How Can ACIST Assist the Cryoballoon Procedure?

Introduction

Since the introduction of the cryoballoon for the treatment of atrial fibrillation (AF), there have been numerous reported technologies that have helped to facilitate this single-shot pulmonary vein isolation (PVI) procedure. Essential to a continuous and robust PVI lesion is the creation of good contact occlusion between the cryoballoon and the antral pulmonary vein (PV). 

The primary Medtronic, Inc. recommendation is to test occlusion by injecting radiopaque contrast agent down the central lumen of the cryoballoon and then utilizing fluoroscopy to detect leaks around the cryoballoon.¹ This strategy of contrast agent leak detection by fluoroscopy has been used since the original cryoballoon procedural description.²

Occlusion leak(s) will tend to push some contrast agent in an anterograde direction over the cryoballoon and into the left atria (LA) chamber (Figure 1). Since the cryoballoon catheter transfers cryothermal energy via direct tissue-to-balloon surface contact, any gaps between contacting surfaces can potentially lead to AF recurrence through gap conduction.^3-4 Most other descriptions of cryoballoon positional docking have dealt with adjunctive tools used to measure “cryoballoon-to-PV” occlusion. 

Originally, the Siklódy lab described a technique of using pressure monitoring during PV occlusion to detect the presence of gaps.⁵ In this same report, transesophageal Doppler echocardiography (TEE) was employed to confirm occlusion and to detect the location of a leak when present via color flow Doppler. More recently, Kosmidou et al⁶ as well as Sorrentino and Dan⁷ have further described the pressure monitoring technique so that general adoption is further facilitated. Similarly, Ottaviano et al⁸ followed up the original Siklódy lab report and examined the benefits of real-time three-dimensional TEE (3D TEE). In this more recent 3D TEE study, it was found that ultrasound was a useful tool for visualizing all PV ostia and the neighboring LA structures. All of these previously reported tools provided efficient guidance for the physician during the cryoballoon procedure to obtain a complete occlusion and successfully isolate all PVs. 

In this article, we review the original Medtronic procedure guide of testing for PV occlusion via injection of contrast agent followed by fluoroscopy examination¹ and describe our experience with a system that utilizes automated and measured delivery of the radiopaque contrast agent. The ACIST CVi (ACIST Medical Systems) fluid delivery system can be employed effectively to inject contrast agent and saline during a cryoballoon AF ablation procedure. 

In Medtronic’s primary description of occlusion testing, these contrast agent/saline fluid switches and injections are done manually by either an open system using a three-way stopcock or a closed system using a manifold setup (Figure 2). In either case, the delivery can be variable with regard to rate of injection, amount of injection, and pressure utilized during injection delivery. Additionally, the “scrubbed-in” cryoballoon assistant will oftentimes report some thumb and finger fatigue when using the traditional syringe delivery system. In addition to a controlled delivery of injected agents, there are additional secondary benefits that we will further describe in this report (Table 1).

HOW DOES THE CONFIGURATION WORK?

The ACIST CVi will make automated switches between saline and radiopaque contrast agent within the unit. Also, the mechanical pump delivery action will ensure that the liquid output is consistent with regard to rate, volume, and pressure. In Table 2, we provide the settings that have been proven to be effective through numerous tests in our own EP laboratory. When injecting for PV occlusion testing, the ACIST outlet tubing can be connected to the cryoballoon catheter so that contrast agent and saline are delivered via the catheter’s inner lumen. Additionally, this ACIST system can be connected directly to the FlexCath sheath, and in this configuration the system can be used to inject contrast agent during a LA/PV angiography. Figure 3 depicts the advantages of using such a system — mainly there is a predictable and robust delivery of contrast agent in each injection so that the physician can gauge occlusion based on comparisons to previous injections. 

In our experience, we found that we were able to use less contrast agent throughout the entire procedure. Our typical experience was to use 8 to 10 ml of contrast agent when testing PV occlusion with the syringe and manifold system. With the use of ACIST, we are able to test occlusion with just 6 ml of contrast agent. When considering that each PV is minimally isolated by a freeze-thaw-freeze cryoballoon application, the employment of ACIST can reduce the amount of contrast agent used by nearly 16 ml per patient. Reduced usage of contrast agent translates into cost savings, and reduction in exposure to the contrast agent may benefit some patients.

ADDITIONAL BENEFITS TO USING ACIST

In any hospital setting, inventory management can be challenging. Thus, a system that has fewer individual parts is of immediate benefit to the hospital staff. Table 3 demonstrates the parts list needed for both the ACIST delivery and a typical manifold or stopcock system. Of note, the disposable parts used during a procedure with ACIST require less inventory management, and the ACIST disposable parts are relatively inexpensive.

Furthermore, the consistent delivery of saline as a flush agent after contrast agent delivery will reduce the viscosity build-up that is sometimes present in the inner lumen of the cryoballoon during manual delivery. Users of manual delivery will often note that “pushing” contrast agent becomes more difficult through the duration of the cryoballoon procedure. Often, this is because of contrast agent residual build-up in the cryoballoon lumen that was not flushed out completely from previous injections. In our experience, the consistent flush rate, volume, and pressure that are used during the saline flush with ACIST will diminish this problem.

Also, the airtight system can be used with the pressure monitoring technique. Even more importantly, this system may potentially reduce some of the difficulties encountered during a manifold-pressure monitoring procedure. As described by Sorrentino and Dan,⁷ even small air bubbles in the hubs and connections of a manifold system may make pressure monitoring difficult and challenging. They also demonstrated that hand motion on the manifold system can transmit hand movement artifact into the pressure waveform measurements.⁷ Since the ACIST configuration will not use a manifold with hand delivery, there is less movement artifact during pressure monitoring recordings.

LAB EXPERIENCE AND FUTURE POTENTIAL APPLICATION 

During our cryoballoon experience, we first started with the manifold system to deliver contrast agent and saline. However, on the 15th cryoballoon procedure, we decided to try the ACIST device. Like most EP labs, the ACIST devices were already present in the adjoining catheterization laboratory. Our immediate reaction was that this device was going to be a regular part of our cryoballoon procedure. Throughout the next several procedures we optimized the delivery parameters and arrived at the settings reported in Table 2. We have now completed almost 50 cryoballoon procedures, and the EP lab has not noted any problems with integrating this piece of equipment into the cryoballoon ablation procedure. 

Currently it is considered standard practice during the cryoballoon procedure that two people are in operation of the Arctic Front catheter system. The primary physician will typically operate the cryoballoon catheter, the FlexCath sheath, and any additional catheter. By comparison, the scrubbed-in assistant will typically operate the guidewire, the Achieve mapping catheter wire, the CryoConsole, and the manifold or ACIST system. As the cryoballoon catheter expands into global markets that become more cost restrictive to the amount of staff in a procedure room, the ACIST device may potentially be able to allow a physician to employ the cryoballoon as a single operator. In our current dual operator system, ACIST has been a welcomed asset to the cryoballoon procedure.

Disclosures: Prasad Palakurthy, MD and Dan Schopf, RN have no conflicts of interest to report. Hae Lim, PhD declares a competing financial interest; he is an employee of Medtronic, Inc., a publicly traded company.

References

1. Arctic Front Cardiac CryoAblation Catheter Pulmonary Vein Isolation Procedure Guide. Medtronic, Inc.
2. Van Belle Y, Janse P, Rivero-Ayerza MJ, et al. Pulmonary vein isolation using an occluding cryoballoon for circumferential ablation: feasibility, complications, and short-term outcome. Eur Heart J. 2007;28:2231-2237. 
3. Fürnkranz A, Chun KR, Nuyens D, et al. Characterization of conduction recovery after pulmonary vein isolation using the “single big cryoballoon” technique. Heart Rhythm. 2010;7:184-190.
4. Ahmed H, Neuzil P, Skoda J, et al. The permanency of pulmonary vein isolation using a balloon cryoablation catheter. J Cardiovasc Electrophysiol. 2010;21:731-737.
5. Siklódy CH, Minners J, Allgeier M, et al. Pressure-guided cryoballoon isolation of the pulmonary veins for the treatment of paroxysmal atrial fibrillation. J Cardiovasc Electrophysiol. 2010;21:120-125.
6. Kosmidou I, Wooden S, Jones B, et al. Direct pressure monitoring accurately predicts pulmonary vein occlusion during cryoballoon ablation. J Vis Exp. 2013;26:1-7.
7. Sorrentino DM, Dan D. A Teaching Guide and Reference: Pressure Monitoring Utilized to Successfully Guide Cryoballoon Occlusion during Pulmonary Vein Isolation. EP Lab Digest. 2013;13:20-24.
8. Ottaviano L, Chierchia GB, Bregasi A, et al. Cryoballoon ablation for atrial fibrillation guided by real-time three-dimensional transoesophageal echocardiography: a feasibility study. Europace. 2013;15:944-950.