Catheter ablation using RFC energy has been established as a curative treatment in patients with PAF.21
However, the creation of point by point RFC energy linear lesions requires the understanding of the individual LA anatomy, including the identification of the PV ostia,3,22
and may be associated with significant procedure-related complications.4–7
In contrast, CTE balloon-based ablation is designed to achieve complete circular lesions around the pulmonary veins, independent of the individual PV anatomy. Therefore, this novel ablation technology may facilitate PVI and improve the safety of the procedure.
Successful PVI using CTE delivered via a balloon approach requires perfect contact to the LA wall around the PVs. Incomplete contact would result in conduction gaps and prevent complete PVI. Complete contact can be rather easily achieved with small balloons, but they would isolate distal PV sites instead of the antrum. Importantly, the antrum has been shown to be not only responsible for AF initiation but also for AF maintenance.23,24
Furthermore, a distal balloon ablation in the septal PVs would particularly increase the risk of PNP.18
Therefore, in this study, we investigated the hypothesis of whether acute PVI of all PVs can be achieved using CTE and a single big balloon in consecutive patients without any prior or intraprocedural LA imaging except angiography. We tested this in the patient population with PAF, because it has been shown that PVI at the antrum level is highly effective.3,25
In this study, we have demonstrated that 98% of all PVs can be isolated using the single big cryoballoon technique only. No additional balloon sizes or catheter-based ‘touch-up’ freezes were used.
In this consecutive series of patients, only two RIPVs could not be isolated. It is well known that the RIPV is the most difficult PV to reach after transseptal puncture. Balloon positioning in the RIPV requires postero-inferior rotation of the whole sheath/balloon system. In a previous study analysing LA MRI data, the mean endoluminal distance from the fossa ovalis to the RIPV was 20.2 mm,26
explaining the difficulty in achieving stable contact and failure of RIPV isolation in the patient with the smallest LA diameter (30 mm). Interestingly, this patient still has remained free of AF episodes, which is in agreement with the observation that the RIPV is the least electrically active PV.27
In the second patient, the transseptal sheath and the balloon could not be stably positioned in the RIPV ostium due to a large type II ASD (1.7 cm).
To obtain PVI with the single big cryoballoon technique, different procedural approaches were developed. First, approaching the superior PVs was mostly straightforward as the superior PVs are in direct alignment with the catheter/balloon position following transseptal puncture. Therefore, a median (Q1; Q2) of only 2 (2; 2) and 2 (1; 2) freezes (RSPV and LSPV) was necessary to obtain PVI. Due to significant overlap of the big balloon with the ostia of the lateral veins, final PVI of the LSPV was usually achieved from the inferior PV after a first freeze was applied to the superior vein (crosstalk technique). This prevented multiple unnecessary applications to the LSPV for complete PVI. The inferior PVs, particularly the RIPV, were more difficult to isolate and required the development of a variety of ablation techniques depending on patients individual anatomy.
Side effects of cryothermal ablation using the single big cryoballoon technique
Phrenic nerve injury
PN injury is a rare (<1%) but severe complication when RFC energy is deployed at the RSPV.28
This complication is significantly higher (up to 10%) when balloon-based ablation strategies are used.15,17,29
Particularly, small balloons located inside the PVs may lead to a short distance to the PN and increased risk of PN injury.18,30
In our study, the single big cryoballoon strategy uses an intentionally oversized balloon covering the proximal LA antrum region with as much distance to the PN as possible. This explains why no PN palsies occurred as long as ablation inside the PVs was avoided. However, if CTE was unintentionally deployed inside the septal PVs, PNP also occurred, which was short-lasting (Patient 18: 28 days and Patient 24: 3 min) after freezing at two large septal PVs (RSPV and RIPV: both 26 mm) and long-lasting (Patient 16: 384 days) after freezing inside an RSPV (Patient 16, PV: 18.2 mm). These findings prove our concept that distal balloon ablation at the septal PVs must be avoided and emphasizes the need for a >28 mm cryoballoon for larger veins. The calculated ratio between PV and balloon sizes indicates that a ratio ≥0.93 should not lead to CTE balloon ablation since even with the 28 mm cryoballoon distal balloon positions and subsequent PNP cannot be avoided in all patients.
The primary endpoint of acute electrical PVI was achieved in almost all PVs. This study did not assess permanent PVI. The chronic course of CTE balloon lesions is not known. A previous study in patients with atrial flutter demonstrated permanent bidirectional block at the right atrial isthmus.31
However, several studies using CTE for catheter ablation of accessory pathways mediated tachycardias, and atrioventricular nodal re-entry tachycardias have shown a higher recurrence rate than with RFC.9,10
AF recurrences in this series may indicate recovered PV conduction. The relatively high recurrence rate (48%) compared with studies using RFC energy is biased by the fact that daily ECG recordings were also obtained within the first 3 months, a time that is generally not taken into consideration (blanking period). Applying a blanking period of 3 months, the rate of AF recurrences decreased (30%). Nevertheless, the chronic lesion assessment after big cryoballoon-induced PVI is mandatory in future studies. Interestingly, only AF recurrence, but not AT, has been observed. Whether this indicates rather large conduction gaps remains speculative.
Two interesting acute observations during CTE balloon ablation were made. First, the crosstalk phenomenon at the lateral PVs indicates that lesions were set at the LA antrum level with the potential limitation of a less chronic effect due to the thickness of the myocardium at this site. Secondly, acute PVI does not necessarily require complete PV occlusion at the initial balloon position, but may be achieved in a stepwise approach as demonstrated by the pull-down technique. This makes electrical isolation of the inferior PVs feasible using the big balloon technique.
In the light of limited financial resources in many countries and the large number of patients with PAF, a simplified ablation strategy for PVI is desirable. The results of this study using only one single big balloon without the need for pre- or intraprocedural LA imaging could make such a strategy also attractive from an economic standpoint.