Commentary
A previous study has demonstrated that during sinus rhythm, conduction
from the right atrium (RA) to the LA occurs via three distinct
sites—Bachmann’s bundle, the rim of the fossa ovalis, and the coronary
sinus.1 However, anatomical and electrophysiological
studies have reported a fourth interatrial conduction over an intercaval
bundle that connects the RA and the carina of the right PVs.2,3 In the era of contact force-guided ablation, a
contiguous and durable lesion is expected.4Nevertheless, the intercaval bundle that connects the RA and the carina
of the right PV bypasses the durable circumferential lesion. Therefore,
when performing repeat ablation after contact force-guided ablation that
requires additional ablation in the carina, AF recurrence due to
reconnection over the intercaval conduction should also be considered a
possible mechanism of recurrence.
In this case, the earliest LA breakthrough was found at the insertion
site of Buchmann’s bundle. The activation timing of the anterior carina
of the right PV was slightly delayed compared to that of Bachmann’s
bundle insertion site. Hence, we suspected a residual conduction over a
previous circumferential region. However, several energy applications
delivered on the circumferential line were unsuccessfully. Therefore, we
considered the possibility of an electrical connection over the
intercaval bundle. Initially, an activation map was created in the LA
during pacing from the RSPV (Figure 2 ). The earliest activation
in the LA was found at the LA breakthrough site of Bachmann’s bundle
during sinus rhythm, and a collision activation pattern was observed
along the circumferential ablation line. This finding suggested that
pacing from the RSPV was blocked at the anterior line, but it was
conducted to the RA via the intercaval bundle and then propagated over
Buchmann’s bundle. We, therefore, created a further activation map for
the RA. The earliest activation site was at the posterior wall of the
RA, anatomically opposite to the right PV carina. Initial energy
applications at the earliest RA activation site prolonged the RSPV
potential, and the second energy application achieved ipsilateral right
PV isolation (Figure 3 ). No further energy applications were
required in the LA.
Contiguous and optimized radiofrequency energy applications improve
lesion durability. Nevertheless, in the presence of an RA-RPV intercaval
bundle, additional energy application within a circumferential line is
required to achieve PV isolation. In the presence of reconduction over
the intercaval bundle, activation mapping or activation sequencing of a
circular mapping catheter demonstrates the earliest activation site at
the anterior carina. This activation might be misinterpreted as residual
conduction over the anterior line where the thick myocardium exits. A
recent study has demonstrated the importance of detailed activation
mapping before initial ablation.5 Patients with two
early activation sites—Bachmann’s bundle and the anterior
carina—frequently required carina ablation, suggesting an epicardial
connection.5 However, detailed activation mapping may
not be helpful for identifying the earliest activation site of the LA
during repeated procedures. Precise annotation is limited where energy
applications were performed previously. Even a slight conduction delay
after a previous ablation may unmask an interatrial connection over the
intercaval bundle. When performing a repeated procedure after AI-guided
ablation requiring RPV carina ablation, it is important to consider
possible reconduction over the intercaval conduction. Activation mapping
during pacing from the RSPV might help distinguish the reconnection
site. Targeting the RA insertion site of the intercaval bundle avoids
the risk of PV stenosis and can, thus, be considered an alternative
target.