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.