Journal of Interventional Cardiac Electrophysiology 4, 307±320(2000) #2000 Kluwer Academic Publishers. Manufactured in The Netherlands. The Effect of Ablation Sequence and Duration on Lesion Shape Using Rapidly Pulsed Radiofrequency Energy Through Multiple Electrodes Ian D. McRury Ph.D., Steve Diamond, Gary Falwell, Alyssa Schlichting, and Christopher Wilson Electrophysiology Division of C.R. Bard Inc., Billerica, MA Abstract. Sequences of energy application to multiple electrodes and a study of ablation duration with distal tip and multi-electrode ablations were explored with a radiofrequency controller that distributes energy from a generator to up to 4 electrodes with various duty cycles. In vitro ablations were performed on bovine left ventricle in circulating blood and lesions in goats were performed to verify the in vitro results. All of the ablation sequences with simultaneous electrode activation of contiguous electrodes resulted in deeper lesions than those created in sequence. There was also no scalloping of the lesion if contiguous elec- trodes were activated simultaneously. During all distal tip ablations, lesion volume and depth was greater after 3 minutes of energy delivery than after 1 minute, but did not increase from 3 minutes to 5 minutes. There was a signi®cant increase in multi- electrode ablation lesion depth with each additional minute in the ablation cycle. The in vivo ablations veri®ed these results at 120 and 300 second ablations. Pulsed energy distal tip ablations resulted in deeper lesions than continuous only if power amplitudes over 50 W were employed. In conclusion, contiguous electrodes in simulta- neous use create lesions that resemble one large lesion rather than two lesions positioned next to each other. Multi-electrode ablation lesions continue to grow at ablation durations of up to 5 minutes compared to distal tip lesions which reach steady-state between 1 and 3 minutes. Pulsed energy delivery to distal tips may result in deeper lesions than conventional if high powers are employed. Key Words. pulsed radiofrequency, multiple electrodes, ablation duration Introduction The radiofrequency ablation of atrial ¯utter is believed to require the creation of a long contin- uous line of ablated tissue as a barrier to conduc- tion between the tricuspid valve annulus and the inferior vena cava [1±5]. One technique for the creation of linear lesions is called a point-to-point ablation. A distal tip catheter is used to perform an initial ablation, then the catheter is moved slightly. A second ablation is then performed. The repetition of this technique can create a line of discrete foci of ablated tissue, and has had reli- able results in the ablation of atrial ¯utter [1±4]. A slight modi®cation of this technique is called the drag technique. In this technique, the cathe- ter is moved in a line concurrent with energy delivery [5]. The use of these techniques has been extended to investigational ablation of atrial ®brillation [6]. Since the inception of the idea of linear abla- tion, the ultimate method for creating the lines of lesion was believed to be with multiple electrodes [7±12]. Using this technique, a catheter could be placed in a single position and ablation through contiguous electrodes would create a linear lesion. The technique has been extensively researched but has had limited clinical success [13]. Most of the failure associated with the use of multiple electrodes can be traced to the limited technology available for attaining intimate contact with the atrial wall with many electrodes. A less cited reason for failure may be a lack of understanding of the electro-thermal dynamics upon which multi-electrode ablation lie. This manuscript attempts to demonstrate the techniques, sequences, and ablation cycle dura- tions necessary for maximizing multi-electrode ablation versus distal tip ablation using a novel pulsed radiofrequency energy method. By using combinations of simultaneous and sequential 307 This study was performed in support of a catheter and energy delivery system of Bard Electrophysiology, a division of C.R. Bard, Inc. Address for correspondence=reprints: Ian D. McRury Ph.D., 55 Technology Park, Suite 1, Lowell, MA 01851 (978) 323- 2258; E-mail: ian.mcrury@crbard.com Received 14 July 1999; accepted 9 September 1999