The cryoballoon catheter (Medtronic, Inc.) is approved to treat drug refractory recurrent symptomatic paroxysmal atrial fibrillation (AF),¹ and it has been given the highest level of recommendation (Class I, Level A) during the treatment of this patient population.^2-4 Safety and efficacy have been well described in the STOP AF FDA trial,¹ and more recently, the second generation balloon (Arctic Front Advance) has been marketed. Several independent studies with the second generation cryoballoon (CB2) have demonstrated a 12-month freedom from AF that is equal to or better than 80%,^5-9 and some of these authors have attributed the advancement in efficacy to the homogenous distribution of refrigerant in the CB2 catheter. However, fewer studies have reported on the economic or efficiency parameters when examining the CB2 catheter.^10,11 

With regard to safety, efficacy, and efficiency, there are several large clinical trials that will contain multiple ablation catheters, including the cryoballoon catheter: FIRE AND ICE (ClinicalTrials.gov identifier: NCT01490814), the FREEZE Cohort Study (ClinicalTrials.gov identifier: NCT01360008), and FreezeAF (ClinicalTrials.gov identifier: NCT00774566). However, until these trials complete and report their findings, we can glean data from single-center reports that may present information on any data regarding efficiencies, economics, or costs. The composite examination of a series of single-center reports may shed some light into these economic measurements until larger randomized clinical trials are completed. 

In this article, we examine the potential efficiencies that may be possible with the cryoballoon system through short and predictable time usage to help maximize staff and EP lab utilization. It is important to note that this study only examined the cryoballoon catheter experience at one center by retrospective review, and there was no long-term patient follow-up.

Methods

In this study, we obtained data from the EP lab procedural notebook, and transferred it to an electronic database for summary and statistical analyses. This was a single-arm, single-center, single-operator retrospective review of the EP procedural notebook with no patient information recordings. Data recordings were of procedural times, equipment usage, ablation measurements, and schedule dates. Hospital medical charts and electronic medical records were not used in this collection series to protect patient information.

Cryoballoon Ablation

The fundamentals of the cryoballoon ablation procedure have been well described previously,^5-9 and our own cryoballoon ablation procedure is similar. In brief, a transesophageal echocardiogram is routinely conducted to assess the left atrium (LA) for thrombus, chamber size, and anatomical structure. Typically, an ICE catheter is used to visualize a single puncture transseptal entry. LA and pulmonary vein (PV) anatomy assessments were conducted using 3D EAM and PV angiography. Cryoballoon delivery was completed using the purpose built steerable sheath and cryoballoon inner-lumen circular mapping catheter. Ablation applications were conducted between three and four minutes per ablation, and a freeze-thaw-freeze approach dictated that a minimum of two cryothermal applications per each PV were used. Diaphragmatic pacing was conducted during right superior PV (RSPV) and right inferior PV (RIPV) ablations to monitor for early phrenic nerve impairment. Entrance and exit block were tested at each PV to verify electrical isolation, and ablation applications were conducted until PV isolation was confirmed.

Data Recordings

The data collection represents all consecutive cryoballoon procedures that were conducted at a single center from June 23, 2011 until August 13, 2013. During the collection period, the cryoballoon manufacturer had released the CB2 catheter. Data collection of the first generation cryoballoon (CB1) encompasses a period from June 23, 2011 until October 18, 2012, and it covers a total of 156 separate CB1 AF ablation procedures. The CB2 data collection started on October 23, 2012 and ended on August 13, 2013, with 96 procedures recorded. The entire data collection encompassed all consecutive cryoballoon cases recorded in a 782-day timespan.

Statistical Analyses

All descriptive statistics were recorded as means with reported standard error of the mean (SEM). For comparisons between continuous variables, a test for normal data distribution was conducted, and then an unpaired two-sample Student’s t-test was used to determine statistically significant interactions. Similarly, for comparisons between discrete variables, a Fisher’s exact probability test was employed. For all tests, statistical significance was set at p<0.05. 

Results

This study examined the number of days that a multiple cryoballoon procedure could be conducted in a single work day. Table 1 demonstrates that when the switch to the CB2 catheter was made, there was a statistically significant increase in the number of days that had three cryoballoon ablation procedures in one day (CB1=3.8% and CB2=12.5%, p=0.012). Each cryoballoon catheter had a 40% usage of single procedure per day, and there was no statistical difference with the number of days that had two procedures in one day (CB1=56.4% and CB2=47.9%, p=0.197).

With regard to cryoballoon equipment usage, there were a total of three procedures that required dual-sized cryoballoon usage (23mm and 28mm) during one procedure because of mismatched PV sizes, and all three procedures were conducted during the usage of the CB1 catheter. The PV sizes of the patients with mismatched PVs were as follows [reported as left superior PV (LSPV), left inferior PV (LIPV), RSPV, and RIPV, respectively]: patient 1 (19mm, 21mm, 15mm, and 10mm); patient 2 (15mm, 13mm, 18mm, and 11mm); and patient 3 (21mm, 15mm, 20mm, and 11mm). CB2 improvements in the therapeutic area (cryoballoon freeze surface coverage) allowed for a freeze zone from distal balloon tip to the equator rather than an equatorial freeze-belt from the CB1 design.^5-9 As a result, during CB2 catheter usage, the 28mm balloon was used in 81% of all cases, which was statistically different from the 50% usage of the 28mm balloon during CB1 catheter ablations (p<0.001). Although the CB2 28mm was frequently used, the CB2 23mm balloon was still utilized, predominately when all four PV were smaller than 15mm in diameter. 

During this data collection period, there was no concerted attempt to minimize the amount of equipment usage during the cryoballoon ablations. Rather, the imaging equipment listed is a reflection of standard and/or typical tools that are used to guide a safe and effective ablation procedure.^5-9 In the total two-year cryoballoon experience, there was better than 80% usage of 3D EAM, ICE imaging, TEE viewing, and PV angiography usage (Table 1). There was no statistical difference in the usage of imaging equipment between the CB1 or CB2 catheters.

Table 2 reports procedural time measurements, fluoroscopy time, radiopaque contrast agent usage, and phrenic nerve palsy (PNP) occurrence, which were all recorded in the EP lab notebook. Procedure time was recorded as first vascular puncture (typically groin) until last sheath exit from the patient. During the entire cryoballoon experience, mean procedure times were below 2.5 hours with no statistical difference between the two generations of cryoballoon. LA dwell time was denoted as the time from transseptal entrance until last sheath exit from the LA. There was no statistical difference in LA dwell times between the CB1 and CB2 catheters, with mean LA dwell times reported as 95 minutes and 91 minutes, respectively. As demonstrated in Table 2, both mean fluoroscopy time and mean contrast agent usage declined when employing the CB2 catheter. In our experience, the increased freeze contact area in the CB2 design led to less balloon repositioning to achieve complete balloon-to-PV occlusion. Consequently, the mean fluoroscopy time decreased by 22%, and the mean contrast agent usage declined by 17% when migrating from the CB1 to CB2 catheter usage (p<0.001 in both comparisons). Also, the incidence of PNP remained the same between both generations of cryoballoon (p=0.999), which was reported as below 5% in total.

Table 3 lists the parameters recorded during PV ablation, including the mean PV diameter sizes, the mean number of ablations per PV, the mean cryoballoon nadir temperature, and the mean time of application per ablation. With regard to PV diameter size, there was a statistically significant increase in mean PV size between CB1 and CB2 patients for every PV except the LSPV. Of note, the left common PV (LCPV) was only present in ten patients during the CB1 experience and in seven patients during the CB2 employment. When accounting the mean number of ablations per PV, there was a statistically significant decrease in the number of ablations during the migration from CB1 to CB2 catheters (2.20 to 2.07, respectively; p=0.014). Mean cryoballoon temperature in every PV was significantly warmer for the CB2 catheter; however, the physician controls the mean nadir temperature by selectively aborting ultra-cold freezes. The mean time per ablation was shorter in duration for the CB2 catheter in every PV comparison. During the CB1 experience, the typical ablation time was four minutes. By contrast, experience with the CB2 catheter had moved the typical ablation time to three minutes.¹² The slightly longer than 180-second mean ablation time during the CB2 experience reflects the gradual change from four- to three-minute dosing in our EP lab. 

The middle collection date for this study was July 18, 2012, with 391 days before and after that date during this retrospective review. In total, there were 128 AF ablation procedures from the start date (June 23, 2011) to the middle collection date, and there were 124 AF ablation procedures from the middle date to the final collection date (August 13, 2013). Consequently, the actual numbers of patients receiving an AF ablation in our study was consistent throughout the study collection, and it was largely a product of patient referral network consistency. Importantly, an easier-to-use CB2 catheter did not lead to more AF ablations in the EP lab, but instead, to more efficient staff and EP lab space utilization by significantly increasing the number of times that a three ablation procedure day can be completed. Finally, EP lab scheduling was facilitated by the predictability of ablation time (Table 2), as variations in procedure times were small for both CB1 and CB2 catheter employment (mean of 134.6 minute + 3.4 SEM versus mean of 128.2 minute + 4.1 SEM, respectively).

Discussion

In this current study, we examined the potential efficiencies that may be possible with the cryoballoon system through short and predictable time usage to help maximize staff and EP lab room utilization. In general, we found that the CB2 catheter allowed for more frequent three-procedure days than compared to the original cryoballoon. During the entire two-year study, approximately 60% of all the AF ablations conducted with the cryoballoon system were multiple procedure days. Potentially, the EP department realized staff and room occupancy savings because of less frequent or repetitive “set-up” and “tear-down” time.

With regard to patient safety, there was a statistically significant decrease in fluoroscopy and contrast agent usage when migrating from the CB1 to CB2 catheter. Additionally, there was no change in the frequency of acute PNP, as it remained below 5% for the entire study. Our single-center reporting of PNP is on the lower incidence rate compared to the STOP AF trial,¹ and it likely reflects our vigilant monitoring of phrenic nerve function by diaphragmatic pacing detection. 

Also, when examining the LIPV, there was a significant reduction in the number of LIPV ablations when comparing the CB1 to CB2 catheter. The LIPV was frequently a challenging vein to isolate with the original cryoballoon as noted by the average of 2.2 ablations being the highest of all typical PVs (LSPV, RSPV, and RIPV), and it was only second to the LCPV, which was ablated in a segmental approach. By decreasing the effective number of LIPV ablations with the CB2 catheter, we potentially lessen the likelihood of creating atrial flutter as a result of multiple wide-area LIPV cryoballoon ablations.

The cryoballoon catheter has been proven to be a cost-effective ablation tool for the management of paroxysmal AF, and it has shown an ability to maintain a high quality of life compared to antiarrhythmic drug therapy.¹³ Furthermore, the cryoballoon has been given the highest recommendation by several society consensus statements for the treatment of symptomatic and drug refractory paroxysmal AF.^2-4 We hope this current study has been able to demonstrate some clinical efficiency when going from the CB1 to CB2 catheter. There are many ways to control healthcare costs in an ever-challenging environment, and physicians should have a choice in selecting equipment based on patient medical need. We believe the cryoballoon system is currently one of the safest ablation catheters with regard to the incidence rate of atrioesophageal fistula.^{2, 14-15} However, there must be a balance between safety, efficacy, and economics, which allows for physician-based medical decisions. 

Study Limitations

This study only examined the cryoballoon catheter experience at one center by retrospective review, and there was no long-term patient follow-up. The mean procedure and mean LA dwell times were not different between the CB1 and CB2 procedures; however, the usage of the CB2 catheter did allow for more three AF ablations/day procedures. This likely reflects physician and staff comfort level with the cryoballoon ablation procedure in general, and may not be generalizable to all other facilities. Also, this study did not report procedural profit margins obtained within an AF ablation procedure. Although the procedures were net profitable, confidentiality agreements with vendors precluded detailed publication.

Conclusions

Procedural tools that create efficiencies and allow for maximization of staff time and hospital space are avenues that can potentially help maintain cost-conscious behaviors without limiting physician-based medical choices. Physicians must ultimately be allowed to select and determine the appropriate medical care based on clinical presentation. 

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

Disclosures: Dr. Seide has no conflicts of interest to report. Hae Lim discloses he is an employee of Medtronic, Inc.

References

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