In vitro study of lesion size dependence on electrode geometry during temperature-controlled radiofrequency ablation

We performed in vitro experiments to compare lesion sizes after ablating with five electrode geometries positioned at either 0° (flat) or 90° (end-on) with respect to the endocardial surface. The RF power was adjusted to maintain a constant thermistor temperature of 70°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°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