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.