ESOPHAGEAL DAMAGE IN RESPONSE TO NONINVASIVE FOCUSED ULTRASOUND FOR TREATMENT OF ATRIAL FIBRILLATION

Open Access
Author:
JAISWAL, DEVINA
Graduate Program:
Bioengineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Dr Nadine B Smith, Thesis Advisor
  • Dr Nadine Barrie Smith, Thesis Advisor
Keywords:
  • single element
  • atrial fibrillation
  • phased array
  • Transesophageal ultrasound transducer
  • in vivo
  • histology
  • cardiac lesion
  • ex vivo
Abstract:
Atrial fibrillation is one of the most common arrhythmias that affects over 2.2 million Americans. A prevailing modality for treating paroxysmal atrial fibrillation is catheter ablation using radiofrequency radiation. However, measurable morbidity and significant costs and time are associated with this modality of treatment. To overcome these issues, a transesophageal ultrasound applicator for noninvasive cardiac ablation was designed, developed and evaluated. Since the esophageal wall is less than 5 mm from the left atrium endocardium in a human subject, it is possible to aim at a selected area of the heart from this position. Therefore, this goal can be achieved by bringing the applicator close to the heart in order to deliver the ultrasound energy to create isolated lesions in myocardial tissue. For this research, single element and two-dimensional random sparse phased arrays were designed and fabricated. Various factors such as simulation results of the transducer and throat anatomy were considered while designing the transesophageal ultrasound transducer. For the spherical single element probe, the element was encased in a 19 mm diameter probe head with an aperture of 20.86 x 10.26 mm2 and had an operating frequency of 1.69 MHz. In this study, the two-dimensional random sparse phased array was also designed to have 48 (8  6) rectangular elements. From this array, 30 active elements were randomly chosen through simulation to operate at the resonance frequency of 1.6 MHz. For the verification of the designs, the prototype probe was tested in ex vivo experiments. Experimental results indicated that the probe was capable of creating a lesion in a porcine heart within ten minutes of exposure duration without damaging the esophagus. The probe was further tested in in vivo experiments on 280 lbs pigs. It was concluded from the histology results that the transducer was able to function adequately without inflicting any heat damage to the esophagus. The transducer delivered sufficient power at the focal region, though the focal length was not sufficient to create a lesion on the heart. It was also concluded that a better animal model is needed to demonstrate the anticipated results. Since there was no heat damage found on the esophagus where the probe was placed, it was concluded that the designed transesophageal probe had a potential application in atrial fibrillation treatment.