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.