Cryoablation for Atrial Fibrillation: Case Study From CarolinaEast Medical Center

Atrial fibrillation is the most common arrhythmia, affecting approximately 2.2 million people in the US alone. The clinical effects of atrial fibrillation stem from the elevated stroke risk, but also from the symptoms caused by it. Reducing the symptoms associated with atrial fibrillation often involves controlling the rapid heart rates. However, despite rate control, many patients with atrial fibrillation remain symptomatic and complain of fatigue, lethargy, dizziness, or shortness of breath. Therefore, maintaining sinus rhythm or a rhythm control strategy becomes the goal of treatment for many patients.

Treatments to maintain normal sinus rhythm first involve initiation of antiarrhythmic medications such as flecainide, sotalol, or amiodarone. However, the efficacy of these medications is often disappointing, with up to a 60–80% failure rate.¹ Furthermore, side effects and contraindications of the medications prevent their use in many patients. Given the disappointing results of antiarrhythmic medications, catheter ablation has become an effective strategy in carefully selected patients to treat atrial fibrillation.

Catheter Ablation

The aim of the ablation procedure is to eliminate the triggers of atrial fibrillation, particularly in patients with paroxysmal atrial fibrillation. For patients with persistent atrial fibrillation, modifying the substrate responsible for maintenance of atrial fibrillation also becomes important. It is believed that the majority of triggers for atrial fibrillation come from muscle fibers located within the pulmonary veins.² As a result, the cornerstone of the ablation is pulmonary vein isolation. Various techniques have been used to achieve isolation, the majority of which use radiofrequency energy. The initial approaches targeted segmental ostial ablation of the pulmonary veins. Recently, wide circumferential ablation has become widely used. Both techniques use electrogram guidance, fluoroscopic guidance, and often employ 3D mapping systems such as Carto (Biosense Webster, Inc., a Johnson & Johnson company, Diamond Bar, CA) or EnSite NavX (St. Jude Medical, St. Paul, MN), to deliver point-by-point lesions around the veins. Isolation is usually verified using a Lasso catheter, which sits inside the vein. The efficacy of this technique has varied depending on the definitions of success and the frequency of follow up. The general consensus from large studies is about a 65–75% success rate for freedom from atrial fibrillation at one year for paroxysmal atrial fibrillation.³ The success rates for persistent atrial fibrillation are generally lower as the target for ablation becomes substrate modification in addition to elimination of triggers.⁴ Reasons for long-term failures for ablation of paroxysmal atrial fibrillation include lack of initial isolation, vein reconnection or other additional triggers besides pulmonary veins.⁵

Recently, the FDA approved the use of the Arctic Front^® Cryoballoon Catheter (Medtronic, Minneapolis, MN) for the treatment of paroxysmal atrial fibrillation. This technique is different in that it can deliver circumferential lesions around the veins using a coolant-filled balloon to freeze the tissue outside the veins. The approval of the catheter is based on the STOP-AF trial, which involved 245 patients with paroxysmal atrial fibrillation who had failed at least one antiarrhythmic drug. After one year, 69.9% of patients randomized to ablation were free of atrial fibrillation versus only 7.3% of patients on antiarrhythmic drugs. The rate of serious adverse events was similar in comparison between drugs and ablation.⁶ There have yet to be any large head-to-head trials comparing radiofrequency ablation with the cryoballoon. The theoretical benefit includes the ability to reliably deliver lesions around the vein in a circumferential manner, potentially shortening the procedure time and possibly the efficacy of isolation.

The CarolinaEast Medical Center is one of the few hospitals in North Carolina that is using the new Medtronic Arctic Front^® Cryoballoon to target atrial fibrillation. Led by Dr. Angela Park, Dr. Christopher Hudson, and technologists Randall Heminger and Michael LaConte, patients in the Eastern Coastal Plain of North Carolina are getting the benefit of this new technology. Having acquired the cryo technology in December 2011, we have done 12 cases so far and on average do about 2 cases per week. Based on our early experience with the cryoballoon, we present a case to illustrate how this has been incorporated into our treatment of atrial fibrillation.

Case Study

The patient is a 39-year-old male with paroxysmal atrial fibrillation. He is generally healthy but has failed flecainide therapy, continuing to have breakthroughs of atrial fibrillation lasting minutes to hours. His other medications include carvedilol 6.25 mg PO BID and Pradaxa (Boehringer Ingelheim) 150 mg PO BID. This was started one month prior to the procedure. His echocardiogram shows normal left ventricular function with normal valvular function. His left atrial size is 3.5 cm. In preparation for the ablation, Pradaxa was stopped 36 hours prior to the procedure.

The procedure was done under general anesthesia in the electrophysiology lab. A transesophageal echo was done prior to the procedure, after the patient was sedated and intubated while on the table. This revealed no evidence of left atrial appendage thrombus. The valves demonstrated normal excursions without significant regurgitation or stenosis. The left atrium was not significantly enlarged. The septum was visualized, and there was no evidence of a patent foramen ovale.

Next, access was obtained into the left and right femoral veins using the Seldinger technique. A 10 French (Fr), 7 Fr, and 5 Fr sheath were inserted into the left femoral vein and two 5 Fr sheaths were placed into the right femoral vein. On the left, a 9 Fr ViewFlex PLUS ICE catheter (St. Jude Medical) was inserted into the 10 Fr sheath and placed fluoroscopically into the right atrium. A duodecapolar super large curve Livewire^™ steerable catheter (St. Jude Medical) was placed through the 7 Fr sheath around the tricuspid annulus and into the coronary sinus. A quadripolar 5 Fr Inquiry^™ steerable deflectable catheter (St. Jude Medical) was placed in the region of the AV node to record a His signal. A nondeflectable 5 Fr Josephson quadripolar catheter was placed through the right 5 Fr sheath into the right ventricle for the baseline electrophysiology study. This was later removed, and both 5 Fr sheaths on the right were replaced with two 8.5 Fr SL1 sheaths (St. Jude Medical) for the transseptal punctures.

The baseline EP study showed normal sinus rhythm: PR interval 160 ms; QRS duration 70 ms; AH interval 70 ms; HV interval of 50 ms; QT interval 420 ms. One to one retrograde conduction was maintained down to 500 ms. Conduction was concentric and decremental with no evidence of an accessory pathway. One to one anterograde conduction was maintained down to 400 ms. The AV nodal effective refractory period at 800 ms was 420 ms. There was no evidence of an anterograde “jump.” There was no inducible SVT with programmed and burst atrial pacing.

The transseptal punctures were completed using two SL1 Fast-Cath Transseptal Guiding catheters (St. Jude Medical), through which a 21 gauge tip, 71 cm transseptal needle was inserted. Using fluoroscopic, intracardiac echo (ICE) and pressure monitoring, two transseptal punctures were completed.

Figure 1 demonstrates both sheaths across the septum with a Biosense Webster 7 Fr 15 mm Lasso catheter in place. This Lasso catheter is used to record signals within the pulmonary vein and help document when pulmonary vein isolation has been achieved. In this LAO view, the duodecapolar catheter and His catheter are also visualized. A total of 15,000 units of heparin is bolused once in the left atrium and a drip is started to maintain an ACT of 300 to 350. Next, one SL1 sheath is exchanged for the 12 Fr FlexCath Sheath using a wire exchange. Once the sheath is in place, the Arctic Front^® 28 mm Cryoballoon is placed through the sheath into the left atrium. It is an over-the-wire system. The wire used is a Rosen Curved Wire Guide, 0.035 inches (Cook Medical, Bloomington, IN). This wire is used to wire individual branches of each pulmonary vein.

Figure 2 demonstrates the wire projecting into a branch of the left superior vein and the balloon tracking over the wire to occlude the ostium of the vein. Contrast is injected, verifying correct positioning.

Once the balloon is positioned into the antrum of the vein with an adequate seal, a total of four minutes of “freeze” is delivered. Correct positioning is verified with contrast injection. Ideally, there should be very little lead of contrast outside the vein. It is recommended that a different branch of each vein be wired to achieve a different contact point on the antrum of the vein with the balloon helping to ensure isolation. Three different branches were wired.

Figure 3 shows pulmonary vein potentials present on the Lasso catheter at the onset of the freeze. After the third freeze, Figure 4 demonstrates electrical isolation of the superior vein as the pulmonary vein potentials are now dissociated from left atrial activity.

Figure 5 shows positioning of the balloon in the left inferior vein. Similarly, three different freezes are completed by wiring a different branch. Once completed, the vein is checked using the Lasso catheter for electrical isolation.

Figure 6 shows positioning of the balloon in the right superior vein. Notice that the 5 Fr Inquiry steerable catheter is placed up into the SVC to pace and capture the phrenic nerve. During the entire freeze in both the right superior and right inferior vein, the physician monitors for diaphragm contraction. Because of the close proximity to the phrenic nerve, any diminution of contraction should prompt termination of the freeze so permanent damage to the nerve does not occur. In this case, there was no evidence of phrenic nerve irritation.

Figure 7 shows positioning in the right inferior vein with the balloon inflated. The right inferior vein is often the most difficult vein to occlude because of the close proximity to the transseptal puncture. 

The endpoint of the procedure is electrical isolation of all four pulmonary veins. If any of the veins cannot be isolated with the balloon, occasionally it is necessary to use a focal catheter to “touch up” gaps. In this case, all four veins were isolated using the balloon.

This patient did well post procedure without any major issues during hospitalization. He was started back on Pradaxa on post-procedure day 1 and discharged on it on post procedure day 2, with the plan to discontinue anticoagulation in three months.

Summary

We are excited to offer patients cryo technology. Based on our early experience, we envision the cryoballoon procedure becoming the cornerstone of therapy for patients with paroxysmal atrial fibrillation. We look forward to continue improving the treatment outcomes for patients with atrial fibrillation in Eastern North Carolina.

References

1. Noheria A, Kumar A, Wylie JV Jr, Josephson ME. Catheter ablation vs antiarrhythmic drug therapy for atrial fibrillation: A systematic review. Ann Intern Med 2008;168:581–586.
2. Haïssaguerre M, Jaïs 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.
3. Wilber DJ, Pappone C, Neuzil P, et al. Comparison of antiarrhythmic drug therapy and radiofrequency catheter ablation in patients with paroxysmal atrial fibrillation: A randomized controlled trial. JAMA 2010;303:333.
4. Oral H, Pappone C, Chugh A, et al. Circumferential pulmonary-vein ablation for chronic atrial fibrillation. N Engl J Med 2006;354:934–941.
5. Nanthakumar K, Plumb VJ, Epstein AE, et al. Resumption of electrical conduction in previously isolated pulmonary veins: rationale for different strategy? Circulation 2004;109:1226–1229.
6. Packer D, et al. Sustained Treatment of Paroxysmal Atrial Fibrillation (STOP-AF). ACC.10/i2 summit.