Cryoballoon Ablation of Atrial Fibrillation: Improving Efficiency While Ensuring Success

Doylestown Hospital (Figure 1) is a 232-bed community hospital in Pennsylvania, approximately 40 miles north of Philadelphia in Bucks County. We began performing cryoballoon ablation for atrial fibril-lation (AF) in 2011, and have now done over 1000 balloon procedures. The development and availability of second-generation balloon technology in 2012 (Arctic Front Advance™, Medtronic) has allowed for a contiguous, hemispheric lesion rather than an equatorial lesion with the first-generation technology. As a result, we have experienced shortened procedure and left atrial dwell times, which have helped maximize our lab’s efficiency and increased our overall success. 

We typically approach first-time procedures with cryoballoon ablation in both paroxysmal AF (on label) and persistent AF (off label) patients. Repeat procedure rates have been demonstrated to be very low in paroxysmal patients¹ and persistent patients,² with high rates of clinical success. 

In this article, we present a typical case from our lab and describe our approach to performing pulmonary vein isolation (PVI) with the cryoballoon technology.

Sample Case

A 68-year-old male with paroxysmal AF refractory to sotalol (CHA₂DS₂-VASc score of 1) had been hospitalized two times for cardioversion. He had a structurally normal heart on echocardio-gram, with a normal ejection fraction and a mildly enlarged left atrium. An anomalous 6 mm right pulmonary vein (PV) was demonstrated on CT scan. PV isolation was done with a 28 mm cryobal-loon, and the patient had an uneventful postoperative course. A post-ablation electroanatomic voltage map is seen in Figure 2, which demonstrates a typical level of isolation when utilizing the larger cryoballoon (also available in a 23 mm size). Our approach for this patient is discussed in detail below, and pertains to our overall strategy for managing the cryoballoon procedure and isolating the pulmonary veins.

After two years, the patient has had no further atrial fibrillation on serial ambulatory rhythm monitoring, and is off of sotalol and oral anticoagulation medication. 

Outline of Approach

Preoperative Management and Testing

We perform our PVI procedures on uninterrupted oral anticoagulants, including novel agents, in keeping with recent data supporting the safety of this approach.³ We typically utilize preoperative CT imaging, and aim to minimize preablation TEE to only persistent or paroxysmal AF patients who have not been on preoperative oral anticoagulation. Reduction in overall TEE rates are similar to other groups’ reports,⁴ and has improved throughput in our preprocedural area while relieving congestion for other noninvasive procedures to be performed. We utilize CT scanning to identify small anomalous veins that may not be readily apparent on intracardiac ultrasound imaging. Regardless of preablation vein size, we typically utilize a 28 mm cryoballoon, even in small left atria or pulmonary vein sizes less than 20 mm. 

Approach to Sedation

Many labs report improved efficiency by utilizing conscious sedation, although in our lab, we typically use general anesthesia. Regardless, faster procedure times and improved venipuncture site management allows us to easily perform two AF ablations a day per lab, with the capacity for more. Given the consistency of procedure times, we typically also schedule either office consults or device patient visits with one lab team. Due to early completion times for our first ablation case of the day, we have moved toward same-day discharge, and are formally studying this with other labs.

Use of Equipment

We utilize single right groin access for a single transseptal, with two left femoral sheaths for intracardiac ultrasound and a decapolar recording catheter. The decapolar catheter is placed in the coronary sinus for left pulmonary vein ablation and at the right subclavian vein for right phrenic nerve pacing during right pulmonary vein ablation. For transseptal, we target a low anterior approach, which better allows for occlusion of the right pulmonary veins; we utilize either SL1 (Abbott) or Mullins (Medtronic) sheaths, often aided by the SafeSept^® Transseptal Guidewire (Pressure Products). Typically, a 28 mm cryoballoon is used, along with either a 15 or 20 mm Achieve™ catheter (Medtronic) to record real-time PV signals during freezing applications. In our lab, the performing physician typically scrubs with a RN or RCIS, as we do not have a fellowship training program; this has enhanced educational opportunities for our lab team and increased investment in the procedure. 

Electroanatomic Mapping

We typically do not use electroanatomic mapping, which improves cost profile. We rarely (<1%) need to utilize radiofrequency for PV isolation, other than for occasionally targeting right atrial flutter. About 5% of the time, we utilize a second 23 mm cryoballoon to target difficult-to-isolate pulmonary veins (typically, a small ovoid-shaped left inferior PV or recessed carina of the left PVs). In our experience, even 3-5 mm anomalous veins can be targeted with a 28 mm cryoballoon and isolated as an individual vein. 

Approach to PVI

We perform PVI only with entrance and exit block regardless of AF duration, in keeping with data from the STAR AF II trial⁵ supporting PVI alone (in an antral or wide circle method) in patients with persistent AF. We utilize adenosine only in difficult-to-isolate PVs, and typically do not use isoproterenol after procedures to test for extra PV triggers. Like many other labs, we struggle with a consistent approach for repeat procedures; however, we typically utilize radiofrequency in patients with recurrence after second-generation balloon procedures, as the veins are often usually chronically isolated.²

PV Occlusion with the Cryoballoon

We utilize PV venography to demonstrate pulmonary vein occlusion (Figure 3, video 1). We value adjunct information collected from intracardiac ultrasound to assess for leaks, particularly inferior and superior leaks, around the cryoballoon (Figure 4, video 2). We combine this with pressure waveform monitoring (Figure 5) to assess vein occlusion. With pressure monitoring, we see a transition from left atrial pressure to RV pressure waveform, signaling PV occlusion. Using all three complementary techniques allows for a consistent and successful approach to durable PV isolation. 

Ablation Dosing

We typically perform either one or two 3-minute freezing applications, depending on time-to-isolation (<40 seconds) and time from nadir temperature to 0 ºC (time to thaw zero or TTO, <10 seconds).⁶ In our lab, we typically perform one freezing application or single-shot dosing if both of these parameters are obtained. We perform esophageal temperature monitoring, and typically stop cryoballoon ablation if esophageal temperature drops below 25 ºC. This approach has led to short left atrial dwell and total procedure times, often between 60-90 minutes.

Post-Procedure Sheath Management

One of the biggest improvements in efficiency has been suture closure of venipuncture sites — specifically, the figure-of-eight stitch. This precludes long manual holds of femoral venipuncture sites, and leads to shorter time under anesthesia, from end of procedure to extubation. This has also markedly shortened lab turnover times. Suture closure has allowed us to consider same-day discharge, even in general anesthesia patients, and we have been doing same-day discharging for our morning PVI patients for over a year without incident.

Phrenic Nerve Monitoring 

Phrenic nerve palsy is a complication that has plagued the cryoballoon technology. We utilize compound motor action potential (CMAP) recording, utilizing a modified lead I surface recording over the right diaphragm in addition to traditional palpation. If attenuation or loss of phrenic nerve function is seen, forced balloon deflation is performed to mitigate risk of phrenic injury. The most important key to preserve phrenic nerve function is proximal balloon position, and we utilize fluoroscopy and ICE imaging to aid in this approach. In the over 1000 balloon cases that we have performed, we have had five patients with palsy that persisted after procedure (<1%, unpublished results). All of these patients recovered phrenic nerve function in follow-up testing by 9 months post procedure, and all but one had recovered by one month post procedure.

Conclusion

Despite these improvements and focus on best practices, issues remain. We actively participate in industry-based and investigator-initiated research to further improve cryoballoon ablation and its application in our patients. We also focus on physician training to maintain consistency in our approach to the cryoballoon procedure. Through this clinical and research network, areas of collaboration have enhanced our knowledge and approach to AF ablation. Through the practices described here, we have found improved overall procedural success and reduced overall post-procedure complications and recurrences in our patients. While further improvements in procedure success are needed, the consistency and reproducibility of cryoballoon ablation has allowed us to increase our referral base and improve daily efficiency in the EP laboratory.

Disclosures: The authors have no conflicts of interest to report regarding the content herein. Outside the submitted work, Dr. Harding reports participation in case proctoring and a speaker’s bureau (Medtronic).

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2. Al-Zubaidi M, Harding J, Sangrigoli R, et al. Etiology of Atrial Fibrillation Recurrence after Previously Successful Pulmonary Vein Isolation with Cryoablation. Abstract, American Heart Association Scientific Sessions, 2016. 
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