Pulmonary veins isolation using cryoballoon and pulsed field ablation for atrial fibrillation: practical techniques in variable scenarios

Abstract

Catheter ablation is the most effective treatment for atrial fibrillation (AF). Electrical pulmonary veins isolation (PVI) forms the cornerstone ablation strategy. Radiofrequency (RF) in combination with 3D mapping system is the traditional ablation approach to treat AF. As a single-shot ablation system, cryoballoon (CB) has been an established ablation modality to facilitate PVI procedure. As a novel non-thermal single-shot ablation technology, pulsed field ablation (PFA) has its unique biophysical profile. Recent studies have demonstrated that PFA allows for efficient and durable PVI. However, the manipulation of single-shot ablation catheter may be different from the conventional point-by-point RF ablation catheter; ablation catheter with fixed size may have practical difficulties in variable anatomy and different clinical scenarios. The present article focuses on the technical aspects, describes the procedural approaches and illustrates the practical techniques of using CB and PFA for PVI, ultimately with the purpose to facilitate the ablation procedure and improve the patients’ clinical outcome.

Introduction

Catheter ablation is the most effective treatment for atrial fibrillation (AF) [1,2,3,4]. Pulmonary vein isolation (PVI) remains the cornerstone of all AF ablation strategies. Using radiofrequency (RF) catheter combined with 3D electroanatomical mapping system is the most well established approach to AF ablation. Single-shot ablation systems have been developed to simplify the PVI procedure. Of these, cryoballoon (CB) ablation (CBA) system has been most investigated and has been an established ablation modality for PVI in patients with paroxysmal and persistent AF [5,6,7].

Recently, pulsed field ablation (PFA) has gained great interest given its favorable characters such as tissue selectivity and ability to avoid collateral tissue damage. Published clinical data have shown that PFA allows for fast, effective, and durable PVI [8,9,10].

When using single-shot ablation system, the catheter manipulation may be different from the conventional point-by-point RF ablation catheter; the ablation catheter with fixed size (e.g. CB 28/23 mm, PFA 31/35 mm) may have technical difficulties in variable anatomy and different clinical scenarios. Based on this rationale, we discuss the procedural approaches and describe the procedural techniques using CB and PFA for AF ablation based on our institutional experience and recent publications.

Foundational practical aspects of CBA and PFA procedure

Table 1 summarizes the foundational practical aspects for CBA and PFA; this includes patient preparation, sedation, esophageal temperature monitoring if needed, groin accesses, anticoagulation, transseptal puncture, anatomy assessment, sheath preparation and exchange, and basic maneuvers of CBA and PFA for PVI.

Table 1 Summary the foundational practical aspects for CBA and PFA

CB-based PVI

CB PVI in conventional case

Our detailed practical technique for AF ablation using CB has been published previously [6, 7]. In summary, as shown in Fig. 1 [6], selective pulmonary vein angiography was performed after transseptal puncture. Figure 1(1) shows the pulmonary vein angiography for right superior pulmonary vein (RSPV), Fig. 1(2) shows the pulmonary vein angiography for left superior pulmonary vein (LSPV), Fig. 1(3) shows the pulmonary vein angiography for left inferior pulmonary vein (LIPV), and Fig. 1(4) shows the pulmonary vein angiography for right inferior pulmonary vein (RIPV).

Fig. 1

Baseline pulmonary vein angiography before CB ablation

Figure 2 shows the process of CB PVI [5]. Figure 2(1) shows LSPV was occluded by cryoballoon using the direct maneuver. Figure 2(2) shows LIPV was occluded by cryoballoon using the hockey-stick maneuver. Figure 2(3) shows RIPV was occluded by cryoballoon using semi hockey-stick maneuver. Figure 2(4) shows RSPV was occluded by cryoballoon using direct maneuver. During the ablation procedure, the esophageal luminal temperature was monitored using a temperature probe. During ablation the right sided pulmonary veins, the phrenic nerve function was monitored by direct stimulation/capturing the phrenic nerve using a decapolar diagnostic catheter. Figure 3 shows sequential real-time isolation of all four pulmonary veins using CB.

Fig. 2

Pulmonary vein occlusion using CB

Fig. 3

Real-time pulmonary vein isolation using CB

CB PVI in particular consideration: CBA for inferior PVs

Our practical technique to isolate the inferior PVs using CB has been published previously [11]. In general, to occlude and isolate the inferior PVs using CB can be difficult due to anatomic aspects and less contact force between the CB and the inferior segment of the inferior PVs. Typically, inferior PVs are located inferior posterior to ipsilateral superior PVs. Therefore after ablation of the LSPV, the steerable sheath should be curved (to inferior direction) and clockwise rotated (to posterior direction); at the same time by referring the baseline angiogram, the soft-tip spiral diagnostic catheter should be advanced into the LIPV while continuously observing the local electrogram information. After ablation the LIPV, the CB should be pulled back into the steerable sheath while the soft-tip spiral diagnostic catheter should be kept in left atrium and protect the steerable sheath. Similarly, the steerable sheath should be curved (to inferior direction) and clockwise rotated (to right sided PV direction); at the same time by referring the baseline angiogram, the soft-tip spiral diagnostic catheter should be advanced into the RIPV while continuously observing the local electrogram information.

The so-called hockey-stick in combination with a pull-down maneuver is commonly used when ablating LIPV and RIPV using CB in our center. Careful PV angiogram showing the PV ostia to PV bifurcation is required and the most caudal branch of the inferior PV should be intubated with the spiral diagnostic catheter. After inflation of the CB, the steerable sheath should be curved down and pushed up and the CB should then be advanced to engage the inferior PV ostia, resulting in a hockey-stick like shape on fluoroscopy. In order to achieve good occlusion the orientation of the steerable sheath, CB and spiral diagnostic catheter should be aligned with the course of the PV, and this may need a cross-check of the fluoroscopy at different angulation (Fig. 4). Typically, it is advisable to advance the steerable sheath to the proximal part of the CB to stabilize the CB and increase the contact between the CB and PV ostia (Fig. 4). After confirmation of good occlusion and stable CB position, we flip back the spiral diagnostic catheter to increase the visualization of the PV potential. In some cases, a suboptimal occlusion remains despite of the hockey-stick maneuver and good co-axiality, typically i.e. small contrast leakage at the inferior segment of the PV; if such situation accepted, subsequently a so-called adjunctive pull-down maneuver after 1 min freeze may help to close the inferior gap area and isolate the PV (as illustrated in Fig. 5) [11].

Fig. 4

Cross-check PV occlusion using hockey-stick maneuver: importance of alignment and co-axiality

Fig. 5

Pulmonary vein isolation using pull-down CB technique

CB PVI for common trunk PV

Left common pulmonary vein (LCPV) is present in 10–20% of the patients and it is the most frequent PV variation. The size and the anatomy of the PV ostia have been reported to impact the efficacy of CB PVI [12]. The development of 28 mm second-generation CB (CB-2) offers a wider antral and more homogeneous freezing area on the balloon surface, resulting in significantly improved procedural and clinical outcomes compared with first-generation CB (CB-1) [7]. Theoretically, CB is undersized to treat large common trunk PV (e.g. > 28 mm). However, in presence of short common trunk, PVI using 28 mm CB-2 appears to be feasible, and the long-term outcome seems not to be compromised as compared to normal PV pattern [13].

Figure 6A, B shows the angiography of a LCPV, with a cranial-anteriorly extended LSPV and a horizontally extended LIPV. The measurement of the common ostia was 24 mm. Figure 6C shows that the spiral diagnostic catheter is positioned in the LSPV, followed by the inflated 28 mm CB-2 covering the common ostia of the LCPV with direct maneuver, resulting in good occlusion of the LCPV. As alternative, operator may also choose to intubate the LIPV with the spiral diagnostic catheter in combination of hockey-stick maneuver to occlude the common ostia of the LCPV, or separately occlude and freeze the LSPV and LIPV.

Fig. 6

CB occlusion/ablation of LCPV using direct maneuver

CB in patient after PV excision

Surgically resected pulmonary vein represents an atypical complex PV anatomy for AF patents indicated to PVI. We have previously described that using the short-tip third-generation CB (CB-3) to perform PVI in such clinical setting [14]. Figure 7A shows a “short-stub” anatomy of the RSPV due to previous pulmonary surgery. A short-tip third-generation cryoballoon (CB-3, 28 mm) was selected for PVI. Figure 7B shows the first occlusion angiography and we observe contrast leak at the roof of RSPV. After using a direct push-up maneuver, the second angiography (Fig. 7C) shows that the RSPV was perfectly occluded. Figure 7D further shows the moment of RSPV isolation and continuous monitoring the compound motor action potential (CMAP) for phrenic nerve function.

Fig. 7

CB PVI in a patient with surgically resected RSPV

CB PVI in patients with vena cava filter

Performing PVI for patients with vena cava filter can be technically challenging. One major concern is mechanic dislodgement of the filter device due to catheter or sheath manipulation during the procedure. We have previously reported CB PVI in such clinical scenario [15]. Figure 8A, B shows that the steerable sheath is advanced through the filter device to superior vena cava over a long guide wire. A single transseptal puncture was then performed using the steerable sheath in combination with a long transseptal puncture needle (as shown in Fig. 8C, D). CB PVI was performed using our conventional CB maneuvers (as detailed in Fig. 8E, F). After the ablation, the ablation catheter and steerable sheath was gently pulled back and angiography showed no dislocation of the filter device (Fig. 8G, H).

Fig. 8

CB PVI in a patient with inferior vena cava filter

CB “S” maneuver for LSPV in patients with floppy atrial septum

Floppy atrial septum may result in poor co-axiality between the steerable sheath and the course of the PV due to compromised force direction delivery at the septum site, making it difficult to occlude the PV and subsequently unsuccessful isolation of the PV. In such situation, LSPV may be the most difficult one to be ablated because of the curving anatomic access. Some particular catheter maneuver may help improve the procedural efficacy. Figure 9 shows an example of using a so-called ‘S’ maneuver for LSPV ablation in a patient with floppy atrial septum. Figure 9A shows the baseline angiography of the LSPV. Using direct maneuver the LSPV was poorly occluded by the CB because of too much anterior force direction of the steerable sheath right after the atrial septum site (Fig. 9B). As then shown in Fig. 9C, E, using a continuous maneuver, i.e. slightly curve, more clockwise torque the steerable sheath and then push-up the CB followed by the steerable sheath, resulting in a “S” shape of the steerable sheath, CB and the spiral diagnostic catheter where the force direction was aligned with the course of the LSPV, the LSPV was then nicely occluded by the CB.

Fig. 9

CB PVI using ‘S’ maneuver for LSPV in a patient with floppy atrial septum

PFA-based PVI

The PFA system consists of (1) a generator which delivers pulsed electrical waveforms over multiple channels (Farastar, Farapulse Inc., Menlo Park, California), (2) a 13-F steerable delivery sheath (Faradrive), and (3) a PFA ablation catheter (Farawave).

The 12-F PFA ablation catheter (Farawave) contains 5 splines, each containing 4 electrodes to deliver pulsed field ablation energy. The PFA ablation catheter can be progressively configured into different poses: from a baseline linear shape for introducing the PFA catheter into the steerable sheath, to a semi-deployed ball or basket pose, and to a fully deployed flower configuration. Two catheter sizes were available: 31 or 35 mm at full deployment.

PFA-based PVI in conventional case

Our detailed practical approach of AF ablation using PFA has been published previously [7, 8, 16].

In brief, selective pulmonary vein angiography was performed after transseptal puncture. The transseptal sheath was then exchanged with the 13-F steerable delivery sheath (Faradrive) using over the wire technique into the left atrium (LA). The sheath was continuously flushed with heparinized saline. The PFA ablation catheter (Farawave) was then advanced via the steerable delivery sheath over a guide wire into the LA to achieve the PVs. PFA ablation started at the LSPV and was carried out in a clockwise fashion (LSPV, LIPV, RIPV, and RSPV). The ablation energy was delivered with a set of microsecond scale, biphasic, unsynchronized 2.0 kV pulses. The duration of each PFA application, consisting of 5 trains of pulses, was 2.5 s.

Each PV was ablated with “8 applications protocol” (Fig. 10) using different configurations, i.e. 2 in basket —> small rotation (for lesion overlapping) —> another 2 in basket —> 2 in flower (for PV antral lesion) —> small rotation —> another 2 in flower. PVs were remapped and PVI was confirmed by electrograms and with differential pacing if necessary. Phrenic nerve function was evaluated by direct phrenic capture during PFA and by observing diaphragmatic motion during inspiration. Luminal esophageal temperature monitoring was not any more performed in our center after the validation phase in our “5S” study [9]. Figure 11A–D shows an example of PFA for each PV with different configurations, and Fig. 11E shows PV potential elimination after first PFA application at LSPV.

Fig. 10

Example of the “8-application” PFA for LSPV

Fig. 11

Example of PFA for each PV with different configurations

PFA for common PV

Our experience shows that PFA-based PVI for patents with common PV appears feasible [9, 10]. As shown in Fig. 12A, B, the baseline angiography revealed left sided common PV (LCPV), and the measurement of the common trunk was 28 mm in diameter. A 35 mm PFA catheter was selected; the guide wire was placed at the LIPV, and the steerable sheath was aligned with the guide wire. The PFA catheter was then gently advanced, following the guide wire, to cover the common trunk of the PV with either “basket” or “flower” configuration (Fig. 12C, D). In case of just short common trunk, sequential treatment of each PV as a conventional case using the PFA catheter should be feasible.

Fig. 12

PFA for LCPV

PFA in patients with common posterior PV

Inferior common pulmonary vein (ICPV), i.e. both inferior pulmonary veins drain via a common trunk, is a rare anatomic variant with less than 1% incidence among patients undergoing AF ablation [17]. The rare anatomic variant per se may increase the difficulty of the ablation procedure. As another consequence of such anatomic variant, the esophagus is in adjacent superiorly, posteriorly and inferiorly to the ICPV. Hence, ablation with thermal energy also exposes such patients to increased risk of atrioesophageal fistula [17, 18]. It has been known that PFA allows for non-thermal, myocardium selective ablation as compared to thermal ablation modalities. Recently, Mittal and colleagues reported PFA in treating AF patient with ICPV [18]. Figure 13A shows the left atrium with ICPV generated by cardiac computer tomography. Figure 13B, C in particular shows the sequential isolation of the common trunk RIPV and LIPV with PFA using the 8-application protocol. After PVI, the LA posterior wall was also treated by PFA in “flower” configuration. Figure 13D shows the 3D voltage map to confirm the isolation of all PVs and the posterior wall of the LA.

Fig. 13

PFA in a patient with inferior common pulmonary vein (ICPV)

PFA in patients with implanted cardiac devices

To perform AF ablation in patients with implanted cardiac devices can be technically challenging. Mechanic dislodgement of the implanted cardiac devices and/or the leads is a potential major complication during the ablation procedure. In such situation, PFA which only needs single transseptal puncture and simplified practical technique appears to be a reasonable option. We have recently reported PFA in patients with patent foramen ovale (PFO) occluder, pacemaker, or implantable cardioverter defibrillator (ICD) [10, 16, 19]. Here, we summarized the technical approach of PFA in a patient with PFO occluder and ICD. Figure 14 shows the transseptal puncture under the guidance of fluoroscopy and transesophageal echocardiography (TEE), importantly without tangling the ICD lead and the PFO occluder. The transseptal puncture site was directly inferior posterior to the PFO occluder. Figure 15 shows the baseline angiography of left common pulmonary vein (LCPV), RIPV and RSPV. A 35 mm PFA ablation catheter was then selected, and all PVs were successfully isolated with the 8-application ablation protocol Fig. 16. After the procedure, TEE and fluoroscopy showed no dislodgement of the PFO occluder and the ICD lead (Fig. 17).

Fig. 14

Transseptal puncture under the guidance of fluoroscopy and TEE before PFA

Fig. 15

Pulmonary vein angiography before PFA in a patient with implanted cardiac device

Fig. 16

PFA PVI in a patient with implanted cardiac device

Fig. 17

Fluoroscopy and TEE after PFA shows no dislocation of the implanted cardiac device

Conclusions

Catheter ablation is the most effective treatment for atrial fibrillation (AF). Electrical pulmonary veins isolation (PVI) forms the cornerstone ablation strategy. Radiofrequency in combination with 3D mapping system is the traditional ablation approach to treat AF. As a single-shot ablation system, cryoballoon (CB) has been an established ablation modality to facilitate PVI procedure. As a novel non-thermal single-shot ablation technology, pulsed field ablation (PFA) has its unique biophysical profile. Recent studies have demonstrated that PFA allows for efficient and durable PVI. However, the manipulation of single-shot ablation catheter may be different from the conventional point-by-point RF ablation catheter; ablation catheter with fixed size may have practical difficulties in variable anatomy and different clinical scenarios. The present article focused on the technical aspects, described the procedural approaches and illustrated the practical techniques of using CB and PFA for PVI, ultimately, with the purpose to facilitate the ablation procedure and improve the patients’ clinical outcome.