Clinical Study Regarding the Anatomical Structures of the Right Atrial Isthmus Using Intra-Cardiac Echocardiography: Implication for Catheter Ablation of Common Atrial Flutter

Novel strategies in the ablation of typical atrial flutter: role of intracardiac echocardiography

Radiofrequency ablation (RFA) of the cavo-tricuspid isthmus (CTI) is one of the most frequently performed procedures in electrophysiology. Despite a high success rate, ablation of the CTI can be unusually difficult in some cases. Multiple tools like angiography, 3D mapping, remote navigation and intracardiac echocardiography (ICE) have been introduced to facilitate typical flutter ablation. This review article summarizes the clinical value of different strategies and tools used for CTI ablation focusing on the importance of approaches utilizing ICE.

Two-dimensional echocardiographic features of the inferior right atrial isthmus: the role of vestibular thickness in catheter ablation of atrial flutter

OBJECTIVES

The aim of this study was to examine the feasibility of transthoracic two-dimensional (2D)-echocardiography in defining the cavo-tricuspid isthmus (CTI) anatomy and its value concerning the ease of catheter ablation of isthmic atrial flutter (AF).

METHODS

CTI analysis was accomplished in 39 cases: 16 necropsy specimens and 23 patients. Sixteen were patients with isthmus-dependent AF and seven controls with other supraventricular re-entrant tachycardias. Two-dimensional transthoracic echocardiography and a right atrium angiogram were performed before radiofrequency catheter ablation (RFCA).

RESULTS

The measurements of the CTI with angiography were compared with those taken with echocardiography and correlation was excellent (r= 0.91; P < 0.0001). In normal patients, the dimension of the vestibular thickness was successfully compared and validated with the histological examination of the necropsy specimens: histology median 6.8 mm, range 4.4-10.5 vs. echo median 6.2 mm, range 5.4-8.7; P: NS. Vestibular thickness was greater in complex than in simple RFCA (13.6 ± 1.9 mm vs. 10.0 ± 2.3 mm; P = 0.01). When vestibular thickness ≥11.5 mm, the ablation prone to be complex (sensitivity 83.3%, specificity 80%, positive predictive value 71.4%, and negative predictive value 88.9%).

CONCLUSIONS

Two-dimensional transthoracic echocardiography clearly depicts the inferior isthmus and, displaying the thickness of the tricuspid vestibule, it was related with complexity of the ablation procedure in isthmus-dependent AF.

Voltage-guided ablation technique for cavotricuspid isthmus-dependent atrial flutter: refining the continuous line

Ablation of the cavotricuspid isthmus has become first-line therapy for "isthmus-dependent" atrial flutter. The goal of ablation is to produce bidirectional cavotricuspid isthmus block. Traditionally, this has been obtained by creation of a complete ablation line across the isthmus from the ventricular end to the inferior vena cava. This article describes an alternative method used in our laboratory. There is substantial evidence that conduction across the isthmus occurs preferentially over discrete separate bundles of tissue. Consequently, voltage-guided ablation targeting only these bundles with large amplitude atrial electrograms results in a highly efficient alternate method for the interruption of conduction across the cavotricuspid isthmus. Understanding the bundle structure of conduction over the isthmus facilitates more flexible approaches to its ablation and targeting maximum voltages in our hands has resulted in reduction of ablation time and fewer recurrences.

Intracardiac echocardiography: clinical utility and application

Intracardiac echocardiography (ICE) broadens the spectrum of available echocardiographic techniques and provides the operator direct visualization of cardiac structures in real time. ICE has clear advantages over fluoroscopy, transthoracic echocardiography, and transesophageal echocardiography as the imaging modality of choice in the cardiac catheterization and electrophysiological laboratories. With the development of steerable phased array catheters with low frequency and Doppler qualities, there is marked improvement in visualization of left-sided structures from the right heart. Appropriate utilization of ICE is likely to maximize safety and efficacy of complex interventional procedures and may improve patient outcomes. Future advances in ICE imaging will further improve the ease of device guidance and, in combination with new imaging modalities, could dramatically improve other applications of echocardiography which may result in improved patient outcomes. This review describes the technical evolution of ICE, the use of ICE in guiding percutaneous interventional procedures and possible future applications of ICE in the ever-growing field of interventional cardiology.

MRI of right atrial function after catheter ablation of atrial flutter

RATIONALE AND OBJECTIVES

Catheter ablation of the cavotricuspid isthmus (CTI) is an effective treatment of right atrial flutter. The objective of this study was to evaluate the changes in CTI length and right atrial (RA) function after radiofrequency ablation of isthmus-dependent atrial flutter (isthmus ablation).

MATERIALS AND METHODS

Magnetic resonance imaging was obtained in 14 patients (2 female, mean age 59 +/- 9) before and after isthmus ablation (mean delay 80 +/- 175 days) using steady-state free precession cine magnetic resonance imaging in right anterior oblique view orientation. Right atrial function (maximum/minimum right atrial volumes, stroke volume, ejection fraction) and maximum/minimum length of the CTI were measured.

RESULTS

After isthmus ablation, maximum RA volume decreased by 13% (P = .02) and minimum RA volume by 22% (P = .01), whereas stroke volume and ejection fraction did not increase significantly (P = .4 and .2, respectively). After ablation, the maximum length of the CTI showed a significant decrease of 19% (P < .001) and the minimum length a decrease of 24% (P < .001). A linear correlation between change in CTI length and number of energy applications during ablation could not be observed (r = .605, P = .22 for minimum length; r = .384, P = .18 for maximum length). After eliminating the outliers in the number of energy applications, a significant correlation between energy applications and change in CTI systolic length was found (r = .808, P = .008).

CONCLUSION

Magnetic resonance imaging to visualize right atrial size and function in right anterior oblique orientation was successfully performed and easy to evaluate for volumetric analysis and determination of CTI length. Scarring of the CTI with the use of catheter ablation leads to a significant and linear decrease in its length and to a subsequent reduction of right atrial volumes, whereas functional parameters such as stroke volume/ejection fraction did not change significantly.

Efficacy of bundle ablation for cavotricuspid isthmus-dependent atrial flutter: combination of the maximum voltage-guided ablation technique and high-density electro-anatomical mapping

INTRODUCTION

Pathological studies have demonstrated that the cavotricuspid isthmus (CTI) is often composed of discrete muscle bundles, which are thought to be represented electrically as high-amplitude electrograms. Based on this observation, we visualized the bundles using an electro-anatomical mapping system (EAMS) and investigate the efficacy of bundle ablation which is an ablation method for selectively targeting high-voltage sites obtained by high-density electro-anatomical mapping along the CTI.

METHODS

Sixty patients with atrial flutter were randomly assigned to cavotricuspid isthmus ablation using a conventional anatomical approach (Group 1) or bundle ablation approach (Group 2). In Group 2, CTI was mapped in detail with EAMS, and we visualized the bundles that were 1.5 mV or more on a bipolar voltage map. Radiofrequency (RF) ablation was delivered sequentially from the maximum voltage site at the shortest distance of the bundle until bidirectional block was achieved.

RESULTS

Bidirectional block was achieved in all patients. Mean ablation times (Group 1, 1,392 + or - 960 s; Group 2, 638 + or - 342 s, p < 0.01), the mean number of RF applications (Group 1, 31.7 + or - 23.6; Group 2, 13.0 + or - 7.0, p < 0.01), and fluoroscopy times (Group 1, 50.4 + or - 28.3 min; Group 2, 42.3 + or - 21.3 min, p < 0.01) were significantly shorter in Group 2 than those in Group 1.

CONCLUSION

Bundle ablation at CTI is highly effective for achieving a bidirectional block requiring shorter ablation times, shorter fluoroscopy times, and fewer RF applications.

Echocardiography-guided interventions

A major advantage of echocardiography over other advanced imaging modalities (magnetic resonance imaging, computed tomographic angiography) is that echocardiography is mobile and real time. Echocardiograms can be recorded at the bedside, in the cardiac catheterization laboratory, in the cardiovascular intensive care unit, in the emergency room-indeed, any place that can accommodate a wheeled cart. This tremendous advantage allows for the performance of imaging immediately before, during, and after various procedures involving interventions. The purpose of this report is to review the use of echocardiography to guide interventions. We provide information on the selection of patients for interventions, monitoring during the performance of interventions, and assessing the effects of interventions after their completion. In this document, we address the use of echocardiography in commonly performed procedures: transatrial septal catheterization, pericardiocentesis, myocardial biopsy, percutaneous transvenous balloon valvuloplasty, catheter closure of atrial septal defects (ASDs) and patent foramen ovale (PFO), alcohol septal ablation for hypertrophic cardiomyopathy, and cardiac electrophysiology. A concluding section addresses interventions that are presently investigational but are likely to enter the realm of practice in the very near future: complex mitral valve repairs, left atrial appendage (LAA) occlusion devices, 3-dimensional (3D) echocardiographic guidance, and percutaneous aortic valve replacement. The use of echocardiography to select and guide cardiac resynchronization therapy has recently been addressed in a separate document published by the American Society of Echocardiography and is not further discussed in this document. The use of imaging techniques to guide even well-established procedures enhances the efficiency and safety of these procedures.

Assessment of the maximum voltage-guided technique for cavotricuspid isthmus ablation during ongoing atrial flutter

OBJECTIVES

We aimed to test the maximum voltage-guided cavotricuspid isthmus (CTI) ablation technique during ongoing atrial flutter.

BACKGROUND

Former pathological and electrophysiological studies clarified that the cavotricuspid isthmus is composed of distinct muscular bundles, which are responsible for the conduction of electrical activation. Based on this observation, a maximum voltage-guided ablation technique (MVGT) was developed. This technique was assessed during pacing from the coronary sinus and was reported to be a feasible method to reach bidirectional isthmus block without the need for a complete anatomic ablation line.

METHODS

This was a prospective, randomized single center study. Twenty patients underwent CTI ablation during atrial flutter. In group I (10 pts) CTI ablation was performed with complete anatomical ablation line. In group II (10 pts) ablation was guided by the highest amplitude potentials on the CTI sequentially until bidirectional isthmus block was reached. The following parameters were compared: acute success rate, procedure time, fluoroscopy time, number of radiofrequency (RF) applications and total RF duration.

RESULTS

In all patients, atrial flutter terminated during ablation. Bidirectional isthmus block could be achieved in all pts. Procedure time was shorter in group II (107 +/- 40 vs 68 +/- 19 min, p < 0.01). Significantly less fluoroscopy was used in group II (22.6 +/- 10.6 vs 12.1 +/- 3.8 min, p < 0.01). There were less RF applications in group II (27.1 +/- 21.5 vs 5.9 +/- 2.4, p < 0.001).

CONCLUSIONS

(1) The major finding of this study is that MVGT is a feasible method even during ongoing atrial flutter. (2) Our data confirm that MVGT is an effective technique for CTI ablation with considerable decrease in procedure and fluoroscopy times.

Challenges and implementation of radiation-force imaging with an intracardiac ultrasound transducer

Intracardiac echocardiography (ICE) has been demonstrated to be an effective imaging modality for the guidance of several cardiac procedures, including radiofrequency ablation (RFA). However, assessing lesion size during the ablation with conventional ultrasound has been limited, as the associated changes within the B-mode images often are subtle. Acoustic radiation force impulse (ARFI) imaging is a promising modality to monitor RFAs as it is capable of visualizing variations in local stiffnesses within the myocardium. We demonstrate ARFI imaging with an intracardiac probe that creates higher quality images of the developing lesion. We evaluated the performance of an ICE probe with ARFI imaging in monitoring RFAs. The intracardiac probe was used to create high contrast, high resolution ARFI images of a tissue-mimicking phantom containing stiffer spherical inclusions. The probe also was used to examine an excised segment of an ovine right ventricle with a RFA-created surface lesion. Although the lesion was not visible in conventional B-mode images, the ARFI images were able to show the boundaries between the lesion and the surrounding tissue. ARFI imaging with an intracardiac probe then was used to monitor cardiac ablations in vivo. RFAs were performed within the right atrium of an ovine heart, and B-mode and ARFI imaging with the intracardiac probe was used to monitor the developing lesions. Although there was little indication of a developing lesion within the B-mode images, the corresponding ARFI images displayed regions around the ablation site that displaced less.

Anatomical characteristics of the cavotricuspid isthmus in patients with and without typical atrial flutter: Analysis with two- and three-dimensional intracardiac echocardiography

INTRODUCTION

The cavotricuspid isthmus (CTI) is crucial in the ablation of typical atrial flutter (AFL), and consequently the CTI anatomy and/or its relation to resistant ablation cases have been widely described in human angiographic studies. Intracardiac echocardiography (ICE) has been shown to be a useful tool for determining detailed anatomical information. Thus, this technology may also allow the visualization of the anatomical characteristics of the CTI, providing an opportunity to further understand the anatomy.

AIM

We conducted a study to compare the anatomy of the CTI between the patients with and without AFL and to characterize the anatomy of the CTI in the patients with AFL resistant to ablation.

MATERIALS AND METHODS

Twelve patients with typical AFL and 20 without AFL were enrolled in the study. Two-dimensional (2D) intracardiac echocardiography (ICE) was performed. The recordings were obtained with a 9F, 9-MHz ICE catheter from the right ventricular outflow tract to the inferior vena cava by pulling the catheter back 0.3 mm at a time under guidance with echocardiographic imaging in a respiration-gated manner. Three-dimensional (3D) reconstruction of the images of the CTI were made with a 3D reconstruction system. After the acquisition of the ICE, the CTI ablation was performed in the patients with AFL.

RESULTS

The 2D and 3D images provided clear visualization of the tricuspid valve, coronary sinus ostium, fossa ovalis and Eustachian valve/ridge (EVR). The CTI was significantly longer in the patients with AFL than in those without AFL (median length 24.6 mm (range 17.0-39.1 mm) versus median length 20.6 mm (range 12.5-28.0 mm), respectively, P < 0.05). However, a deep recess due to a prominent EVR was observed in 9 of 12 (75%) patients with AFL and in 12 of 20 (60%) patients without AFL (N.S.). A deep recess and the relatively long CTI were related to aging in all the study patients, and that relationship was similar in a limited number of patients without AFL. In five patients with AFL resistant to ablation, a deep recess and prominent EVR were observed.

CONCLUSIONS

The 2D and 3D ICE were useful for visualizing the complex anatomy of the CTI and identifying the anatomical characteristics of the CTIs refractory to ablation therapy. The anatomical changes observed in the CTI region may simply be the result of aging and may partially be involved in the development of AFL.

Cavotricuspid Isthmus Conduction is Dependent on Underlying Anatomic Bundle Architecture: Observations Using a Maximum Voltage-Guided Ablation Technique

OBJECTIVES

We hypothesized an ablation strategy directly targeting muscle bundles might demonstrate functionally distinct "routes" of conduction, potentially shortening ablation times.

BACKGROUND

Pathological study demonstrated that the cavotricuspid isthmus is composed of distinct anatomically defined bundles, many with intervening gaps of connective tissue.

METHODS

A line was mapped in the "6 o'clock" region and bipolar electrogram amplitude measured during pullback. Zones of peak voltage were ablated first regardless of position. RF was delivered using either a 5-mm externally irrigated catheter, or an 8-mm nonirrigated catheter. The zone of largest remaining voltage was then sequentially targeted until conduction.

RESULTS

Eighteen patients were recruited and followed for 7.9 +/- 1.9 months block occurred (mean age 64 +/- 11.6 years, male:female ratio 14:4). Bi-directional block was achieved in all patients with recurrence of atrial flutter in 1 patient. Mean total RF times was 4.7 +/- 2.8 minutes with a mean of 6.1 +/- 3.3 applications, procedure time was 127.3 +/- 37.7 minutes, and fluoroscopy time was 25.5 +/- 12.0 minutes. Two patterns of block were observed in the study group. Pattern A described no change in conduction times until block, observed in 6 (33%); pattern B described a stepwise block with discrete "jumps," observed in 12 (67%).

CONCLUSIONS

An ablation strategy targeting high-voltage isthmus electrograms obviates the need for a complete anatomic line. This finding together with discrete "jumps" during ablation is consistent with the concept of conduction over discrete bundles rather than a diffuse sheet of muscle.

Intracardiac Echocardiography for Percutaneous Mitral Valve Repair in a Swine Model

BACKGROUND

High-quality live imaging assessment of cardiac valves and cardiac anatomy is crucial for the success of percutaneous catheter-based mitral valve (MV) repair techniques. We examined the use of intracardiac echocardiography (ICE) in providing online ICE images necessary for successful perctunaneous MV repair by Alfieri stitch technique-based percutaneous edge-to-edge device in a swine model.

METHODS

ICE was performed in 20 healthy adult pigs (90 +/- 8 kg, mean +/- SEM). A 10F ICE catheter was advanced through the left femoral vein and the right jugular vein. Images were obtained from the right atrium, left atrium, right ventricle, and pulmonary artery. Fluoroscopy was used to locate the position of ICE catheter tip in different imaging windows.

RESULTS

An echocardiographic protocol was developed for focused visualization of target cardiac structures during the process of percutaneous MV repair. This included visualization of interatrial septum to guide transeptal puncture; to confirm transit of guidewire into the left atrium, across the MV into the left ventricle and across the aortic valve into the aorta; to assist in central positioning of guide catheter in the left atrium above and then across MV leaflets; and to visualize middle scallops of anterior and posterior MV leaflets in short- and long-axis views. Finally, location and orientation of the orifice of the therapy catheter against each MV leaflet was visualized to enable successful capture of MV leaflets, to confirm successful deployment of suture and double orifice (figure of 8" appearance of MV, and finally to confirm central deployment of clip at the site of suture.

CONCLUSION

An ICE protocol was developed to visualize serial cardiac structures to guide deployment of suture into the A2-P2 scallops of the MV and to confirm final result before release of clip.