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.