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.