Estimation of radiofrequency ablation lesion formation
Radiofrequency ablation lesion formation is dependent on tissue exposure to heat generated by radiofrequency current. Since the early use of radiofrequency ablation, tissue temperature has been indirectly measured using a thermostat located at the catheter tip.10However, myocardial surface temperature does not correctly reflect intramural heating, and fails to estimate lesion size.11
Instead, GI has been measured using the radiofrequency energy generated during ablation.3-5 However, GI is not commonly recognized as a marker of sufficient ablation lesion formation. The problem with GI is that it is influenced by the electrical properties of not only the myocardium but also skin, subcutaneous tissue, lungs and other structures in the mediastinum and breast wall, making it a bulk measurement. Conversely, LI measurement is based on the near electric field generated at the catheter tip, and is therefore theoretically more specific to the near-field myocardium beneath the catheter than GI. The present study and a prior study consistently demonstrated a poor correlation between GI and LI, and a larger impedance drop during RFA in LI than in GI at ablation points without gaps.8 These clinical data also suggest that LI represents near-field electrical properties, and support the hypothesis that LI is superior for impedance monitoring compared with GI during radiofrequency ablation.