The patient was a 62-year-old male with hypertension, type 2 diabetes, and hyperlipidemia who developed atrial fibrillation with a rapid rate. The initial attempt at cardioversion was unsuccessful, and rate control was subsequently achieved only after using three agents, one of which was amiodarone. Thyroid function was normal, and transesophageal echocardiography demonstrated the absence of left atrial clots and a dilated left atrium with a volume index of 45 mL/m2. Cardioversion was attempted again two weeks after achieving rate control as described above, but sinus rhythm could not be maintained. The patient remained symptomatic and was referred to EP for possible ablation.
After discussion with the patient, we decided on an extensive ablation strategy involving pulmonary vein isolation (PVI), including elimination of all electrograms on the left atrial roof and posterior wall, accomplished with use of a cryoballoon (Arctic Front Advance, Medtronic) and aided by the Navik 3D system (APN Health LLC) for navigation.
A preoperative computed tomography (CT) angiogram revealed a large left atrium with four discrete PVs (Figure 1). The CT image was used to help identify the PVs during the procedure. Intracardiac echocardiography was used to guide the transseptal puncture, following which a FlexCath Advance Steerable Sheath (Medtronic) was advanced into the left atrium. A 9 French intraesophageal temperature probe marked the location of the esophagus.
A multipolar Achieve mapping catheter (Medtronic), preloaded within the cryoballoon, was advanced into the left superior pulmonary vein (LSPV), and PV occlusion was verified. During each freeze, the location of the cryoballoon and its relationship to the esophageal temperature probe was verified using the Navik 3D system. Two-dimensional fluoroscopic images of the balloon location and temperature probe were acquired using LAO 20 and AP views, allowing the system to compute a three-dimensional location. Following application of two cryoablation lesions, the cryoballoon was positioned in the left inferior pulmonary vein (LIPV), and its location and relationship to the esophagus were determined utilizing Navik 3D (Figure 2).
In Figure 2A, the esophagus is shown overlying the left-sided veins. Note that the distal half of the balloon (the cooling surface) overlays the esophageal temperature probe only when the cryoballoon was positioned in the LIPV in this AP view. This is confirmed by the cranial, or roof, view (Figure 2B) and left lateral view (Figure 2C).
Cryoablation was performed in each left vein for three minutes, followed by a two-minute confirmatory lesion after entrance block was achieved. Adequacy of entrance and exit block was checked by monitoring PV electrograms from the spiral catheter and by pacing from any electrograms remaining after cryoablation. The minimum esophageal temperature during cryoablation in the LIPV was 29.8°C with a balloon temperature of -41°C. We expected to see some drop in esophageal temperature owing to the proximity of the esophagus to the LIPV, which was 15.3 mm in this patient.
Determination of cryoballoon location in all views is important for assessing the risk of thermal injury to the esophagus. In this patient, subtle repositioning of the balloon was performed by allowing the circular catheter to cannulate a more superior branch of the LSPV. This had the effect of directing the balloon slightly away from the esophageal temperature probe while maintaining PV occlusion.
Following cryoablation of the left-sided veins, electrograms on the roof of the left atrium were eliminated while retaining the catheter in the LSPV (to act as a stabilizer), while the cryoballoon was withdrawn by half a balloon length. When a stable position was achieved with good contact with the roof, a three-minute lesion was delivered. Balloon proximity and orientation with respect to the esophagus were carefully monitored with Navik 3D. After completion of the first lesion, the balloon was withdrawn by half a balloon length, directed against the roof using the cryoballoon’s intrinsic deflection mechanism, and another three-minute lesion was delivered. Four lesions were required to cover the entire roof area (Figure 3). The posterior wall was isolated in similar fashion, using the circular catheter in the LIPV as a rail.
To complete PVI, the right superior pulmonary vein (RSPV) and right inferior pulmonary vein (RIPV) were isolated similarly to the left-sided veins (Figure 4), and phrenic nerve pacing was performed during cryoballoon applications in these veins. The location of the cryoballoon was favorable for both distance and balloon orientation as shown on Navik 3D, and there was no thermal impact on esophageal temperature. The contiguous portions of the roof and posterior wall were ablated by withdrawing the balloon from the corresponding vein by one-third of a balloon length and exerting counterclockwise torque on the sheath. Figure 5 depicts the complete lesion set for all four PVs, left atrial roof, and the posterior wall.
The adequacy of electrogram elimination of the roof and posterior wall was checked with the Achieve catheter connected to the CardioLab (GE Healthcare) patient monitoring system for electrogram recording and analysis. No electrogram >0.2 MV was seen, confirming success of the roof and posterior wall debulking. The complete procedure time after transseptal puncture was 95 minutes. Total fluoroscopy time and dose used following transseptal puncture were 16.6 minutes and 228 mGy, respectively.
ABOUT THE TECHNOLOGY
The Navik 3D system is a new tool that helps electrophysiologists to safely and quickly perform atrial fibrillation ablation. Its open-architecture system promotes simplicity and ease of use in EP ablation procedures through its compatibility with all standard EP tools, including catheters, balloons, and temperature probes.
In practice, objects in the x-ray field of view are often of known, constant dimensions. For example, the size of ablation catheters, temperature probes, and cryoballoons are known. A single-plane fluoroscopy unit can be used to determine the location of the cryoballoon by recording images in two planes at an angle to each other (for example, left anterior oblique [LAO] 20 and anteroposterior [AP] views) if the two views are obtained with the object remaining in a constant position.1 This information can then be used to compute the 3D location of the cryoballoon and graphically render it.2 Computer algorithms are utilized to compensate for cardiac motion and respiratory excursion.
The case presented here describes persistent atrial fibrillation cryoablation using a novel system. Recent literature has reported improved success for patients with persistent atrial fibrillation utilizing both PVI and ablation of the posterior wall.3 Owing to the proximity of the esophagus to the posterior left atrial wall, possible thermal damage to the esophagus must be considered and guarded against. Use of 3D mapping technology allows for visualization of the esophageal temperature probe in relation to the distal end of the cryoballoon (or cooling area) during ablation, helping to direct the cryoballoon away from the esophagus to prevent injury.
It has been reported that atrial flutter accounts for about half of all recurrences following endocardial catheter ablation.4 Construction of a left atrial roofline using the cryoballoon may help prevent occurrence of atrial flutter. Use of Navik 3D also allows for real-time visualization of gaps in ablation lines. This, along with the ability to direct the cryoballoon away from the esophagus during ablation, allows for safer and more effective ablation of persistent atrial fibrillation.
Cryoballoon ablation of the pulmonary veins, roof, and posterior wall was successfully performed in this case without injury to the esophagus. Use of Navik 3D allowed visualization of the cryoballoon location as the roof and posterior wall were ablated, and enabled us to eliminate any gaps. Localization of the esophageal temperature probe in relation to the cryoballoon reduces the chances of esophageal injury.
Disclosure: The authors have no conflicts of interest to report regarding the content herein. Outside the submitted work, Ms. Erickson reports receipt of personal fees for limited contracting work for APN Health until March 2018.
- Djelmami-Hani M. A novel approach to cardiac 3D mapping. EP Lab Digest. 2018;18(9).
- Sra J, Krum D, Choudhuri I, et al. Identifying the third dimension in 2D fluoroscopy to create 3D cardiac maps. JCI Insight. 2016;1(21):e90453.
- Aryana A, Baker JH, Espinosa Ginic MA, et al. Posterior wall isolation using the cryoballoon in conjunction with pulmonary vein ablation is superior to pulmonary vein isolation alone in patients with persistent atrial fibrillation: A multicenter experience. Heart Rhythm. 2018;15(8):1121-1129.
- Calkins H, Hindricks G, Cappato R, et al. 2017 HRS/EHRA/ECAS/APHRS/SOLAECE expert consensus statement on catheter and surgical ablation of atrial fibrillation: Executive summary. Europace. 2018;20(1):157-208.