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We tested the performance of a multielectrode RF ablation system during in vivo procedures in the right atrium. A total of 75% of the RF applications resulted in complete lesions at the gaps between electrodes and 90% of them were considered potentially therapeutic, as they were transmural and expended along the intended contour. The average total procedure and fluoroscopy times were 83.4 and 5.9 min, respectively. Average power varied between 15 and 114 W. No sudden impedance rise occurred and no char was found by post-ablation inspection. The average impedance was 105/spl plusmn/16 /spl Omega/, with one electrode on, and 75/spl plusmn/12 /spl Omega/ when two electrodes were simultaneously on. The average maximal lesion length and width were 59.2/spl plusmn/11.7 and 7.1/spl plusmn/1.2-mm.

Long and contiguous lesions may cure AF. We analyzed a multielectrode steerable catheter capable of creating such lesions. For optimal temperature control purposes, based on analytical and experimental data, one temperature sensor was placed at each end of the long coil electrodes. In vitro ablations were performed to analyze the catheter performance. At set temperatures of 70/spl deg/C, 85% of the lesions were contiguous. All lesions created at set temperatures of 80 and 90/spl deg/C were contiguous. No sudden impedance rises occurred. The lesion length increased linearly with the number of electrodes. Power to reach set temperature was larger and the impedance decreased as more electrodes were connected in the ablation circuit.

The locations of current density maxima can provide information about the locations of temperature maxima. Our goals were: (1) to find the optimal place of the temperature sensor used for temperature-controlled ablation; (2) to assess at which locations char is more likely to occur. Using finite element modeling, we analyzed the current density distribution for a 8Fr/5 mm straight and a 8Fr/8 mm valve ablation electrodes. The maximal current densities occurred at the tip of the electrodes. Hence, it is best to place the temperature sensor, which provides input for the temperature control, at the electrode tip. Also, the analysis showed that using an electrically insulating coating layer at the junction between the electrode and the catheter body significantly reduced the local current density, therefore the local temperature. This avoids the formation of charring. >

We performed in vitro experiments to compare lesion sizes after ablating with five electrode geometries positioned at either 0/spl deg/ (flat) or 90/spl deg/ (end-on) with respect to the endocardial surface. The RF power was adjusted to maintain a constant thermistor temperature of 70/spl deg/C. The maximum lesion lengths, depths, and widths were measured for each lesion and compared to those corresponding to a 8Fr/4 mm straight control electrode. In the end-on catheter tip orientation, the primary determinant of lesion size was the diameter of the tip. This was consistent except for the 8Fr/8 mm valve electrode which required more input power to maintain a 70/spl deg/C thermistor temperature because of the larger surface area. The 8Fr/8 mm valve electrode had a larger surface area with which to conduct heat from the tissue and to be convectively cooled by the surrounding saline. In the flat orientation, the surface area was the main predictor of lesion size. The 8Fr/8 mm valve electrode was the only electrode in the flat orientation to produce significantly different lesion size than the control. None of the electrode geometries or orientations produced charring. >

The significant changes in power with tissue-electrode angle suggested that the lesions were more predictable when ablating with temperature-based RF generators, rather than non-temperature systems. The maximal tissue temperature was reached at locations within the tissue a fraction of a millimeter away from the ablation electrode surface. The errors in tissue temperature prediction introduced by temperature sensors placed inside the electrode changed with blood flow rate and tissue-electrode angle. This study shows that to reduce tissue temperature prediction errors, during temperature-controlled ablation it was better to use a temperature sensor placed at the tip rather than at the center of the ablation electrode.