Three-Dimensional Mapping of Cardiac Arrhythmias

The value of ripple mapping in the age of coherent mapping in scar-related atrial tachycardia

BACKGROUND

An accurate display of scar-related atrial tachycardia (ATs) is a key determinant of ablation success. The efficacy of ripple mapping (RM) in identifying the mechanism and critical isthmus of scar-related ATs during coherent mapping is unknown.

METHODS

A total of 97 patients with complex ATs who underwent radiofrequency catheter ablation at our center between October 2018 and September 2022 were included. ATs was mapped using a multielectrode mapping catheter on the CARTO3v7 CONFIDENCE module. Coherent and RM were used to identify the reentrant circuit.

RESULTS

The mechanisms of 128 ATs were analyzed retrospectively (84 anatomic-reentrant ATs and 44 non-anatomic reentrant ATs). The median AT cycle length was 264 ± 25ms. The correct diagnosis was achieved in 83 ATs (68%) using only coherent mapping. Through coherent mapping plus RM, 114 ATs (84.2%) were correctly diagnosed (68% vs. 89%, p = .019). In non-anatomical reentrant ATs, 81% of the diagnostic rate was achieved by reviewing both coherent and ripple mapping compared to reviewing coherent mapping alone (81% vs. 52%, p = .03). Reviewing coherent mapping and ripple mapping showed a higher diagnostic rate in patients who underwent cardiac surgery than those with Coherent mapping alone (64% vs. 88%, p = .04).

CONCLUSION

Coherent mapping combined with RM was superior to coherent mapping alone in identifying the mechanism of scar-related ATs post-cardiac surgery and non-anatomic reentrant ATs.

Institutional experience report on the target contouring workflow in the radiotherapy department for stereotactic arrhythmia radioablation delivered on conventional linear accelerators

PURPOSE

In stereotactic arrhythmia radioablation (STAR), the target is defined using multiple imaging studies and a multidisciplinary team consisting of electrophysiologist, cardiologist, cardiac radiologist, and radiation oncologist collaborate to identify the target and delineate it on the imaging studies of interest. This report describes the workflow employed in our radiotherapy department to transfer the target identified based on electrophysiology and cardiology imaging to the treatment planning image set.

METHODS

The radiotherapy team was presented with an initial target in cardiac axes orientation, contoured on a wideband late gadolinium-enhanced (WB-LGE) cardiac magnetic resonance (CMR) study, which was subsequently transferred to the computed tomography (CT) scan used for treatment planning-i.e., the average intensity projection (AIP) image set derived from a 4D CT-via an axial CMR image set, using rigid image registration focused on the target area. The cardiac and the respiratory motion of the target were resolved using ciné-CMR and 4D CT imaging studies, respectively.

RESULTS

The workflow was carried out for 6 patients and resulted in an internal target defined in standard anatomical orientation that encompassed the cardiac and the respiratory motion of the initial target.

CONCLUSION

An image registration-based workflow was implemented to render the STAR target on the planning image set in a consistent manner, using commercial software traditionally available for radiation therapy.

Atrial cardiomyopathy: An entity of emerging interest in the clinical setting

Since 1995, the concept of atrial cardiomyopathy (ACM) has been associated with myocardial fibrosis. Despite a consensus document in 2016, ACM's definition primarily relies on histopathological findings. The focus on diagnostic criteria for ACM is driven by the potential link to thromboembolic events even independently on atrial fibrillation (AF). The complexity of the mutual relationships between ACM and AF makes difficult any assessment of the thromboembolic risk associated to ACM per se. ACM's thrombogenicity is a multifaceted clinical phenomenon involving electrical, functional, and structural modifications. Factors such as cardiovascular risk factors (e.g., hypertension), common cardiac comorbidities (e.g., heart failure), and extracardiac conditions (e.g., neuromuscular disorders) can promote atrial derangement, triggering atrial fibrillation (AF) and increasing the risk of thromboembolic events. Several diagnostic methods are available to detect the key features of ACM, including electrical changes assessed by surface and intracavitary ECG, and structural and functional alterations evaluated through echocardiography and cardiac magnetic resonance (CMR). These methods can be complemented by electro-anatomical mapping (EAM) to enhance the accuracy of myocardial tissue characterization and assessment of atrial fibrosis. Although certain clinical conditions (e.g., atrial high-rate episodes, AHREs; embolic stroke of undetermined source, ESUS) often exhibit atrial alterations in their thromboembolic presentations, recent randomized trials have failed to demonstrate the benefits of oral anticoagulation in patients with ACM without AF. However, ACM constitutes the substrate for the development of AF, as proposed in the AF European guidelines under the 4S-AF scheme. This review emphasizes the lack of a diagnostic gold standard and the need for clinical criteria for ACM, aiming to better understand the potential therapeutic implications of atrial structural and functional derangements, even in the absence of clinical evidence of AF.

Fundamentals of Cardiac Mapping

To characterize cardiac activity and arrhythmias, electrophysiologists can record the electrical activity of the heart in relation to its anatomy through a process called cardiac mapping (electroanatomic mapping, EAM). A solid understanding of the basic cardiac biopotentials, called electrograms, is imperative to construct and interpret the cardiac EAM correctly. There are several mapping approaches available to the electrophysiologist, each optimized for specific arrhythmia mechanisms. This article provides an overview of the fundamentals of EAM.

Directed Networks as a Novel Way to Describe and Analyze Cardiac Excitation: Directed Graph Mapping

Networks provide a powerful methodology with applications in a variety of biological, technological and social systems such as analysis of brain data, social networks, internet search engine algorithms, etc. To date, directed networks have not yet been applied to characterize the excitation of the human heart. In clinical practice, cardiac excitation is recorded by multiple discrete electrodes. During (normal) sinus rhythm or during cardiac arrhythmias, successive excitation connects neighboring electrodes, resulting in their own unique directed network. This in theory makes it a perfect fit for directed network analysis. In this study, we applied directed networks to the heart in order to describe and characterize cardiac arrhythmias. Proof-of-principle was established using in-silico and clinical data. We demonstrated that tools used in network theory analysis allow determination of the mechanism and location of certain cardiac arrhythmias. We show that the robustness of this approach can potentially exceed the existing state-of-the art methodology used in clinics. Furthermore, implementation of these techniques in daily practice can improve the accuracy and speed of cardiac arrhythmia analysis. It may also provide novel insights in arrhythmias that are still incompletely understood.

Biomarkers Associated with Atrial Fibrosis and Remodeling

Atrial fibrillation is the most common rhythm disturbance encountered in clinical practice. Although often considered as solely arrhythmic in nature, current evidence has established that atrial myopathy constitutes both the substrate and the outcome of atrial fibrillation, thus initiating a vicious, self-perpetuating cycle. This myopathy is triggered by stress-induced (including pressure/volume overload, inflammation, oxidative stress) responses of atrial tissue, which in the long term become maladaptive, and combine elements of both structural, especially fibrosis, and electrical remodeling, with contemporary approaches yielding potentially useful biomarkers of these processes. Biomarker value becomes greater given the fact that they can both predict atrial fibrillation occurrence and treatment outcome. This mini-review will focus on the biomarkers of atrial remodeling (both electrical and structural) and fibrosis that have been validated in human studies, including biochemical, histological and imaging approaches.

Local activation time sampling density for atrial tachycardia contact mapping: how much is enough?

Aims

Local activation time (LAT) mapping forms the cornerstone of atrial tachycardia diagnosis. Although anatomic and positional accuracy of electroanatomic mapping (EAM) systems have been validated, the effect of electrode sampling density on LAT map reconstruction is not known. Here, we study the effect of chamber geometry and activation complexity on optimal LAT sampling density using a combined in silico and in vivo approach.

Methods and results

In vivo 21 atrial tachycardia maps were studied in three groups: (1) focal activation, (2) macro-re-entry, and (3) localized re-entry. In silico activation was simulated on a 4×4cm atrial monolayer, sampled randomly at 0.25–10 points/cm² and used to re-interpolate LAT maps. Activation patterns were studied in the geometrically simple porcine right atrium (RA) and complex human left atrium (LA). Activation complexity was introduced into the porcine RA by incomplete inter-caval linear ablation. In all cases, optimal sampling density was defined as the highest density resulting in minimal further error reduction in the re-interpolated maps. Optimal sampling densities for LA tachycardias were 0.67 ± 0.17 points/cm² (focal activation), 1.05 ± 0.32 points/cm² (macro-re-entry) and 1.23 ± 0.26 points/cm² (localized re-entry), P = 0.0031. Increasing activation complexity was associated with increased optimal sampling density both in silico (focal activation 1.09 ± 0.14 points/cm²; re-entry 1.44 ± 0.49 points/cm²; spiral-wave 1.50 ± 0.34 points/cm², P < 0.0001) and in vivo (porcine RA pre-ablation 0.45 ± 0.13 vs. post-ablation 0.78 ± 0.17 points/cm², P = 0.0008). Increasing chamber geometry was also associated with increased optimal sampling density (0.61 ± 0.22 points/cm² vs. 1.0 ± 0.34 points/cm², P = 0.0015).

Conclusion

Optimal sampling densities can be identified to maximize diagnostic yield of LAT maps. Greater sampling density is required to correctly reveal complex activation and represent activation across complex geometries. Overall, the optimal sampling density for LAT map interpolation defined in this study was ∼1.0–1.5 points/cm².

Arrhythmia Mechanisms Revealed by Ripple Mapping

Ripple mapping is a novel method of 3D intracardiac electrogram visualisation that allows activation of the myocardium to be tracked visually without prior assignment of local activation times and without interpolation into unmapped regions. It assists in the identification of tachycardia mechanism and optimal ablation site, without the need for an experienced computer-operating assistant. This expert opinion presents evidence demonstrating the benefit of Ripple Mapping, compared with traditional electroanatomic mapping techniques, for the diagnosis and management of atrial and ventricular tachyarrhythmias during electrophysiological procedures.

Recent advances in rhythm control for atrial fibrillation

Atrial fibrillation (AF) remains a difficult management problem. The restoration and maintenance of sinus rhythm-rhythm control therapy-can markedly improve symptoms and haemodynamics for patients who have paroxysmal or persistent AF, but some patients fare well with rate control alone. Sinus rhythm can be achieved with anti-arrhythmic drugs or electrical cardioversion, but the maintenance of sinus rhythm without recurrence is more challenging. Catheter ablation of the AF triggers is more effective than anti-arrhythmic drugs at maintaining sinus rhythm. Whilst pulmonary vein isolation is an effective strategy, other ablation targets are being evaluated to improve sinus rhythm maintenance, especially in patients with chronic forms of AF. Previously extensive ablation strategies have been used for patients with persistent AF, but a recent trial has shown that pulmonary vein isolation without additional ablation lesions is associated with outcomes similar to those of more extensive ablation. This has led to an increase in catheter-based technology to achieve durable pulmonary vein isolation. Furthermore, a combination of anti-arrhythmic drugs and catheter ablation seems useful to improve the effectiveness of rhythm control therapy. Two large ongoing trials evaluate whether a modern rhythm control therapy can improve prognosis in patients with AF.

Ripple mapping: Initial multicenter experience of an intuitive approach to overcoming the limitations of 3D activation mapping

BACKGROUND

Ripple mapping (RM) displays electrograms as moving bars over a three-dimensional surface displaying bipolar voltage, and has shown in a single-center series to be effective for atrial tachycardia (AT) mapping without annotation of local activation time or window-of-interest assignment. We tested the reproducibility of these findings in operators naïve to RM, using it for the first time in postablation AT.

METHODS

Maps were collected with multielectrode catheters and CARTO ConfiDENSE. A diagnosis of the tachycardia mechanism was made using RM and an assessment of operator confidence was made according to a three-grade scale (1 highest-3 lowest).

RESULTS

The first 20 patients (64 ± 9 years, median two previous ablations) undergoing RM-guided AT ablation across five sites were studied. High-density maps (2,935 ± 1,328 points) in AT (CL = 296 ± 95 milliseconds) were collected. Macroreentrant ATs bordered by scar or anatomical obstacles were identified in n = 12 (60%), small reentrant ATs around scar in n = 3 (15%), and focal ATs from scar in n = 5 (25%). Diagnostic confidence with RM was grade 1 in n = 13 (65%), where operators felt confident to proceed to ablation without entrainment. Ablation offered the correct diagnosis n = 18 (90%). Retrospective review of the accompanying LAT maps demonstrated potential sources for error related to the window of interest selection, interpolation, and differentiating regions of scar during tachycardia on the voltage map.

CONCLUSION

RM was easy to adopt by operators using it for the first time, and identified the correct target for ablation with high diagnostic confidence in most cases of complex AT.

Three-dimensional mapping of cardiac arrhythmias - string of pearls -

The evolution of 3-dimensional (D) mapping systems has contributed to improved procedures for ablation of complex tachyarrhythmia in terms of providing detailed anatomical information along with the ability to integrate with pre-acquired computed tomography/magnetic resonance imaging/intracardiac echocardiography images, reducing the radiation exposure, and producing activation and substrate maps. 3-D mapping systems are categorized as magnetic based vs. impedance based according to the catheter location technology, and are also classified as contact based vs. non-contact based according to the data collection technology. Contact-based mapping systems are used widely, in which a series of electrograms is taken sequentially in contact with the heart, thus requiring a relatively stable and sustained arrhythmia to create an activation map. Non-contact mapping systems, however, allow a beat-to-beat analysis of the activation even in non-sustained, polymorphic, or hemodynamically intolerant tachycardia. In this article, the clinical utility of 3-D mapping systems is discussed based on the literature and on experience, with particular emphasis on the non-contact mapping system.