Pulmonary Vein Isolation: The Arctic Circle vs. Spot Welding

In this article, the authors describe their experience using Medronic's Arctic Front^® at Memorial Advanced Cardiovascular Institute.

Since the early work of the Bordeaux group demonstrating the importance of pulmonary vein (PV) depolarizations initiating atrial fibrillation,¹ pulmonary vein isolation (PVI) has been the cornerstone for ablative therapy to mitigate paroxysmal atrial fibrillation (PAF). Catheter-based techniques have essentially relied on delivering radiofrequency (RF) energy to contiguous regions of the left atrium in a circumferential manner near the pulmonary vein orifices. When successful transmural lesions are created, electrical isolation of the pulmonary veins is achieved. Unfortunately, gaps may occur in this ablative perimeter that allow continued conduction of abnormal impulses from the pulmonary veins to the atria. “Reconnection” may also occur in regions which were initially isolated, perhaps due to lack of true transmurality of the lesion. Many reports of repeat ablation for recurrent PAF show that PV reconnection occurs in at least 50% of patients.²

Our institution is a community hospital that has had an active ablation program for atrial fibrillation as well as complex ventricular dysrhythmias since 2006. Our atrial fibrillation ablation program had been more heavily weighted toward patients having symptomatic, persistent, drug refractory atrial fibrillation. Prior to using the Medtronic Arctic Front^® Cryoballoon system, our methodology of choice for both paroxysmal and persistent atrial fibrillation mainly utilized the following techniques:

1. Preprocedure CT scans
2. Use of Biosense Webster’s CartoSound^™ and CartoMerge^™
3. The Biosense Webster 4mm saline irrigated catheter for ablation, (usually F-J curve ThermoCool^®)
4. Use of either St. Jude Medical’s SL1, SR0, or Agilis^™ sheath for transseptal puncture as well as catheter manipulation within the left atrium.
5. An approach of pulmonary vein antral isolation (PVAI) alone for PAF, but usually the addition of a superior roof line in persistent atrial fibrillation.
6. Additional RF lesions, if needed, including a low posterior line connecting the PV circles, a left inferior PV to mitral annular line for left atrial flutter if present; coronary sinus lesions and localized focal lesions if indicated in more complex cases.

With this approach, we had been able to decrease our fluoroscopic time to generally less than 35 minutes even for complex persistent AF, and typically less than 20 minutes for PAF.

The addition of intracardiac echocardiography coupled with electroanatomic mapping was invaluable to achieve this reduction in fluoroscopic times and markedly improved safety from the standpoint of:

1. Transseptal puncture
2. Visualization of the esophagus
3. Visualization and Doppler assessment of the pulmonary veins before, during and after ablation
4. Real-time assessment for pericardial effusion

If the radiofrequency catheter-based approach is akin to “sequential spot welding” around the PV ostium, balloon cryoablation of the PV is an attempt to create a simultaneous circumferential scar (“Arctic Circle”) with subzero temperatures. A prerequisite for the success of either technique is highly dependent upon excellent physical contact between the energy transducer and the atrial tissue. In the case of electrode catheters, the force of electrode tissue contact is critical to achieve transmural lesions,³ while in the case of a balloon catheter for cryoablation, complete occlusion of the pulmonary vein ostium is critical to achieve a true circumferential scar. Occlusion also prevents localized warming of the balloon tissue perimeter due to blood flow around the balloon from the vein being targeted. We felt that the Medtronic Arctic Front^® cryoballoon approach to PV isolation was an important tool to treat healthier patients with symptomatic PAF, who are most likely to have PV triggers as the main underlying etiology for their arrhythmia. We were the first institution in the state of Indiana to perform catheter ablation for atrial fibrillation with this technique, and are encouraged by the initial results and safety of the system. Our standard approach has been as follows:

1. Warfarin or dabigatran stopped two days prior to procedure (will perform procedure up to INR of 2.0).
2. TEE on any patient not in sinus rhythm on the day of the procedure. Preprocedure CTs on all patients to define PV anatomy and size.
3. Conscious sedation with IV midazolam, fentanyl and dexmedetomidine (Precedex^®) on most patients; general endotracheal anesthesia if the patient has significant sleep apnea.
4. Lab personnel: Attending electrophysiologist, one RN (monitors patient and administers drugs, sedation, heparin), three radiology technicians (one is first assistant with the electrophysiologist, one operates the cryo console and intracardiac ultrasound machine, and one monitors the EP monitoring system and stimulator).
5. Three-catheter approach: 

• Left femoral vein: 

• 7F sheath: Coronary sinus decapolar (moved to SVC/RA junction for right phrenic nerve pacing during right PV cryoablation);
• 11F sheath: Biosense Webster SoundStar^™ intracardiac echocardiographic catheter.

• Right femoral vein:

• 8F St. Jude Medical, Daig Division SL1 sheath with Cook Medical’s transseptal needle for transseptal puncture

6. ACT kept at 300–400 seconds during case with 100u/kg intravenous heparin bolus immediately after placing femoral sheaths, followed by an infusion rate of 1000U/hour and adjusted every 30 minutes to maintain the ACT in the desired range.
7. 

• Insert and retain 0.035”, 180 cm wire in LSPV through transseptal sheath followed by removal of SL1 sheath and dilator (Figure 1A).
• Insert and remove short 14F sheath and dilator over the 180 cm wire to expand right femoral vein entry site (improves ability to insert Medtronic FlexCath^® Steerable Sheath, 15F outer, 12F inner diameter).
• Advance  FlexCath^® sheath over 180 cm wire into left atrium (Figure 1B).
• Pass Arctic Front^® cryoballoon catheter (28mm) through FlexCath^® sheath using the Achieve^™ spiral catheter as the guide after appropriate flushing and preparation of the Arctic Front^® catheter, Tuohy valve, and balloon.

8. Guiding of Achieve^™ catheter into pulmonary vein followed by fluoroscopic visualization of intravenous contrast injected into PV via Arctic Front^® catheter (Figure 2). ICE was also used to guide the catheter and cryoballoon toward the PV, and color flow Doppler was used to assess PV occlusion (Figures 3A and 3B).
9. Cryoballoon freeze initiated with vein ablation sequence of LSPV, LIPV, RIPV, RSPV; typically two 240-second applications to each vein.
10. Assessment of PV isolation by examining PV potentials either during the cryo lesion or post completion during sinus rhythm or CS pacing.
11. Use of a 4mm or 8mm RF ablation catheter through the FlexCath^® sheath to ablate any incomplete isolated segments of PVs.

We did not use the Achieve^™ catheter for our first two cases, but have used it since then. This catheter allows for a single transseptal puncture, and is a very efficient way to perform the procedure and assess for PV isolation, avoiding multiple catheter/wire exchanges. It should be kept in mind that the Achieve^™ is a 3.3 French, 8-pole electrode catheter (1 mm electrode with 4 mm spacing) and comes in two loop sizes (15 and 20 mm). PV connections and electrograms may be fairly easily identified, and seen to disappear during cryoablation (Figure 4).

Preliminary Results

In our first 15 cases, we have had no procedure-related complications, including the absence of any groin complications. Twelve out of the 15 were done with conscious sedation and three with general endotracheal anesthesia. There were no differences in patient perception or discomfort related to the procedure. The use of dexmedetomidine (Precedex^®) greatly enhanced the ability to perform the procedure without general anesthesia. All patients tolerated phrenic nerve pacing without any discomfort.

PV isolation of all veins was achieved in 13/15 patients with the cryoballoon alone and in a total of 57/61 veins targeted. A 4mm or 8mm catheter was used to complete the isolation in the cases with incomplete isolation. The veins requiring additional catheter RF ablation included two left inferior veins and two right inferior veins. No cases of right diaphragm paralysis occurred. In only one case was a right inferior cryoablation lesion terminated early due to concern of a decrease in right diaphragm pulsation. It turned out that the catheter pacing the phrenic nerve had moved, leading to loss of capture. After repositioning of the catheter, the cryolesion was completed without event. Temperatures achieved during cryoablation have ranged from -38° C to -71° C. 

Procedure times have ranged from 1.8 hours to 4 hours, fluoroscopic times from 20 minutes to 70 minutes, and intravenous contrast use of 40 cc to 180 cc. We have continued antiarrhythmic medications, including class IC or class III agents, in all patients except for two patients who had intolerable side effects from antiarrhythmic agents. Ten of the 15 remain in sinus rhythm without symptomatic recurrence, including the two not taking antiarrhythmic agents (mean follow up only 1 month). We plan to discontinue antiarrhythmic agents 8–12 weeks following the procedure in the remaining patients if they remain free of recurrent arrhythmia. All patients are on either dabigatran 150 mg bid or warfarin as well as 81 mg aspirin daily. Of the five with early recurrences, two have had required cardioversion, and the other three continue to have paroxysmal atrial fibrillation, although less frequently than prior to the procedure.

Conclusions

Cryoablation using the Arctic Front^® system appears to be safe and effective for PVI in patients with paroxysmal atrial fibrillation. In our opinion, the learning curve is heavily dependent on the previous experience of the operator in performing PV isolation with RF catheter ablation. Familiarity with ICE techniques is also very helpful. The Arctic Front^® uses a fairly large 15F sheath, which does require care in handling to prevent complications. Institutions should have appropriate credentialing criteria for both initiation and maintenance of privileges related to operator training and experience.

At this time, the Arctic Front^® system is FDA approved for patients with symptomatic, drug-refractory, paroxysmal atrial fibrillation. Future research will be needed to define whether there is a role for this technique in select patients with persistent atrial fibrillation, or whether cryoballoon ablation of the pulmonary veins will prove to have better long-term results in creating permanent PVI compared to RF catheter ablation.

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1. Haïssaguerre M, Jais P, Shah DC, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med. 1998;339:659-666.
2. Callans DJ, Gerstenfeld EP, Dixit S, et al. Efficacy of repeat pulmonary vein isolation procedures in patients with recurrent atrial fibrillation. J Cardiovasc Electrophysiol. 2004;15:1050=1055. 
3. Haines D. Determinants of lesion size during radiofrequency catheter ablation: The role of electrode-tissue contact pressure and duration of energy delivery. J Cardiovasc Electrophysiol. 1991;2:509-515.