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).