WHY A LARGE TIP ELECTRODE MAKES A DEEPER RADIOFREQUENCY LESION - EFFECTS OF INCREASE IN ELECTRODE COOLING AND ELECTRODE-TISSUE INTERFACE AREA

Increase in RF Lesion Depth with Larger Electrode. Introduction: Incre asing electrode size allows an increase in radiofrequency lesion depth . The purpose of this study was to examine the roles of added electrod e cooling and electrode-tissue interface area in producing deeper lesi ons. Methods and Results: In 10 dogs, the thigh muscle was exposed and superfused with heparinized blood. An 8-French catheter with 4- or 8- mm tip electrode was positioned against the muscle with a blood flow o f 350 mL/min directed around the electrode. Radiofrequency current was delivered using four methods: (1) electrode perpendicular to the musc le, using variable voltage to maintain the electrode-tissue interface temperature at 60 degrees C; (2) same except the surrounding blood was stationary; (3) perpendicular electrode position, maintaining tissue temperature (3.5-mm depth) at 90 degrees C; and (4) electrode parallel to the muscle, maintaining tissue temperature at 90 degrees C. Electr ode-tissue interface temperature, tissue temperature (3.5- and 7.0-mm depths), and lesion size were compared between the 4- and 8-mm electro des in each method. In Methods 1 and 2, the tissue temperatures and le sion depth were greater with the 8-mm electrode. These differences wer e smaller without blood flow, suggesting the improved convective cooli ng of the larger electrode resulted in greater power delivered to the tissue at the same electrode-tissue interface temperature. In Method 3 (same tissue current density), the electrode-tissue interface tempera ture was significantly lower with the 8-mm electrode. With parallel or ientation and same tissue temperature at 3.5-mm depth (Method 4), the tissue temperature at 7.0-mm depth and lesion depth were greater with the 8-mm electrode, suggesting increased conductive heating due to lar ger volume of resistive heating because of the larger electrode-tissue interface area. Conclusion: With a larger electrode, both increased c ooling and increased electrode-tissue interface area increase volume o f resistive heating and lesion depth.