Electrode impedance: An indicator of electrode-tissue contact and lesion dimensions during linear ablation

Pre-ablation impedance was evaluated for its ability to detect electrode-ti ssue contact and allow creation of long uniform linear lesions with a multi -electrode ablation catheter. The study consisted of 2 parts, both of which used the in vivo pig thigh muscle model. In part 1, a 7 Fr. multi-electrod e catheter was held in 3 electrode-tissue contact conditions: (1) non-conta ct; (2) light contact with a 30 g downward force; and (3) tight contact wit h a 90 g downward force. Impedances were measured in unipolar, modified uni polar and bipolar configurations using a source with frequencies from 100 H z to 500 kHz. Compared with non-contact, the impedance increased 35 +/- 22 % with 30 g contact pressure and 68 +/- 40 % when the contact pressure was increased to 90 g across the range of frequencies studied. In part 2, the s ame catheter was held against the tissue with different forces. Pre-ablatio n impedance was measured using a 10 kHz current. Phased radiofrequency ener gy was applied to the 5 electrodes simultaneously using 10 W power at each electrode for 120 s. A total of 32 linear lesions were created. The lesion dimensions correlated with pre-ablation impedance. A unipolar impedance gre ater than or equal to 190 Ohm indicates 95 % possibility to create a unifor m linear lesion of at least 3 mm depth with our ablation system. We conclud e that pre-ablation impedance may be a useful indicator for predicting elec trode-tissue contact and the ability to create a continuous and transmural linear lesion with a multi-electrode catheter.