Electroanatomic Mapping and Ablation of Macroreentrant Atrial Tachycardia: Comparison Between Successfully and Unsuccessfully Treated Cases

High-density characterization of the sinus rhythm: a new functional substrate map of scar-related atrial tachycardia

BACKGROUND

Reentrant atrial tachycardias (ATs) utilize critical isthmus (CI) for the maintenance of the circuit. The electrophysiological characteristics and clinical implications of the targeted CI regions of reentrant ATs during sinus rhythm (SR) were not clear. Therefore, our research aims at studying the electrical properties of the CI sites for scar-related reentrant ATs and the functional substrate mapping identified during SR.

METHODS

Patients mapped with high-density catheters during SR and reentrant ATs were retrospectively analyzed. The CI regions of the reentrant ATs were confirmed by the combination of the activation map and the entrainment. The substrate mapping was analyzed for wavefront propagation, conduction velocity, and electrogram patterns.

RESULTS

Twenty patients with 22 reentrant ATs that underwent high-density maps were analyzed at 2 hospitals. Mapping performed during SR identified a scar region of 23.0 ± 13.6% of the left atrium. Regions of the CI in SR were characterized by low voltage (0.3 ± 0.2 mV), conduction slowing (0.4 ± 0.2 m/s), and fractionated electrogram (duration 62.5 ± 13.9 ms). Substrate mapping during SR showed that the regions of the CI located with the low-voltage zone in 16 out of 22 CI (72.7%), the deceleration zone in 15 out of 22 CI (68.2%), and late atrial activation in 12 out of 22 CI (54.5%). Targeting regions of CI achieve 94% of termination or change of the reentrant circuit. At 6.2 ± 7.1 months, there was 75% freedom from atrial arrhythmia.

CONCLUSIONS

Novel high-density mapping can identify the functional substrates during SR and guide ablation. Low-voltage areas with conduction slowing are putative predictors of the CI for the maintenance of the reentrant ATs.

Functional substrate mapping characteristics during sinus rhythm predicts critical isthmus of reentrant atrial tachycardia

BACKGROUND

Atrial tachycardia (AT) is a commonly encountered rhythm disorder in patients with underlying atrial scar. The role of atrial late activation mapping during sinus rhythm to predict the critical isthmus (CI) of AT has yet to be systematically evaluated. We aimed to investigate the relationship between the functional substrate mapping (FSM) characteristics and the CI of reentrant ATs in patients with underlying atrial low-voltage areas.

METHODS

Patients with history of left AT who underwent catheter ablation with 3D mapping using high-density mapping were enrolled. Voltage map and isochronal late activation mapping were created during sinus/paced rhythm to detect deceleration zones (DZ). Electrograms with continuous-fragmented morphology were also tagged. After induction of AT, activation mapping was performed to detect CI of the tachycardia. Atrial tachyarrhythmia (ATa) recurrence was defined as detection of atrial fibrillation or AT (≥30 s) during the follow-up.

RESULTS

Among 35 patients [mean age: 62 ± 9, gender: 25 (71.5%) female] with left AT, a total of 42 reentrant ATs induced. Voltage mapping during sinus rhythm revealed low-voltage area of 37.1 ± 23.8% of the left atrium. The mean value of bipolar voltage, EGM duration, and conduction velocity during sinus rhythm corresponding to CI of ATs were 0.18 ± 0.12 mV, 133 ± 47 ms, and 0.12 ± 0.09 m/s, respectively. Total number of DZs per chamber was 1.5 ± 0.6, which were located in the low-voltage zone (<0.5 mV) detected by high-density mapping. All CIs of reentry were colocalized with DZs detected during FSM. The positive predictive value of DZs to detect CI of inducible ATs is 80.4%. Freedom from ATa after the index procedure was 74.3% during a mean follow-up of 12.2 ± 7.5 months.

CONCLUSION

Our findings demonstrated the utility of FSM during sinus rhythm to predict the CI of AT. DZs displayed continuous-fragmented signal morphology with slow conduction which may guide to tailor ablation strategy in case of underlying atrial scar.

Pathophysiology of Atypical Atrial Flutters

Atypical atrial flutters are complex supraventricular arrhythmias that share different pathophysiological aspects in common. In most cases, the arrhythmogenic substrate is essentially embodied by slow-conducting areas eliciting re-entrant circuits. Although atrial scarring seems to promote slow conduction, these arrhythmias may occur even in the absence of structural heart disease. To set out the ablation strategy in this setting, three-dimensional mapping systems have proved invaluable over the last decades, helping the cardiac electrophysiologist understand the electrophysiological complexity of these circuits and easily identify critical areas amenable to effective catheter ablation.

Mapping and Ablation of Atypical Atrial Flutters

Atypical atrial flutters are complex, hard-to-manage atrial arrhythmias. Catheter ablation has progressively emerged as a successful treatment option with a remarkable role played by irrigated-tip catheters and 3D electroanatomic mapping systems. However, despite the improvement of these technologies, the ablation results may be still suboptimal due to the progressive atrial substrate modification occurring in diseased hearts. Hence, a patient-tailored approach is required to improve the long-term success rate in this scenario, aiming at achieving specific procedure end points and detecting any potential arrhythmogenic substrate in each patient.

Procedural Feasibility and Long-Term Efficacy of Catheter Ablation of Atypical Atrial Flutters in a Wide Spectrum of Heart Diseases: An Updated Clinical Overview

Atypical atrial flutters (AAFL) are difficult-to-manage atrial arrhythmias, yet potentially amenable to effective radiofrequency catheter ablation (CA). However, data on CA feasibility are only sparingly reported in the literature in different clinical settings, such as AAFL related to surgical correction of congenital heart disease. The aim of this review was to provide an overview of the clinical settings in which AAFL may occur to help the cardiac electrophysiologist in the prediction of the tachycardia circuit location before CA. Moreover, the role and proper implementation of cutting-edge technologies in this setting were investigated as well as which procedural and clinical factors are associated with long-term failure to maintain sinus rhythm (SR) to find out which patients may, or may not, benefit from this procedure. Not only different surgical and non-surgical scenarios are associated with peculiar anatomical location of AAFL, but we also found that CA of AAFL is generally feasible. The success rate may be as low as 50% in surgically corrected congenital heart disease (CHD) patients but up to about 90% on average after pulmonary vein isolation (PVI) or in patients without structural heart disease. Over the years, the progressive implementation of three-dimensional mapping systems and high-density mapping tools has also proved helpful for ablation of these macro-reentrant circuits. However, the long-term maintenance of SR may still be suboptimal due to the progressive electroanatomic atrial remodeling occurring after cardiac surgery or other interventional procedures, thus limiting the likelihood of successful ablation in specific clinical settings.

Expert-enhanced machine learning for cardiac arrhythmia classification

We propose a new method for the classification task of distinguishing atrial fibrillation (AFib) from regular atrial tachycardias including atrial flutter (AFlu) based on a surface electrocardiogram (ECG). Recently, many approaches for an automatic classification of cardiac arrhythmia were proposed and to our knowledge none of them can distinguish between these two. We discuss reasons why deep learning may not yield satisfactory results for this task. We generate new and clinically interpretable features using mathematical optimization for subsequent use within a machine learning (ML) model. These features are generated from the same input data by solving an additional regression problem with complicated combinatorial substructures. The resultant can be seen as a novel machine learning model that incorporates expert knowledge on the pathophysiology of atrial flutter. Our approach achieves an unprecedented accuracy of 82.84% and an area under the receiver operating characteristic (ROC) curve of 0.9, which classifies as "excellent" according to the classification indicator of diagnostic tests. One additional advantage of our approach is the inherent interpretability of the classification results. Our features give insight into a possibly occurring multilevel atrioventricular blocking mechanism, which may improve treatment decisions beyond the classification itself. Our research ideally complements existing textbook cardiac arrhythmia classification methods, which cannot provide a classification for the important case of AFib↔AFlu. The main contribution is the successful use of a novel mathematical model for multilevel atrioventricular block and optimization-driven inverse simulation to enhance machine learning for classification of the arguably most difficult cases in cardiac arrhythmia. A tailored Branch-and-Bound algorithm was implemented for the domain knowledge part, while standard algorithms such as Adam could be used for training.

Ablation of atrial tachycardia in the setting of prior mitral valve surgery

BACKGROUND

Data regarding catheter ablation of post-surgical atrial tachycardia occurring after mitral valve surgery are scarce. Through a search of the literature, this study aimed to assess the feasibility of catheter ablation and the characteristics of atrial arrhythmias ablated in these patients.

METHODS

Studies assessing the main procedure parameters and the electrophysiologic findings of the investigated atrial tachycardia were selected. The electrophysiologic mechanism (focal vs. re-entrant arrhythmias), site of arrhythmia origin (left atrium vs. right atrium) and their anatomic correlation with specific surgical access and/or prior Cox-Maze IV procedure were all addressed.

RESULTS

Eleven studies including 206 patients undergoing catheter ablation of 297 post-surgical arrhythmia morphologies occurring after mitral valve surgery were considered. Major complications were observed in 2 patients only (0.9%). Restoration of sinus rhythm was achieved in 96% of patients. Macro-reentrant arrhythmia was mostly observed (90.4%) with a non-negligible proportion of focal arrhythmia (9.6%). Left-sided arrhythmia was common (54.4%,) but cavotricuspid isthmus-dependent arrhythmia was frequently reported (33%). Although specific atriotomies showed trends towards peculiar locations of the investigated arrhythmia, Cox-Maze IV procedure was the only independent predictor for left-sided arrhythmia (OR=17.3; 95% CI 7.2-41.2; P<0.0001).

CONCLUSIONS

Catheter ablation of post-surgical arrhythmia occurring after mitral valve surgery is feasible, and, in this setting, the vast majority of the arrhythmia morphologies are based on macro-reentry and in about one third of cases show cavotricuspid isthmus-dependent arrhythmia. Prior Cox-Maze-IV associated with mitral valve surgery is an independent predictor of left-sided arrhythmia possibly due to non-transmural surgical lesions.

Is the mid-diastolic isthmus always the best ablation target for re-entrant atrial tachycardias?

AIMS

We evaluated the ability of an ultrahigh mapping system to identify the most convenient Rhythmia ablation target (RAT) in intra-atrial re-entrant tachycardias (IART) in terms of the narrowest area to transect to interrupt the re-entry.

METHODS

A total of 24 consecutive patients were enrolled with a total of 26 IARTs. The Rhythmia mapping system was used to identify the RAT in all IARTs.

RESULTS

In 18 cases the RAT matched the mid-diastolic phase of the re-entry whereas in 8 cases the RAT differed. In these patients, the mid-diastolic tissue in the active circuit never represented the area with the slowest conduction velocity of the re-entry. The mean conduction velocity at the mid-diastolic site was significantly slower in the group of patients in which the RAT matched the mid-diastolic site (P = 0.0173) and that of the remaining circuit was significantly slower in the group in which the RAT did not match (P = 0.0068). The mean conduction velocity at the RAT was comparable between the two groups (P = 0.66).

CONCLUSION

Identifying the RAT in challenging IARTs by means of high-density representation of the wavefront propagation of the tachycardia seems feasible and effective. In one-third of cases this approach identifies an area that differs from the mid-diastolic corridor.

A new electrophysiologic triad for identification and localization of the critical isthmus in atrial flutter

INTRODUCTION

Atypical atrial flutter (AFL) is a supraventricular arrhythmia that can be treated with catheter ablation. However, this strategy yields suboptimal results and the best approach is yet to be defined. Carto® electroanatomical mapping (EAM) version 7 displays a histogram of the local activation times (LAT) of the tachycardia cycle length (TCL), in addition to activation and voltage maps. Using these EAM tools, the study aimed to assess the ability of an electrophysiologic triad to identify and localize the critical isthmus in AFL.

METHODS

Retrospective analysis using Carto® EAM of a single center registry of individuals who underwent left AFL ablation over one year. Subjects with non-left AFL, no high-density EAM, under 2000 points or no left atrium wall or structure mapping were excluded. Sites where arrhythmia is terminated via ablation were compared to an electrophysiologic triad comprising areas of low-voltage (0.05 to 0.3 mV), deep histogram valleys (LAT-valleys) with less than 20% density points relative to the highest density zone and a prolonged LAT-valley duration, which included 10% or more of the TCL. The longest LAT-valley was designated as the primary valley, while additional valleys were named as secondary.

RESULTS

A total of nine subjects (six men, median age 75, interquartile range 71-76 years) were included. All patients presented with left AFL and 66% had a history of ablation for atrial fibrillation and/or flutter. The median TCL and collected points were 254 ms (220-290) and 3300 (IQR 2410-3926) points, respectively. All individuals with AFL presented with at least one LAT-valley on the analyzed histograms, which corresponded to heterogeneous low voltage areas (0.05 to 0.3 mV) and affected more than 10% of TCL. Six of the nine patients presented with a secondary LAT-valley. All arrhythmias were terminated successfully following radiofrequency ablation at the primary LAT-valley location. After a minimum three-month follow-up all patients remained in sinus rhythm.

CONCLUSION

An electrophysiologic triad identified the critical isthmus in AFL for all patients. Further studies are needed to assess the usefulness of this algorithm in improving catheter ablation outcomes.

Advanced Cardiac Signal Recording

Implantable loop recorders allow prolonged and continuous single-lead electrocardiogram recording, with the pivotal addition of remote monitoring. They have significantly shortened time to electrocardiographic diagnosis and appropriate therapy of many bradyarrhythmias/tachyarrhythmias and proved helpful in arrhythmia burden definition, offering invaluable information in the diagnostic workup for syncope and atrial fibrillation. Advanced cardiac signal recording is also possible by transesophageal catheters. They have been used to orient diagnosis during wide and narrow QRS complex tachycardias and also to perform minimally invasive pacing. Intracardiac electrophysiologic study remains, however, essential for diagnosis of several arrhythmias in the perspective of curative catheter ablation.

Simplified progressive approach for the ablation of scar related atrial macroreentrant tachycardias

INTRODUCTION

Radiofrequency ablation of scar related right atrial flutter is challenging. Long procedures, prolonged fluoroscopic times and high percentages of recurrences are of concern. We present a simple and progressive approach based on a single electroanatomic map of the right atrium.

METHODS

Twenty-two consecutive patients with atrial flutter and history of cardiac surgery were included. An electrophysiologic study was performed to define localization (left or right) and cavo-tricuspid isthmus participation using entrainment mapping. After a critical isthmus was localized, ablation was performed with an external irrigated tip catheter with a power limit of 30 W. Potential ablation sites were confirmed by entrainment.

RESULTS

The predominant cardiopathy was atrial septal defect. All arrhythmias were localized in the right atrium; mean cycle length of the clinical flutter was 274 ± 31 ms. Only 40% had cavo-tricuspid isthmus participation. None of the patients with successful ablation had recurrences after 13 ± 9.4 months of follow-up.

CONCLUSIONS

A progressive approach with only one activation/voltage CARTO(®) map of the atrium and ablation of all potential circuits is a highly effective method for ablating scar related macroreentrant atrial arrhythmias.

Characterization of Anatomic Ventricular Tachycardia Isthmus Pathology After Surgical Repair of Tetralogy of Fallot

Background—

Although catheter ablation has been used to target the critical isthmuses for re-entrant monomorphic ventricular tachycardia in tetralogy of Fallot, the anatomy and histology of these regions have not been fully characterized. Autopsy hearts with tetralogy of Fallot were evaluated to clarify the pathological substrate.

Methods and Results—

Twenty-seven hearts with the diagnosis of tetralogy of Fallot were examined. Anatomically defined isthmuses included (1A) ventriculotomy-to-tricuspid annulus, (1B) ventriculotomy-to-ventricular septal defect patch, (2) ventriculotomy-to-pulmonary annulus, (3) pulmonary annulus-to-ventricular septal defect patch, and (4) ventricular septal defect patch-to-tricuspid annulus. Length and wall thickness were measured for all specimens, and light microscopy was performed for those surviving surgery. For subjects ≥5 years at death, isthmuses 1A and 1B were present in 88%, isthmus 2 in 25%, isthmus 3 in 94%, and isthmus 4 in 13%. Isthmus 1A had the greatest dimensions (mean length, 3.9±1.08; thickness, 1.5±0.3 cm), isthmus 1B intermediate dimensions (mean length, 2.4±0.8; thickness, 1.1±0.4 cm), and isthmuses 2, 3, and 4 the smallest dimensions (mean length, 1.5±0.5, 1.4±0.8, and 0.6±0.4 cm; thickness, 0.5±0.2, 0.6±0.2, and 0.3±0.04 cm, respectively). Histological examination (n=7) revealed increased fibrosis in anatomic isthmuses relative to nonisthmus controls.

Conclusions—

Consistencies in isthmus dimensions and histology are found among patients with repaired tetralogy of Fallot. Isthmus 1A is associated with the largest morphological dimensions, whereas the nearby newly described isthmus 1B is significantly smaller. Of isthmuses with the smallest dimensions, isthmus 3 is the most common.

Spontaneous left atrial reentry tachycardias : radiofrequency ablation and outcome

AIMS

Spontaneous left atrial reentry tachycardias (LART) in patients without previous cardiac surgical or catheter ablation are rare. Several therapeutic concepts of catheter ablation have been suggested: linear lesions (LL), circumferential pulmonary vein isolation (PVI), and both (LL + PVI).

METHODS AND RESULTS

In all, 28 consecutive symptomatic patients with 51 LARTs presented to our institution for catheter ablation. Electroanatomical mapping was performed on 25 patients. Three patients were ablated conventionally during LART; 25 patients (89.3 %) had extensive low-voltage areas in the left atrium (atrial myopathy). One of the following ablation strategies was applied: first, LL (n = 8), second, PVI + LL (n = 11), and third PVI alone (n = 9). Fourteen patients (50 %) had a recurrent arrhythmia during a mean follow-up of 12.2 ± 11.1 months. Six patients presented with a recurrent LART (21.4 %), 4 with LART and atrial fibrillation (Afib) (14.3 %), and 4 with Afib (14.3 %). The recurrence rate of any arrhythmia (LART and Afib) was 37.5 % in the LL group, 44.4 % in the PVI group, and 63.6 % in the PVI + LL group (ns); the recurrence rate of LARTs was 12.5 % in the LL group, 22.2 % in the PVI group, and 63.6 % in the PVI + LL group (p < 0.05).

CONCLUSION

Atrial tachyarrhythmia recurrence after ablation of spontaneous LART in mid-term is considerable. Stable LARTs are effectively treated by LL. PVI alone may be an acceptable alternative, especially in patients with unstable LARTs and Afib. However, the risk of recurrent LARTs after a more extensive strategy with PVI and LL is considerable, probably due to proarrhythmic effects of long linear lesions.