Utilizing the Cryoballoon to Isolate the PVs: Do Not Fear the Common

Over the last 25 years, the treatment of patients with heart rhythm disorders has evolved dramatically, and the management of atrial fibrillation (AF) is no exception. Before this renaissance of cardiac therapy, it was ethical in the late 1980s to withhold warfarin (Coumadin) from patients with AF at high risk of stroke and instead administer placebo in randomized clinical trials (the Copenhagen AFASAK study¹ and the SPAF study²). Since then, two newer antiarrhythmic drugs (AADs) have received FDA approval and are now available to treat patients with AF: Tikosyn^® (dofetilide) in 1999 and Multaq^® (dronedarone) in 2009. This doubled the drug options available to patients with AF who also have structural heart disease. In just the last two years, two novel anticoagulants have been FDA approved: Pradaxa^® (dabigatran) and Xarelto^® (rivaraxaban). Additionally, a third anticoagulation drug, Eliquis (apixaban), appears promising for reducing the risk of stroke and systemic embolism in the setting of non-valvular AF (the ARISTOTLE study).³

These developments in medication therapy have been mirrored by ever-advancing techniques and technologies in the realm of catheter-based ablation. In the management of AF, pulmonary vein targeting strategies still remain the “cornerstone” of most AF ablation procedures.⁴ However, there are many options available to the electrophysiologist (EP) to achieve the required endpoint of pulmonary vein isolation (PVI). There are multiple energy sources (e.g., cryotherapy, radiofrequency, and laser), and there are many delivery systems from which to choose (e.g., point-by-point catheter, balloon based, and multi-electrode). Furthermore, some of these technologies may also integrate navigation and remote operation.

These advancements, coupled with data from randomized clinical trials and operator experience, have resulted in updated recommendations for patient selection. There is now expert consensus that patients with symptomatic, paroxysmal AF, who have failed at least one antiarrhythmic drug, should be considered for ablation therapy. A Class I recommendation for this subgroup means that the “benefits of the AF ablation procedure markedly exceed the risks, and that AF ablation should be performed.”⁴ Of course, these statements apply to an assumed “appropriately” trained operator in an “experienced” center, and will vary based on patient comorbidities and patient-specific considerations.

As any individual working in the EP lab will attest, many factors have now coalesced to markedly increase the number of patients offered ablation of AF. Over the last decade, the number of hospitals which have invested in electrophysiology suites capable of performing basic and advanced ablation procedures has risen with this demand. Similarly, new tools are being developed to assist the operator in performing PVI with the hopes that a particular device will prove to simplify the procedure for the physician and EP team, be safer for the patient, and also be more effective at maintaining normal sinus rhythm.

Adopting Cryoballoon Technology

In mid-December 2010, the FDA approved the Arctic Front^® Cardiac CryoAblation Catheter system (Medtronic, Inc.) for the treatment of drug-refractory recurrent PAF. This FDA approval was based on the results of the STOP AF trial, which demonstrated a significant improvement in freedom from AF in patients who underwent ablation with this technology compared to those patients randomized to AADs.⁵ The system uses nitrous oxide to cool the inner-balloon and contacted cardiac tissue. To date and worldwide, more than 37,000 patients have undergone a PVI procedure using the cryoballoon (personal communication, Medtronic, Inc.).

As with any new technology, there is a learning curve for both the physician and those working with the physician in caring for the patient during the ablation procedure. The success of the procedure begins with patient selection. Many physicians, me included, have an inclination to be particularly selective in the patient population treated during these initial procedures. We look for the ideal patient with few comorbidities. We also look for ideal PV anatomy. 

But what is an ideal anatomy for the cryoballoon (or any other device for that matter)? Electrophysiologists just beginning to employ the cryoballoon may dream of a patient with mostly circular veins that are similar in size and which do not include a common ostium or middle vein; in short, a left atrial (LA) anatomy depicted in illustrations found in every anatomy textbook. But how often does this anatomy present itself in our patients, and should we consider patients with non-ideal PV anatomy as candidates for cryoballoon ablation as we decide which technology to apply to which patient during our cryoballoon learning curve? 

It is clear from radiologic studies of the LA that there is considerable normal variability to the PV drainage pattern. For example, between 18–29% of patients have more than two right-sided pulmonary veins.⁴ While a single venous ostium (common) on the right is rare,⁶ a left common ostium can be seen in greater than 30% of patients and as high as 59% in certain populations.⁷ In light of this data, it should not be surprising that five of the first ten patients I considered for cryoballoon ablation had a left common ostium. I routinely obtain pre-procedure imaging with CT on all patients. However, depending on the interpreting radiologist or cardiologist, the formal report does not always contain a detailed description of potential variant anatomy, which is often described, albeit correctly, as being a “normal pulmonary venous drainage pattern.” It is only when personally reviewing the images that I can begin to plan a strategy for the procedure.

When I decided to commit to a trial of adopting this cryoballoon technology, I determined that I would first select patients with paroxysmal AF who had not previously undergone AF ablation. While I was prepared to perform adjunct RF ablation on patients if needed, I felt that there were distinct advantages in developing a methodology, particularly with a new procedure, and applying this technology to variant PV anatomy as the need would arise. 

The quest for the patient with the “ideal” PV anatomy must be balanced with the importance of the “ideal” patient volume to ensure safe and effective therapy. This is particularly important during the learning curve seen with each new technology. The left common ostium is common enough that if its mere presence were to exclude the patient from consideration of cryoballoon therapy, the establishment of a regular and consistent procedural strategy and approach may be hindered. This can impact all members of the EP team. 

As noted above, of my first ten patients, five had a left common PV (LCPV) ostium. The method I utilized to isolate the LCPV in each of the five patients was a segmental approach (Figure 1). After performing transseptal puncture with a standard 8.5 Fr SL1 Fast-Cath Guiding Introducer (St. Jude Medical) and Brockenbrough BRK-1 curved needle (St. Jude Medical), I advanced a 0.035 wire into a branch of the LCPV (usually the superior branch). This was fixed in place as I exchanged the long sheath for a FlexCath^® Steerable Sheath (Medtronic, Inc). The guidewire was subsequently removed. Next the Achieve^™ Mapping Catheter with a circular fixed loop of 20 mm was inserted through the lumen of the 28 mm Arctic Front cryoablation catheter, and the whole system was advanced through the FlexCath sheath. 

In order to demonstrate pulmonary venous antral occlusion, I typically utilize three techniques: 1) monitoring of pressure waveform at the catheter tip; 2) observing color Doppler via intracardiac echocardiography at PV ostium; and 3) examining selective pulmonary venography by fluoroscopy. All three monitoring techniques are still useful to confirm intended cryoballoon orientation even in the absence of complete ostial occlusion, which can occur in challenging PV anatomy such as LCPV. For example, a “leak” on the inferior border would be expected when positioning the cryoballoon to ablate superiorly on a large LCPV (Figure 1B).

When attempting to isolate the LCPV ostium, it is important to be able to manipulate the cryoballoon to reach the targeted region. There are several methods that could be employed individually or in combination based on physician preference or on specific antral shape/size. As with individual PVs, I advance the Achieve catheter into multiple branches of the superior and inferior veins to vary balloon positioning. The pre-procedure CT imaging is very helpful to this end, and while I do not perform 3D electroanatomic mapping in these patients, I do render the 3D CT image for review during the procedure. There are at least three maneuvers that could be performed with the FlexCath Steerable Sheath to better target the region of interest for ablation: 1) the sheath may be advanced or retracted; 2) the sheath may be gently torqued clockwise or counterclockwise in order to ensure appropriate in-plane support of the cryoballoon; and 3) the sheath may be deflected unidirectionally as needed up to 90 degrees. Additionally, the cryoballoon catheter has its own deflection mechanism which I have used on occasion to obtain better occlusion or to ensure appropriate in-plane alignment of cryoballoon and PV.

By employing the above maneuvers with a segmental approach, I was able to create entrance and exit block in each of these five patients with a LCPV ostium. However, additional applications of cryoballoon therapy were needed in the segmental approach of the LCPV. In these five patients, the number of four-minute cryoablation freezes ranged from 4 to 8 applications, with a mean of 6.4 cryoballoon applications per LCPV (Table 1). As denoted in Table 1, the time to achieve -30 ºC was rapid (mean of 28 seconds) and the average temperature nadir lower (-51 ºC) in the patient who required only four applications of cryotherapy to achieve isolation compared with the other patients. Lastly, there were no significant differences in left atrial dwell time, fluoroscopy exposure, or total procedure time in these patients with a LCPV ostium compared with the other five patients making up my first ten cryoballoon ablation cases. Figure 1 is an image series depicting this segmental approach to ablation in patient #3.

Importantly, LCPV ostium isolation was performed with the first-generation Arctic Front cryoballoon in four of the five patients. Typically, first-generation tools serve an important role in product development because feedback from end-users oftentimes results in a more refined second-generation catheter. One limitation relevant to any common vein isolation is that the first-generation cryoballoon required a parallel and in-plane approach to facilitate a perpendicular alignment of the cryoballoon’s equatorial freeze zone with the antral entrance of the PV. Any approach that was less than parallel could and oftentimes did limit the effectiveness of venous isolation. Because of this product limitation, many early physician adopters to the cryoballoon technology had chosen to not cryoablate more complex PV anatomies. The summer 2012 release of the second-generation cryoballoon, known as the Arctic Front Advance^™ Cardiac CryoAblation Catheter, attempts to address this impediment. The new catheter has twice as many spray jets (eight jets total) and a more distally located injection coil, as well as some nitrous oxide flow rate adjustments that allow for more uniform distal cooling with a broader zone of effective freeze — now extending from the equator to the distal end of the balloon.

Physicians who perform ablations know that electrical isolation of a LCPV ostium can be challenging regardless of the energy source and energy delivery method that is employed.⁸ However, it may be particularly important to ensure isolation of the LCPV, when present, as it may represent a common source of “arrhythmogenic atrial ectopy.”⁹ Isolating complex PV anatomy (e.g., LCPV ostium) will often follow the development and implementation of newer ablation technologies, and cryoballoon ablation is no exception. There is already a published case report describing the use of a 23 mm Arctic Front cryoballoon in the isolation of an unusual pulmonary venous return — a common ostium of the left and right inferior PVs.¹⁰ The reality of the EP lab is that there are very few “ideal” patients, and the training approach is to become confident with your equipment to handle “non-ideal” situations. The hope of this article is to supply the new user with some guidance when tackling LCPV ablations.

As a new user of the technology, I have made a conscious effort to consistently and methodically utilize the cryoballoon to attempt to isolate the PVs even in the patient with more complex PV anatomy. While admittedly frustrating at times, this has ultimately served my patients well. As with any new tool, my comfort level continues to increase with experience, and my early outcomes have been favorable. I certainly appreciate the “ideal” patient, but no longer fear the “common.” n

Disclosures: The author reports that he is on the Speaker’s Bureau for Medtronic, St. Jude Medical, and Boehringer Ingelheim.

Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest’s editorial board.

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