4 Discussion
This meta-analysis provides a more comprehensive assessment of HPSD RFA and conventional RFA in patients with AF. Our results suggest that HPSD RFA may be more effective with higher first-pass isolation and freedom from atrial arrhythmia and lower acute PVR when compared with conventional RFA. However, there was no difference in safety outcomes between two groups. Unlike previous studies8,9,32, our study had more findings. In our study, there was no difference in PVR between the two groups that described redo procedures. In subgroup analysis, there was no difference between the two groups using AI/LSI guided ablation for freedom from atrial arrhythmia. And HPSD group with a power setting of 40-50W had better efficacy when compared with conventional group.
PVI is the cornerstone of AF ablation 33, however, PVR is frequent and is mostly the result of catheter instability, tissue edema, and a reversible non-transmural injury 34. One of the main reasons for AF recurrence is the recovery of the conduction between the pulmonary veins and left atrium 35, so continuous and transmural lines are key to the success of ablation. In animal studies, the lesions were wider and HPSD ablation resulted in 100% contiguous lines with transmural lesions which improved lesion-to-lesion uniformity 36. In 6 swine, HPSD ablation was performed using the QDOT MICROTMCatheter at a setting of 90W for 4s and conventional ablation was delivered using a Thermocool Smarttouch SF Catheter at a setting of 30W for 30s, Barkagan et al found that all lines remained intact after 30 days in HPSD ablation, while none of the lines were continuous in conventional ablation37. Although there was variation in the definition of freedom from arrhythmia in each study and the use of AADs, our analysis favors the HPSD RFA strategy over LPLD RFA strategy for lower acute PVR, higher first-pass isolation and higher freedom from atrial arrhythmia. Nevertheless, in our analysis, there was no difference between two groups in PVR during the redo procedure. Some patients might have had recurrence during the follow-up period, but they did not undergo redo procedures. Furthermore, the follow-up was determined to one year, therefore all the reasons above may underestimate the rate of chronic PVR.
However, the appropriate power for the RF ablation is not clear. One study 31 used higher power of 70W for 5-7s and demonstrated significantly less arrhythmia recurrence during one-year follow-up (26.9% vs 34.9%, P < 0.013) with no major complications. The QDOT-FAST trial 38 used 90W for 4s per site in 52 patients with paroxysmal atrial fibrillation and 94.2% patients were in sinus rhythm at 3 months with one pseudoaneurysm and one asymptomatic thromboembolism. In our meta-analysis, mostly half of studies of HPSD RFA used 50W and the others using 45-50W. For freedom from atrial arrhythmia at one year, the HPSD RFA group demonstrated higher efficacy with the power setting of 45-50W, whereas the two groups were similar with the power setting of 50W. To reduce complications when ablating with 50W on the posterior atrial wall, ablation duration was shorter than that of 40/45W. Less total energy and shallower lesions which possibly not reaching transmural, resulting in no difference in the recurrence rate between the two groups39. Winkle et al 40 reported that 6 independent predictors affected the outcomes for HPSD ablation including age, gender, type of AF, left atrial size, type of catheter and posterior wall isolation. Therefore, further studies will be required to explore the most optimal power and duration for HPSD RFA to bring the highest clinical value.
Previous studies indicate force time integral (FTI) as a target value to achieve permanent PVI, while not considering power settings. Consequently, only 72% of PVs remained isolated in 3 months41. AI is a novel ablation quality marker that incorporates contact force (CF), time and power in a weighted formula and LSI is a multi-parametric index incorporating CF and radiofrequency current data across time. Many reports demonstrated that AI or LSI can be used as the correlation index of pulmonary vein persistent isolation42,43. HPSD-AI or LSI groups had lower recurrence of atrial arrhythmia at 12 months, higher first-pass isolation, lower acute PVR and similar complication rates in the AI-guided group compared with non-AI-guided group 32,44. Okamatsu et al45 studied a group of persistent AF patients undergoing AI-guided PVI with target values of 550 for anterior and 400 for posterior left atrial regions, with 22% patients demonstrating late PVR during repeat procedures after 2 months and 95% patients were in sinus rhythm at 12 months. However, freedom from atrial arrhythmia and acute PVR failed to demonstrate a significant advantage with AI or LSI in our analysis. It is regrettable that only 5 studies were included in our subgroup analysis with AI or LSI guided procedure, of which only 4 studies and 2 studies respectively illustrated freedom from atrial arrhythmia at one year and acute PVR rates. We did not analyze first-pass isolation because only one study reported this data. Therefore, more well-designed and large-scale RCTs are required to confirm these findings.
Safety during elective PVI procedures is of worthwhile concern. Radiofrequency catheter ablation is a technique where conductive and resistive heating are delivered through electrode catheters to myocardial tissue creating a thermal lesion. Irreversible myocardial tissue injury with cellular death occurs once the temperature of approximately 50℃ has been reached, whereas conductive heating transfers thermal energy directly to deeper tissue 46. Unlike conventional ablation, the HPSD ablation strategy results in a higher resistive heating and lower conductive heating, which may reduce collateral injury to surrounding structures such as the esophagus36,47. Late gadolinium enhancement MRI of the oesophagus in 574 patients following AF ablation using HPSD settings of 50 W for 5 seconds reported a 14.3% incidence of moderate to severe thermal oesophageal late gadolinium enhancement with no fistulas22. Takemoto et al 48 reported that high power settings based on the AI or LSI might reduce the collateral thermal damage comparing use of 20W and 40W with the same AI or LSI for RF applications. HPSD RFA strategies performed at 45-50W have very low complication rates 49. Likewise, in our analysis, there was no difference between the two groups across each subgroup analysis.
In terms of procedure duration, RF duration and fluoroscopy time, the HPSD RFA strategy represents distinct advantages compared with the conventional RFA strategy whether in the subgroup analysis or not. Additionally, the reduction in procedure times can decrease the intravenous fluid volumes administered to patients which may benefit patients with cardiac insufficiency. Finally, less radiation exposure will also benefit both patients and physicians 9.
To conclude, our results of the pooled analysis favour the use of HPSD settings over conventional settings. However, more RCT studies are needed to further assess the above results.