One Lab’s Approach to Cryo Pulmonary Vein Isolation

Introduction

In recent years, ablation strategies aimed at curing atrial fibrillation have completely changed the landscape of clinical electrophysiology. The efficacy of pulmonary vein isolation, particularly for the treatment of paroxysmal atrial fibrillation, has consistently been shown to be an effective treatment for atrial fibrillation.¹ Patients that were once doomed to either incapacitating symptoms or a lifetime of often very expensive medications with potentially lethal side effects (or both, given the ineffectiveness of the medications) now have the option of a potentially curative procedure.

However, this new era in the treatment of the most common sustained arrhythmia is not without its curses as well. Complications associated with ablation remain all too common, and the need for redo procedures even more common.² I do not need to describe the technical difficulties of the procedure to those who have been involved in those challenging cases that seem to take all day. As the technology has advanced, equipment such as 3D mapping systems, irrigated radiofrequency (RF) ablation catheters, and intracardiac echocardiography have increased both the success and the safety of the procedure. However, since the success rate is lower and the complication rate is higher than other ablations, such as SVT or RVOT VT ablations, it is still problematic for those of us who perform ablations for the potential goal to safely cure people.

As part of a continued attempt to provide safe, effective, and innovative care for patients, I recently started using the Arctic Front® cryoballoon (Medtronic, Minneapolis, MN) for pulmonary vein isolation. This article will detail my initial experience with the technology.

Approach and Techniques

Point-by-point RF ablation of the pulmonary veins is fraught with problems. The use of RF on often very thin tissue, the risk of damage to the surrounding structures, and the risk of gaps in the ablation sets with resultant atrial tachycardias are some of the major limitations. The cryoballoon system offers the ability to ablate in a full circle around the pulmonary veins, and the most recent system allows the operator to simultaneously map the pulmonary veins and ablate through a single transseptal. I have found the system to be very easy to use and to produce higher success rates than point-by-point RF. Additionally, at least in patients undergoing PVI only, left atrial tachycardias are almost unheard of.

My approach begins with a CT of the chest and a transesophageal echocardiogram the day before the procedure. Patients on dabigatran are asked to hold their anticoagulation for three days prior, whereas patients on warfarin continue it without interruption. High-risk patients, such as those that have had a stroke, are asked to continue warfarin if they are on it, and I transition them to warfarin if they take another oral anticoagulant as I am reluctant to perform the ablation while on dabigatran or rivaroxaban.

After the catheters are in place, I routinely use intracardiac echocardiography (ICE) for transseptal access. I use the larger AcuNav catheter (Biosense Webster, Inc., a Johnson & Johnson company, Diamond Bar, CA), as I find it provides superior images of the veins compared to the smaller ICE catheter. When tenting of the fossa ovalis is seen, I cross with the SafeSept^™ Transseptal Guidewire (Pressure Products, Inc., San Pedro, CA), and when the wire is in the left atrium but before the needle or dilator, I give a heparin bolus and check the first ACT in 10 minutes. I make every effort to make my transseptal puncture low and anterior, as the first step to successfully ablating the right inferior vein is a well-positioned transseptal puncture.

Through an SL1 sheath (St. Jude Medical, St. Paul, MN), I place a circular mapping catheter. With this I quickly create a high-density map of the left atrium. In fact, the geometry is generally created and registered to the CT scan before the first ACT is checked (10 minutes). Many operators rely primarily or even solely on fluoroscopy, but I feel that the map is invaluable. The EnSite system (St. Jude Medical) visualizes the intraluminal circular mapping catheter used with the cryoballoon, and assists with navigation and voltage mapping. This allows me to determine exactly where the mapping catheter is both during ablation and when checking for isolation after ablation, and the 3D work environment is useful for sub-selecting individual branches for positioning the balloon. This, for example, is very helpful when ablating a common os by using a segmental approach.

After the map is constructed, the initial transseptal sheath is exchanged over a wire for the FlexCath, which is part of the ablation system. My order of battle is usually LS, LI, RS, and finally RI. I use a deflectable quadripolar catheter that I place in the RV for pacing during ablation of the left-sided veins (asystole can occasionally occur when ablating the left-sided veins), and I move it to the SVC to pace the phrenic nerve during ablation of the right veins. Prior to ablation, I perform a contrast injection to assure good occlusion of the vein. In addition to this, I use color Doppler imaging with the ICE catheter. This is particularly useful in obese patients who often have poor venograms, or in patients in whom I wish to avoid using contrast, such as those with renal dysfunction or a contrast allergy. Another method I use to monitor the effectiveness of the lesion is to watch the slope of the temperature curve (the steeper the better) and to monitor for pulmonary vein delay, then isolation with the mapping catheter. If I am able to see real-time PV electrograms during ablation and do not see isolation or at least substantial delay (into or past the far-field ventricular potential that is usually seen) within 60–90 seconds, I come off and reposition the balloon. I feel it is very useful to rely on multiple modalities to monitor the lesion, that way if one does not look good (a poor occlusion seen on venogram) but the others do (no leak seen on color Doppler, rapid delay then isolation of the vein), I am assured that I will have a good result. Only relying on one modality may result in unnecessary ablation or ineffective ablations.

One of the often-challenging aspects of using the intraluminal circular mapping catheter is differentiating far-field atrial potentials from PV potentials. When one is able to place the catheter in the vein and see the typical three-component electrogram (far-field atrial, PV, far-field ventricular), as well as see the PV potential separate out from the atrial potential, then disappear, it is obvious. But often the catheter has to be placed too deep in the vein to observe the potentials during ablation, and after ablation the catheter is pulled back into the antrum to check for isolation. In particular, along the anterior regions of the left-sided veins, left atrial appendage signals can mimic PV potentials. Here it is often useful to utilize the map, first by shadowing the catheter in the antrum pre ablation and saving a snapshot of the electrograms. Then, after ablation, the catheter can be repositioned in the same location where it was initially shadowed, and the pre- and post-ablation electrograms can be compared. Pacing from the mapping catheter to determine if exit block has been achieved is helpful as well.

After I have isolated the veins, I observe a waiting period, during which time I perform the baseline EP study. I then recheck all of the veins for entrance and exit block with the intraluminal circular mapping catheter. I do not routinely use isoproterenol to look for non-PV triggers, but I generally will in redo procedures. As I re-check the veins, I also re-map them with the mapping system. After the case is done, I give a printed copy of the pre- and post-ablation map to the patients. They really appreciate being able to have something tangible that shows what was done during the ablation, and to have a memento to take home. They often bring these images — crinkled, folded, and re-folded after they have shown their friends and family — with them to their follow-up visits. The more we can involve patients in their own care, the more satisfied they are.

Discussion

I have been very pleased with this new technique for pulmonary vein isolation. To date, I have only short-term follow up (just under a year), but in a very heterogeneous patient population including persistent and paroxysmal, older and younger patients, first time and redo ablations, as well as those with and without structural heart disease, my success rate has far exceeded my RF success rate. Obviously, as my follow up is extended, there will be some attrition rate as more people recur, but overall I have been very pleased with the system. Paroxysmal PVI-only patients routinely take no more than two hours, which includes making a baseline map, a waiting period, entrance and exit block, and making a post re-map.

Certainly this will not be the final chapter in ablation for atrial fibrillation. The transseptal hole is very large (15 French), when the veins are of very different sizes, using a single balloon size can be difficult if not impossible, oval-shaped PV ostia are quite challenging, and the risk of esophageal damage, though probably reduced, has not been eliminated. I am sure that the future will bring even more effective and safer ablation systems, such as the circular RF catheter that is currently being developed. To borrow a term from the current political lexicon, perhaps “alternative energy sources” will prove superior to cryothermia or RF. For the meantime, however, I feel that the cryoballoon has provided electrophysiology laboratories with a very effective, safe, and efficient tool for pulmonary vein isolation.

The road to a cure for atrial fibrillation is long, winding, and fraught with setbacks. The more we learn, the more questions we have. The only question that has been answered, for the most part anyway, is what the preferable ablation is for paroxysmal atrial fibrillation. The answer appears to be pulmonary vein isolation. But how and with what energy source is still very debatable. Even more questions arise when it come to the treatment of persistent atrial fibrillation. Clearly PVI alone is often not sufficient, but what else should be done? Lines? Complex fractionated atrial electrograms? Other non-PV triggers? Hybrid procedures? In addition, given how much we have learned about the proarrhythmic potential of ablation, particularly linear ablation, how much is too much? Despite questions and setbacks, however, the happiness that patients experience when they are completely liberated from their arrhythmia, associated drugs, and symptoms, makes me optimistic about the future of our field.

References

1. HRS/EHRA/ECAS Expert Consensus Statement on Catheter and Surgical Ablation of Atrial Fibrillation: Recommendations for Personnel, Policy, Procedures and Follow-Up. A report of the Heart Rhythm Society (HRS) Task Force on Catheter and Surgical Ablation of Atrial Fibrillation Developed in partnership with the European Cardiac Arrhythmia Society (ECAS); in collaboration with the American College of Cardiology (ACC), American Heart Association (AHA), and the Society of Thoracic Surgeons (STS). Endorsed and approved by the governing bodies of the American College of Cardiology, the American Heart Association, the European Arrhythmia Society, the European Heart Rhythm Association, the Society of Thoracic Surgeons, and the Heart Rhythm Society. Europace 2007;9:335–379.
2. Shah RU, Freeman JV, Shilane D, et al. Procedural complications, rehospitalizations, and repeat procedures after catheter ablation for atrial fibrillation. J Am Coll Cardiol 2012;59:143–149.