Graduation Year

2021

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Stephen E. Saddow, Ph.D.

Committee Member

Karl Muffly, Ph.D.

Committee Member

Gokhan Mumcu, Ph.D.

Committee Member

Mark Jaroszeski, Ph.D.

Committee Member

Andrew Hoff, Ph.D.

Keywords

Basket catheter, High blood pressure, Hypertension, Resistant hypertension

Abstract

The American Heart Association (AHA) reported in March 2020, hypertension (HT) is a major risk factor for cardiovascular diseases and heart stroke. Resistant hypertension (RH) is a subset of HT and affects 11-16% of hypertensive patients. RH is diagnosed when a patient cannot achieve blood pressure control despite taking three or more medications and is a serious clinical management challenge.

Renal denervation (RD) using radiofrequency (RF) ablation is an accepted form of RH therapy. RD devices are typically delivered through femoral access into the renal artery with the assistance of a standard guided sheath. In the European Union (EU), the approved RD devices are mostly single electrodes with a ground pad over the exterior body with the risk of skin burns. Other RD devices incorporate an inflatable balloon that risks blocking renal blood flow during treatment.

At the time of this dissertation research, the Food and Drug Administration (FDA) has not approved any RD device for use in the USA except for investigational purposes. Human trials started with the well-known Symplicity HTN-1 (Medtronic, Dublin, Ireland) treating enrolled patients in June 2007, and results were promising. Trials continued with HTN-2 then HTN-3 (Funded by Medtronic; SYMPLICITY HTN-3 ClinicalTrials.gov, NCT01418261), which did not significantly reduce HT in a sham control study. All the human trials were performed with unipolar with grounding pad RD devices. Therefore, new devices that focus energy on the ablation zone without the risks of skin burn from grounding pads and without compromising renal blood flow are urgently required.

A basket catheter with bipolar electrodes has been developed to perform targeted controlled ablation through Joule heating induction resulting in tissue temperature increased within the range of 60°C to 100°C starting from the normal body temperature of 37°C as a baseline. In this research, the following contributions to the state of the art have been made: (1) novel electrode design whereby the dimensions and geometry were successfully simulated and optimized via finite element model (FEM) based computer simulation, (2) simulations included both the surrounding artery and connective tissue electrical properties to predict the ablation zone dimensions to achieve renal nerve ablation, (3) a Thermo-Chromic Phantom (TCP) tissue phantom was used to validate the in-vitro ablation zone with the computer FEM model, (4) the geometry, shape, and form of the ablation zone were visually compared to simulations and demonstrated high concordance indicating that the computer model was valid, (5) electrode design over basket catheter splines does not require a balloon, so it has the advantage of no renal artery blood flow blockage during ablation, and bipolar electrode design does not require a grounding pad resulting in the elimination of skin burns risks. Furthermore, there is no need for active cooling, and the catheter has short ablation times and the lowest power requirement of existing designs to perform the ablation.

The bipolar RF ablation electrode deserves further research and development as a potential alternative to catheter-based RD in vivo devices. The bipolar configuration and innovative design presented in this study ensure that the current density is focused on the target tissue, thus reducing the energy transferred to renal blood. Furthermore, the computational RF ablation model estimates renal artery ablation zones for highly targeted renal denervation in patients with resistant hypertension.

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