IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 47, NO. 1, JANUARY 2000 23 A New Catheter Design Using Needle Electrode for Subendocardial RF Ablation of Ventricular Muscles: Finite Element Analysis and in vitro Experiments Eung Je Woo, Member, IEEE, Supan Tungjitkusolmun, Student Member, IEEE, Hong Cao, Student Member, IEEE, Jang-Zern Tsai, Student Member, IEEE, John G. Webster*, Life Fellow, IEEE, Vicken R. Vorperian, and James A. Will Abstract—Radio-frequency (RF) cardiac ablation has been very successful for treating arrhythmias related with atrioventricular junction and accessory pathways with successful cure rates of more than 90%. Even though ventricular tachycardia (VT) is a more se- rious problem, it is known to be rather difficult to cure VT using RF ablation. In order to apply RF ablation to VT, we usually need to create a deeper and wider lesion. Conventional RF ablation elec- trodes often fail to produce such a lesion. We propose a catheter- electrode design including one or more needle electrodes with a di- ameter of 0.5–1.0 mm and length of 2.0–10 mm to create a lesion large enough to treat VT. One temperature sensor could be placed at the middle of the needle electrode for temperature-controlled RF ablation. From finite element analyses and in vitro experiments, we found that the depth of a lesion is 1–2 mm deeper than the in- sertion depth of the needle and the width increases as we increase the diameter of the needle and the time duration. We showed that a single needle electrode can produce a lesion with about 10-mm width and any required depth. If a wider lesion is required, more than one needle with suggested structures can be used. Or, repeated RF ablations around a certain area using one needle could produce a cluster of lesions. In some cases, a catheter with both conventional electrode and needle electrode at its tip may be beneficial to take advantage of both types of electrode. Index Terms—Needle electrode, RF cardiac ablation, ventricle. I. INTRODUCTION R ADIO-FREQUENCY (RF) cardiac ablation has been very successful in treating certain types of arrhythmias related with atrioventricular junction and accessory pathways with cure rates of more than 90%. However, it is not widely used to treat ventricular tachycardia (VT). When applied to the ventricle, RF ablation has been shown to be successful only in a limited number of patients with bundle branch or idiopathic VT [1], [2]. Manuscript received July 9, 1998; revised June 24, 1999. This work was sup- ported by the National Institutes of Health (NIH) under Grant HL56143. The work of E. J. Woo was supported by the Korea Research Foundation, Support for Faculty Research. Asterisk indicates corresponding author. E. J. Woo is with the School of Electronics and Information, Kyung Hee Uni- versity, 1 Sochen-ni, Kihung-eop, Yongin, Kyongki-do, Korea 449-701. S. Tungjitkusolmun, H. Cao, and J.-Z. Tsai, are with the Department of Elec- trical and Computer Engineering, University of Wisconsin-Madison, Madison, WI 53706 USA. *J. G. Webster is with the Department of Biomedical Engineering, Univer- sity of Wisconsin-Madison, 1415 Engineering Dr., Madison, WI 53706 USA (e-mail: webster@engr.wisc.edu). V. R. Vorperian is with the Department of Medicine, University of Wisconsin- Madison, Madison, WI 53792 USA. J. A. Will is with the Department of Animal Health and Biomedical Science, University of Wisconsin-Madison, Madison, WI 53706 USA. Publisher Item Identifier S 0018-9294(00)00251-2. In order to apply RF ablation techniques to the treatment of VT, two important questions must be answered. First, how can we localize the abnormal regions within the ventricle? Second, how can we create a lesion (or lesions) that is deep and wide enough to cure VT? Currently, considerable research and devel- opment efforts are attempting to answer the first question using a 64-electrode basket mapping catheter, computerized electro- physiology recorder, different pacing methods, and so on [2]. In this paper, we assume that the localization is properly performed and will focus on techniques to create lesions with a desired size and shape. Since the required size and shape of a lesion and also the anatomical structure of the heart are different depending on the location within the heart, we should use different designs of ablation electrode depending on the locations and characteris- tics of arrhythmogenic sites. For the ventricle where we need to create lesions throughout the cardiac wall with a thickness of 10 mm or more in some cases, we believe that needle type elec- trodes will be advantageous in creating deep and wide lesions and at the same time ensuring good tissue–electrode contact. Furthermore, since the electrode is inserted within the cardiac tissue, we will need to apply a smaller amount of RF power to create a larger lesion. Needles have been used in chemical cardiac ablation where formalin or concentrated ethanol is injected epicardially [3] or endocardially [4], [5] into cardiac tissue to create tissue necrosis. However, currently RF cardiac ablation is preferred to chemical ablation in most cases. In RF ablation, needle electrodes have been more widely used to create a larger lesion in the prostate probably due to the requirements imposed by the anatomical structures [6], [7]. To our knowledge, there are only two published studies using needle electrodes in RF cardiac ablation. Ohtake et al. tried RF ablation of ventricles using a needle electrode inserted epicar- dially during intraoperative animal experiments using 12 mon- grel dogs [8]. By inserting a needle electrode with a diameter of 0.7 mm to a depth of 3 mm through the epicardium, they could achieve the ablation of deeper areas of the myocardium com- pared with conventional epicardial surface ablation. Daly et al. also reported experimental results using an epi- cardial needle electrode for RF ablation of the myocardium of 11 adult mongrel dogs [9]. They used a needle electrode with 0.8-mm outer diameter and introduced 5 mm of the needle into the myocardium through the epicardium. They measured the in- tramyocardial temperature at five locations at 1 mm up to 5 mm 0018–9294/00$10.00 © 2000 IEEE