Design of Focused Ultrasound Array for Non-Invasive Transesophageal Cardiac Ablation

Atrial fibrillation (AF) is the most common type of arrhythmia, affecting more than 2.2 million Americans. One effective treatment is cardiac ablation, which shows a high rate of success in treating paroxysmal AF. As a prevailing modality for this treatment, catheter ablation using radiofrequency has been effective, but comes with measurable morbidity and significant costs and time associated with this procedure for permanent or persistent AF. To address these issues, an ultrasound applicator for cardiac ablation without surgical incisions or blood contact was designed, developed and evaluated in this study. To initially design a transesophageal applicator using therapeutic ultrasound capable of creating atrial lesions from the esophagus, sound pressure fields in a simple tissue model were numerically determined. Based on the simulation results for transducer arrays together with current transesophageal medical devices and the throat anatomy, we designed, fabricated, and tested a focused ultrasound applicator that can be inserted into the esophagus for noninvasive cardiac ablation. The ultimate goal in this project is to bring this applicator as close as possible to the heart to effectively deliver ultrasound energy and create electrically isolating lesions in myocardial tissue, which replicate the currently used Maze procedure. The transducer design is a two-dimensional sparse phased array with flat tapered elements operating at 1.6 MHz. This array uses 64 active elements spatially sampled from 195 rectangular elements. Its probe head housing is 19 mm in diameter and incorporates an acoustic window. A prototype applicator has been successfully tested in vitro using fresh porcine myocardial tissue. The results demonstrated a potential applicability of an ultrasound applicator to transesophageal cardiac surgery in AF treatment.