Ablation settings (RF power, time, CF and CFV) and relative tissue impedance drop changes
A total of 4406 ablation lesions were screened for the analysis. Among them, 274 lesions were removed due to short duration and non-availability of LSI values and 874 lesions due to sudden and progressive impedance rise during RF delivery [20W: 95 lesions (11%); 30W: 69 lesions (20%); 40W: 710 (24%)]. The final analysis considered 3258 study ablations lesions. The baseline characteristics of the study patients are showed in Table 1. Of note, no steam pops were recorded during the study ablation procedures.
As presented in Table 2, use of higher RF powers translated into progressively higher Max-Imp-∆ and Max-Imp-% despite shorter ablation durations.
The incremental time analysis showed a logarithmic relation between impedance drop and time in each RF power group, consisting in a first steep increase in impedance drop followed by a progressively slower impedance drop until plateau. The per-patient analysis showed progressively higher percentage impedance drop values at time of plateau with the use of higher power (20W = 8.6 ± 2.2%; 30W = 10.4 ± 3.8%; 40W = 11 ± 2.5%; p = 0.0057) which also corresponded to shorter times to plateau (20W RF time at plateau = 30.9 ± 9.5 sec; 30W RF time at plateau = 25.1 ± 12.7 sec; 40W RF time at plateau = 21 ± 7 sec; p < 0.0005). As shown in Figure 2, the combined analysis of all-patients lesions showed the same trends. The plateau values of the curves corresponded to percentage impedance drop values of 8.59% at 34.5 sec, 10.32% at 30 sec, and 10.94% at 21.5 sec for RF powers of 20W, 30W, and 40W respectively. In all cases, the average maximum impedance drops and times to plateau for all patients fell very near to the mean values computed from individual patients and well within their standard deviations.
In all RF power groups, weak correlations were observed between mean CF and impedance drop (20W RF power: ρ = 0.061, p = 0.094; 30W RF power: ρ = 0.148, p = 0.015; 40W RF power: ρ = 0.205, p < 0.0001) and between CFV and impedance drop (20W RF power: ρ = -0.202, p < 0.0005; 30W RF power: ρ = 0.225, p = 0.0002; 40W RF power: ρ = 0.021, p = 0.316). However, if grouping the ablation lesions according to range of mean CF used and to range of CFV, progressively higher Max-Imp-% values were seen with higher mean CF and lower CFV in the 20W and the 40W group, as showed in Table 3. In the 30W group, increase of mean CF from 10-15 g to > 15 g and reduction of CFV from >5 to ≤ 5 g in the 5-10 g and > 15 g CF sub-groups translated in reduction rather than in increase of Max-Imp-%, however the number of observations in these subgroups was quite small with a larger variance of the data. In each power group the largest Max-Imp-% increase was observed when increasing the mean CF from < 5g to 5-10g.
The independent effect of mean CF and CFV on impedance drop within each RF power group was also confirmed by a mixed-effect model analysis (see supplementary section).