Esophagus imaging for catheter ablation of atrial fibrillation: comparison of two methods with showing of esophageal movement

State of the art paper: Cardiac computed tomography of the left atrium in atrial fibrillation

The clinical spectrum of atrial fibrillation means that a patient-individualized approach is required to ensure optimal treatment. Cardiac computed tomography can accurately delineate atrial structure and function and could contribute to a personalized care pathway for atrial fibrillation patients. The imaging modality offers excellent spatial resolution and has been utilised in pre-, peri- and post-procedural care for patients with atrial fibrillation. Advances in temporal resolution, acquisition times and analysis techniques suggest potential expanding roles for cardiac computed tomography in the future management of patients with atrial fibrillation. The aim of the current review is to discuss the use of cardiac computed tomography in atrial fibrillation in pre-, peri- and post-procedural settings. Potential future applications of cardiac computed tomography including atrial wall thickness assessment and epicardial fat volume quantification are discussed together with emerging analysis techniques including computational modelling and machine learning with attention paid to how these developments may contribute to a personalized approach to atrial fibrillation management.

Preoperative Personalization of Atrial Fibrillation Ablation Strategy to Prevent Esophageal Injury: Impact of Changes in Esophageal Position

INTRODUCTION

Due to changes in esophageal position, preoperative assessment of the esophageal location may not mitigate the risk of esophageal injury in catheter ablation for atrial fibrillation (AF). This study aimed to assess esophageal motion and its impact on AF ablation strategies.

METHODS AND RESULTS

Ninety-seven AF patients underwent 2 computed tomography (CT) scans. The area at risk of esophageal injury (AAR) was defined as the left atrial surface ≤3 mm from the esophagus. On CT1, ablation lines were drawn blinded to the esophageal location to create 3 ablation sets: individual pulmonary vein isolation (PVI), wide antral circumferential ablation (WACA), and WACA with linear ablation (WACA+L). Thereafter, ablation lines for WACA and WACA+L were personalized to avoid the AAR. Rigid registration was performed to align CT1 onto CT2, and the relationship between ablation lines and the AAR on CT2 was analyzed. The esophagus moved by 3.6 [2.7 to 5.5] mm. The AAR on CT2 was 8.6 ± 3.3 cm² , with 77% overlapping that on CT1. High body mass index was associated with the AAR mismatch (standardized β 0.382, P <0.001). Without personalization, AARs on ablation lines for individual PVI, WACA, and WACA+L were 0 [0-0.4], 0.8 [0.5-1.2], 1.7 [1.2-2.0] cm² . Despite the esophageal position change, the personalization of ablation lines for WACA and WACA+L reduced the AAR on lines to 0 [0-0.5] and 0.7 [0.3-1.0] cm² (P <0.001 for both).

CONCLUSION

The personalization of ablation lines based on a preoperative CT reduced ablation to the AAR despite changes in esophageal position. This article is protected by copyright. All rights reserved.

Relationship between the posterior atrial wall and the esophagus: esophageal position during atrial fibrillation ablation

Background

Atrial fibrillation ablation implies a risk of esophageal thermal injury. Esophageal position can be analyzed with imaging techniques, but evidence for esophageal mobility is inconsistent.

Objectives

The purpose of this study was to analyze esophageal position stability from one procedure to another and during a single procedure.

Methods

Esophageal position was compared in 2 patient groups. First, preprocedural multidetector computerized tomography (MDCT) of first pulmonary vein isolation and redo intervention (redo group) was segmented with ADAS 3D™ to compare the stability of the atrioesophageal isodistance prints. Second, 3 imaging modalities were compared for the same procedure (multimodality group): (1) preprocedural MDCT; (2) intraprocedural fluoroscopy obtained with the transesophageal echocardiographic probe in place with CARTOUNIVU™; and (3) esophageal fast anatomic map (FAM) at the end of the procedure. Esophageal position correlation between different imaging techniques was computed in MATLAB using semiautomatic segmentation analysis.

Results

Thirty-five redo patients were analyzed and showed a mean atrioesophageal distance of 1.2 ± 0.6 mm and a correlation between first and redo procedure esophageal fingerprint of 91% ± 5%. Only 3 patients (8%) had a clearly different position. The multi-imaging group was composed of 100 patients. Esophageal position correlation between MDCT and CARTOUNIVU was 82% ± 10%; between MDCT and esophageal FAM was 80% ± 12%; and between esophageal FAM and CARTOUNIVU was 83% ± 15%.

Conclusion

There is high stability of esophageal position between procedures and from the beginning to the end of a procedure. Further research is undergoing to test the clinical utility of the esophageal fingerprinted isodistance map to the posterior atrial wall.

Protection of the esophagus during catheter ablation of atrial fibrillation

Esophageal injury still occurs with high frequency during ablation of atrial fibrillation (AF). The purpose of this study is to provide a review of methods to protect the esophagus from injury during AF ablation. Despite advances in imaging and ablation, the potential risk of esophageal injury during AF ablation remains an important concern with a high occurrence of esophageal injury (≈15%). There have been numerous studies evaluating varied techniques for esophageal protection including active cooling and displacement of the esophagus. These techniques are reviewed in this manuscript as well as the role of esophageal protection in managing patients undergoing AF ablation procedure.

Detection of oesophageal course during left atrial catheter ablation

BACKGROUND

Oesophageal changes and injuries were recorded after atrial fibrillation(AF) ablation procedures. The reduction of power in the posterior left atrial(LA) wall(closest to the oesophagus) and the monitoring of temperature in the oesophagus(OE) reduced oesophageal injuries. The intracardiac-echocardiography(ICE) with a Cartosound module provides two-dimensional imaging (2D) to assess detailed cardiac anatomy and its relationship with the OE. The aim of this study was to highlight the safety and feasibility of 3D-reconstruction of the oesophageal course in left atrial catheter ablation(CA) procedures without OE temperature probe or quadripolar catheter to guide ICE OE reconstruction.

METHODS

180 patients(PT) underwent left atrial ablation. AF ablation were 125(69.5%); incisional left atrial tachycardias(IAFL) were 37(20.6%); left atrial tachycardias(LAT) were 19(10.6%). The LA and pulmonary vein anatomies were rendered by traditional electroanatomic mapping(EAM) and merged with an ICE anatomic map. In 109 PT ICE imaging was used to create a geometry of the OE(group A). A quadripolar catheter was used in 71 PT to show OE course associated to ICE(group B).

RESULTS

Ablation energy delivery was performed outside the broadest OE anatomy borders. The duration of procedures was longer in group B vs group A Fluoroscopy time was lower in Group A than Group B(Group A 7 ± 3.2 vs 19.2 ± 2.4 min; p < 0.01).

CONCLUSIONS

OE monitoring with ICE is safe and feasible. Oesophageal anatomy is complex and variable. Many PT will have a broad oesophageal boundary, which increases the risk of untoward thermal injury during posterior LA ablation. ICE with 3D construction of the OE enhances border detection of the OE, and as such, should decrease the risk of oesophageal injury by improving avoidance strategies without intra-oesophageal catheter visualization.

Current Status of Esophageal Protection

Catheter ablation of atrial fibrillation necessitates ablation on the posterior left atrium. The anterior esophagus touches the posterior left atrium, although its course is highly variable. The proximity of the left atrium to the esophagus confers risk of injury with radiofrequency and cryoablation owing to the heat transfer that occurs with thermal ablation. Early detection of esophageal temperature changes with probes may decrease the extent of damage to the esophagus, but evidence is mixed. Avoiding ablation on the esophagus with esophageal deviation and modifying ablation approaches may decrease the risk of injury.

Distance between the left atrium and the vertebral body is predictive of esophageal movement in serial MR imaging

PURPOSE

MRI or CT imaging can be used to identify the esophageal location prior to left atrial ablation, but the esophagus may move making the location unreliable when ablating to minimize esophageal injury. The aim of this study was to evaluate esophageal position and movement based on serial MRI imaging with the goal of identifying imaging and clinical characteristics that can predict the esophageal movement.

METHODS

Fifty patients undergoing 190 MRI scans were analyzed. The relative position of the esophagus in each MRI along with clinical and imaging characteristics was quantified, including the gap between the left atrium (LA) and the vertebral body (GAP), an anatomic space in which the esophagus can move.

RESULTS

A mean of 3.8 MRIs was analyzed per patient. Sixteen patients (32.0%) experienced significant lateral esophageal movement of more than 10 mm. In the significant movement group, body mass index (BMI) was higher (33.0 ± 6.5 vs 28.8 ± 5.3, p = 0.02) and the GAP was significantly larger (7.1 ± 2.5 vs 4.8 ± 5.1 mm, p = 0.04). Multivariate logistic regression analysis revealed that the GAP ≤ 4.5 mm was the only independent predictor of the esophagus not moving (odds ratio = 9.25, 95% confidence interval = 1.72 to 49.67, p = 0.0095).

CONCLUSIONS

A GAP of less than 4.5 mm between the LA and the vertebral body is associated with lack of esophageal movement (< 10 mm). This suggests that the measurement of GAP < 4.5 mm may be used to predict the esophageal location in patients undergoing atrial ablation.

Long-term mobility of the esophagus in patients undergoing catheter ablation of atrial fibrillation: data from computer tomography and 3D rotational angiography of the left atrium

PURPOSE

Computed tomography (CT) and 3D rotational angiography (3DRA) of the left atrium (LA) are used to evaluate the esophagus prior to radiofrequency ablation for atrial fibrillation. The aim of this study was to compare preprocedural and periprocedural views of the esophagus and the left atrium.

METHODS

From September 2011 to August 2012, 3DRA and CT of the LA were performed on 56 patients before they underwent catheter ablation of atrial fibrillation. The 3DRA was performed periprocedurally, and the CT was performed an average of 20 days prior to the procedure. 3D models of the LA and the esophagus were then segmented on the EP Navigator V 3.1 workstation. Five positions of the esophagus, A-E, in order from left to right, were evaluated.

RESULTS

The most common position of the esophagus was behind the left part of the LA (CT, position B (n = 26)) and behind the central part of the LA (3DRA, position C (n = 21)). The maximum shift of the esophagus was three positions, and the average shift was 0.857 ± 0.766 of a position. There was a shift of one position in 44.6 % of the patients, two positions in 17.9 %, and three positions in 1.8 %. A statistically significant difference was found between the positions of the esophagus when the 3DRA and CT evaluations were compared.

CONCLUSIONS

The most common position of the esophagus was behind the middle and left part of the LA. The outpatient views of the esophagus obtained before ablation did not reflect the position of the esophagus at the beginning of the procedure.

Use of oral gadobenate dimeglumine to visualise the oesophagus during magnetic resonance angiography in patients with atrial fibrillation prior to catheter ablation

BACKGROUND

Atrio-oesophageal fistula was first reported as a fatal complication of surgical endocardial and percutaneous endocardial radiofrequency ablation for atrial fibrillation, with an incidence after catheter ablation between 0.03% and 0.5%. Magnetic resonance angiography (MRA) was usually performed to obtain pre-procedural 3D images, used to merging into an electro-anatomical map, guiding step-by-step ablation strategy of AF. Our aim was to find an easy, safe and cost-effective way to enhance the oesophagus during MRA.

METHODS

In 105 consecutive patients, a right-left phase encoding, free breathing, 3D T1 MRA sequence was performed in the axial plane, >24 hours before catheter ablation, using an intravenous injection of gadobenate dimeglumine contrast medium. The oesophagus was enhanced using an oral gel solution of 0.7 mL gadobenate dimeglumine contrast medium mixed with approximately 40 mg thickened water gel, which was swallowed by the patients on the scanning table, immediately before the MRA sequence acquisition.

RESULTS

The visualisation of the oesophagus was obtained in 104/105 patients and images were successfully merged, as left atrium and pulmonary veins, into an electro-anatomical map, during percutaneous endocardial radiofrequency ablation. All patients tolerated the study protocol and no immediate or late complication was observed with the oral contrast agent administration. The free-breathing MRA sequence used in our protocol took 7 seconds longer than MRA breath-hold conventional sequence.

CONCLUSION

Oesophagus visualization with oral gadobenate dimeglumine is feasible for integration of oesophagus anatomy images into the electro-anatomical map during AF ablation, without undesirable side effects and without significantly increasing cost or examination time.

Assessment of oesophageal position by direct visualization with luminal contrast compared with segmentation from pre-acquired computed tomography scan-implications for ablation strategy

AIMS

Atrio-oesophageal fistula is a rare but often fatal complication of catheter ablation for atrial fibrillation (AF). Various strategies are employed to evaluate the oesophageal position in relation to the posterior left atrium (LA). These include segmentation of the oesophagus from a pre-acquired computed tomography (CT) scan and direct, real-time assessment of the oesophageal position using contrast at the time of the procedure.

METHODS AND RESULTS

One hundred and fourteen patients with drug-refractory AF underwent CT scanning prior to AF ablation. The LA and oesophagus were segmented from this scan. The oesophagus was deemed midline, ostial if it crossed directly behind any of the pulmonary vein (PV) ostia, or antral if it passed within 5 mm of a PV ostium. Under general anaesthesia at the time of ablation, the same patients were administered contrast via an oro-gastric tube to outline the oesophagus. Catheters were placed at the PV ostia and oesophageal position in relation to the PVs was established radiographically using a postero-anterior view. Oesophageal position assessed by real-time assessment correlated with the CT scan in only 59% of patients. In 34% the oesophagus was more right sided on direct visualization, while in 7% it was more left sided.

CONCLUSION

Segmentation of the oesophagus from the CT scan did not correlate the real-time oesophageal position at the time of the procedure in over 40% of patients under general anaesthesia. Reliance on the determination of oesophageal position by previously acquired CT may be misleading at best and provide a false sense of security when ablating in the posterior LA.

Impact of cardiac computed tomography of the interatrial septum before pulmonary vein isolation

BACKGROUND

Multidetector computed tomography (MDCT) may be useful to identify patients with patent foramen ovale (PFO). The aim of this study was to analyze whether a MDCT performed before pulmonary vein isolation reliably detects a PFO that may be used for access to the left atrium.

METHODS AND RESULTS

In 79 consecutive patients, who were referred for catheter ablation of symptomatic paroxysmal or persistent atrial fibrillation (AF), the presence of a PFO was explored by MDCT and transesophageal echocardiography (TEE). TEE was considered as the gold standard, and quality of TEE was good in all patients. In 16 patients (20.3%), MDCT could not be used for analysis because of artifacts, mainly because of AF. On TEE, a PFO was found in 15 (23.8%) of the 63 patients with usable MDCT. MDCT detected six PFO of which four were present on TEE. This corresponded to a sensitivity of 26.7%, a specificity of 95.8%, a negative predictive value of 80.7%, and a positive predictive value of 66.7%. The receiver operating characteristics curve of MDCT for the detection of PFO was 0.613 (95% confidence interval 0.493-0.732).

CONCLUSIONS

MDCT may detect a PFO before pulmonary isolation. However, presence of AF may lead to artifacts on MDCT impeding a meaningful analysis. Furthermore, in this study sensitivity and positive predictive value of MDCT were low and therefore MDCT was not a reliable screening tool for detection of PFO.

Prevention of atrial-esophageal fistula after catheter ablation of atrial fibrillation

PURPOSE OF REVIEW

The formation of atrial-esophageal fistula after catheter ablation for atrial fibrillation is a rare but devastating complication with high mortality. Prevention is of utmost importance. We review the usefulness of currently available preventive measures.

RECENT FINDINGS

Recent studies using endoscopy after atrial fibrillation ablation show the development of esophageal ulcerations in 14-17% of the patients. Risk factors for the occurrence of esophageal ulcerations seem to be a high esophageal luminal temperature during ablation, increased power during energy application at the posterior left-atrial wall, a short left atrium-to-esophagus distance, the use of nasogastric tubes and general anesthesia. The main available tools for prevention of atrial-esophageal fistula include: 1) Assessment of the esophagus position in the preprocedural CT/MRI scan. Its usefulness is limited by the potential of the esophagus to move. 2) Tagging of the esophagus and real-time visualization of its course during the procedure. This can be achieved by introduction of a catheter into the esophagus and visualization in the three-dimensional electroanatomical system, by intracardiac ultrasound or by fluoroscopy. 3) Continuous monitoring of the esophageal luminal temperature during ablation with special temperature sensors. 4) Reduction of power during energy application at the posterior left-atrial wall in close proximity to the esophagus. Despite application of preventive measures, cases of atrial-esophageal fistulas have been reported.

SUMMARY

Several measures for prevention of atrial-esophageal fistula formation are available nowadays. Although these measures cannot completely eliminate the risk of fistula, it appears prudent to apply a combination of them during atrial fibrillation ablation.

Esophagus silhouette extraction and reconstruction from fluoroscopic views for cardiac ablation procedure guidance

Cardiac ablation involves the risk of serious complications when thermal injury to the esophagus occurs. This paper proposes to reduce the risk of such injuries by a proactive visualization technique, improving physician awareness of the esophagus location in the absence of or in addition to a reactive monitoring device such as a thermal probe. This is achieved by combining a graphical representation of the esophagus with live fluoroscopy. Toward this goal, we present an automated method to reconstruct and visualize a 3-D esophagus model from fluoroscopy image sequences acquired using different C-arm viewing directions. In order to visualize the esophagus under fluoroscopy, it is first biomarked by swallowing a contrast agent such as barium. Images obtained in this procedure are then used to automatically extract the 2-D esophagus silhouette and reconstruct a 3-D surface of the esophagus internal wall. Once the 3-D representation has been computed, it can be visualized using fluoroscopy overlay techniques. Compared to 3-D esophagus imaging using CT or C-arm CT, our proposed fluoroscopy method requires low radiation dose and enables a simpler workflow on geometry-calibrated standard C-arm systems.