Efficacy of LI monitoring for sufficient ablation lesion formation during PV isolation
The present study showed that ablation points with a gap had a significantly smaller LI drop. In addition, a smaller LI drop most effectively predicted the presence of a conduction gap among impedance parameters. Radiofrequency ablation lesion formation is dependent on the temperature of the tissue heated by radiofrequency current,12 and the myocardial impedance drop during RFA is explained by increased ion movement as a result of heat-promoted ion channel activity on the myocardial cell membrane.13 Therefore, an LI drop specifically represents a myocardial impedance drop due to tissue heating, and can thereby act as an intramural thermometer. An LI drop is thus expected to provide accurate information on thermal lesion formation.
The association between a conduction gap and low pre-RFA LI may have been observed because the low pre-RFA LI acted as an indicator of catheter-tip contact with the myocardium, given that LI is a synthesized impedance of catheter-myocardium and catheter-blood impedance. LI has previously been reported to correlate with the proximity and contact area between the catheter tip and myocardium.6
Post-RFA LI was not different between ablation points with and without a gap, although post-RFA LI may reflect myocardial heating at the end of RFA. The problem with impedance measurements at specific time points is that they are highly dependent on the baseline blood pool and myocardial electrical properties, which differ considerably among individuals. Prior studies reported that the LI of a catheter tip floating in the left atrial blood pool varies from 80 to 120 ohm,8 and myocardial properties such as the proportion of fibrotic tissue influence LI.8,14 Therefore, it would be difficult to identify a specific post-RFA LI cut-off value for predicting sufficient lesion formation.