We report a large, prospective, multicenter series of paroxysmal AF patients undergoing 4 different treatment strategies including the largest experience using a VOM-EI over a 12-month follow-up period.
The main results of this study were: (1) Overall, the VOM-EI failed to significantly improve the clinical efficacy of the PVI for paroxysmal AF. (2) The success rate of RF combined with a VOM-EI was significantly lower than that of a CB alone (88 and 66 %, p= 0.0033). (3) The success rate of the MIB afforded by the VOM-EI was high and did not differ between Groups RF + VOM-EI and CB + VOM-EI. (4) Using the CB was the only predictor of an AF-free survival among all treatment arms.
We previously demonstrated that a VOM-EI was useful for treating perimitral atrial flutter by reliably achieving bidirectional MI block . We were also able to show that there was regional parasympathetic denervation around the MI area . These clinical aspects of the VOM-EI may be expected to facilitate the clinical efficacy of the ablation of AF.
The CB technology offers the possibility of the PVI with a single energy application as an alternative to a point-by-point RF current ablation , , , and the CB has been increasingly used for treating AF because of the relative technical simplicity and steeper learning curve . However, the clinical results have been hampered by left-sided ATs in approximately 8~10 %, and those ATs were associated with the MI area , . Macroreentrant tachycardia involving the mitral annulus-PMF causes 33 % to 60 % of post-PV isolation atrial flutters , . Therefore, construction of MIB could be regarded as one of the necessary ablation procedures even in paroxysmal AF.
At 12-months of follow-up, approximately 65 % of the Group RF and 80 % of the Group CB patients were free of AF recurrences in the present study, and that was in line with the recent articles analysing the mid-term outcomes , , , . However, no left-sided ATs have ever been documented in all four groups of patients during the follow-up period, and these results could be associated with the antiarrhythmic effects of preventiong AF recurrences by a VOM-EI procedure . . Lyan et al., reported that 26 out of 238 (10.9 %) AF patients underwent a redo ablation for AT. Nine out of 26 (34.6 %) patients had perimetral reentrant AT after the CB application. An additive EI-VOM might be beneficial in terms of preventing perimetral AT .
In Group RF + VOM-EI, reconnected PVs sites were observed in 20/52 (38.5 %) patients predominantly in the left inferior PVs where a VOM-EI had already created low voltage areas and no further touch-up RF applications were performed in the first session, because a successful PVI could be performed by applying RF energy at the antral area where the residual atrial electrograms remained. In general, the anatomical course of the VOM arises from the middle or proximal portion of the CS and runs toward the inferior aspect of the LIPV. Therefore, the antral atrial tissue at the inferior aspect of the LIPV is susceptible to be ablated by the VOM-EI. In those cases, our approach was to spare the RF energy applications in the area where no atrial electrograms were recorded from the tip of the ablation catheter for a successful PVI of the LIPV. In sporadic cases, such low voltage areas were detected at the posterior wall of the LSPV, and that kind of characteristic could be expected in cases that had a relatively long VOM coursing toward the LSPV area.
A high reconnection rate of the LIPV meant that the durability of the lesion around the PVs created by the VOM-EI was not sufficient. This might be the reason why the long-term clinical outcome of Group CB was significantly better than that of Group RF + VOM-EI. Considering that the VOM is an epicardial structure, the VOM-EI is expected to ablate the epicardium first and may not reach to the endocardial myocardium as effectively or as durably. CB ablation in the LIPV, when combined with a VOM-EI, did not have a high LIPV reconnection rate. It is possible that if RF energy applications had been performed at those “silent” areas, the rate of the freedom from AF in Group CB could have been comparable to that of Group RF. In addition, Guler et al., demonstrated that the CB provided additional substrate modification owing to the balloon and PV mismatch and could provide a lesion formation at the posterior wall of the left atrium, which is the most affected part of left atrium  That might inflience on the results of the present study.
A previous report demonstrated the necessity of a combined epicardial (inside CS) and endocardial RF catheter ablation of the VOM area was required to eliminate the VOM potentials . In the present study, the success rate of constructing an MIB was 68 out of 80 (83 %) in Group RF + VOM-EI and 47 out of 52 (90 %) in Group CB + VOM-EI, respectively (p= 0.23). This was overall a higher success rate than usually reported in the literature  with a lower rate of RF application inside the CS as compared to the other study , and may highlight a unique utility of this procedure.
In this study, we failed to demonstrate any significant further improvement in the clinical efficacy in terms of preventing AF recurrences by adding a VOM-EI to the PVI by ablation using the CB or RF energy in patients with paroxysmal AF. According to the recent report, the one-year clinical outcome using the CB for the PVI in patients with persistent AF was not satisfactory . Even though the acute success rate of the PVI was 100 %, the 1-year clinical success rate was 69 % with the use of the second-generation CB. Of note, left-sided ATs were documented in 13 % of the study patients. Those ATs could have been prevented by adding a VOM-EI procedure to the PVI. A VOM-EI has multifactorial effects for facilitating the clinical efficacy of the catheter ablation of AF. As we previously reported, the VOM-EI was able to abolish the non-pulmonary vein ectopy, which degenerated into AF by the VOM-EI . In addition, this procedure might be expected to provoke significant parasympathetic denervation effects in the left atrium, which could contribute to the improvement in the success rate of vagally mediated AF , . A durable PVI in addition to a VOM-EI might be expected to improve the rate of freedom from AF recurrences, and further investigation will be required.