Animal studies on HPSD
Several animal studies have studied the efficacy and safety of HPSD
ablation for PV isolation. Researchers have studied several combinations
of high power settings ranging from 50 W to 80 W for 5 s with a
temperature cut-off of 60o C with a CF sensing
catheter in an in vitro model and a sheep model. The HPSD ablation
settings resulted in 100% transmural lesions and reduced collateral
damage compared with ablation at 40 W for 30 s in the right atrium.
Steam pops were noted at power > 70 W or longer duration
ablation (8% incidence for 40 W/30 s and 11% for 80 W/5
s).26 In an ex-vivo and in-vivo animal study,
predictably increased lesion size was noted with greater power delivery
or longer RF time. However, the same proportional increase in power will
produce a significantly larger lesion volume compared with a
proportional change in RF duration. Lesion volume proportionally
increases with increase in power and only half as much for ablation
duration provided the CF remains constant.27 In yet
another porcine study, the time needed to create a 4-mm deep lesion
decreased from just over 20 s for 20 W to 6–7 s for 50 W with a CF of
20 g. This suggests that high power and short duration lesions might
help to reduce collateral injury.28
In a recent animal study by Leshem et al, HPSD ablation with 90 W/4 s
resulted in higher power, average and maximal temperature, and larger
impedance drop as compared to standard ablation using 25 W/20 s for PV
isolation in a swine model. The catheter tissue temperature was noted to
increase to an average of 63.2 o C ± 75o C due to resistive heating. This was sufficient to
cause a full wall thickness lesion in thin tissue like the
atrium.21 Power was modulated automatically with a
sensitive thermocouple system which enabled real-time temperature
recording to prevent tissue boiling and steam pops. The 90 W/4 s
ablation lesions were observed to be full thickness while the 25 W/20 s
lesions resulted in some partial thickness lesions with many gaps
between them. It was hypothesized that catheter irrigation led to an
”endocardial preservation” effect at lower power longer duration
ablation due to irrigation‐induced endocardial cooling before resistive
heating caused irreversible tissue injury.