HPSD ablation: Procedure Outcomes
A randomized pilot study compared AF outcomes at different power outputs titrated to echogenic microbubble formation for PV isolation using a 3.5 mm open-irrigation tip catheter as well as an 8-mm tip catheter.34 In patients undergoing ablation at 50 W (3.5 mm open-irrigation tip catheter), the freedom from AF was 82% at 6 months, compared to 78% in those undergoing ablation at 70 W (8-mm tip catheter group) and only 66% in those undergoing ablation at 35 W (3.5 mm open-irrigation tip catheter). In another study, operators reported the use of 50 W for short periods (2-5 seconds at each location) using a ”dragging” technique of moving the catheter through a small area to minimize time dependent deep tissue heat transfer.46The reported freedom from AF was 85% after 1 or 2 ablations with a mean follow‐up of 338 days.46 Winkle et al have also reported this technique of “perpetual motion” using open irrigated catheters at 50 W with short durations for each site. Delivery of short 50 W ablations had better long-term freedom from AF and shorter procedural, left atrial and fluoroscopy times as compared with lower power longer duration ablation lesions.41
The concern with the “dragging” technique is the possibility of catheter instability and insufficient contact force at each location which can lead to tissue edema. Even with HPSD RF application, insufficient tissue contact with <5 g of contact force cannot be compensated by just increasing RF power and will lead to suboptimal lesions.25 Commonly used real time surrogates for durable lesion formation are force-time integral (FTI), lesion index (LSI) and now a novel lesion quality marker, ablation index (AI) are used to increase lesion quality.47 Catheter instability can be circumvented to some extent using steerable sheaths, atrial pacing and use of high frequency, jet ventilation.48 The absolute time required for catheter stability is shorter with HPSD ablation which results in higher proportion of RF applications producing irreversible injury as compared to LPLD ablation.
In a recent prospective study by Yavin et al39comparing 112 patients undergoing HPSD ablation with 112 historical controls undergoing standard ablation, the authors found higher acute success with HPSD ablation (90.2% vs. 83%, p = 0.006), shorter RF time (17.2 +/- 3.4 min vs. 31.1 +/- 5.6 min, p<0.001) as well as lower incidence of chronic pulmonary vein (PV) reconnections (16.6% patients vs. 52.2% patients, p = 0.03). The authors also observed that in a higher proportion of HPSD applications, catheter motion was less than 1 mm during 50% or more of the application duration, thereby allowing energy delivery with greater stability.39HPSD ablation (70 W/ 5-7 s) has also demonstrated significantly greater freedom from AF during 1-year follow-up (83.1% vs 65.1% P < 0.013) compared to conventional power controlled protocol (30-40 W/ 20-40 s) using a standard non-CF sensing irrigated ablation catheter.29 In the Q-DOT FAST trial, using 90 W/ 4 s and thermocouple temperature cut-off at 65-70°C, PV isolation was achieved in all 52 patients acutely with success rate of 94.2% at 3 months.23 These findings underline the importance of power as an important weighted parameter in lesion quality and durability.