Radiofrequency multielectrode catheter ablation in the atrium

Abstract

We developed a temperature-controlled radiofrequency (RF) system which can ablate by delivering energy to up to six 12.5 mm long coil electrodes simultaneously. Temperature feedback was obtained from temperature sensors placed at each end of coil electrodes, in diametrically opposite positions. The coil electrodes were connected in parallel, via a set of electronic switches, to a 150 W 500 kHz temperature-controlled RF generator. Temperatures measured at all user-selected coil electrodes were processed by a microcontroller which sent the maximum value to the temperature input of the generator. The generator adjusted the delivered power to regulate the temperature at its input within a 5 degrees C interval about a user-defined set point. The microcontroller also activated the corresponding electronic switches so that temperatures at all selected electrodes were controlled within a 5 degrees C interval with respect to each other. Physical aspects of tissue heating were first analysed using finite element models and current density measurements. Results from these analyses also constituted design input. The performance of this system was studied in vitro and in vivo. In vitro, at set temperatures of 70 degrees C, 85% of the lesions were contiguous. All lesions created at set temperatures of 80 and 90 degrees C were contiguous. The lesion length increased almost linearly with the number of electrodes. Power requirements to reach a set temperature were larger as more electrodes were driven by the generator. The system impedance decreased as more electrodes were connected in the ablation circuit and reached a low of 45.5 ohms with five coil electrodes in the circuit. In vivo, right atrial lesions were created in eight mongrel canines. The power needed to reach 70 degrees C set temperature varied between 15 and 114 W. The system impedance was 105+/-16 ohms, with one coil electrode in the circuit, and dropped to 75+/-12 ohms when two coil electrodes were simultaneously powered. The length and the width of the lesion set varied between 17.6+/-6.1 and 59.2+/-11.7 mm and 5.9+/-0.7 and 7.1+/-1.2 mm respectively. No sudden impedance rises occurred and 75% of the lesions were contiguous. From the set of contiguous lesions, 90% were potentially therapeutic as they were transmural and extended over the entire target region. The average total procedure and fluoroscopy times were 83.4 and 5.9 min respectively. We concluded that the system can safely perform long and contiguous lesions in canine right atria.

Modeling bipolar phase-shifted multielectrode catheter ablation

“…We have utilized the FEM analysis to study several electrode designs such as needle electrodes, and uniform current density electrodes [14], [15]. Panescu et al described the structures and the controlling mechanism of a typical MEC ablation system that had bidirectional steering and carried up to six 7F 12.5-mm-long metal coil electrodes [12]. The system was capable of delivering RF power simultaneously to any user-selected combination of coils.…”

“…We used MSC/PATRAN v.7.0 (The MacNeal-Schwendler Co., Los Angeles, CA) for mesh generation and ABAQUS v.5.8 (Hibbitt, Karlsson & Sorensen, Inc., Farmington Hills, MI) for solution and postprocessing on a HP C180 UNIX workstation with 1,152-MB RAM and 34-GB hard disk. Table I lists the material properties used in this study [12].…”

“…When ablation time was longer than 120 s, the lesion depth and continuity 0018-9294/02$17.00 © 2002 IEEE TABLE I THERMAL AND ELECTRICAL PROPERTIES OF THE MATERIALS IN THE FINITE-ELEMENT MODELS were slightly different from the values observed when using 0 angle. Panescu et al presented in vitro and in vivo studies of current densities and thermal profiles generated by MEC [12] for long multielectrode structures, and the mechanical features of a steerable catheter and performance of a multielectrode multitemperature-sensor temperature controller. Zheng et al performed in vivo ablation on pig thigh muscle with a six-electrode linear catheter.…”

“…Current ablation catheters are affected by the edge effect-the formation of hot spots along the junction of the metal electrode with the insulating catheter-due to a sudden shift of electrical properties at the boundary [12], [14].…”

Thermal—electrical finite element modelling for radio frequency cardiac ablation: Effects of changes in myocardial properties

“…The values of myocardial properties used in FE modelling for RF ablation in previous studies vary significantly (PANESCU et al, 1999;SHAHIDI and SAVARD, 1994). To investigate the importance of the accuracy of myocardial properties, we simulated RF ablation for both power-controlled and temperature-controlled modes.…”