LI-guided RFCA considering the lesion size and interlesion distance
In RFCA for AF, PVI is the most effective procedure,[1] and the creation of secure RF lesions avoiding conduction gaps is essential to achieve a durable PVI.[21] [22] Recently, the Rhythmia module with an LI-sensing catheter was developed as a unique concept to determine the lesion size by the RF application. LI drops have been reported to be superior for predicting lesion size than FTIs [12] [15], and LI-guided PVI can provide a sufficient RF application along with the characteristics of the local myocardial tissue. Das M et al. reported that the optimal threshold of the LI drop for predicting gaps for anterior/roof segments was 16.1 ohms (positive predictive value for block: 96.3%) and for posterior/inferior segments it was 12.3 ohms (positive predictive value for block: 98.1%) with MiFi.[23] Our present study suggested that the lesion formation and LI parameters were changed by the different catheter angles (Figures 4 and 5). The LI drop and maximum lesion width at 90° were significantly lower and smaller than those at 30°, although lesion depths were not different among the three angles. This result suggests that the LI drop accurately reflects the difference in the lesion widths as the lesion volume changes with a perpendicular contact angle. Although indices such as FTI, LSI, and AI have been reported as useful parameters to predict RF lesion formation, it is impossible to recognize the differences in actual lesion formation (depth and width) by the catheter angle, which were observed in the present study. Therefore, LI-guided RFCA would allow us to adjust the ablation strategy, such as an optimal interlesion distance, to create continuous linear lesions considering the lesion widths.
Differences in the impact of the contact angle between MiFi and STABLEPOINT
In the present study, we evaluated 2 different LI-sensing ablation catheters. Notable differences between the 2 catheters for the LI were that the LI rise at 90° was lower than at 30° under 5 and 10 g of CF for the STABLEPOINT (Figure 4C), while there were no angular dependences for the LI rise under all CFs in the MiFi (Figure 4A). These results could be explained by the differences in the features of the 2 electrodes measuring the LI in each catheter. In the MiFi, the LI was measured between 3 microelectrodes and the 2nd ring electrode, and only the maximum LI was selected as the actual LI. On the other hand, the STABLEPOINT does not have a microelectrode, so the LI was measured between the whole distal tip and the 2nd ring electrode. Therefore, the tissue contact area or distance from the tissue to the LI measuring electrodes would be changed by the catheter contact angles. Therefore, the LI in STABLEPOINT would be affected by a larger area than for MiFi. In other words, the LI change affected by the myocardial tissue would be relatively smaller, especially with the more perpendicular catheter angle for STABLEPOINT, resulting in angular differences in the LI rise. In contrast, LI in the MiFi would be affected by a smaller area, i.e., the LI parameters in the MiFi would be more sensitive to tissue information. As a result, it is considered better to have a microelectrode to acquire more local LI information.
Since the size of the distal tips of STABLEPOINT was smaller (4 mm) than that of the MiFi (4.5 mm), the lesion sizes were larger for STABLEPOINT. Therefore, the %LI drop and %LI rise values (Supplemental Figure) were due to the different features of the catheters. On the other hand, the approximate curves were well fitted with the natural logarithm equation of %LI drop vs. maximum lesion widths (Figure 7A) and lesion depths (Figure 7B) for the 2 catheters. The absolute values of the LI parameters were different, but the association between the percent changes of the LI drop and lesion size were similar between the 2 catheters; therefore, the %LI drop can be a useful value for the concept of an LI-guided RFCA.