Focal atrial tachycardia after pulmonary vein isolation: noninvasive mapping with electrocardiographic imaging (ECGI)

Electrocardiographic imaging in the atria

The inverse problem of electrocardiography or electrocardiographic imaging (ECGI) is a technique for reconstructing electrical information about cardiac surfaces from noninvasive or non-contact recordings. ECGI has been used to characterize atrial and ventricular arrhythmias. Although it is a technology with years of progress, its development to characterize atrial arrhythmias is challenging. Complications can arise when trying to describe the atrial mechanisms that lead to abnormal propagation patterns, premature or tachycardic beats, and reentrant arrhythmias. This review addresses the various ECGI methodologies, regularization methods, and post-processing techniques used in the atria, as well as the context in which they are used. The current advantages and limitations of ECGI in the fields of research and clinical diagnosis of atrial arrhythmias are outlined. In addition, areas where ECGI efforts should be concentrated to address the associated unsatisfied needs from the atrial perspective are discussed.

Electrocardiographic Imaging for Atrial Fibrillation: A Perspective From Computer Models and Animal Experiments to Clinical Value

Electrocardiographic imaging (ECGI) is a technique to reconstruct non-invasively the electrical activity on the heart surface from body-surface potential recordings and geometric information of the torso and the heart. ECGI has shown scientific and clinical value when used to characterize and treat both atrial and ventricular arrhythmias. Regarding atrial fibrillation (AF), the characterization of the electrical propagation and the underlying substrate favoring AF is inherently more challenging than for ventricular arrhythmias, due to the progressive and heterogeneous nature of the disease and its manifestation, the small volume and wall thickness of the atria, and the relatively large role of microstructural abnormalities in AF. At the same time, ECGI has the advantage over other mapping technologies of allowing a global characterization of atrial electrical activity at every atrial beat and non-invasively. However, since ECGI is time-consuming and costly and the use of electrical mapping to guide AF ablation is still not fully established, the clinical value of ECGI for AF is still under assessment. Nonetheless, AF is known to be the manifestation of a complex interaction between electrical and structural abnormalities and therefore, true electro-anatomical-structural imaging may elucidate important key factors of AF development, progression, and treatment. Therefore, it is paramount to identify which clinical questions could be successfully addressed by ECGI when it comes to AF characterization and treatment, and which questions may be beyond its technical limitations. In this manuscript we review the questions that researchers have tried to address on the use of ECGI for AF characterization and treatment guidance (for example, localization of AF triggers and sustaining mechanisms), and we discuss the technological requirements and validation. We address experimental and clinical results, limitations, and future challenges for fruitful application of ECGI for AF understanding and management. We pay attention to existing techniques and clinical application, to computer models and (animal or human) experiments, to challenges of methodological and clinical validation. The overall objective of the study is to provide a consensus on valuable directions that ECGI research may take to provide future improvements in AF characterization and treatment guidance.

Noninvasive Mapping and Electrocardiographic Imaging in Atrial and Ventricular Arrhythmias (CardioInsight)

Electrocardiographic imaging is a mapping technique aiming to noninvasively characterize cardiac electrical activity using signals collected from the torso to reconstruct epicardial potentials. Its efficacy has been demonstrated clinically, from mapping premature ventricular complexes and accessory pathways to of complex arrhythmias. Electrocardiographic imaging uses a standardized workflow. Signals should be checked manually to avoid automatic processing errors. Reentry is confirmed in the presence of local activation covering the arrhythmia cycle length. Focal breakthroughs demonstrate a QS pattern associated with centrifugal activation. Electrocardiographic imaging offers a unique opportunity to better understand the mechanism of cardiac arrhythmias and guide ablation.

Individualized ablation strategy guided by live simultaneous global mapping to treat persistent atrial fibrillation

Atrial fibrillation (AF) is the most common clinical arrhythmia encountered. Catheter ablation has become the first-line therapy for symptomatic drug-refractory paroxysmal and persistent AF. Although pulmonary vein electrical isolation is still the cornerstone of the ablation strategy, the clinical outcome particularly in treating persistent AF is suboptimal. Significant efforts have been applied with live global chamber mapping of AF aimed to identify patient-specific drivers and/or maintainers located outside of the pulmonary veins to further improve the outcome of catheter ablation. Within this review, we present an overview of contemporary global chamber AF mapping technologies and characteristics, with a particular focus on global, noncontact, dipole density mapping illustrated with a clinical case of persistent AF ablation using this novel methodology.

Noninvasive Imaging of Human Atrial Activation during Atrial Flutter and Normal Rhythm from Body Surface Potential Maps

Background

Knowledge of atrial electrophysiological properties is crucial for clinical intervention of atrial arrhythmias and the investigation of the underlying mechanism. This study aims to evaluate the feasibility of a novel noninvasive cardiac electrical imaging technique in imaging bi-atrial activation sequences from body surface potential maps (BSPMs).

Methods

The study includes 7 subjects, with 3 atrial flutter patients, and 4 healthy subjects with normal atrial activations. The subject-specific heart-torso geometries were obtained from MRI/CT images. The equivalent current densities were reconstructed from 208-channel BSPMs by solving the inverse problem using individual heart-torso geometry models. The activation times were estimated from the time instant corresponding to the highest peak in the time course of the equivalent current densities. To evaluate the performance, a total of 32 cycles of atrial flutter were analyzed. The imaged activation maps obtained from single beats were compared with the average maps and the activation maps measured from CARTO, by using correlation coefficient (CC) and relative error (RE).

Results

The cardiac electrical imaging technique is capable of imaging both focal and reentrant activations. The imaged activation maps for normal atrial activations are consistent with findings from isolated human hearts. Activation maps for isthmus-dependent counterclockwise reentry were reconstructed on three patients with typical atrial flutter. The method was capable of imaging macro counterclockwise reentrant loop in the right atrium and showed inter-atria electrical conduction through coronary sinus. The imaged activation sequences obtained from single beats showed good correlation with both the average activation maps (CC = 0.91±0.03, RE = 0.29±0.05) and the clinical endocardial findings using CARTO (CC = 0.70±0.04, RE = 0.42±0.05).

Conclusions

The noninvasive cardiac electrical imaging technique is able to reconstruct complex atrial reentrant activations and focal activation patterns in good consistency with clinical electrophysiological mapping. It offers the potential to assist in radio-frequency ablation of atrial arrhythmia and help defining the underlying arrhythmic mechanism.

Body Surface Electrocardiographic Mapping for Non-invasive Identification of Arrhythmic Sources

The authors describe a novel three-dimensional, 252-lead electrocardiography (ECG) and computed tomography (CT)-based non-invasive cardiac imaging and mapping modality. This technique images potentials, electrograms and activation sequences (isochrones) on the epicardial surface of the heart. This tool has been investigated in the normal cardiac electrophysiology and various tachyarrhythmic, conduction and anomalous depo-repolarisation disorders. The clinical application of this system includes a wide range of electrical disorders like atrial arrhythmias (premature atrial beat, atrial tachycardia, atrial fibrillation), ventricular arrhythmias (premature ventricular beat, ventricular tachycardia) and ventricular pre-excitation (Wolff-Parkinson-White syndrome). In addition, the system has been used in exploring abnormalities of the His-Purkinje conduction like the bundle branch block and intraventricular conduction disturbance and thereby useful in electrically treating the associated heart failure (cardiac resynchronisation). It has a potential role in furthering our understanding of abnormalities of ventricular action potential (depolarisation [Brugada syndrome and repolarisation], long QT and early repolarisation syndromes) and in evaluating the impact of drugs on His-Purkinje conduction and cardiac action potential.

Noninvasive reconstruction of cardiac electrical activity: update on current methods, applications and challenges

Electrical activity at the level of the heart muscle can be noninvasively reconstructed from body-surface electrocardiograms (ECGs) and patient-specific torso-heart geometry. This modality, coined electrocardiographic imaging, could fill the gap between the noninvasive (low-resolution) 12-lead ECG and invasive (high-resolution) electrophysiology studies. Much progress has been made to establish electrocardiographic imaging, and clinical studies appear with increasing frequency. However, many assumptions and model choices are involved in its execution, and only limited validation has been performed. In this article, we will discuss the technical details, clinical applications and current limitations of commonly used methods in electrocardiographic imaging. It is important for clinicians to realise the influence of certain assumptions and model choices for correct and careful interpretation of the results. This, in combination with more extensive validation, will allow for exploitation of the full potential of noninvasive electrocardiographic imaging as a powerful clinical tool to expedite diagnosis, guide therapy and improve risk stratification.

Electrocardiographic imaging of heart rhythm disorders: from bench to bedside

Noninvasive electrocardiographic imaging (ECGI; also called ECG mapping) can reconstruct potentials, electrograms, activation sequences, and repolarization patterns on the epicardial surface of the heart with high resolution. ECGI can possibly be used to quantify synchrony, identify potential responders/nonresponders to cardiac resynchronization therapy, and guide electrode placement for effective resynchronization therapy. This article provides a brief description of the ECGI procedure and selected previously published examples of its application in important clinical conditions, including heart failure, cardiac resynchronization therapy, atrial arrhythmias, and ventricular tachycardia.

Comparative analysis of diagnostic 12-lead electrocardiography and 3-dimensional noninvasive mapping

The clinical utility of noninvasive electrocardiographic imaging has been demonstrated in a variety of conditions. It has recently been shown to have superior predictive accuracy and higher clinical value than validated 12-lead electrogram algorithms in the localization of arrhythmias arising from the ventricular outflow tract, and displays similar potential in other conditions.

Noninvasive mapping to guide atrial fibrillation ablation

Atrial fibrillation (AF) is a dynamic rhythm. Noninvasive mapping overcomes many previous barriers to mapping such a dynamic rhythm, by providing a beat-to-beat, biatrial, panoramic view of the AF process. Catheter ablation of AF drivers guided by noninvasive mapping has yielded promising clinical results and has advanced understanding of the underlying pathophysiologic processes of this common heart rhythm disorder.

Non Invasive ECG Mapping To Guide Catheter Ablation

Since more than 100 years, 12-lead electrocardiography (ECG) is the standard-of-care tool, which involves measuring electrical potentials from limited sites on the body surface to diagnose cardiac disorder, its possible mechanism and the likely site of origin. Several decades of research has led to the development of a 252-lead-ECG and CT-scan based, three dimensional, electro-imaging modality to non-invasively map abnormal cardiac rhythms including fibrillation. These maps provide guidance towards ablative therapy and thereby help advance the management of complex heart rhythm disorders. Here, we describe the clinical experience obtained using non-invasive technique in mapping the electrical disorder and guide the catheter ablation of atrial arrhythmias (premature atrial beat, atrial tachycardia, atrial fibrillation), ventricular arrhythmias (premature ventricular beats) and ventricular pre-excitation (Wolff-Parkinson-White syndrome).

Validation of novel 3-dimensional electrocardiographic mapping of atrial tachycardias by invasive mapping and ablation: a multicenter study

OBJECTIVES

This study prospectively evaluated the role of a novel 3-dimensional, noninvasive, beat-by-beat mapping system, Electrocardiographic Mapping (ECM), in facilitating the diagnosis of atrial tachycardias (AT).

BACKGROUND

Conventional 12-lead electrocardiogram, a widely used noninvasive tool in clinical arrhythmia practice, has diagnostic limitations.

METHODS

Various AT (de novo and post-atrial fibrillation ablation) were mapped using ECM followed by standard-of-care electrophysiological mapping and ablation in 52 patients. The ECM consisted of recording body surface electrograms from a 252-electrode-vest placed on the torso combined with computed tomography-scan-based biatrial anatomy (CardioInsight Inc., Cleveland, Ohio). We evaluated the feasibility of this system in defining the mechanism of AT-macro-re-entrant (perimitral, cavotricuspid isthmus-dependent, and roof-dependent circuits) versus centrifugal (focal-source) activation-and the location of arrhythmia in centrifugal AT. The accuracy of the noninvasive diagnosis and detection of ablation targets was evaluated vis-à-vis subsequent invasive mapping and successful ablation.

RESULTS

Comparison between ECM and electrophysiological diagnosis could be accomplished in 48 patients (48 AT) but was not possible in 4 patients where the AT mechanism changed to another AT (n = 1), atrial fibrillation (n = 1), or sinus rhythm (n = 2) during the electrophysiological procedure. ECM correctly diagnosed AT mechanisms in 44 of 48 (92%) AT: macro-re-entry in 23 of 27; and focal-onset with centrifugal activation in 21 of 21. The region of interest for focal AT perfectly matched in 21 of 21 (100%) AT. The 2:1 ventricular conduction and low-amplitude P waves challenged the diagnosis of 4 of 27 macro-re-entrant (perimitral) AT that can be overcome by injecting atrioventricular node blockers and signal averaging, respectively.

CONCLUSIONS

This prospective multicenter series shows a high success rate of ECM in accurately diagnosing the mechanism of AT and the location of focal arrhythmia. Intraprocedural use of the system and its application to atrial fibrillation mapping is under way.

Noninvasive electroanatomic mapping of human ventricular arrhythmias with electrocardiographic imaging

The rapid heartbeat of ventricular tachycardia (VT) can lead to sudden cardiac death and is a major health issue worldwide. Efforts to identify patients at risk, determine mechanisms of VT, and effectively prevent and treat VT through a mechanism-based approach would all be facilitated by continuous, noninvasive imaging of the arrhythmia over the entire heart. Here, we present noninvasive real-time images of human ventricular arrhythmias using electrocardiographic imaging (ECGI). Our results reveal diverse activation patterns, mechanisms, and sites of initiation of human VT. The spatial resolution of ECGI is superior to that of the routinely used 12-lead electrocardiogram, which provides only global information, and ECGI has distinct advantages over the currently used method of mapping with invasive catheter-applied electrodes. The spatial resolution of this method and its ability to image electrical activation sequences over the entire ventricular surfaces in a single heartbeat allowed us to determine VT initiation sites and continuation pathways, as well as VT relationships to ventricular substrates, including anatomical scars and abnormal electrophysiological substrate. Thus, ECGI can map the VT activation sequence and identify the location and depth of VT origin in individual patients, allowing personalized treatment of patients with ventricular arrhythmias.

Electroanatomical mapping and radiofrequency ablation of tachycardia originating in pulmonary vein in an adult patient

A 29-year-old male was admitted to our outpatient clinic because of palpitation and documented narrow QRS arrhythmia. Based on the ECG, supraventricular tachycardia was diagnosed, electrophysiological examination was indicated and ablation therapy was recommended. During positioning of the catheter the patient developed arrhythmia. On the coronary sinus catheter the activation spread from distal to proximal electrodes, suggesting left atrial origin. During atrial entrainment pacing long return cycle was observed and distal coronary sinus pacing resulted in a 15 ms longer cycle length than the arrhythmia. Therefore, the left atrial origin of the arrhythmia was confirmed and double transseptal puncture was performed. Lasso and irrigated tip catheter were introduced into the left atrium and electroanatomical mapping was performed with CARTO3 system. After electroanatomical mapping the origin of tachycardia was located proximally in the left superior pulmonary vein. Ablation was started at the earliest activation point, where acceleration was observed and the arrhythmia stopped after the first ablation. Pulmonary vein isolation was completed, and bidirectional block could be confirmed. After 30 minutes the arrhythmia was not inducible. During follow-up, Holter-examination was negative and the patient remained asymptomatic. The pulmonary vein tachycardia is a supraventricular arrhythmia that can occur at any age, but the diagnosis based on the ECG is not always simple. Detailed electroanatomical mapping is very important in the diagnosis of this type of arrhythmia, although it can be verified with conventional electrophysiological methods as well. Focal ablation may be a therapeutic option; however, total isolation of pulmonary veins can be more effective. Orv. Hetil., 2011, 152, 1374–1378.

Pathophysiological mechanisms of atrial fibrillation: a translational appraisal

Atrial fibrillation (AF) is an arrhythmia that can occur as the result of numerous different pathophysiological processes in the atria. Some aspects of the morphological and electrophysiological alterations promoting AF have been studied extensively in animal models. Atrial tachycardia or AF itself shortens atrial refractoriness and causes loss of atrial contractility. Aging, neurohumoral activation, and chronic atrial stretch due to structural heart disease activate a variety of signaling pathways leading to histological changes in the atria including myocyte hypertrophy, fibroblast proliferation, and complex alterations of the extracellular matrix including tissue fibrosis. These changes in electrical, contractile, and structural properties of the atria have been called "atrial remodeling." The resulting electrophysiological substrate is characterized by shortening of atrial refractoriness and reentrant wavelength or by local conduction heterogeneities caused by disruption of electrical interconnections between muscle bundles. Under these conditions, ectopic activity originating from the pulmonary veins or other sites is more likely to occur and to trigger longer episodes of AF. Many of these alterations also occur in patients with or at risk for AF, although the direct demonstration of these mechanisms is sometimes challenging. The diversity of etiological factors and electrophysiological mechanisms promoting AF in humans hampers the development of more effective therapy of AF. This review aims to give a translational overview on the biological basis of atrial remodeling and the proarrhythmic mechanisms involved in the fibrillation process. We pay attention to translation of pathophysiological insights gained from in vitro experiments and animal models to patients. Also, suggestions for future research objectives and therapeutical implications are discussed.

Noninvasive characterization of epicardial activation in humans with diverse atrial fibrillation patterns

BACKGROUND

Various mechanisms of atrial fibrillation (AF) have been demonstrated experimentally. Invasive methods to study these mechanisms in humans have limitations, precluding continuous mapping of both atria with sufficient resolution. In this article, we present continuous biatrial epicardial activation sequences of AF in humans using noninvasive electrocardiographic imaging (ECGI).

METHODS AND RESULTS

In the testing phase, ECGI accuracy was evaluated by comparing ECGI with co-registered CARTO images during atrial pacing in 6 patients. Additionally, correlative observations from catheter mapping and ablation were compared with ECGI in 3 patients. In the study phase, ECGI maps during AF in 26 patients were analyzed for mechanisms and complexity. ECGI noninvasively imaged the low-amplitude signals of AF in a wide range of patients (97 procedural success). Spatial accuracy for determining initiation sites from pacing was 6 mm. Locations critical to maintenance of AF identified during catheter ablation were identified by ECGI; ablation near these sites restored sinus rhythm. In the study phase, the most common patterns of AF were multiple wavelets (92), with pulmonary vein (69) and non-pulmonary vein (62) focal sites. Rotor activity was seen rarely (15). AF complexity increased with longer clinical history of AF, although the degree of complexity of nonparoxysmal AF varied widely.

CONCLUSIONS

ECGI offers a noninvasive way to map epicardial activation patterns of AF in a patient-specific manner. The results highlight the coexistence of a variety of mechanisms and variable complexity among patients. Overall, complexity generally increased with duration of AF.

Toward discerning the mechanisms of atrial fibrillation from surface electrocardiogram and spectral analysis

Atrial fibrillation (AF) is the main cause of stroke and the most common sustained arrhythmia, afflicting about 2.3 million Americans. Clinical treatment and management of AF would benefit from a noninvasive and global assessment of the arrhythmia; however, that avenue seems currently limited in part by our poor understanding of arrhythmia itself. Experimental studies of AF in the isolated sheep heart demonstrated that high-frequency sources in the posterior wall of the left atrium drive the fibrillatory activity throughout both atria. Motivated by those results and by a growing body of work investigating how measurements of the cycle length of activity in patients during AF can contribute to its treatment, we focused our analysis on the dispersion of dominant frequency (DF) of the activity during AF in humans. Using electroanatomic mapping and Fourier methods, we generated 3-dimensional intracardiac DF maps of the atria in patients before AF ablation procedures and identified relatively small high-DF (HDF) sites. In patients with paroxysmal AF, the HDF sites are often localized to the posterior left atrium near the ostia of the pulmonary veins. In contrast, patients with permanent AF demonstrate HDF sites that are more often localized to the atria than the posterior left atrium-pulmonary vein junction. In our study, ablation at HDF sites resulted in significant slowing of the arrhythmia and termination of sustained AF in 87% of patients with paroxysmal AF. Furthermore, we found that abolishing, by ablation, preexisting left atrium to right atrium DF gradients predicted long-term freedom of AF in both paroxysmal and persistent AF patients. Overall, the analysis of intracardiac electrical recordings in the frequency domain has greatly enhanced our understanding of its underlying mechanisms and may contribute to monitoring drug effects and guide ablation procedures aiming at its termination. On the other hand, current body surface mapping methods have also suggested better correlations between surface AF frequency and intracardiac local DFs as compared with spatiotemporal activation patterns. Therefore, further study of the correlation of spectral observables obtained from the atria and from the surface electrocardiogram during AF seems to have the potential to advance our ability to diagnose and discern mechanisms of AF noninvasively.

The surgical treatment of atrial fibrillation

Atrial fibrillation is a complex disease affecting a significant portion of the general population. Although medical therapy is the mainstay of treatment, intervention plays an important role in selected patients. The Cox-Maze procedure is the gold standard for the surgical treatment of atrial fibrillation and has more than 90% success in eliminating atrial fibrillation. Ablation technologies have played a key role in simplifying this technically demanding procedure and making it available to more patients. A myriad of new lesion sets and approaches were introduced over the last decade which has made the operative treatment of atrial fibrillation less invasive and more confusing.

Application of L1-norm regularization to epicardial potential solution of the inverse electrocardiography problem

The electrocardiographic inverse problem of computing epicardial potentials from multi-electrode body-surface ECG measurements, is an ill-posed problem. Tikhonov regularization is commonly employed, which imposes penalty on the L2-norm of the potentials (zero-order) or their derivatives. Previous work has indicated superior results using L2-norm of the normal derivative of the solution (a first order regularization). However, L2-norm penalty function can cause considerable smoothing of the solution. Here, we use the L1-norm of the normal derivative of the potential as a penalty function. L1-norm solutions were compared to zero-order and first-order L2-norm Tikhonov solutions and to measured 'gold standards' in previous experiments with isolated canine hearts. Solutions with L1-norm penalty function (average relative error [RE] = 0.36) were more accurate than L2-norm (average RE = 0.62). In addition, the L1-norm method localized epicardial pacing sites with better accuracy (3.8 +/- 1.5 mm) compared to L2-norm (9.2 +/- 2.6 mm) during pacing in five pediatric patients with congenital heart disease. In a pediatric patient with Wolff-Parkinson-White syndrome, the L1-norm method also detected and localized two distinct areas of early activation around the mitral valve annulus, indicating the presence of two left-sided pathways which were not distinguished using L2 regularization.