Optimization of late gadolinium enhancement cardiovascular magnetic resonance imaging of post-ablation atrial scar: a cross-over study

Computational modeling of cardiac electrophysiology and arrhythmogenesis: toward clinical translation

The complexity of cardiac electrophysiology, involving dynamic changes in numerous components across multiple spatial (from ion channel to organ) and temporal (from milliseconds to days) scales, makes an intuitive or empirical analysis of cardiac arrhythmogenesis challenging. Multiscale mechanistic computational models of cardiac electrophysiology provide precise control over individual parameters, and their reproducibility enables a thorough assessment of arrhythmia mechanisms. This review provides a comprehensive analysis of models of cardiac electrophysiology and arrhythmias, from the single cell to the organ level, and how they can be leveraged to better understand rhythm disorders in cardiac disease and to improve heart patient care. Key issues related to model development based on experimental data are discussed, and major families of human cardiomyocyte models and their applications are highlighted. An overview of organ-level computational modeling of cardiac electrophysiology and its clinical applications in personalized arrhythmia risk assessment and patient-specific therapy of atrial and ventricular arrhythmias is provided. The advancements presented here highlight how patient-specific computational models of the heart reconstructed from patient data have achieved success in predicting risk of sudden cardiac death and guiding optimal treatments of heart rhythm disorders. Finally, an outlook toward potential future advances, including the combination of mechanistic modeling and machine learning/artificial intelligence, is provided. As the field of cardiology is embarking on a journey toward precision medicine, personalized modeling of the heart is expected to become a key technology to guide pharmaceutical therapy, deployment of devices, and surgical interventions.

Atrial Ablation Lesion Evaluation by Cardiac Magnetic Resonance: Review of Imaging Strategies and Histological Correlations

Cardiac magnetic resonance (CMR) imaging is a valuable noninvasive tool for evaluating tissue response following catheter ablation of atrial tissue. This review provides an overview of the contemporary CMR strategies to visualize atrial ablation lesions in both the acute and chronic postablation stages, focusing on their strengths and limitations. Moreover, the accuracy of CMR imaging in comparison to atrial lesion histology is discussed. T2-weighted CMR imaging is sensitive to edema and tends to overestimate lesion size in the acute stage after ablation. Noncontrast agent-enhanced T1-weighted CMR imaging has the potential to provide more accurate assessment of lesions in the acute stage but may not be as effective in the chronic stage. Late gadolinium enhancement imaging can be used to detect chronic atrial scarring, which may inform repeat ablation strategies. Moreover, novel imaging strategies are being developed, but their efficacy in characterizing atrial lesions is yet to be determined. Overall, CMR imaging has the potential to provide virtual histology that aids in evaluating the efficacy and safety of catheter ablation and monitoring of postprocedural myocardial changes. However, technical factors, scanning during arrhythmia, and transmurality assessment pose challenges. Therefore, further research is needed to develop CMR strategies to visualize the ablation lesion maturation process more effectively.

Fully-modelled blood-focused variable inversion times for 3D late gadolinium-enhanced imaging

PURPOSE

Variable heart rate during single-cycle inversion-recovery Late Gadolinium-Enhanced (LGE) scanning degrades image quality, which can be mitigated using Variable Inversion Times (VTIs) in real-time response to R-R interval changes. We investigate in vivo and in simulations an extension of a single-cycle VTI method previously applied in 3D LGE imaging, that now fully models the longitudinal magnetisation (fmVTI).

METHODS

The VTI and fmVTI methods were used to perform 3D LGE scans for 28 3D LGE patients, with qualitative image quality scores assigned for left atrial wall clarity and total ghosting. Accompanying simulations of numerical phantom images were assessed in terms of ghosting of normal myocardium, blood, and myocardial scar.

RESULTS

The numerical simulations for fmVTI showed a significant decrease in blood ghosting (VTI: 410 ± 710, fmVTI: 68 ± 40, p < 0.0005) and scar ghosting (VTI: 830 ± 1300, fmVTI: 510 ± 730, p < 0.02). Despite this, there was no significant change in qualitative image quality scores, either for left atrial wall clarity (VTI: 2.0 ± 1.0, fmVTI: 1.8 ± 1.0, p > 0.1) or for total ghosting (VTI: 1.9 ± 1.0, fmVTI: 2.0 ± 1.0, p > 0.7).

CONCLUSIONS

Simulations indicated reduced ghosting with the fmVTI method, due to reduced Mz variability in the blood signal. However, other sources of phase-encode ghosting and blurring appeared to dominate and obscure this finding in the patient studies available.

Quantification of right atrial fibrosis by cardiac magnetic resonance: verification of the method to standardize thresholds

INTRODUCTION AND OBJECTIVES

Late gadolinium-enhanced cardiac magnetic resonance (LGE-CMR) allows noninvasive detection of left atrial fibrosis in patients with atrial fibrillation (AF). However, whether the same methodology can be used in the right atrium (RA) remains unknown. Our aim was to define a standardized threshold to characterize RA fibrosis in LGE-CMR.

METHODS

A 3 Tesla LGE-CMR was performed in 53 individuals; the RA was segmented, and the image intensity ratio (IIR) calculated for the RA wall using 1 557 767 IIR pixels (40 994±10 693 per patient). The upper limit of normality of the IIR (mean IIR+2 standard deviations) was estimated in healthy volunteers (n=9), and patients who had undergone previous typical atrial flutter ablation (n=9) were used to establish the dense scar threshold. Paroxysmal and persistent AF patients (n=10 each) were used for validation. IIR values were correlated with a high-density bipolar voltage map in 15 patients undergoing AF ablation.

RESULTS

The upper normality limit (total fibrosis threshold) in healthy volunteers was set at an IIR = 1.21. In the postablation group, 60% of the maximum IIR pixel (dense fibrosis threshold) was calculated as IIR = 1.29. Endocardial bipolar voltage showed a weak but significant correlation with IIR. The overall accuracy between the electroanatomical map and LGE-CMR to characterize fibrosis was 56%.

CONCLUSIONS

An IIR > 1.21 was determined to be the threshold for the detection of right atrial fibrosis, while an IIR > 1.29 differentiates interstitial fibrosis from dense scar. Despite differences between the left and right atria, fibrosis could be assessed with LGE-CMR using similar thresholds in both chambers.

Catheter ablation improved ejection fraction in persistent AF patients: a DECAAF-II sub analysis

AIMS

The aim of our study was to assess differences in post-ablation atrial fibrillation (AF) recurrence and burden and to quantify the change in LVEF across different congestive heart failure (CHF) subcategories of the DECAAF-II population.

METHODS AND RESULTS

Differences in the primary outcome of AF recurrence between CHF and non-CHF groups was calculated. The same analysis was performed for the three subgroups of CHF and the non-CHF group. Differences in AF burden after the 3-month blanking period between CHF and non-CHF groups was calculated. Improvement in LVEF was calculated and compared across the three CHF groups. Improvement was also calculated across different fibrosis stages. There was no significant differences in AF recurrence and AF burden after catheter ablation between CHF and non-CHF patients and between different CHF subcategories. Patients with heart failure with reduced ejection fraction (HFrEF) experienced the greatest improvement in EF following catheter ablation (CA, 16.66% ± 11.98, P < 0.001) compared to heart failure with moderately reduced LVEF, and heart failure with preserved EF (10.74% ± 8.34 and 2.00 ± 8.34 respectively, P-value < 0.001). Moreover, improvement in LVEF was independent of the four stages of atrial fibrosis (7.71 vs. 9.53 vs. 5.72 vs. 15.88, from Stage I to Stage IV respectively, P = 0.115).

CONCLUSION

Atrial fibrillation burden and recurrence after CA is similar between non-CHF and CHF patients, independent of the type of CHF. Of all CHF groups, those with HFrEF had the largest improvement in LVEF after CA. Moreover, the improvement in ventricular function seems to be independent of atrial fibrosis in patients with persistent AF.

Quantifying the impact of shape uncertainty on predicted arrhythmias

BACKGROUND

Personalised computer models are increasingly used to diagnose cardiac arrhythmias and tailor treatment. Patient-specific models of the left atrium are often derived from pre-procedural imaging of anatomy and fibrosis. These images contain noise that can affect simulation predictions. There are few computationally tractable methods for propagating uncertainties from images to clinical predictions.

METHOD

We describe the left atrium anatomy using our Bayesian shape model that captures anatomical uncertainty in medical images and has been validated on 63 independent clinical images. This algorithm describes the left atrium anatomy using Nmodes=15 principal components, capturing 95% of the shape variance and calculated from 70 clinical cardiac magnetic resonance (CMR) images. Latent variables encode shape uncertainty: we evaluate their posterior distribution for each new anatomy. We assume a normally distributed prior. We use the unscented transform to sample from the posterior shape distribution. For each sample, we assign the local material properties of the tissue using the projection of late gadolinium enhancement CMR (LGE-CMR) onto the anatomy to estimate local fibrosis. To test which activation patterns an atrium can sustain, we perform an arrhythmia simulation for each sample. We consider 34 possible outcomes (31 macro-re-entries, functional re-entry, atrial fibrillation, and non-sustained arrhythmia). For each sample, we determine the outcome by comparing pre- and post-ablation activation patterns following a cross-field stimulus.

RESULTS

We create patient-specific atrial electrophysiology models of ten patients. We validate the mean and standard deviation maps from the unscented transform with the same statistics obtained with 12,000 Monte Carlo (ground truth) samples. We found discrepancies <3% and <2% for the mean and standard deviation for fibrosis burden and activation time, respectively. For each patient case, we then compare the predicted outcome from a model built on the clinical data (deterministic approach) with the probability distribution obtained from the simulated samples. We found that the deterministic approach did not predict the most likely outcome in 80% of the cases. Finally, we estimate the influence of each source of uncertainty independently. Fixing the anatomy to the posterior mean and maintaining uncertainty in fibrosis reduced the prediction of self-terminating arrhythmias from ≃14% to ≃7%. Keeping the fibrosis fixed to the sample mean while retaining uncertainty in shape decreased the prediction of substrate-driven arrhythmias from ≃33% to ≃18% and increased the prediction of macro-re-entries from ≃54% to ≃68%.

CONCLUSIONS

We presented a novel method for propagating shape uncertainty in atrial models through to uncertainty in numerical simulations. The algorithm takes advantage of the unscented transform to compute the output distribution of the outcomes. We validated the unscented transform as a viable sampling strategy to deal with anatomy uncertainty. We then showed that the prediction computed with a deterministic model does not always coincide with the most likely outcome. Finally, we found that shape uncertainty affects the predictions of macro-re-entries, while fibrosis uncertainty affects the predictions of functional re-entries.

Quantification of left atrial fibrosis by 3D late gadolinium-enhanced cardiac magnetic resonance imaging in patients with atrial fibrillation: impact of different analysis methods

Aims

Various methods and post-processing software packages have been developed to quantify left atrial (LA) fibrosis using 3D late gadolinium-enhancement cardiac magnetic resonance (LGE-CMR) images. Currently, it remains unclear how the results of these methods and software packages interrelate.

Methods and results

Forty-seven atrial fibrillation (AF) patients underwent 3D-LGE-CMR imaging prior to their AF ablation. LA fibrotic burden was derived from the images using open-source CEMRG software and commercially available ADAS 3D-LA software. Both packages were used to calculate fibrosis based on the image intensity ratio (IIR)-method. Additionally, CEMRG was used to quantify LA fibrosis using three standard deviations (3SD) above the mean blood pool signal intensity. Intraclass correlation coefficients were calculated to compare LA fibrosis quantification methods and different post-processing software outputs. The percentage of LA fibrosis assessed using IIR threshold 1.2 was significantly different from the 3SD-method (29.80 ± 14.15% vs. 8.43 ± 5.42%; P &lt; 0.001). Correlation between the IIR-and SD-method was good (r = 0.85, P &lt; 0.001) although agreement was poor [intraclass correlation coefficient (ICC) = 0.19; P &lt; 0.001]. One-third of the patients were allocated to a different fibrosis category dependent on the used quantification method. Fibrosis assessment using CEMRG and ADAS 3D-LA showed good agreement for the IIR-method (ICC = 0.93; P &lt; 0.001).

Conclusions

Both, the IIR1.2 and 3SD-method quantify atrial fibrotic burden based on atrial wall signal intensity differences. The discrepancy in the amount of LA fibrosis between these methods may have clinical implications when patients are classified according to their fibrotic burden. There was no difference in results between post-processing software packages to quantify LA fibrosis if an identical quantification method including the threshold was used.

Multimodality Imaging in the Study of the Left Atrium

The left atrium (LA) plays a vital role in maintaining normal cardiac function. Many cardiac diseases involve the functioning of the LA directly or indirectly. For this reason, the study of the LA has become a priority for today's imaging techniques. Assessment of LA size, function and wall characteristics is routinely performed in cardiac imaging laboratories when a patient undergoes transthoracic echocardiography. However, in cases when the LA is the focus of disease management, such as in atrial fibrillation or left atrial appendage closure, the use of multimodality is critical. Knowledge of the usefulness of each cardiac imaging technique for the study of LA in these patients is crucial in order to choose the most appropriate treatment. While echocardiography is the most widely performed technique for its evaluation and the study of wall deformation analysis is increasingly becoming more reliable, multidetector computed tomography allows a detailed analysis of its anatomy to be carried out in 3D reconstructions that help in the approach to interventional treatments. In addition, the evaluation of the wall by cardiac magnetic resonance imaging or the generation of electroanatomical maps in the electrophysiology room have become essential tools in the treatment of multiple atrial pathologies. For this reason, the goal of this review article is to describe the basic anatomical and functional information of the LA as well as their study employing the main imaging techniques currently available, so that practitioners specializing in cardiac imaging techniques can use these tools in an accurate and clinically useful manner.

Ablation Lesion Assessment with MRI

Late gadolinium enhancement (LGE) MRI is capable of detecting not only native cardiac fibrosis, but also ablation-induced scarring. Thus, it offers the unique opportunity to assess ablation lesions non-invasively. In the atrium, LGE-MRI has been shown to accurately detect and localise gaps in ablation lines. With a negative predictive value close to 100% it can reliably rule out pulmonary vein reconnection non-invasively and thus may avoid unnecessary invasive repeat procedures where a pulmonary vein isolation only approach is pursued. Even LGE-MRI-guided repeat pulmonary vein isolation has been demonstrated to be feasible as a standalone approach. LGE-MRI-based lesion assessment may also be of value to evaluate the efficacy of ventricular ablation. In this respect, the elimination of LGE-MRI-detected arrhythmogenic substrate may serve as a potential endpoint, but validation in clinical studies is lacking. Despite holding great promise, the widespread use of LGE-MRI is still limited by the absence of standardised protocols for image acquisition and post-processing. In particular, reproducibility across different centres is impeded by inconsistent thresholds and internal references to define fibrosis. Thus, uniform methodological and analytical standards are warranted to foster a broader implementation in clinical practice.

Atrial CARdiac Magnetic resonance imaging in patients with embolic stroke of unknown source without documented Atrial Fibrillation (CARM-AF): Study design and clinical protocol

Background

Initiation of anticoagulation therapy in ischemic stroke patients is contingent on a clinical diagnosis of atrial fibrillation (AF). Results from previous studies suggest thromboembolic risk may predate clinical manifestations of AF. Early identification of this cohort of patients may allow early initiation of anticoagulation and reduce the risk of secondary stroke.

Objective

This study aims to produce a substrate-based predictive model using cardiac magnetic resonance imaging (CMR) and baseline noninvasive electrocardiographic investigations to improve the identification of patients at risk of future thromboembolism.

Methods

CARM-AF is a prospective, multicenter, observational cohort study. Ninety-two patients will be recruited following an embolic stroke of unknown source (ESUS) and undergo atrial CMR followed by insertion of an implantable loop recorder (ILR) as per routine clinical care within 3 months of index stroke. Remote ILR follow-up will be used to allocate patients to a study or control group determined by the presence or absence of AF as defined by ILR monitoring.

Results

Baseline data collection, noninvasive electrocardiographic data analysis, and imaging postprocessing will be performed at the time of enrollment. Primary analysis will be performed following 12 months of continuous ILR monitoring, with interim and delayed analyses performed at 6 months and 2 and 3 years, respectively.

Conclusion

The CARM-AF Study will use atrial structural and electrocardiographic metrics to identify patients with AF, or at high risk of developing AF, who may benefit from early initiation of anticoagulation.

Optimal Ablation Settings Predicting Durable Scar Detected Using LGE-MRI after Modified Left Atrial Anterior Line Ablation

(1) Background: The modified anterior line (MAL) has been described as an alternative to the mitral isthmus line. Despite better ablation results, achieving a bidirectional line block can be challenging. We aimed to investigate the ablation parameters that determine a persistent scar on late-gadolinium enhancement magnet resonance imaging (LGE-MRI) as a surrogate parameter for successful ablation 3 months after MAL ablation. (2) Methods: Twenty-four consecutive patients who underwent a MAL ablation have been included. The indication for MAL was perimitral flutter (n = 5) or substrate ablation in the diffuse anterior left atrial (LA) low-voltage area in persistent atrial fibrillation (AF) (n = 19). The MAL was divided into three segments: segment 1 (S1) from mitral annulus to height of lower region of left atrial appendage (LAA) antrum; segment 2 (S2) height of lower region of LAA antrum to end of upper LAA antrum; segment 3 (S3) from end of upper LAA antrum to left superior pulmonary vein. Ablation was performed using a contact force irrigated catheter with a power of 40 Watt and guided by automated lesion tagging and the Ablation Index (AI). The AI target was left to the operator’s choice. An inter-lesion distance of ≤6 mm was recommended. The bidirectional block was systematically evaluated using stimulation maneuvers at the end of procedure. All patients underwent LGE-MRI imaging at 3 months, regardless of symptoms, to identify myocardial lesions (scars). (3) Results: Bidirectional MAL block was achieved in all patients. LGE-MRI imaging revealed scarring in 45 of 72 (63%) segments. In all three segments of MAL, ablation time and AI were significantly higher in scarred areas compared with non-scar areas. The mean AI value to detect a durable scar was 514.2 in S1, 486.7 in S2 and 485.9 in S3. The mean ablation time to detect a scar was 20.4 s in S1, 22.1 s in S2 and 20.2 s in S3. Mean contact force and impedance drop were not significantly different between scar and non-scar areas. (4) Conclusions: Targeting optimal AI values is crucial to determine persistent left atrial scars on an LGE-MRI scan 3 months after ablation. AI guided linear left atrial ablation seems to be effective in producing durable lesions.

LA-Net: A Multi-Task Deep Network for the Segmentation of the Left Atrium

Although atrial fibrillation (AF) is the most common sustained atrial arrhythmia, treatment success for this condition remains suboptimal. Information from magnetic resonance imaging (MRI) has the potential to improve treatment efficacy, but there are currently few automatic tools for the segmentation of the atria in MR images. In the study, we propose a LA-Net, a multi-task network optimised to simultaneously generate left atrial segmentation and edge masks from MRI. LA-Net includes cross attention modules (CAMs) and enhanced decoder modules (EDMs) to purposefully select the most meaningful edge information for segmentation and smoothly incorporate it into segmentation masks at multiple-scales. We evaluate the performance of LA-Net on two MR sequences: late gadolinium enhanced (LGE) atrial MRI and atrial short axis balanced steady state free precession (bSSFP) MRI. LA-Net gives Hausdorff distances of 12.43 mm and Dice scores of 0.92 on the LGE (STACOM 2018) dataset and Hausdorff distances of 17.41 mm and Dice scores of 0.90 on the bSSFP (in-house) dataset without any post-processing, surpassing previously proposed segmentation networks, including U-Net and SEGANet. Our method allows automatic extraction of information about the LA from MR images, which can play an important role in the management of AF patients.

Extent of Left Atrial Fibrosis Correlates with Descending Aorta Proximity at 3D Late Gadolinium Enhancement Cardiac MRI in Patients with Atrial Fibrillation

PURPOSE

To determine whether the distance between the descending aorta and left atrial (LA) wall correlates with the amount of fibrosis quantified in the posterior left inferior pulmonary vein (LIPV) area of the LA in patients with atrial fibrillation (AF).

MATERIALS AND METHODS

In this retrospective study, patients with AF underwent cardiac MRI in sinus rhythm prior to a pulmonary vein isolation procedure (July 2018 to February 2020). The mean distance (distance_mean) and shortest distance (distance_short) between the descending aorta and the LA wall were measured on three-dimensional (3D) contrast-enhanced MR angiograms; distance_mean was defined as the average of five measurements at different levels between the descending aorta and the LA wall. The extent of LA fibrosis, both global fibrosis and regional fibrosis within the LIPV area, was derived from postprocessed, 3D, late gadolinium-enhanced images. Associations between the extent of fibrosis and the proximity of the descending aorta were analyzed by using correlative and multivariable analyses.

RESULTS

A total of 47 (mean age, 60 years ± 8 [standard deviation]; 31 men) patients were included for analysis. The extent of fibrosis in the posterior LIPV area was correlated with the distance_mean (r _s = -0.48; P < .01) and distance_short (r _s = -0.49; P < .01). Patients with a short distance between the descending aorta and LA wall (defined as a distance_short < 2 mm) had a higher percentage of fibrosis in the posterior LIPV area than patients with a distance_short greater than 2 mm (38.7% ± 22.7 vs 21.2% ± 17.8; P < .01).

CONCLUSION

The distance between the descending aorta and LA was correlated with the extent of quantified fibrosis within the posterior LIPV area.Keywords: MRI, Cardiac, Left Atrium Supplemental material is available for this article. © RSNA, 2022.

Left atrial evaluation by cardiovascular magnetic resonance: sensitive and unique biomarkers

Left atrial (LA) imaging is still not routinely used for diagnosis and risk stratification, although recent studies have emphasized its importance as an imaging biomarker. Cardiovascular magnetic resonance is able to evaluate LA structure and function, metrics that serve as early indicators of disease, and provide prognostic information, e.g. regarding diastolic dysfunction, and atrial fibrillation (AF). MR angiography defines atrial anatomy, useful for planning ablation procedures, and also for characterizing atrial shapes and sizes that might predict cardiovascular events, e.g. stroke. Long-axis cine images can be evaluated to define minimum, maximum, and pre-atrial contraction LA volumes, and ejection fractions (EFs). More modern feature tracking of these cine images provides longitudinal LA strain through the cardiac cycle, and strain rates. Strain may be a more sensitive marker than EF and can predict post-operative AF, AF recurrence after ablation, outcomes in hypertrophic cardiomyopathy, stratification of diastolic dysfunction, and strain correlates with atrial fibrosis. Using high-resolution late gadolinium enhancement (LGE), the extent of fibrosis in the LA can be estimated and post-ablation scar can be evaluated. The LA LGE method is widely available, its reproducibility is good, and validations with voltage-mapping exist, although further scan-rescan studies are needed, and consensus regarding atrial segmentation is lacking. Using LGE, scar patterns after ablation in AF subjects can be reproducibly defined. Evaluation of 'pre-existent' atrial fibrosis may have roles in predicting AF recurrence after ablation, predicting new-onset AF and diastolic dysfunction in patients without AF. LA imaging biomarkers are ready to enter into diagnostic clinical practice.

Late gadolinium enhancement-MRI determines definite lesion formation most accurately at 3 months post ablation compared to later time points

AIMS

Neither the long-term development of ablation lesions nor the capability of late gadolinium enhancement (LGE)-MRI to detect ablation-induced fibrosis at late stages of scar formation have been defined. We sought to assess the development of atrial ablation lesions over time using LGE-MRI and invasive electroanatomical mapping (EAM).

METHODS AND RESULTS

Ablation lesions and total atrial fibrosis were assessed in serial LGE-MRI scans 3 months and >12 months post pulmonary vein (PV) isolation. High-density EAM performed in subsequent repeat ablation procedures served as a reference. Serial LGE-MRI of 22 patients were analyzed retrospectively. The PV encircling ablation lines displayed an average LGE, indicative of ablation-induced fibrosis, of 91.7% ± 7.0% of the circumference at 3 months, but only 62.8% ± 25.0% at a median of 28 months post ablation (p < 0.0001). EAM performed in 18 patients undergoing a subsequent repeat procedure revealed that the consistent decrease in LGE over time was owed to a reduced detectability of ablation-induced fibrosis by LGE-MRI at time-points > 12 months post ablation. Accordingly, the agreement with EAM regarding detection of ablation-induced fibrosis and functional gaps was good for the LGE-MRI at 3 months (κ .74; p < .0001), but only weak for the LGE-MRI at 28 months post-ablation (κ .29; p < .0001).

CONCLUSION

While non-invasive lesion assessment with LGE-MRI 3 months post ablation provides accurate guidance for future redo-procedures, detectability of atrial ablation lesions appears to decrease over time. Thus, it should be considered to perform LGE-MRI 3 months post-ablation rather than at later time-points > 12 months post ablation, like for example, prior to a planned redo-ablation procedure.

Effect of DrOnedarone on atrial fibrosis progression and atrial fibrillation recurrence postablation: Design of the EDORA randomized clinical trial

Background

Atrial fibrillation (AF) recurrence after catheter ablation is associated with worse outcomes and quality of life. Left atrial (LA) structural remodeling provides the essential substrate for AF perpetuation. Baseline extent and the progression of LA fibrosis after ablation are strong predictors of postprocedural AF recurrence. Dronedarone is an antiarrhythmic drug proven to efficiently maintain sinus rhythm.

Objective

We sought to investigate the effect of the antiarrhythmic drug Dronedarone in decreasing LA fibrosis progression and AF recurrence after ablation of AF patients.

Methods

EDORA (NCT04704050) is a multicenter, prospective, randomized controlled clinical trial. Patients with persistent or paroxysmal AF undergoing AF ablation will be randomized into Dronedarone versus placebo/standard of care. The co‐primary outcomes are the recurrence of atrial arrhythmias (AA) within 13 months of follow‐up after ablation and the progression of left atrial fibrosis postablation. All patients will receive a late‐gadolinium enhancement magnetic resonance imaging at baseline, 3‐ and 12‐month follow‐up for the quantification of LA fibrosis and ablation‐related scarring. AA recurrence and burden will be assessed using a 30‐day ECG patch every 3 months with daily ECG recordings in between. Quality of life improvement is assessed using the AFEQT and AFSS questionnaires.

Conclusion

EDORA will be the first trial to assess the progression of LA structural remodeling after ablation and its association with Dronedarone treatment and ablation success in a randomized controlled fashion. The trial will provide insight into the pathophysiology of AF recurrence after ablation and may provide potential therapeutic targets to optimize procedural outcomes.

How to do left atrial late gadolinium enhancement: a review

BACKGROUND

Quantification of left atrial late gadolinium enhancement is a powerful clinical and research tool. Fibrosis burden has been shown to predict the success of pulmonary vein isolation, post-ablation reoccurrence, and major adverse cardiovascular events such as stroke.

OVERVIEW

The standardized cardiovascular magnetic resonance imaging protocols 2020 update describes the key components of the examination. This review is a more in-depth guide, geared toward building left atrial late gadolinium enhancement imaging from the ground up. The standard protocol consists of the following: localization, pulmonary vein magnetic resonance angiography, cardiac cines, left ventricular, and atrial late gadolinium enhancement. We also review typical segmentation and post-processing techniques, as well as discuss pitfalls, limitations, and potential future innovations in this area.

CONCLUSIONS

With sufficient experience and optimized protocols, left atrial late gadolinium enhancement imaging is a strong addition to the cardiac magnetic resonance imaging repertoire.

Left atrial fibrosis progression detected by LGE-MRI after ablation of atrial fibrillation

BACKGROUND

Left atrial (LA) fibrosis is thought to be a substrate for atrial fibrillation (AF) and can be quantified by late gadolinium enhancement magnetic resonance imaging (LGE-MRI). Fibrosis formation in LA is a dynamic process and may either progress or regress following AF ablation. We examined the impact of postablation progression in LA fibrosis on AF recurrence.

METHODS

LA enhancement in LGE-MRI was quantified in 127 consecutive patients who underwent first time AF ablation. Serial LGE-MRIs were done prior to AF ablation, 3 months postablation and at least 12 months after second LGE-MRI. Transient postablation lesion (TL) was defined as atrial enhancement caused by ablation lesions that was detected on the first (3 month) but not on the second postablation LGE-MRI. New fibrosis (NF) was defined as atrial enhancement detected on the most recent LGE-MRI, at least 15 months after the ablation procedure. AF recurrence and its correlation with TL and NF was assessed in all patients during the follow-up period.

RESULTS

An increase of 1% NF increased the chance of postablation AF recurrence by 3% (hazard ratio [HR] 1.03, 95% CI 1-1.06, P = .05). TL had no significant impact on recurrence (P = .057). After adjusting for cardiovascular risk factors, HR increased as NF became greater. Greater volume of NF (≥21%) corresponded with lower arrhythmia-free survival (37% vs 62%, P = .01).

CONCLUSION

NF formation postablation of AF is a novel marker of long-term procedural outcome. Extensive NF is associated with significantly higher risk of atrial arrhythmia recurrence.

CemrgApp: An interactive medical imaging application with image processing, computer vision, and machine learning toolkits for cardiovascular research

Personalised medicine is based on the principle that each body is unique and will respond to therapies differently. In cardiology, characterising patient specific cardiovascular properties would help in personalising care. One promising approach for characterising these properties relies on performing computational analysis of multimodal imaging data. An interactive cardiac imaging environment, which can seamlessly render, manipulate, derive calculations, and otherwise prototype research activities, is therefore sought-after. We developed the Cardiac Electro-Mechanics Research Group Application (CemrgApp) as a platform with custom image processing and computer vision toolkits for applying statistical, machine learning and simulation approaches to study physiology, pathology, diagnosis and treatment of the cardiovascular system. CemrgApp provides an integrated environment, where cardiac data visualisation and workflow prototyping are presented through a common graphical user interface.

Cardiac MRI and Fibrosis Quantification

Left atrial fibrosis plays an important role in the pathophysiology of atrial fibrillation. Left atrial ablation is an effective and increasingly used strategy to restore and maintain sinus rhythm in patients with atrial fibrillation. Late gadolinium enhancement (LGE) MRI and custom image analysis software have been used to visualize and quantify preablation atrial fibrosis and postablation scar and new fibrosis formation. This article reviews technical aspects of imaging atrial fibrosis/scar by LGE-MRI; use of atrial fibrosis and scar in predicting outcomes; applications of LGE-MRI to assess ablation lesions and optimize ablation parameters while avoiding collateral damage.

Journal of Cardiovascular Magnetic Resonance: 2017/2018 in review

There were 89 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2017, including 76 original research papers, 4 reviews, 5 technical notes, 1 guideline, and 3 corrections. The volume was down slightly from 2017 with a corresponding 15% decrease in manuscript submissions from 405 to 346 and thus reflects a slight increase in the acceptance rate from 25 to 26%. The decrease in submissions for the year followed the initiation of the increased author processing charge (APC) for Society for Cardiovascular Magnetic Resonance (SCMR) members for manuscripts submitted after June 30, 2018. The quality of the submissions continues to be high. The 2018 JCMR Impact Factor (which is published in June 2019) was slightly lower at 5.1 (vs. 5.46 for 2017; as published in June 2018. The 2018 impact factor means that on average, each JCMR published in 2016 and 2017 was cited 5.1 times in 2018. Our 5 year impact factor was 5.82.In accordance with Open-Access publishing guidelines of BMC, the JCMR articles are published on-line in a continuus fashion in the chronologic order of acceptance, with no collating of the articles into sections or special thematic issues. For this reason, over the years, the Editors have felt that it is useful for the JCMR audience to annually summarize the publications into broad areas of interest or themes, so that readers can view areas of interest in a single article in relation to each other and contemporaneous JCMR publications. In this publication, the manuscripts are presented in broad themes and set in context with related literature and previously published JCMR papers to guide continuity of thought within the journal. In addition, as in the past two years, I have used this publication to also convey information regarding the editorial process and as a "State of our JCMR."This is the 12th year of JCMR as an open-access publication with BMC (formerly known as Biomed Central). The timing of the JCMR transition to the open access platform was "ahead of the curve" and a tribute to the vision of Dr. Matthias Friedrich, the SCMR Publications Committee Chair and Dr. Dudley Pennell, the JCMR editor-in-chief at the time. The open-access system has dramatically increased the reading and citation of JCMR publications and I hope that you, our authors, will continue to send your very best, high quality manuscripts to JCMR for consideration. It takes a village to run a journal and I thank our very dedicated Associate Editors, Guest Editors, Reviewers for their efforts to ensure that the review process occurs in a timely and responsible manner. These efforts have allowed the JCMR to continue as the premier journal of our field. This entire process would also not be possible without the dedication and efforts of our managing editor, Diana Gethers. Finally, I thank you for entrusting me with the editorship of the JCMR as I begin my 4th year as your editor-in-chief. It has been a tremendous experience for me and the opportunity to review manuscripts that reflect the best in our field remains a great joy and highlight of my week!

Verification of threshold for image intensity ratio analyses of late gadolinium enhancement magnetic resonance imaging of left atrial fibrosis in 1.5T scans

The use of cardiovascular magnetic resonance imaging left atrial late gadolinium enhancement (LA LGE) is increasing for fibrosis evaluation though the use is still limited to specialized centres due to complex image acquisition and lack of consensus on image analyses. Analysis of LA LGE with image intensity ratio (IIR) (pixel intensity of atrial wall normalized by blood pool intensity) provides an objective method to obtain quantitative data on atrial fibrosis. A threshold between healthy myocardium and fibrosis of 1.2 has previously been established in 3T scans. The aim of the study was to reaffirm this threshold in 1.5T scans. LA LGE was performed using a 1.5T magnetic resonance scanner on: 11 lone-AF patients, 11 age-matched healthy volunteers (aged 27-44) and 11 elderly patients without known history of AF but varying degrees of comorbidities. Mean values of IIR for all healthy volunteers +2SD were set as upper limit of normality and was reproduced to 1.21 and the original IIR-threshold of 1.20 was maintained. The degree of fibrosis in lone-AF patients [median 9.0% (IQR 3.9-12.0)] was higher than in healthy volunteers [2.8% (1.3-8.3)] and even higher in elderly non-AF [20.1% (10.2-35.8), p = 0.001]. The previously established IIR-threshold of 1.2 was reaffirmed in 1.5T LA LGE scans. Patients with lone AF presented with increased degrees of atrial fibrosis compared to healthy volunteers in the same age-range. Elderly patients with no history of AF showed significantly higher degrees of fibrosis compared to both groups with younger individuals.

Atrial Fibrosis by Late Gadolinium Enhancement Magnetic Resonance Imaging and Catheter Ablation of Atrial Fibrillation: 5-Year Follow-Up Data

Background

Late gadolinium enhancement magnetic resonance imaging is an effective tool for assessment of atrial fibrosis. The degree of left atrial fibrosis is a good predictor of atrial fibrillation (AF) ablation success at 1 year, but the association between left atrial fibrosis and long‐term ablation success has not been studied.

Methods and Results

Late gadolinium enhancement magnetic resonance images of sufficient quality to quantify atrial fibrosis were obtained before the first AF ablation in 308 consecutive patients. Left atrial fibrosis was classified in 4 Utah stages (I, 0–10%; II, 10–20%; III, 20–30%; and IV, >30%). Patients were followed up for up to 5 years until the time of first arrhythmia recurrence or second ablation. A total of 308 patients were included; the mean age was 64.5±12.1 years, and 63.4% were men. During follow‐up, 157 patients experienced an arrhythmia recurrence and 106 patients underwent a repeated ablation. A graded effect was observed in which patients with more advanced atrial fibrosis were more likely to experience recurrent AF (hazard ratio for stage IV versus stage I, 2.73; 95% confidence interval, 1.57–4.75) and undergo a repeated ablation (proportional odds ratio for stage IV versus stage I, 5.19; 95% confidence interval, 2.12–12.69).

Conclusions

The degree of left atrial fibrosis predicts the success of AF ablation at up to 5 years follow‐up. In patients with advanced atrial fibrosis, AF ablation is associated with a high procedural failure rate.

The Role of Cardiac Magnetic Resonance Imaging to Detect Cardiac Toxicity From Cancer Therapeutics

PURPOSE OF REVIEW

The emerging complexity of cardiac toxicity caused by cancer therapies has created demand for more advanced non-invasive methods to better evaluate cardiac structure, function, and myocardial tissue characteristics. Cardiac magnetic resonance imaging meets these needs without exposure to ionizing radiation, and with superior spatial resolution.

RECENT FINDINGS

Special applications of cardiac magnetic resonance (CMR) to assess for cancer therapy-induced cardiac toxicity include the detection of subclinical LV dysfunction through novel methods of measuring myocardial strain, detection of microcirculatory dysfunction, identification of LV and LA fibrosis, and more sensitive detection of inflammation caused by immune checkpoint inhibitors. CMR plays a significant role in the non-invasive workup of cardiac toxicity from cancer therapies, with recent advancements in the field that have opened avenues for further research and development.

Prognostic and functional implications of left atrial late gadolinium enhancement cardiovascular magnetic resonance

BACKGROUND

Left atrial (LA) late gadolinium enhancement (LGE) on cardiovascular magnetic resonance (CMR) imaging is indicative of fibrosis, and has been correlated with reduced LA function, increased LA volume, and poor procedural outcomes in cohorts with atrial fibrillation (AF). However, the role of LGE as a prognostic biomarker for arrhythmia in cardiac disease has not been examined.

METHODS

In this study, we assessed LA LGE using a 3D LGE CMR sequence to examine its relationships with new onset atrial arrhythmia, and LA and left ventricular (LV) mechanical function.

RESULTS

LA LGE images were acquired in 111 patients undergoing CMR imaging, including 66 patients with no prior history of an atrial arrhythmia. During the median follow-up of 2.7 years (interquartile range (IQR) 1.8-3.7 years), 15/66 (23%) of patients developed a new atrial arrhythmia. LA LGE ≥10% of LA myocardial volume was significantly associated with an increased rate of new-onset atrial arrhythmia, with a hazard ratio of 3.16 (95% CI 1.14-8.72), p = 0.026. There were significant relationships between LA LGE and both LA ejection fraction (r = - 0.39, p < 0.0005) and echocardiographic LV septal e' (r = - 0.24, p = 0.04) and septal E/e' (r = 0.31, p = 0.007).

CONCLUSIONS

Elevated LA LGE is associated with reduced LA function and reduced LV diastolic function. LA LGE is associated with new onset atrial arrhythmia during follow-up.

Mind the gap: Quantification of incomplete ablation patterns after pulmonary vein isolation using minimum path search

Pulmonary vein isolation (PVI) is a common procedure for the treatment of atrial fibrillation (AF) since the initial trigger for AF frequently originates in the pulmonary veins. A successful isolation produces a continuous lesion (scar) completely encircling the veins that stops activation waves from propagating to the atrial body. Unfortunately, the encircling lesion is often incomplete, becoming a combination of scar and gaps of healthy tissue. These gaps are potential causes of AF recurrence, which requires a redo of the isolation procedure. Late-gadolinium enhanced cardiac magnetic resonance (LGE-CMR) is a non-invasive method that may also be used to detect gaps, but it is currently a time-consuming process, prone to high inter-observer variability. In this paper, we present a method to semi-automatically identify and quantify ablation gaps. Gap quantification is performed through minimum path search in a graph where every node is a scar patch and the edges are the geodesic distances between patches. We propose the Relative Gap Measure (RGM) to estimate the percentage of gap around a vein, which is defined as the ratio of the overall gap length and the total length of the path that encircles the vein. Additionally, an advanced version of the RGM has been developed to integrate gap quantification estimates from different scar segmentation techniques into a single figure-of-merit. Population-based statistical and regional analysis of gap distribution was performed using a standardised parcellation of the left atrium. We have evaluated our method on synthetic and clinical data from 50 AF patients who underwent PVI with radiofrequency ablation. The population-based analysis concluded that the left superior PV is more prone to lesion gaps while the left inferior PV tends to have less gaps (p < .05 in both cases), in the processed data. This type of information can be very useful for the optimization and objective assessment of PVI interventions.