Feasibility of Intravascular Ultrasound Ablation and Imaging Catheter for Treatment of Atrial Fibrillation Serena H. Wong, Greig C. Scott, Steven M. Conolly, Girish Narayan, and David H. Liang Departments of Electrical Engineering and Cardiovascular Medicine Stanford University Stanford, CA Abstract— Atrial fibrillation (AF) affects 1% of the population and is responsible for 15-20% of all strokes [1]; this results in more than 460,000 hospitalizations and a cost of more than $2.8 billion per year. Clinical studies show that circumferential pulmonary vein ablation, a surgical procedure that creates contiguous patterns of lesions that electrically isolate regions of the atria, have been effective in curing AF [2]. However, current minimally invasive catheter procedures that use radiofrequency (RF) electrodes under fluoroscopic guidance are often unable to create these contiguous patterns. Difficulties arise in visualizing the anatomy and location of previous lesions and moving the catheter tip to those locations, particularly in the dynamic environment of the heart. Not only can intravascular ultrasound arrays deliver dy- namically, steerable therapy, they can also image the region of interest with good tissue contrast to correctly position the lesion. We propose the use of an intracardiac linear ultrasound array placed at the end of a 7 French catheter. Previously, we showed an intracardiac-sized transducer (20 mm by 2 mm) can create temperature rises of 45 degrees necessary for ablation. In this work, we illustrate the possibility of visualizing such a high intensity focused ultrasound (HIFU) lesion with conventional ultrasound imaging. I. I NTRODUCTION An intracardiac ultrasound transducer addresses the issues of precisely positioning lesions and visualizing these lesions and anatomy during the AF procedure. Ultrasound therapy can be dynamically and electronically steered to precise locations as the transducer is roughly anchored in particular position; this dynamic steering can compensate for cardiac motion and variable anatomy. Unlike fluoroscopy, ultrasound imaging also provides real-time images of tissue and lesions with good tissue contrast. This can offer significant improvement in the ability to treat arrhythmias [4], [5], [6]. Separate ultrasound imaging probes have been used to guide high intensity focused ultrasound (HIFU) transducers by displaying the anatomy and also detecting past lesions as bright echogenic regions [7], [8], [9]. Though these echogenic regions fade 1-2 min after HIFU application, they persist for long enough periods to guide the placement of adjacent lesions for formation of contiguous patterns. Figure 1 illustrates the operation of our proposed device. The ultrasound transducer is anchored near the ostium of a pulmonary vein and secured with a balloon placed in the pulmonary vein. First the ultrasound transducer operates in imaging mode to locate the distance to the heart wall and the location of previous burns. After imaging, the ultrasound balloon to stabilize catheter catheter pulmonary vein left atria transducer array balloon to stabilize catheter catheter pulmonary vein left atria transducer array lesion balloon to stabilize catheter catheter pulmonary vein left atria transducer array rotation lesion a) Image b) Focus and Burn c) Rotate Fig. 1. An illustration of the catheter function. (a) The array will image the region of interest. (b) The anatomy and location of previously formed lesions will be identified and used to dynamically focus the therapy. (c) The catheter will be rotated and the process will repeat until a contiguous circumferential lesion is formed around the pulmonary vein. is dynamically focused and steered, and a continuous wave signal is applied to the transducer to produce a lesion. The catheter is then rotated and the process of imaging and ablation repeats. The ability to examine the region of interest and dynamically adjust the focus makes ultrasound ideal for intracardiac surgery. We previously demonstrated that an intracardiac-sized trans- ducer can produce the focal intensities necessary for ablation using a fixed focus system [3]. We will show that lesions formed from this system can be visualized using conventional ultrasound. II. METHODS AND SETUP To reduce the complexity of building a full-fledged array system, we used a fixed focus system to create the lesion and a conventional ultrasound system to image the lesion. The fixed focus system consisted of a (20 mm by 2 mm) single element transducer (APC 880, APC International, Ltd.) and a focusing cylindrical reflector (10 mm focal length). We positioned the tissue at the reflector’s focal point and angled the transducer to 2005 IEEE Ultrasonics Symposium 0-7803-9383-X/05/$20.00 (c) 2005 IEEE 1751