Relationships between impedance drop and FTI/LSI
Correlation analyses showed a stronger correlation of LSI with impedance drop (ρ = 0.319; p < 0.0001) compared to FTI with impedance drop (ρ = 0.263; p < 0.0001).
The incremental FTI analysis showed progressively lower FTI values corresponding to higher percentage impedance drop values at plateau with increasing RF power (see supplementary section).
The incremental LSI analysis showed a first linear phase of impedance drop increase over LSI followed by a plateau phase. Due to unavailability of LSI data in the first few seconds of RF delivery, the LSI curves started with a minimum LSI of 2. At any LSI stage, impedance drop was progressively higher with increasing RF power. The per-patient analysis showed progressively higher LSI values required to reach plateau of impedance drop with increasing RF power used (20W: LSI = 4.2 ± 0.5; 30W: LSI = 4.6 ± 1.5; 40W: LSI = 5.4 ± 0.5; overall p < 0.0015), with higher impedance drop reached at plateau (20W = 8.6 ± 2.2%; 30W = 10.4 ± 3.8%; 40W = 11 ± 2.6%; overall p = 0.0062). As shown in Figure 3, the combined analysis of all patients’ lesions showed the same trends of the per-patient analysis. The 20W, 30W and 40W curves reached plateaus corresponding to percentage impedance drop values of 8.71% at LSI 4.7, 10.43% at LSI 5.5, and 11.07% at LSI 5.9 respectively. In all cases, the average maximum impedance drops and LSI values to plateau for all patients fell very near to the mean values computed from individual patients and well within their standard deviations.
Figure 4 represents graphically the impact of different combinations of RF power, CF and CFV on Max-Imp-% and the corresponding LSI. Each line represents a combination of RF power and range of CFV, while the various points of the lines are the mean CF. Mean CF showed a larger effect on impedance drop in the 40W group than in the 20W group. Vice versa, CFV showed a more pronounced effect on impedance drop in the 20W group than in the 40W one. Provided a mean CF of at least 5 g, use of 40W produced a bigger impedance drop irrespective of target LSI or CFV. In each RF power group, approximate LSI values indicative of achievement of Max-Imp-% could be identified for the different ranges of CF. However, depending on the range of CFV, each LSI value corresponded to two different actual values of Max-Imp-% achieved.