Discussion:
Our study demonstrated that in this population of patients with paroxysmal AF, the presence of an atypical PV anatomy with an LCPV had no effect on CBA outcomes and event-free survival. In addition, our study findings revealed that among the anatomical indices, only the ostial area of the LIPV showed a trend towards being a predictor of recurrence of AA following CBA.
A few studies have suggested that atypical PV anatomy is associated with a higher incidence of AF.17,18In our study participants the incidence of typical PV anatomy was 82.5% which is slightly higher compared to previous studies which suggest the incidence to be around 70-75%.19-21Nonetheless, the presence of an atypical anatomic pattern did not have a significant influence on CBA outcomes. Circumferential isolation of the LCPV can be technically challenging with cryoablation given its larger sized ostia. Thus, the presence of an atypical PV anatomy affecting CBA outcomes has been an ongoing source of discussion. To date, studies evaluating the presence of an LCPV affecting ablation success have shown variable results.5,6,14,15,22However, these studies were limited by a small sample size, a mixed population of both paroxysmal and persistent AF, and a majority of them employed the RF ablation technique. On reviewing the existing literature, we identified only one small single-center study which exclusively looked at paroxysmal AF patients undergoing CBA.23 Our findings are in agreement with this study wherein the presence of a variant PV anatomy had no influence on outcomes.
Another area of interest in CBA outcomes involves an assessment of the ovality of the individual PVs. Successful CBA requires optimal circumferential adhesion of the cryoballoon catheter at the level of the PV ostium. Excessive ovality can limit catheter adhesion leading to sub-optimal tissue contact, thereby affecting CBA outcomes. To assess whether ovality affected outcomes, we specifically looked at measures of ovality, which included the EI and OI of individual PVs. As an extension for evaluating measures of ovality, we decided to assess if the PVA at the level of the ostium influences CBA results. For our study population, the ovality of the LIPV was greater compared to the RIPV, and there was a strong trend towards the LSPV being more oval than the RSPV. This is partially in agreement with prior studies, which indicated that left-sided veins were more oval compared to their right-sided counterparts.12,24,25On further stratifying our results by the presence or absence of AA recurrence, no significant difference was observed for all the measures of PV ovality. Moreover, on univariate followed by multivariate analysis, none of the anatomical indices were predictors of recurrence of AA.
Prior studies have evaluated the role of PV anatomy in influencing mid-term outcomes following CBA.13,26Schmidt and colleagues studied a mixed population of drug refractory paroxysmal and persistent AF patients undergoing CBA. Their finding revealed that in patients with post-procedure AF recurrence, left-sided PVs were more oval compared to patients without recurrence, but no significant association was noted for the right-sided PVs.13 Our study results were contrary to these findings, and none of the anatomical PV indices showed any significant correlation to mid-term CBA success. One possible explanation for this finding could be the small sample size in the present study, and well as our study population of exclusively paroxysmal AF patients. Furthermore, in a similar study population of paroxysmal AF patients undergoing CBA, other anatomic parameters such as a sharp left lateral ridge between the left PVs and LA appendage and a sharp carina between the LSPV and LIPV predicted acute and mid-term failure. Additionally, for the RIPV, this study concluded that parameters such as a non-perpendicular angle between the axis of the PV and ostial plane and an early branching PV with a change in axis angle predicted failure.26While our study focused on mid-term outcomes following CBA, other studies have evaluated parameters of acute procedural success such as degree of occlusion and nadir balloon temperature in relation to PV diameters, ostial area and ovality indices.12,16,27
Our study is a first of its kind evaluating whether the presence of an atypical PV anatomy or PV anatomic characteristics predict mid-term outcomes exclusively in paroxysmal AF patients. Although constrained by a small sample size, our results did not show any particular association between PV anatomy and CBA failure in paroxysmal AF patients. In addition, though our study population had a fair percentage of atypical PV anatomy and oval left-sided PVs, procedural difficulties could have been negated by a segmental, non-occlusive, approach to ablation, as well as by additional CBA applications as needed until durable PV isolation was achieved. Finally, pre-procedural imaging with cCT or cardiac MRI continues to play an important role in defining PV anatomy to help guide electroanatomical mapping and PVI during the CBA procedure.