The Achieve Circular Mapping Catheter Used to Create Electroanatomical Maps for Focal RF Ablation in the EnSite Velocity System

Introduction

Atrial fibrillation (AF) ablation has become an established procedure for the treatment of drug refractory and symptomatic AF.¹ In the U.S., focal radiofrequency (RF) and cryoballoon ablation catheters have come to dominate the FDA-approved catheters for AF ablation. More recently, a lively and spirited debate has come to challenge the single importance of focal pulmonary vein (PV) triggers.² Currently, the AF ablation community is also assessing the importance of substrate involvement3 and rotational asynchronous foci4 in the maintenance of AF burden. Central to the theoretical interpretation, translation, and treatment of AF is the creation of accurate and precise electroanatomical (EA) maps of the left atrium (LA). Simply, when AF is complex, EA mapping is still important and necessary. 

For the cryoballoon system, the circular eight-electrode Achieve Mapping Catheter (Medtronic, Inc.) is most commonly used as an inner lumen cryoballoon mapping catheter that allows for single transseptal procedures.^5-8 An original design intent of the Achieve catheter was to replace the guidewire during deployment of the cryoballoon and allow for real-time monitoring of pulmonary vein isolation (PVI).⁸ Thus, the shaft of the Achieve is composed of three different caliber materials which allow for a combination of flexibility and support: 1) the proximal 132 cm long stainless steel shaft is 0.034”; 2) a 1 cm overlapping segment is 0.043”; and 3) the distal 13 cm shaft is 0.037”. The distal catheter ends in two loop diameters (either 15 mm or 20 mm) with 4 mm or 6 mm inter-electrode spacing, respectively. Usage of the Achieve mapping catheter with the cryoballoon in a single transseptal procedure has led to statistically significant efficiencies compared to a double transseptal cryoballoon procedural approach that uses a traditional 20-pole mapping catheter. Specifically, procedure times were shortened by better than 10% and fluoroscopy times were reduced by better than 20% in two independent examinations.^6,7

Non-cryoballoon users may have little or no knowledge (and/or experience) with the Achieve mapping catheter. However, this circular mapping catheter is also able to create useful EA maps when used with focal RF ablation catheters and an open mapping system like the EnSite Velocity or EnSite NavX systems (St. Jude Medical, Inc.). Mainly, the compliance in the distal loop and distal 13 cm shaft of the Achieve allows for the creation of EA maps with potentially less false space and distortion due to the flexible tip design. Specifically, the flexible thin-wire design allows for better survey and demarcation of the LA compared to stiffer shaft and larger cylinder diameter designs that are typically found in traditional 20-pole mapping catheters. Stiffer mapping catheters are prone to bouncing, whipping, skipping, and chattering, all of which can contribute to false space and distortion in the EA map.

During most ablation procedures, an accurate anatomical view of the surface substrate is necessary as about 40% of all patients undergoing AF ablation have variant PV and LA anatomies.⁹ The LA chamber can be filled with ridges, pouches, fibrosis, and septal raphe. For instance, approximately 15% of ablation patients will display roof pouches.^10,11 These pouches can vary in depth from 3 mm to 9 mm, and in diameter from 5 mm to 13 mm.¹⁰ In addition, septal and anterior ridges were observed in 32% of these AF patients.¹⁰

Often, it is the presence of variant or abnormal LA structures that will make a focal RF ablation difficult, and pre-procedural CT/MRI scans can be somewhat helpful when navigating a torturous LA. However, these CT or MRI images can often be several years old or have been taken during a period before severe LA remodeling. A better approach is to integrate the CT/MRI image with a real-time EA map of the LA. When used together, these imaging systems can have several advantages: 1) they can help explain unexpected/unintentional catheter motion; 2) they can reduce the amount of required fluoroscopy; and 3) they can guide efficient lesion placement for a safe and effective procedural ablation. 

In this article, we describe a case study that will help to demonstrate the procedural supplies, techniques, and methods that will facilitate a focal RF ablation procedure while utilizing the Achieve mapping catheter.

Methods and Case Study

This 50-year-old male patient had a long history of drug-resistant and reoccurring AF. He had undergone two previous failed AF ablations in 2008 and 2011 at another hospital.  After physician consultation, the patient elected to undergo this current AF ablation procedure. The patient had an existing pre-procedural CT scan that was used to evaluate the LA and PV dimensions, and this image was segmented and loaded into the EnSite Velocity mapping system. On the day of the procedure, a transesophageal echocardiogram was performed to exclude the presence of intracardiac thrombus. In preparation for the AF ablation procedure, the patient was intubated and placed under general anesthesia, and an esophageal temperature probe was used to monitor temperatures during the ablation procedure.

Femoral venous access was obtained using four separate entries: 1) one 7 French (Fr) sheath on the left for a Dynamic duodecapolar diagnostic catheter (Boston Scientific); 2) one 7 Fr sheath on the left for a Woven quadripolar diagnostic catheter (Boston Scientific); 3) one 9 Fr sheath on the left for an AcuNav^™ Ultrasound Catheter (Biosense Webster Inc., a Johnson & Johnson company); and 4) one 8 Fr sheath on the right for a Direx^™ Steerable Introducer Sheath (Boston Scientific). Transseptal entrance was then made using a transseptal needle (Bard TSX; Boston Scientific) in the Direx steerable sheath while under visual guidance with the AcuNav ultrasound catheter and fluoroscopy. Once across the septum, a standard therapeutic dose of heparin was delivered and the 20 mm Achieve mapping catheter was deployed inside the Direx sheath.

An EA map of the LA was created utilizing the EnSite Velocity mapping system and the Achieve mapping catheter (Figure 1). When comparing the EnSite anatomical map to the pre-procedure CT (Figure 2), it is apparent that the combination usage of the Achieve catheter and EnSite Velocity creates LA surface anatomies that are in strong agreement with the CT image. A fusion program is available to merge CT and EnSite images; however, our current protocol is to use only the EA map during the ablation procedure once we are satisfied with the CT-to-EA image congruence.

The Achieve mapping catheter was then exchanged with a closed irrigated ablation catheter (Chilli Cooled Ablation Catheter, Boston Scientific). RF energy was delivered by the Chilli catheter at a target temperature of 40^oC and a maximum output of 35W per ablation site. After completion of the circular lesions around the left and right PVs, the Chilli ablation catheter was used to create a roof line and a lateral isthmus line (Figure 1, panel C). At the conclusion of all RF ablations, diagnostic pacing revealed complete PVI. The Achieve mapping catheter can be used to confirm PVI by both exit and entrance block, and it can also be used to create a post-ablation voltage map. Prior to the completion of the procedure, the AcuNav ultrasound catheter was used to rule out pericardial effusion. The patient finished the procedure with no complications. To date, the patient has continued routine follow-up examinations and has remained free of AF symptoms for five months.  

Discussion

The Achieve inner lumen circular mapping catheter had an original design intent to allow single transseptal puncture usage with the cryoballoon while allowing for several other advantages, including: 1) real-time monitoring of the PVI during ablation; 2) wire support of the balloon throughout the deployment; and 3) assessment of PVI after the completed ablation. In this article, we describe the employment of the octapolar Achieve mapping catheter in a focal RF ablation procedure as an efficient, effective, and cost-reducing approach compared to traditional 20-pole mapping catheters. 

A primary advantage of the Achieve mapping catheter is the relative flexibility of this mapping catheter compared to more traditional circular mapping catheters. The flexible shaft and loop design of the Achieve allow for robust EA mapping of the LA without false space. Notice in Figure 1 (panel A) the mostly uniform distribution of mapping points from the Achieve catheter as viewed on the EnSite Velocity system. Additionally, EA maps are created with the same voltage thresholds as traditional mapping catheters (~1.5mV to 2.5mV). Also in Figure 2 (panels A and C), morphological structures that are present on the anterior LA surface via CT are also present in spatial congruence on the EnSite EA map.

The Achieve mapping catheter can also be an economic alternative when using a circular mapping catheter. In this case report, we utilized a single transseptal technique with exchange between the Chilli RF ablation catheter and the Achieve mapping catheter done in the Direx sheath. Utilization of single transseptal procedures can potentially save time and money, and exchanges with the Achieve catheter were done easily because of the thin-wire design. However, when using the Achieve mapping catheter, it is important to be sure that the sheath is compatible. Specifically, because of the thin-wire design, physician users must avoid using sheaths with small side port opening or holes so that the Achieve wire does not become lodged in those openings. 

Conclusion

The goal of this article was to demonstrate the use of the Achieve mapping catheter in a focal RF ablation procedure and supply some helpful technical insights. A traditional 20-pole circular mapping catheter can sometimes have sharper signal quality because of the close electrode spacing than compared to the octapolar Achieve mapping catheter. Additionally, the Achieve mapping catheter does lack the variability in diameter sizes, which can make mismatched PVs as well as common PV trunks difficult to map in some patients.

However, the flexible shaft design of the Achieve mapping catheter can prove useful during EA mapping by reducing false space and distortion due to mapping catheter bouncing and chattering, which can be present during the employment of traditional 20-pole circular mapping catheters. An advantage of obtaining a precise anatomic map is that it can eliminate the need to obtain a pre-ablation CT or MRI, which is currently used as an anatomic reference or for registration. This elimination would potentially save the patient time, decrease the overall cost of the procedure, and reduce radiation exposure to the patient — all without sacrificing quality or patient safety.

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

Disclosure: Dr. Chawla and Deb Zastrow, RN, BSN have no conflicts of interest to report regarding the content herein. Hae Lim, PhD declares a competing financial interest; he is an employee of Medtronic, Inc., a publicly traded company. Ms. Zastrow reports employment with Unity Point Health - St. Luke’s Hospital. 

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