Design and evaluations of a phased ultrasound array for transesophageal cardiac ablation

Atrial fibrillation is one of the most common arrhythmia, affecting over 2.2 million Americans. A prevailing modality for treating paroxysmal atrial fibrillation is catheter ablation using radiofrequency. However, measurable morbidity and significant costs and time are associated with this modality of treatment of permanent or persistent atrial fibrillation. In order to overcome these issues, a transesophageal ultrasound applicator for noninvasive cardiac ablation was designed, developed and evaluated. Various factors, simulation results of transducer arrays, current transesophageal medical devices, and throat anatomy, were considered while designing a phased ultrasound transducer that can be inserted into the esophagus. For this research, a two-dimensional random sparse phased array with an aperture size of 20.7 mm × 10.2 mm with flat tapered elements as a transesophageal ultrasound applicator was fabricated and evaluated in ex vivo experiments. The ultrasound applicator was designed to operate at a frequency of 1.6 MHz. The feasibility of the sparse phased array was tested by submerging the array and the fresh tissue into phosphate buffer saline (PBS) solution and directing the ultrasound directly onto the tissue. Both the bovine liver and porcine heart developed lesion at the target site as a result of 8~15 minutes of array operation. The lesion had an average length of 7 ± 2 mm and a width of 5 ± 2 mm. Experimental results indicate that sufficient power was delivered by the array at the focal point to produce ablation while not grossly damaging the tissue surrounding the area of interest. These results demonstrate a potential application of the ultrasound applicator for noninvasive transesophageal cardiac surgery in atrial fibrillation treatment.