to “burn” the tissue responsible for the arrhythmia (i.e. to make lesions). Radiofrequency (RF) catheter ablation strategies to treat AF are complex, technically challenging, and require a high degree of skill and physical effort. Furthermore, the motion of the heart as it beats and the patient breathes can affect the contact the catheter tip makes with the heart during the therapy delivery. This makes it very difficult for the physician to deliver lesions effectively. Because of these problems, it is not uncommon that lesions are delivered inadequately, leaving untreated tissue that can result in the recurrence of AF symptoms. Currently, nearly half of all patients return for a second procedure.

To avoid repeat procedures, ablation lesions must be precisely placed in specific locations within the heart chamber – lesions must be adjacent to one another and share a common border. Additionally, these lesions must be reliably durable and cover the entire heart-wall thickness. One key element that governs lesion production is stable contact force between the catheter tip and heart tissue. With the advent of force-sensing ablation catheters, physicians can monitor the amount of force the catheter makes with the tissue in real-time. However, physicians are limited in controlling the force and have no way to improve force stability and keep it constant during RF delivery.

My thesis describes the development and evaluation of two novel robotic technologies designed to address these problems. Specifically, I introduce the Catheter Contact-Force Controller (CFC) and the Steerable Sheath and Catheter Robotic Navigation System (SSC-RNS). These platforms are used in conjunction with standard, commercially available ablation instruments to provide automated catheter-tissue contact-force control and precise remote catheter navigation. I discuss their design and development as well as how these systems performed on a lab-bench and in pre-clinical studies. I show that the CFC is effective in stabilizing the force during lesion delivery, resulting in uniform lesions despite the presence of motion. Use of the SSC-RNS led to improved location accuracy of catheter navigation compared to manual procedures.

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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