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.     

Intracardiac echocardiography using the AcuNav ultrasound catheter during percutaneous balloon mitral valvuloplasty

During the past 10 years, there has been a trend toward and an interest in the use of catheter-based interventions to perform procedures that were once only approached surgically. The problem with the catheter-based approach has been procedure-related complications. Improved imaging of cardiac structures while undertaking interventional procedures may help to prevent or allow for early identification of these complications. Transesophageal echocardiography has been used during catheter-based procedures as a guide, and has both advantages and disadvantages. Intracardiac echocardiography is a relatively new imaging technique that also provides an enhanced view of cardiac structures and may also allow for the safe and efficient performance of catheter-based procedures. We report the first case of successful percutaneous balloon mitral valvuloplasty done under ultrasound guidance using an intracardiac echocardiography catheter (10F, 5-10 MHz) (Acunav). The strengths and weaknesses of this approach are described and compared with transesophageal echocardiography and older intracardiac echocardiography devices.     

Intracardiac echocardiography (9 MHz) in humans: methods, imaging views and clinical utility

A new low-frequency (9 MHz, 9 Fr) catheter-based ultrasound (US) transducer has been designed that allows greater depth of cardiac imaging. To demonstrate the imaging capability and clinical utility, intracardiac echocardiography (ICE) using this lower frequency catheter was performed in 56 patients undergoing invasive electrophysiological procedures. Cardiac imaging and monitoring were performed with the catheter transducer placed in the superior vena cava (SVC), right atrium (RA) and/or right ventricle (RV). In all patients, ICE identified distinct endocardial structures with excellent resolution and detail, including the crista terminalis, RA appendage, caval and coronary sinus orifices, fossa ovalis, pulmonary vein orifices, ascending aorta and its root, pulmonary artery, RV and all cardiac valves. The left atrium and ventricle were imaged with the transducer at the limbus fossa ovalis of the interatrial septum and in the RV, respectively. ICE was important in identifying known or unanticipated aberrant anatomy in 11 patients (variant Eustachian valve, atrial septal aneurysm and defect, lipomatous hypertrophy, Ebstein's anomaly, ventricular septal defect, tetralogy of Fallot, transposition of the great arteries, disrupted chordae tendinae and pericardial effusion) or in detecting procedure-related abnormalities (narrowing of SVC-RA junction orifice or pulmonary venous lumen, atrial thrombus, interatrial communication). In patients with inappropriate sinus tachycardia, ICE was the primary ablation catheter-guidance technique for sinus node modification. With ICE monitoring, the evolution of lesion morphology with the three imaging features including swelling, dimpling and crater formation was observed. In all patients, ICE was contributory to the mapping and ablation process by guiding catheters to anatomically distinct sites and/or assessing stability of the electrode-endocardial contact. ICE was also used to successfully guide atrial septal puncture (n = 9) or RA basket catheter placement (n = 4). Thus, ICE with a new 9-MHz catheter-based transducer has better imaging capability with a greater depth. Normal and abnormal cardiac anatomy can be readily identified. ICE proved useful during electrophysiological mapping and ablation procedures for guiding interatrial septal puncture, assessing placement and contact of mapping and ablation catheters, monitoring ablation lesion morphological changes, and instantly diagnosing cardiac complications.     

Electroanatomic mapping of the right atrium with a right atrial basket catheter and three-dimensional intracardiac echocardiography

The ablation of arrhythmias progresses towards an approach based upon application of linear lesions between nonconducting anatomic/electrical areas. Hence the identification of detailed anatomy together with electrical behavior becomes increasingly important. This study aims to achieve true electroanatomic mapping by the use of three-dimensional intracardiac imaging of the right atrium combined with use of a right atrial basket to obtain detailed electrical information. We studied nine patients, seven requiring atrial flutter ablation. A 9 Fr, 9 MHZ intracardiac echo catheter was pulled back from SVC to IVC using respiratory and ECG gating. The images, recorded on a Clearview ultrasound machine, were reconstructed using commercially available software. The intracardiac basket was placed into the atrium using the markers and fluoroscopy to allow orientation. Isochronal maps were obtained from the basket in sinus rhythm, pacing from different sites within the atrium and in atrial flutter. Isochronal maps were constructed and superimposed on the ICE image. The maps with pacing were consistent with that which was expected, confirming the validity of this approach. We were able to visualize changes in activation sequence following the placement of bidirectional isthmus block. True electroanatomic mapping is possible by the use of three-dimensional ICE reconstruction of the right atrium with electrical activation obtained from an intracardiac basket. This has significance for anatomically based arrhythmia ablations such as the ablation of atrial flutter, atrial fibrillation, with transcatheter MAZE procedures and pulmonary vein isolation. Further developments in software will allow such maps to be produced simultaneously with greater rapidity.     

Recent advances in echocardiography

Important recent developments have occurred in echocardiography that are already being used clinically. Portable ultrasound devices that weigh less than five pounds are capable of performing a complete bedside echo exam. An intracardiac echocardiographic catheter has recently been introduced that can be placed intracardiac via a vein and navigated within right heart chambers to obtain detailed anatomical landmarks that guide catheter based interventional procedures such as intracardiac ablation and closure of atrial septal defects and patent foramen ovale. Tissue Doppler imaging is finding its role in detecting mechanical asynchrony in patients with congestive heart failure who might benefit from biventricular pacing. The availability of real-time 3D echocardiography has for the first time made assessment of complex cardiac anatomy possible. This review discusses each of these new developments and their potential impact on the practice of echocardiography and cardiology in general.     

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.     

Recent advances in echocardiography

Important recent developments have occurred in echocardiography that are already being used clinically. Portable ultrasound devices that weigh less than five pounds are capable of performing a complete bedside echo exam. An intracardiac echocardiographic catheter has recently been introduced that can be placed intracardiac via a vein and navigated within right heart chambers to obtain detailed anatomical landmarks that guide catheter based interventional procedures such as intracardiac ablation and closure of atrial septal defects and patent foramen ovale. Tissue Doppler imaging is finding its role in detecting mechanical asynchrony in patients with congestive heart failure who might benefit from biventricular pacing. The availability of real-time 3D echocardiography has for the first time made assessment of complex cardiac anatomy possible. This review discusses each of these new developments and their potential impact on the practice of echocardiography and cardiology in general.     

Real-time three-dimensional transesophageal echocardiography for guiding interventional electrophysiology: feasibility study

At present, there are limited methods of acquiring three-dimensional visualization of cardiac structure and function in real-time during interventional electrophysiology procedures. Images acquired for integration of computerized tomography and magnetic resonance imaging with electroanatomic mapping systems are static and are obtained earlier in time. The purpose of this study was to test the feasibility of real-time three-dimensional transesophageal echocardiography for the guidance of interventional electrophysiological studies. A matrix array transducer with 504 channels operating at 5 MHz in a 1 cm diameter steerable esophageal probe was used in conjunction with a scanner capable of real-time 3D scanning of pyramidal volumes from 65 degrees to 120 degrees at rates up to 30 volumes per second. This device has a spatial resolution of approximately 3 mm at 5 cm depth. The authors acquired real-time three-dimensional images of anatomic landmarks of value for electrophysiological procedures in five closed chest canines. Real-time, three-dimensional ultrasound imaging was also used for visualization and guidance of interventional catheter devices within the canine heart. Real-time three-dimensional images of the atria, pulmonary veins, and coronary sinus were acquired. Real-time 3-D color flow Doppler was employed to confirm patency. Multiple image planes of image volumes and rendered views were used to track catheter position and orientation. Images of left veno-atrial junctions have been confirmed by dissection. This study has demonstrated the feasiblity of using real-time three-dimensional transesophageal echocardiography for guiding interventional electrophysiology. The technology has the potential to fill a niche as an adjunct modality for cost-effective real-time interventional guidance and assessment, providing catheter and pacing lead visualization simultaneously with functional volumetric cardiac imaging.     

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.     

Intracardiac echocardiography: current developments

Intracardiac echocardiography refers to the method of imaging cardiac structures from intracardiac locations with the use of ultrasound catheters. Advances in catheter-based interventional cardiologic procedures to treat cardiovascular lesions and the problems encountered during those procedures due to inadequate guidance provided by fluoroscopy have given the impetus to develop other guidance modalities. Experimental explorations with intracardiac ultrasound probes have indicated that detailed visualization of cardiac structures in real-time is possible by intracardiac ultrasound. Recent advances in catheter-based ultrasound technology make it feasible to safely pass small-sized catheters in humans into various intracardiac locations and acquire images of valvular structures and various chambers. Experience with 20 MHz ultrasound catheters indicates that high resolution images of normal and abnormal structures can be obtained if the catheter is manipulated close to the region of interest. The problem of the limited depth of field associated with 20 MHz catheters has led to the fabrication of catheters with lower frequency ultrasound elements. Experimental and clinical experience with 12.5 MHz ultrasound catheters points to the capability and potential of intracardiac echocardiography to not only display normal structures but also aid in the identification of valvular abnormalities, chamber dysfunction and pericardial effusions. In addition, aortic disorders such as acute dissection, coarctation and atherosclerotic disease could be delineated. Similarly, abnormalities involving the pulmonary arteries such as pulmonary embolism, organized thrombi, peripheral pulmonary arterial stenoses, and pulmonary hypertension-induced vascular changes could be recognized. Many modifications in the catheter design are being explored. With further work in the area of catheter technology and ultrasound image processing, intracardiac echocardiography is likely to become a clinical tool.     

CT-guided cardiac electrophysiology

Recent advances in cardiac electrophysiology with revolutionary development of transcutaneous procedures have required electrophysiologists to have precise knowledge of the spatial anatomy of the heart, and thus, led to the increasing use of cardiac imaging procedures such as multidetector CT (MDCT). The introduction of 64-detector (and higher) scanners has made it possible to visualize the anatomic landmarks that are essential for both diagnostic and therapeutic cardiac procedures and, in selected cases, prevention of procedure-related complications. Future work with these emerging imaging techniques will further characterize how cardiac CT can aid cardiologists to dissect the microscopic anatomy of the heart, optimize success rates, and potentially minimize inherent risks of the cardiac interventions. In this review, we focus on the latest developments in the application of MDCT for electrophysiologic interventions.     

Dynamic three-dimensional visualization of the left ventricle by intracardiac echocardiography

Cardiac function and hemodynamics are routinely evaluated during catheterization in patients with heart disease. Although intracardiac echocardiography (ICE) has been employed in guiding electrophysiology procedures, it has not been effectively used in assessing hemodynamics. We tested the utility of ICE in measuring left ventricular (LV) volume throughout the cardiac cycle. In four normal dogs (weight = 26 to 37 kg), a 10-F sheath was inserted through the femoral artery and placed inside the LV along its major axis. An ICE catheter (9 F, 9 MHz) was then inserted through the sheath into the LV. The ICE catheter was pulled back inside the sheath in 1-mm intervals starting from the apex, and 2-D tomographic images were continuously acquired while gating to respiration. Subsequently, the ICE catheter was replaced by a conductance catheter to measure single-beat volume signals. Stroke volume was determined by thermodilution for validation. All measurements were made in each dog while pacing the atrium at two different cycle lengths (range = 300 to 500 ms). The endocardial boundary was digitized from the ICE images throughout the cardiac cycle and LV volume was computed by integrating multiple segments along the major axis (range = 55 to 70 mm). We found that ICE accurately reconstructed LV 3-D anatomy. Stroke volume by ICE was in excellent agreement with thermodilution (error = 3.8 +/- 3.0%, r = 0.99, n = 8) and was highly reproducible. Morphology of LV volume signals correlated well with corresponding instantaneous volume signals derived by conductance (r = 0.93, n = 8). In conclusion, ICE accurately reconstructs LV anatomy and volume throughout the cardiac cycle in the normal heart. This approach could facilitate interventional diagnostic and therapeutic procedures.     

Real-time transesophageal three-dimensional echocardiography for guidance of percutaneous cardiac interventions: first experience

Recently, a new generation of transesophageal echocardiography (TEE) probes with a novel matrix array technique was introduced, allowing three-dimensional (3D) presentation of cardiac structures in real-time. This article aims to describe our first experiences with this new technique in the guidance of percutaneous cardiac interventions in the catheter laboratory. We used a matrix array 3D TEE probe connected to a 3D-capable echocardiographic system. The 3D TEE system provides exact imaging of the pathomorphology of cardiac structures as well as intracardiac catheters and devices in real-time. We applied this innovative technique to monitor percutaneous cardiac interventions in the catheter laboratory, such as atrial septal defect (ASD) or patent foramen ovale (PFO) closures, revalving procedures such as percutaneous transvenous mitral valve annuloplasty (PTMA), aortic valve replacements, and electrophysiological procedures. Our findings demonstrate that real-time 3D TEE provides a novel imaging technique to guide interventions in the catheter laboratory, providing fast and complete information about the underlying pathomorphology, improving spatial orientation, and additionally monitoring online the procedure without loss of image quality. These benefits may accelerate the learning curve and improve confidence of the interventional cardiologist in order to increase safety, accuracy, and efficacy of interventional cardiac procedures.     

Three-Dimensional Echocardiography in Adult Congenital Heart Disease

Advances in transducer technology have made three-dimensional echocardiography feasible for routine use in the echocardiographic assessment of cardiovascular disease. Real-time three-dimensional echocardiography (RT3DE) has potential to be especially useful in the evaluation of patients with congenital heart disease, by providing a detailed assessment of complex morphologic abnormalities and the spatial relationships of intracardiac structures. In patients with congenital heart disease, the ability to accurately assess cardiac chamber volumes and ejection fraction is important for determining the timing of intervention. In this article, we review the published literature on the use of 3DE in the assessment of morphology, chamber volume, and function in patients with congenital heart disease, as well as the use of RT3DE to guide interventional procedures.     

The role of echocardiography in diagnosing space-occupying lesions of the heart

In contrast to primary cardiac tumors, which are less frequent and mostly benign in nature, the majority of intracardiac tumors are metastatic lesions. Cardiac ultrasound has evolved enormously since its emergence in the 1950s and is presently the modality of choice for imaging space-occupying lesions of the heart; it provides high quality, real-time images that are extremely valuable in the evaluation of cardiac masses. Although transthoracic echocardiography is an excellent initial diagnostic technique to evaluate and diagnose cardiac masses, transesophageal echocardiography provides superior image resolution and better visualization of cardiac masses in patients with suboptimal transthoracic echocardiography studies. Computed tomography and magnetic resonance imaging are additional tools used for cardiac imaging and may provide useful information in addition to that obtained by echocardiography, especially when the images obtained by the latter are suboptimal.     

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.     

心内组织多普勒超声显像标测心脏传导系统心肌兴奋心肌电和机械兴奋多参数显像

目的 探讨高分辨力心内超声组织组织勒显像技术标测心脏传导系统心肌电兴奋诱导心肌收缩的可行性和应用范围。方法 用5条狗开胸模型,通过11F血管鞘从右颈内静脉或股静脉插入10F心内超声导管分别置留于上腔静脉、右心房和右心室,刺激电极随机置入心室壁内（心外膜下心肌和心内膜下心肌）,应用二维灰阶超声观察并测量窦房结、右心房壁、房室交界区,室间隔和左心室游离壁的解剖结构;采用心内超声组织多普勒显像技术获取窦性心律上述各点的二维、M型心肌速度和加速度图像;在心室起搏时记录心肌速度和加速度起始的分布,其心肌机械兴奋的空间部位和时相分别与刺激电极的部位与电刺激时相比较。结果 心内起声清晰显示窦房结、心房壁、房室交界是区和室室间隔及心室游离壁的细微解剖结构。心电图P波起始后,窦房结区域内速度和加速度明显增高,窦性尽律心房壁心肌收缩和舒张期为均匀一致速度和加速度分布,心电图P-R间期内,房室交界区心肌速度或加速度增高起始于其上部并向下分布传导至室间隔上部,心电图QRS波起始处,室间隔内心肌速度和加速度分布呈“Y”字形,人工电刺激诱导心肌速度和加速度增高的起始点位于电刺激局部,直径小于5mm;心肌机械收缩延迟小于7 s(帧频为140帧/s）;心室壁内心肌速度和加速度传播分布呈同心圆状。结论 心内超声组织多普勒显像技术能够实时同步精确标测心脏传导系统解剖和与电活动相关的心肌机械运动,此超声成像技术对心律扮演的诊断和治疗具重要潜在影响。有助于准确指导心脏介入治疗,观察心室壁内心肌速度和加速度时间顺序的分布和大小变化,有可能提示心室心肌纤维的结构和功能。     

Transesophageal Echocardiography to Improve Positioning of Radiofrequency Ablation Catheters in Left-Sided Wolff-Parkinson-White Syndrome

Two patients with the Wolff-Parkinson-White syndrome who underwent successful radiofrequency catheter ablation of their left-sided bypass tracts are described. Transesophageal echocardiography, a relatively new echocardiographic technique, was utilized in both patients and provided excellent visualization of intracardiac anatomy as well as the catheter tip. Transesophageal echocardiography was also synergistic with fluoroscopy and the intracardiac electrogram in providing more precise catheter placement. In addition, the use of transesophageal echocardiography may reduce fluoroscopic exposure and shorten the procedure time.     

State‐of‐the‐art multimodality approach to assist ablations in complex anatomies—From 3D printing to virtual reality

Imaging of the heart anatomy plays an important role, especially in catheter ablation for the treatment of arrhythmias in adults with congenital heart disease (ACHD). We present a comprehensive overview of the current state‐of‐the‐art modalities available to plan and guide catheter ablation in an ACHD patient. In addition to the clinical assessment of the computed tomography and the integration of 3D reconstructions into the electroanatomical mapping system, 3D printing and virtual reality assessment showed its value in preprocedural planning of the intervention.