THE EFFECTS OF ELECTRODE-TISSUE CONTACT ON RADIOFREQUENCY LESION GENERATION

During the generation of radio frequency (RF) lesions in the ventricul ar myocardium, the maintenance of adequate electrode-tissue contact is critically important. In this study, lesion dimensions and temperatur e and impedance changes were evaluated while controlling electrode-tis sue contact levels (-5, 0, +1, and +3 mm) and power levels (10, 20, an d 30 W). This data was used to assess the ability of impedance and tem perature monitoring to provide useful information about the quality of electrode-tissue contact. The results show that as the electrode-tiss ue contact increases, so does the amount of temperature rise. With the electrode floating in blood (-5 contact), the average maximum tempera ture increase with 20 and 30 W was only 7 +/- 1 and 11 +/- 2 degrees C , respectively. At 20 and 30 W the temperature plateaued shortly after the initiation of power application. With good electrode-tissue conta ct (+1 mm or +3 mm), the temperature increase within the first 10 seco nds was significantly greater than the temperature increase from basel ine with poor contact (0 mm or -5 mm) and reached a maximum of 60 +/- 1 degrees C after 60 seconds of pow er ap plication. As the electrode- tissue contact increased, so did the rate and level of impedance decre ase. However, the rate of impedance decrease was slower compared to th e rate of temperature rise. With the electrode floating in blood, the maximum impedance decreases with 20 and 30 W were 6 +/- 6 Omega and 9 +/- 5 Omega, respectively. The impedances plateaued after a few second s of power application. With the electrode in good contact, the maximu m impedance decreases with 20 and 30 W were 25 +/- 2 Omega and 20 +/- 6 Omega, respectively. In these cases the rate of the impedance decrea se plateaued after 40 seconds of power application. The increase in le sion diameter and depth correlate well with decreasing impedance and i ncreasing temperature. However, lesion depth appears to correlate bett er with impedance than temperature. We conclude that, since the electr ode-tissue contact is not known prior to the application of power to t he endocardium, in the absence of a temperature control system, the po wer should initially be set at a low level. The power should be increa sed slowly over 20-30 seconds, and then maintained at its final level for at least 90 seconds to allow for maximal lesion depth maturation. The power level should be lowered if the impedance drop exceeds 15 Ome ga.