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.
Cardiac lesions are created to act as barriers which prohibit the transmission of cardiac myocyte contractile activity from one side of the lesion to the other. Testing for conduction block is the main way to acutely confirm the effectiveness of this therapy. There are two general methods used to test for conduction block. These methods are called: (1) "exit block testing" and (2) "entrance block testing." In this study, two different devices were used on n = 3D5 swine to determine if the method of lesion assessment (exit vs. entrance block testing) affected the ability to correctly identify if acute conduction block was achieved. No significant difference was found between conclusions drawn from either method of lesion assessment. However, the most robust lesion assessment will occur when both methods are employed so that the physician has the most information available for analysis.
Atrial fibrillation is one of the most common arrhythmias that affects over 2.2 million Americans each year. Catheter ablation, one of the effective treatments, has shown high rate of success in treating paroxysmal atrial fibrillation. Currently, radiofrequency which is being used for catheter ablation is an invasive procedure. Measurable morbidity and significant costs and time are associated with this modality of treatment of permanent or persistent atrial fibrillation. In order to address these issues, a transesophageal ultrasound applicator for noninvasive cardiac ablation was designed, developed and evaluated. The ultrasound energy delivered by the phased array was used to create a lesion in the myocardial tissue. 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 sparse phased array with flat tapered elements was fabricated and evaluated in in vivo experiments. Five pigs were anesthetized; the array was passed transesophagealy and positioned over the heart. An operating frequency of 1.6 MHz and 8∼15 minutes of array operation resulted in both single and multiple lesions on atrial and ventricular myocardium. The average size of lesions was 5.1±2.1 mm in diameter and 7.8±2.5 mm in length. Experimental results indicate that the array delivered sufficient power to produce ablation at the focal point 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.
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