Comparative study of fluoroscopy and intracardiac echocardiographic guidance for the creation of linear atrial lesions

Intracardiac echocardiography in paediatric and congenital cardiac ablation shortens procedure duration and improves success without complications

AIMS

Common to adult electrophysiology studies (EPSs), intracardiac echocardiography (ICE) use in paediatric and congenital heart disease (CHD) EPS is limited. The purpose of this study was to assess the efficacy of ICE use and incidence of associated complications in paediatric and CHD EPS.

METHODS AND RESULTS

This single-centre retrospective matched cohort study reviewed EPS between 2013 and 2022. Demographics, CHD type, and EPS data were collected. Intracardiac echocardiography cases were matched 1:1 to no ICE controls to assess differences in complications, ablation success, fluoroscopy exposure, procedure duration, and arrhythmia recurrence. Cases and controls with preceding EPS within 5 years were excluded. Intracardiac echocardiography cases without an appropriate match were excluded from comparative analyses but included in the descriptive cohort. We performed univariable and multivariable logistic regression to assess associations between variables and outcomes. A total of 335 EPS were reviewed, with ICE used in 196. The median age of ICE cases was 15 [interquartile range (IQR) 12-17; range 3-47] years, and median weight 57 [IQR 45-71; range 15-134] kg. There were no ICE-related acute or post-procedural complications. There were 139 ICE cases matched to no ICE controls. Baseline demographics and anthropometrics were similar between cases and controls. Fluoroscopy exposure (P = 0.02), procedure duration (P = 0.01), and arrhythmia recurrence (P = 0.01) were significantly lower in ICE cases.

CONCLUSION

Intracardiac echocardiography in paediatric and CHD ablations is safe and reduces procedure duration, fluoroscopy exposure, and arrhythmia recurrence. However, not every arrhythmia substrate requires ICE use. Thoughtful selection will ensure the judicious and strategic application of ICE to enhance outcomes.

Safety of fluoroless radiofrequency catheter ablation for atrial fibrillation in patients with pre-existing cardiac implantable electronic device: A single-center study

BACKGROUND

Radiofrequency catheter ablation (RFA) for atrial fibrillation (AF) is being increasingly performed without fluoroscopy. This study aims to determine the safety of fluoroless RFA for patients with pre-existing cardiac implantable electronic devices (CIED).

METHODS

This is a single-center, single-operator, retrospective, observational study of 225 consecutive fluoroless RFA procedures for AF from June 1, 2019 to June 1, 2022. All procedures were performed with intracardiac echocardiography (ICE) support. Patients with pre-existing CIED were extracted from the database. Each CIED was interrogated at the start and end of each procedure and at 30-day follow-up. Pre- and post-procedure CIED interrogations were compared for any change in device or lead parameters. Patients were tracked for any subsequent device malfunction.

RESULTS

Out of 225 fluoroless AF ablations, 25 (10.2%) had pre-existing CIED (14 dual-chamber pacemakers, three dual-chamber defibrillators, three single-chamber defibrillators, one single chamber pacemaker, and four biventricular devices). Mean patient age was 71 ± 6 years. The mean duration of indwelling CIED was 1804 ± 1645 days (range: 78-6267 days). One (4%) patient had lead-related fibrin on ICE imaging. There was no significant difference in lead(s) threshold, impedance, or sensing post procedure or at 30-day follow-up compared to pre procedure. None of the patients required lead revision. There were no intra- or post-op thromboembolic events or subsequent device infection. One patient underwent CIED extraction after 11 months for an unrelated secondary device infection.

CONCLUSIONS

Radiofrequency catheter ablation for AF can be safely performed without fluoroscopy in patients with pre-existing CIED.

Left atrial thickness and acute thermal injury in patients undergoing ablation for atrial fibrillation: Laser versus radiofrequency energies

INTRODUCTION

Thermally induced cardiac lesions result in necrosis, edema, and inflammation. This tissue change may be seen with ultrasound. In this study, we sought to use intracardiac echocardiography (ICE) to evaluate pulmonary vein tissue morphology and assess the acute tissue changes that occur following radiofrequency (RF) or laser ablation for atrial fibrillation (AF).

METHODS AND RESULTS

Patients with AF underwent pulmonary vein isolation (PVI) using irrigated RF or laser balloon. Pre- and post-ablation ICE imaging was performed from within each pulmonary vein (PV). At least 10 transverse imaging planes per PV were evaluated and each plane was divided into eight segments. The PV/atrial wall thickness and the luminal area were measured at each segment. Twenty-seven patients underwent PVI (15 with laser, 12 with RF). Ninety-eight pulmonary veins were analyzed (58 PVs laser; 40 PVs RF). At baseline, there were no regional differences in PV wall thickness in the right-sided veins. The anterior regions of left superior pulmonary vein (LSPV) and left inferior pulmonary vein (LIPV) were significantly thicker compared with the posterior and inferior regions (p < .01). Post-ablation, PV wall thickness in RF group increased 24.1% interquartile range (IQR) (17.2%-36.7%) compared with 1.2% IQR (0.4%-8.9%) in laser group, p = .004. In all PVs, RF ablation resulted in significantly greater percent increase in wall thickness compared with laser. Additionally, RF resulted in more variable changes in regional PV wall thickness; with more increases in wall thickness in anterior versus posterior LSPV (75.4 ± 58.5% vs. 46.8 ± 55.6%, p < .01), anterior versus posterior right superior pulmonary vein (RSPV) (62.9 ± 63.9% vs. 44.6 ± 51.7%, p < .05), and superior versus inferior RSPV (69.1 ± 45.4% vs. 35.9 ± 45%, p < .05). There were no significant regional differences in PV wall thickness changes for the laser group.

CONCLUSIONS

Rotational ICE can be used to measure acute tissue changes with ablation. Regional variability in baseline wall thickness was nonuniformly present in PVs. Acute tissue changes occurred immediately post-ablation. Compared with laser balloon, RF shows markedly more thickening post-ablation with significant regional variations.

Automatically steering cardiac catheters in vivo with respiratory motion compensation

A robotic system for automatically navigating ultrasound (US) imaging catheters can provide real-time intra-cardiac imaging for diagnosis and treatment while reducing the need for clinicians to perform manual catheter steering. Clinical deployment of such a system requires accurate navigation despite the presence of disturbances including cyclical physiological motions (e.g., respiration). In this work, we report results from in vivo trials of automatic target tracking using our system, which is the first to navigate cardiac catheters with respiratory motion compensation. The effects of respiratory disturbances on the US catheter are modeled and then applied to four-degree-of-freedom steering kinematics with predictive filtering. This enables the system to accurately steer the US catheter and aim the US imager at a target despite respiratory motion disturbance. In vivo animal respiratory motion compensation results demonstrate automatic US catheter steering to image a target ablation catheter with 1.05 mm and 1.33° mean absolute error. Robotic US catheter steering with motion compensation can improve cardiac catheterization techniques while reducing clinician effort and X-ray exposure.

How To Achieve Durable Pulmonary Vein Antral Isolation?

The inability to achieve durable pulmonary vein isolation(PVI) remains a major limitation to a catheter ablation for thew treatment of atrial fibrillation(AF), potentially resulting in AF recurrence.In this review,we discuss the research performed investigating methods to improve lesion permanence for the goal of durable PVI.Investigations evaluted procedural techniques,various catheres utilized, adjunctive pharamacologic therapy and novel energy sources designed to improve ablation lesion permanence are discussed.

Why is intracardiac echocardiography helpful? Benefits, costs, and how to learn

Current interventional procedures in structural heart disease and cardiac arrhythmias require peri-interventional echocardiographic monitoring and guidance to become as safe, expedient, and well-tolerated for patients as possible. Intracardiac echocardiography (ICE) complements and has in part replaced transoesophageal echocardiography (TEE), including real-time three-dimensional (RT-3D) imaging. The latter is still widely accepted as a method to prepare for and to guide interventional treatments. In contrast to TEE, ICE represents a purely intraprocedural guiding and imaging tool unsuitable for diagnostic purposes. Patients tolerate ICE much better, and the method does not require general anaesthesia. Accurate imaging of the particular pathology, its anatomic features, and spatial relation to the surrounding structures is critical for catheter and wire positioning, device deployment, evaluation of the result, and for ruling out complications. This review describes the peri-interventional role of ICE, outlines current limitations, and points out future implications. Two-dimensional ICE has become a suitable guiding tool for a variety of percutaneous treatments in patients who are conscious or under monitored anaesthesia care, whereas RT-3DICE is still undergoing clinical testing. Continuous TEE monitoring under general anaesthesia remains a widely accepted alternative.

Cryoballoon in atrial fibrillation ablation

Encouraging results of ablation therapy in patients with paroxysmal atrial fibrillation (AF) have prompted changes in professional practice guidelines. The most recent European guidelines have suggested that ablation might be offered as first-line therapy in selected patients. Cryoballoon ablation is a promising technology in interventional AF therapy. Two different sizes of the cryoballoon are currently available: a smaller (23 mm) and a larger (28 mm) balloon relative to the ostial diameter of the pulmonary veins. New tools, the circular mapping catheter and the use of intracardiac echocardiography, provide important periprocedural information. A meta-analysis of previous studies revealed outcome data with an AF-free survival rate of 72.83% at the 1-year follow-up in paroxysmal AF patients undergoing cryoballoon ablation. The most frequent, but reversible complication is phrenic nerve palsy with reported incidences up to 10%. All efforts must be taken to overcome this limitation, since the overall major complication rate tends to be lower in cryoballoon compared to radiofrequency ablation. In persistent AF, reported results in cryoballoon ablation had a limited success rate below 50% after a single procedure. A double balloon approach using both cryoballoon sizes might overcome some of the limitations in persistent AF. Prospective data and randomized studies are required. This article outlines the current status of cryoballoon technology in AF ablation therapy.

A 10-Fr ultrasound catheter with integrated micromotor for 4-D intracardiac echocardiography

We developed prototype real-time 3-D intracardiac echocardiography catheters with integrated micromotors, allowing internal oscillation of a low-profile 64-element, 6.2-MHz phased-array transducer in the elevation direction. Components were designed to facilitate rotation of the array, including a low-torque flexible transducer interconnect and miniature fixtures for the transducer and micromotor. The catheter tip prototypes were integrated with two-way deflectable 10-Fr catheters and used in in vivo animal testing at multiple facilities. The 4-D ICE catheters were capable of imaging a 90° azimuth by up to 180° elevation field of view. Volume rates ranged from 1 vol/sec (180° elevation) to approximately 10 vol/sec (60° elevation). We successfully imaged electrophysiology catheters, atrial septal puncture procedures, and detailed cardiac anatomy. The elevation oscillation enabled 3-D visualization of devices and anatomy, providing new clinical information and perspective not possible with current 2-D imaging catheters.

The use of intracardiac echocardiography and other intracardiac imaging tools to guide noncoronary cardiac interventions

The limitations of standard fluoroscopy have led to the development of improved imaging techniques to guide noncoronary cardiac interventions. Imaging tools that are used in the interventional laboratory can be categorized as invasive and noninvasive. Noninvasive cardiac imaging tools include ultrasound, computed tomography, and magnetic resonance imaging. These modalities can generate high-resolution images of the heart and are increasingly being used to guide cardiac interventions. Despite these advances, there remains a strong role for invasive imaging tools in the interventional laboratories. Such invasive imaging tools include transesophageal echocardiography, intracardiac echocardiography, intracardiac endoscopy, and electroanatomic mapping systems. Despite the risks inherent to the invasive nature of these tools, these modalities can provide excellent real-time, detailed images that can be invaluable in guiding certain cardiac interventions. This review will propose the features of an ideal intracardiac imaging tool, summarize the intracardiac imaging tools that are currently available or under development to guide noncoronary cardiac interventional procedures, and suggest opportunities for improvement. One opportunity in this field is to couple imaging systems directly with the interventional devices themselves. The use of intracardiac imaging to guide select cardiac procedures including transseptal catheterization, catheter ablation procedures for arrhythmias, and percutaneous placement of cardiac valves and closure devices will also be discussed. Most of this review will be devoted to intracardiac echocardiography, which currently has the broadest number of 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.

Forward-looking intracardiac ultrasound imaging using a 1-D CMUT array integrated with custom front-end electronics

Minimally invasive catheter-based electrophysiological (EP) interventions are becoming a standard procedure in diagnosis and treatment of cardiac arrhythmias. As a result of technological advances that enable small feature sizes and a high level of integration, nonfluoroscopic intracardiac echocardiography (ICE) imaging catheters are attracting increasing attention. ICE catheters improve EP procedural guidance while reducing the undesirable use of fluoroscopy, which is currently the common catheter guidance method. Phased-array ICE catheters have been in use for several years now, although only for side-looking imaging. We are developing a forward-looking ICE catheter for improved visualization. In this effort, we fabricate a 24-element, fine-pitch 1-D array of capacitive micromachined ultrasonic transducers (CMUT), with a total footprint of 1.73 mm x 1.27 mm. We also design a custom integrated circuit (IC) composed of 24 identical blocks of transmit/ receive circuitry, measuring 2.1 mm x 2.1 mm. The transmit circuitry is capable of delivering 25-V unipolar pulses, and the receive circuitry includes a transimpedance preamplifier followed by an output buffer. The CMUT array and the custom IC are designed to be mounted at the tip of a 10-Fr catheter for high-frame-rate forward-looking intracardiac imaging. Through-wafer vias incorporated in the CMUT array provide access to individual array elements from the back side of the array. We successfully flip-chip bond a CMUT array to the custom IC with 100% yield. We coat the device with a layer of polydimethylsiloxane (PDMS) to electrically isolate the device for imaging in water and tissue. The pulse-echo in water from a total plane reflector has a center frequency of 9.2 MHz with a 96% fractional bandwidth. Finally, we demonstrate the imaging capability of the integrated device on commercial phantoms and on a beating ex vivo rabbit heart (Langendorff model) using a commercial ultrasound imaging system.

Imaging in catheter ablation for atrial fibrillation: enhancing the clinician's view

Catheter ablation is an effective treatment for symptomatic atrial fibrillation. A thorough understanding of the left atrium anatomy and its adjacent structures is critical for the success of the procedure and for avoiding complications. Pre-procedural imaging aims at determining left atrial size, anatomy, and function and is also used to rule out an atrial thrombus. During the procedure, while fluoroscopy remains the gold standard imaging modality for guiding transseptal catheterization and catheter ablation, numerous other imaging modalities have been developed to improve 3D navigation and ablation. Finally, post-operative imaging intends to monitor heart function and to search for potential complications like pulmonary vein stenosis or the rare but dramatic atrio-oesophageal fistula. This review discusses the relative merits of all imaging modalities available in the context of catheter ablation of atrial fibrillation.

Full-motion two- and three-dimensional pulmonary vein imaging by intracardiac echocardiography after pulmonary vein isolation

BACKGROUND

The pulmonary veins (PVs) are topographically complex and motile, so angiographic visualization of the PVs anatomy is limited. An imaging technique that accurately portrays the pulmonary vein (PV) anatomy would be valuable during and after catheter ablation procedures.

PURPOSE

We investigated whether three-dimensional (3D) intracardiac echocardiography (ICE) can visualize radiofrequency (RF)-induced tissue changes after PV isolation.

METHODS

We performed 3D ICE studies with a 9F, 9-MHz ICE catheter after segmental or extended PV isolation. The ICE catheter was placed 3-4 cm inside the PV ostium and mounted onto a pullback device. Sequential two-dimensional (2D) images of the full length of the vein were obtained in 0.3 mm steps with cardiac and respiratory cycle gating. Each image was fed into a computer, and the aggregate data set was reconstructed into a 3D, full-motion image. RF lesion location and lesion size were studied on 67 pullback images from 29 patients.

RESULTS

The 2D and 3D reconstruction was possible for 27 left superior PVs, 13 left inferior PVs, 26 right superior PVs, and one right inferior PV. The ablation site was identified 3-7 mm inside the PV ostium, and a 1/2 - 4/5 circumferential area was ablated with no clinically relevant stenosis. No significant differences were found on the ablated area or ablation site between segmental and extensive PV isolation.

CONCLUSION

The 2D and 3D ICE of the PVs provides detailed anatomical information of the proximal PVs, and RF-induced tissue changes in the PV wall can be visualized by ICE.

The acoustic lens design and in vivo use of a multifunctional catheter combining intracardiac ultrasound imaging and electrophysiology sensing

A multifunctional 9F intracardiac imaging and electrophysiology mapping catheter was developed and tested to help guide diagnostic and therapeutic intracardiac electrophysiology (EP) procedures. The catheter tip includes a 7.25-MHz, 64-element, side-looking phased array for high resolution sector scanning. Multiple electrophysiology mapping sensors were mounted as ring electrodes near the array for electrocardiographic synchronization of ultrasound images. The catheter array elevation beam performance in particular was investigated. An acoustic lens for the distal tip array designed with a round cross section can produce an acceptable elevation beam shape; however, the velocity of sound in the lens material should be approximately 155 m/s slower than in tissue for the best beam shape and wide bandwidth performance. To help establish the catheter's unique ability for integration with electrophysiology interventional procedures, it was used in vivo in a porcine animal model, and demonstrated both useful intracardiac echocardiographic visualization and simultaneous 3-D positional information using integrated electroanatomical mapping techniques. The catheter also performed well in high frame rate imaging, color flow imaging, and strain rate imaging of atrial and ventricular structures.

Atrial fibrillation: a historical perspective

Atrial fibrillation (AF) undoubtedly has become one of the most well studied arrhythmias today in terms of pathophysiology and diagnostic and therapeutic (interventional) electrophysiology. Although it lends itself to an apparently easy diagnosis on a surface ECG, myriad electromechanical mechanisms underlie its origin. An era of technology has been reached that makes AF not only "treatable" but also potentially "curable." This article aims at walking through the historical corridors and maze that have led to the present-day understanding of this most common yet complex arrhythmia.

Feasibility of noncontact intracardiac ultrasound ablation and imaging catheter for treatment of atrial fibrillation

Atrial fibrillation (AF) affects 1% of the population and results in a cost of 2.8 billion dollars from hospitalizations alone. Treatments that electrically isolate portions of the atria are clinically effective in curing AF. However, such minimally invasive catheter treatments face difficulties in mechanically positioning the catheter tip and visualizing the anatomy of the region. We propose a noncontact, intracardiac transducer that can ablate tissue and provide rudimentary imaging to guide therapy. Our design consists of a high-power, 20 mm by 2 mm, 128-element, transducer array placed on the side of 7-French catheter. The transducer will be used in imaging mode to locate the atrial wall; then, by focusing at that location, a lesion can be formed. Imaging of previously formed lesions could potentially guide placement of subsequent lesions. Successive rotations of the catheter will potentially enable a contiguous circular lesion to be created around the pulmonary vein. The challenge of intracardiac-sized transducers is achieving high intensities (300-5000 W/cm2) needed to raise the temperature of the tissue above 43 degrees C. In this paper, we demonstrate the feasibility of an intracardiac-sized transducer for treatment of atrial fibrillation. In simulations and proof-of-concept experiments, we show a 37 degrees C temperature rise in the lesion location and demonstrate the possibility of lesion imaging.

Ablation of Atrial Fibrillation

Due in large part to the growing dissatisfaction with traditional pharmacologic approaches to atrial fibrillation (AF) management, and fueled by both the fruits of basic and clinical investigation into the nature of AF initiation and maintenance and the explosive development in catheter-based technologies, AF ablation has matured from a purely investigational technique to a viable--and often preferred--strategy for treating patients suffering from this arrhythmia. Future insights and developments will help us refine our treatment strategies, making AF ablation safer, faster, and more effective. As the prevalence of AF in the general population continues to expand, the goal of optimizing our approach to AF becomes ever more important--and more pressing.

Avoiding Microbubbles Formation During Radiofrequency Left Atrial Ablation Versus Continuous Microbubbles Formation and Standard Radiofrequency Ablation Protocols: Comparison of Energy Profiles and Chronic Lesion Characteristics

BACKGROUND

Radiofrequency (RF) energy parameters and chronic lesion characteristics associated with the microbubbles formation have not been yet fully elucidated.

OBJECTIVES

The objective of this study was to compare the energy profiles and chronic lesion characteristics associated with RF ablation of the pulmonary vein antrum using three different ablation protocols: (1) avoiding microbubbles; (2) continuous microbubble formation; (3) temperature-guided ablation.

METHODS

A 4-mm tip ablation catheter was used for creating RF ablation lesions in 15 adult mongrel dogs. All ablation lesions were created at the posterior aspect of the PV antrum in each animal. Avoiding microbubbles (group 1, n = 5 dogs, 23 lesions), continuous microbubble formation (group 2, n = 5 dogs, 22 lesions), and temperature-guided (group 3, n = 5 dogs, 19 lesions, target temperature 60 degrees C/power limit 50 W) ablation lesions were analyzed.

RESULTS

Group 1 showed significantly lower power (19 +/- 8.6 W), lower temperature (50 +/- 4.8 degrees C), higher efficiency-of-heating index (2.9 +/- 0.8 degrees C/W), and lower impedance (109 +/- 24.4 Omega) than groups 2 (38 +/- 8.4 W; 63 +/- 10 degrees C; 1.8 +/- 0.8 degrees C/W; 148 +/- 34.4 Omega) and 3 (44 +/- 12 W; 57 +/- 2.4 degrees C; 1.4 +/- 0.5 degrees C/W; 139 +/- 23.1 Omega) (P < 0.001 vs groups 2 and 3). During ablation, no significant events were detected in group 1, but 11 cases of audible pop, 11 cases of catheter tip charring, and 1 case of fatal myocardial perforation were observed in groups 2 and 3. Transmural lesions were more frequently created in group 1.

CONCLUSION

RF energy delivery applying "avoiding microbubbles" protocol seems to be associated with higher degree of safety and efficacy when compared to temperature-guided and continuous microbubble-formation ablation protocols.

Imaging techniques in cardiac electrophysiology

Modern cardiac electrophysiology procedures include catheter-based arrhythmia ablation and transvenous device implantation, which are highly dependent on accurate, real-time cardiac imaging. With the realization that anatomic structures are critical to successful electrophysiologic procedures, accurately defining a patient's cardiac anatomy has become more important. Fluoroscopy allows for 2D imaging of cardiac structures in real-time, and is used to guide catheter and lead placement, but does not allow for visualization of soft tissues. Intracardiac echocardiography allows for both direct visualization of anatomic structures within the heart and real-time imaging during catheter placement. Despite advances in intracardiac echocardiography catheters that allow for larger windows, the ability to accurately delineate anatomic structures depends on the patient's anatomy and operator experience. Neither of these techniques allows for electrical mapping of the heart; however, both anatomic and electrical intracardiac mapping can be achieved with advanced mapping systems. These systems allow for real-time catheter localization, help elucidate cardiac anatomy, evaluate electrical activation during arrhythmias and guide catheter placement for deliverance of radiofrequency current. More recently, 3D cardiac computed tomography has been used to accurately define intracardiac anatomy; however, catheter tracking and electrical mapping cannot be performed by computed tomography. Mapping systems are now being merged with computed tomography images to produce an accurate anatomic and electrical map of the heart to guide catheter ablations. The objective of this paper is to describe the current imaging and mapping techniques used in electrophysiologic procedures.

Intrapericardial echocardiography: a novel catheter-based approach to cardiac imaging

BACKGROUND

Transvascular catheter-based intracardiac echocardiography has been successfully used to help guide catheter ablation and electrophysiologic procedures. It has recently been demonstrated that catheters can be safely placed into the pericardial space to allow for epicardial cardiac mapping and ablation. We evaluated the feasibility of catheter-based intrapericardial echocardiography (IPE) during such procedures to identify cardiac structures and visualize intracardiac catheters.

METHODS

IPE was performed in 7 goats by placing a phased-array ultrasound transducer contained within a 10F steerable catheter into the pericardial space using the same transthoracic subxyphoid approach as used to map and ablate epicardial ventricular tachycardia. Images were obtained of cardiac structures and of intracardiac ablation catheters. After the procedure, the hearts were harvested to assess for possible IPE-related lesions.

RESULTS

The IPE catheter could be easily placed inside the pericardial space in all animals. In 7 of 7 cases, longitudinal and short-axis views of right- and left-sided chambers and valves were obtained, similar in orientation to transesophageal echocardiography. Visualization of atrial appendages (6/7), pulmonary veins (6/7), coronary arteries (6/7), and coronary sinus (3/6) was also feasible. Assessment of intracardiac transvalvar and venous blood flow was achieved by spectral and color Doppler. The ablation catheter could be clearly visualized inside cardiac chambers. No arrhythmias were induced with IPE catheter manipulation. After harvesting the hearts, no lesions resulting from the procedure were observed.

CONCLUSION

In this experimental setting, IPE was able to provide detailed images of cardiac structures and establish the relative position of the ablation catheter.

Novel uses of intracardiac echocardiography with a phased-array imaging catheter

A newer phased-array ultrasound imaging catheter (AcuNav, Siemens, Moutainview, Calif) provides comprehensive anatomic and physiologic data during cardiac interventions. The role of this catheter in percutaneous closure procedures, transseptal ablative procedures, and valvular interventions has been reported. We describe an expanded role of intracardiac echocardiography using AcuNav imaging catheter (Siemens) in 2 clinical situations.

Catheter-based intracardiac echocardiography in the interventional cardiac laboratory

Recent advances in technology have engendered a renewed enthusiasm in the use of intracardiac echocardiography (ICE) to guide and assess cardiac interventions. AcuNav is a phased-array sector imaging probe equipped with color and spectral Doppler capabilities. Previous-generation imaging catheters yielded unfamiliar limited-depth radial images with no flow information. Current imaging technology such as the AcuNav has not only consolidated the role of ICE but opened newer applications in the interventional laboratory. ICE has clear advantages over transesophageal echocardiography as the imaging modality of choice in the cardiac catheterization and electrophysiological laboratories. We review the technical evolution of ICE and describe the expanded utility of the AcuNav imaging catheter during cardiac interventions.

Role of intracardiac ultrasound in interventional electrophysiology

PURPOSE OF REVIEW

Interventional procedures in the electrophysiology and catheterization laboratory are rapidly advancing. Critical to the advancement of these procedures is accurate identification of critical anatomic landmarks and catheter position. Fluoroscopy remains the mainstay for general identification of anatomic landmarks but is inadequate for the precise imaging needed for complex procedures. Precise imaging of anatomic landmarks and catheter position is now possible during the procedure with the use of intracardiac echocardiography (ICE). This paper reviews the rapid development and utilization of ICE in interventional electrophysiology.

RECENT FINDINGS

Several recent studies show ICE as a major contribution to providing a safer, more reliable, and more cost-effective means of accomplishing the tasks performed by existing techniques. In the electrophysiology laboratory, the dependence on this new technology has been due to the rapid development of catheter-based radiofrequency ablation of the pulmonary veins for treatment of atrial fibrillation. Since the initial use of ICE in facilitating ablation of atrial fibrillation, other uses for ICE are continuously being identified.

SUMMARY

A comprehensive look is provided at the history and development of this new technology along with the most recent applications of ICE in interventional electrophysiology.

Real time quantification of low temperature radiofrequency ablation lesion size using phased array intracardiac echocardiography in the canine model: comparison of two dimensional images with pathological lesion characteristics

OBJECTIVE

To evaluate the feasibility of quantifying low temperature radiofrequency catheter ablation (RFCA) lesions using a phased array intracardiac echocardiography (ICE) catheter--with better tissue penetration and in a deflectable device-in the canine model.

INTERVENTION

Low temperature radiofrequency (RF) energy (50-60 degrees C at up to 40 W) was delivered to the left ventricle in 11 beagles for 60 seconds, using an 8 French catheter with a deflectable tip and a 4 mm distal electrode.

MAIN OUTCOME MEASURES

Comparison of the width and depth of RFCA lesions measured by ICE with pathological findings.

RESULTS

33 RF energies were delivered in 11 dogs. 31 lesions (94%) were confirmed at necropsy. 27 of 31 ablation lesions (87%) were detected by ICE. The mean (SD) width and depth of the ICE detected lesions were 10.4 (2.6) mm and 5.7 (1.9) mm, respectively. Pathological findings showed that RFCA lesions consisted of inner and outer layers. Macroscopically, the mean (SD) width and depth of the inner layers were 7.6 (2.3) mm and 3.6 (1.2) mm and those for the whole layers were 10.0 (2.8) mm and 5.3 (1.5) mm, respectively. Microscopically, the inner and outer layers corresponded to necrotic and oedematous areas, respectively. The ICE detected lesion size had better correlation with the pathological measurements of the whole layers in width (r = 0.911) and in depth (r = 0.756).

CONCLUSION

The real time evaluation of RFCA lesion size using the phased array ICE is feasible, even with a low temperature RF application. However, ICE slightly overestimates RFCA lesion size compared with pathological necrotic lesion size.

Phased-array intracardiac echocardiography for defining cavotricuspid isthmus anatomy during radiofrequency ablation of typical atrial flutter

INTRODUCTION

Cavotricuspid isthmus (CTI) topography includes ridges, pouches, recesses, and trabeculations. These features may limit the success of radiofrequency ablation (RFA) of typical atrial flutter (AFL). The aim of this study was to assess the utility of phased-array intracardiac echocardiography (ICE) for imaging the CTI and monitoring RFA of AFL.

METHODS AND RESULTS

Fifteen patients (mean age 64 +/- 9 years) underwent ICE assessment (imaging frequency 7.5-10 MHz) before and after RFA of AFL. The ICE catheter was positioned at the inferior vena cava-right atrial junction and the following parameters were measured: (1) CTI length from the tricuspid valve to the eustachian ridge; (2) extent of CTI pouching; and (3) thickness pre/post RFA of the anterior, mid, and posterior CTI. CTI length was 35 +/- 6 mm at end-ventricular systole but shorter (30 +/- 6 mm) and more pouched at end-ventricular diastole (P = 0.02). A pouch or recess was seen in 11 of 15 patients (mean depth 6 +/- 2 mm). The septal CTI was more pouched than the lateral CTI, but the latter had more prominent trabeculations. Trabeculations were seen in 10 of 15 patients, and at these locations the CTI was 4.6 +/- 1 mm thick. Anterior, mid, and posterior CTI thickness pre-RFA was 4.1 +/- 0.8, 3.3 +/- 0.5, and 2.7 +/- 0.9 mm, respectively (P < 0.001 by analysis of variance). ICE guided RFA away from unfavorable CTI features (recesses/thick trabeculations). RFA applications created discrete CTI lesions that coalesced, forming diffuse CTI swelling. Post-RFA thickness was as follows: anterior 4.8 +/- 0.8 mm (P = NS vs pre); mid 3.8 +/- 0.8 mm (P = 0.05 vs pre); and posterior 3.8 +/- 0.8 mm (P = 0.02 vs pre).

CONCLUSION

Phased-array ICE permits novel real-time CTI imaging with excellent endocardial resolution and may facilitate RFA of AFL.

Cardioscopic guidance of linear lesion creation for radiofrequency ablation

BACKGROUND

The broad use of catheter ablation of atrial fibrillation is limited by the difficulty inherent in creating transmural linear lesions under fluoroscopy. Therefore, we evaluated cardioscopy as a more accurate method of guiding the catheter for the placement of linear lesions.

METHODS

Nineteen swine underwent endocardial ablation to create linear conduction block lesions in the right atrium under cardioscopy (group I, n = 13) or fluoroscopy (group II, n = 6). In both groups, the linear lesion was created between the superior and inferior vena cava, perpendicular to hexapolar electrodes placed on the epicardial surface. Each swine received two pairs of epicardial hexapolar electrodes: one pair to measure the conduction delay time across the ablated line and another pair for pacing. The time spent to complete the ablation, number of trials and effective ablations, ratio of effective ablations to trials, length of the lesion, conduction delay under pacing, and postmortem pathology were compared between the two groups.

RESULTS

Statistically significant differences were found for the time required for ablation, ratio of effective ablation to total number of trials, and conduction delay. Histologic analysis revealed more homogenous, continuous lesions in group I.

CONCLUSIONS

Cardioscopy facilitated the placement of a conduction block line more efficiently than ablation performed under fluoroscopy. Landmarks of tissue relevant to ablation are readily visualized by cardioscopy. Moreover, cardioscopy can be useful for the development of a guiding catheter for the ablation of atrial fibrillation.

IVUS guidance of thoracic and complex abdominal aortic aneurysm stent-graft repairs using an intracardiac echocardiography probe: preliminary report

PURPOSE

To report our learning experience using an intracardiac echocardiography (ICE) probe to guide endovascular aortic procedures.

METHODS

Between November 1999 and July 2001, 17 patients (12 men; mean age 73.1+/-2.3 years) underwent endovascular repair of 9 thoracic, 6 complex abdominal, and 2 thoracoabdominal aortic aneurysms. The most suitable dimensions and configuration of the stent-graft were based on preoperative computed tomographic (CTA) or magnetic resonance (MRA) angiography. Intraoperative intravascular ultrasound (IVUS) imaging was obtained using a 9-F, 9-MHz ICE probe, 110 cm in length, inserted through a 10-F, 55 degrees precurved long polyethylene sheath.

RESULTS

The endografts were deployed as planned by CTA or MRA. Before stent-graft deployment, interrogation with the ICE probe visualized the aortic arch and descending thoracoabdominal aorta without position-related artefacts and identified the sites of stent-graft fixation. After stent-graft deployment, visualization with the ICE probe detected the need for additional procedures in 8 patients, including 2 incompletely expanded thoracic grafts, which were treated with adjunctive balloon angioplasty. In 1 patient, ICE probe interrogation determined that the lesion was inappropriate for endovascular exclusion.

CONCLUSIONS

ICE probe interrogation provides accurate information on the anatomy of thoracic and abdominal aortic aneurysms and allows rapid identification of attachment sites and stent-graft characteristics. It might be considered as a valid imaging modality for monitoring all phases of endovascular procedures.

Ablation of atrial fibrillation

Associated with significant morbidity and mortality, atrial fibrillation is one of the most common cardiac rhythm disorders. Cure of this arrhythmia has been elusive over the years, despite development of different antiarrhythmic drugs and advances in the understanding of its pathophysiology. Initial experience with catheter ablation procedures based on the creation of linear lesions in both atria has been disappointing, but has led to the key observation that focal triggers localized in the pulmonary veins are responsible for initiation of atrial fibrillation, and thus are suitable targets for catheter ablation. With advances in technology and larger experience, it has become clear that electrical isolation of all four pulmonary veins from the left atrium provides the higher cure rates. However, the procedure is still operator dependent and is associated with a small but significant risk of pulmonary vein stenosis. Further simplification of the isolation techniques and refinement in the catheter design will allow more widespread use of this procedure and higher success rate.

Intracardiac echocardiography-guided, anatomically based radiofrequency ablation of focal atrial fibrillation originating from pulmonary veins

OBJECTIVES

In patients with a pulmonary vein (PV) source for atrial fibrillation (AF), we sought the use of intracardiac echocardiography (ICE) to evaluate PV anatomy, guide radiofrequency (RF) ablation and monitor for acute stenosis during ablation.

BACKGROUND

A focal source for AF may be found in the proximal component of the PVs and can be effectively treated by ablative techniques. However, the procedure may be challenging due to the complex anatomy of the left atrium and PVs, uncertain catheter positioning within the PVs and difficulties in mapping atrial extrasystoles, which may be rare or repeatedly induce AF and require cardioversion.

METHODS

Sixty-four patients were referred for RF ablation of a focal source of AF, and 56 were identified as having AF triggers in > or =1 PV. Using ICE guidance, RF lesions were applied around the circumference of the vein near the os until there was electrical isolation.

RESULTS

Lesions were placed in 82 veins (36 right superior PV, 33 left superior PV, 9 left inferior PV, 4 right inferior PV); 24 +/- 12 lesions per vein were necessary to create electrical isolation with a fluoroscopic time of 11 +/- 4 min and a mean of 22% reduction in luminal area. After a follow-up of 13 +/- 7 months, 66% of patients remained free of AF, and another 13% responded better to medications.

CONCLUSIONS

We describe an anatomic approach to PV electrical isolation in which ICE is used to define the anatomy, guide RF ablation and monitor for acute PV changes.

Anatomic and hemodynamic imaging using a new vector phased-array intracardiac catheter

BACKGROUND

We used a new vector, phased-array intracardiac catheter (AcuNav) with complete 2-dimensional imaging and Doppler capabilities to describe a systematic approach for a detailed anatomic and hemodynamic cardiac assessment.

METHODS

In 14 dogs, the intracardiac echocardiographic catheter was inserted through an 11F venous access and placed in the right side of the heart to perform a comprehensive ultrasound examination of the heart.

RESULTS

Imaging was successful in all dogs. All 4 cardiac chambers and valves were imaged clearly in multiple orientations. Additional structures seen included the vena cavae, coronary sinus, right and left appendages, interarterial septum, coronary arteries, and all 4 pulmonary veins. Intra-abdominal structures, such as the aorta, liver, and hepatic veins were also visualized. A complete Doppler examination of intracardiac and paracardiac flows was also possible.

CONCLUSION

AcuNav is a unique intracardiac imaging device, which allows comprehensive structural and functional cardiac assessment.

Catheter-based interventions guided solely by a new phased-array intracardiac imaging catheter: in vivo experimental studies

BACKGROUND

Intracardiac echocardiography (ICE) has had useful but limited use during interventional procedures because of technologic limitations. We used a novel phased-array ICE device (AcuNav) with 2-dimensional sector imaging and full Doppler capability to see whether it could guide cardiac interventions without fluoroscopy.

METHODS

Twelve dogs were studied, and we performed atrial septostomy, tricuspid, and pulmonary valve disruption using only ICE. Preinterventional and postinterventional anatomic and hemodynamic data were noted.

RESULTS

All attempts were successful in the placement of the ICE catheter (100%). We attempted septostomy on 11 dogs and were successful 8 times (73%). Tricuspid valve disruption and balloon dilatation were performed successfully on 5 dogs (100%). We attempted pulmonary valve disruption on 4 dogs and could always correctly place the guidewire (100%). We performed pulmonary valve balloon dilatation on one dog (25%). A comprehensive echocardiographic examination was always possible.

CONCLUSION

This new ICE device can guide interventions without fluoroscopy. However, further studies are needed to evaluate whether it can replace fluoroscopy.

Modeling bipolar phase-shifted multielectrode catheter ablation

Atrial fibrillation (AFIB) is a common clinical problem affecting approximately 0.5-1% of the United States population. Radio-frequency (RF) multielectrode catheter (MEC) ablation has successes in curing AFIB. We utilized finite-element method analysis to determine the myocardial temperature distribution after 30 s, 80 degrees C temperature-controlled unipolar ablation using three 7F 12.5-mm electrodes with 2-mm interelectrode spacing MEC. Numerical results demonstrated that cold spots occurred at the edges of the middle electrode and hot spots at the side electrodes. We introduced the bipolar phase-shifted technique for RF energy delivery of MEC ablation. We determined the optimal phase-shift (phi) between the two sinusoidal voltage sources of a simplified two-dimensional finite-element model. At the optimal phi, we can achieve a temperature distribution that minimizes the difference between temperatures at electrode edges. We also studied the effects of myocardial electric conductivity (sigma), thermal conductivity (k), and the electrode spacing on the optimal phi. When we varied sigma and kappa from 50% to 150%, optimal phi ranged from 29.5 degrees to 23.5 degrees, and in the vicinity of 26.5 degrees, respectively. The optimal phi for 3-mm spacing MEC was 30.5 degrees. We show the design of a simplified bipolar phase-shifted MEC ablation system.

Advances in cardiac electrophysiology and pacing

Significant advances have been made in the management of cardiac arrhythmias. New technology has enhanced the ability to understand and treat a variety of tachycardias. Excitement and caution surround ablative approaches for atrial fibrillation. The role of ICDs and class III antiarrhythmic drugs in the management of patients at risk for sudden cardiac death has been clarified. A new indication for cardiac pacing is evolving as a supplemental treatment for patients with refractory congestive heart failure. These and other advances provide numerous exciting options for management of cardiac patients.

Catheter ablation of atrial fibrillation: challenges and promise

Although atrial fibrillation is the most common sustained arrhythmia that requires medical attention, it remains a challenge to treat. Nevertheless, considerable progress has been made toward developing curative, catheter-based treatments for selected patients with atrial fibrillation. The most significant clinical observation during electrophysiologic testing in patients with atrial fibrillation has been a recognition of the importance of the pulmonary veins for the initiation of this arrhythmia. In addition to being the most common site of arrhythmogenic foci that trigger the onset of atrial fibrillation, the unique electrophysiologic characteristics of the pulmonary veins may serve to perpetuate established atrial fibrillation. Because of the very short-duration refractory periods that are measured within the pulmonary veins, these structures may serve as a site of high frequency activation due to reentrant activation with small wavelengths. Catheter ablation strategies that are designed to ablate the site of triggering foci with the pulmonary veins have been very successful in selected patients with paroxysmal atrial fibrillation, although the risk of recurrent arrhythmias remains relatively high. In addition, ablation strategies that are designed to electrically isolate the pulmonary veins from the bulk of the left atrium are likely to lead to improvements in the long-term outcome of ablation. For patients with permanent atrial fibrillation, considerable progress has been made in the restoration of sinus rhythm by linear ablation strategies in the left atrium. It is likely that a comprehensive nonpharmacologic treatment for atrial fibrillation will incorporate the lessons learned from each of these approaches and lead to a genuine cure of this vexing arrhythmia.