Image Intensity Ratio Research Articles

Low conduction velocity is a key factor for localisation of reentrant drivers for atrial fibrillation

Abstract Background Atrial Fibrillation (AF) is a prevalent cardiac arrhythmia globally, associated with heightened risks of stroke, dementia, and heart failure. Catheter ablation, the sole curative therapy for AF, yields suboptimal success rates for persistent AF cases. Understanding the mechanisms and dynamics of AF remains challenging, hindering treatment advancements. Novel ablation strategies aimed at targeting substrates harbouring AF reentrant drivers (RD), such as low-voltage ablation and rotor-based ablation, have yet to demonstrate superiority over the gold standard ablation strategy – pulmonary vein isolation. Purpose The purpose of the study is to integrate in-silico 3D left atrial (LA) simulations and explainable artificial intelligence (AI) to pinpoint key factors for RD localisation in persistent AF, aiming to improve the mechanistic understanding of AF and help develop a more effective ablation strategy. Methods 3D LA models were derived from magnetic resonance images of 41 patients and combined with atrial cell electrophysiology models. Persistent AF was initiated in each patient-specific LA model with fast pacing, and five functional features (action potential duration (APD), conduction velocity (CV), wavelength, APD spatial gradient, CV spatial gradient, and wavelength spatial gradient) and three structural features (fibrotic density, fibrotic entropy, and image intensity ratio) were evaluated. A random forest AI model was trained to classify phase singularities corresponding to the RDs (PS-RD) in five distinct tissue classes (total LA tissue, healthy tissue, fibrotic border zone, dense fibrotic tissue, and PS-RD tissue) based on the functional and structural features. Shapley additive explanations (SHAP) analysis was then used to find the most influential feature in the AI model’s decision process. Results Simulations of the patient-specific LA models revealed that RDs were typically localised in regions with the lowest atrial CV, which often coincided with patches of dense fibrotic tissue. In a five-fold cross-validation, the random forest AI model achieved high accuracy in classifying PS-RD regions: a mean ROC AUC of 0.99 ± 0.010, a mean F1 score of 0.86 ± 0.034, a mean recall of 0.95 ± 0.058, and a mean precision score of 0.79 ± 0.085. The further SHAP analysis revealed that low CV was the key determinant in classifying the PS-RD regions. Conclusion Our study combined AF computational modelling and explainable AI to identify the key factors in RD localisation. Both the computational and AI models concluded that low CV was the most important determinant in localising RDs. These findings provide mechanistic evidence for the efficacy of ablation strategies that target low CV atrial areas for persistent AF patients.

The correlation between left atrium voltage mapping and 3D late gadolinium enhancement cardiac magnetic resonance imaging findings in naive AF ablation candidate

Abstract Introduction The extent of the efficacy of late gadolinium enhancement cardiac MR (LGE-CMR) in depicting left atrial (LA) fibrosis in atrial fibrillation (AF) patients, compared to invasive Electroanatomical Mapping (EAM), is ongoing research field, while the highest degree of accuracy found when using ADAS program. Earlier studies focused mainly on post-ablation patients, employing segmentation (quality) and point-by-point (PBP) comparison methods. The non-invasive LGE-CMR-based fibrosis map shows promise for preprocedural planning and real-time guidance. Aim Evaluate LGE-CMR-based LA fibrosis precision in ablation-naïve AF patients using ADAS software, comparing it to the gold standard EAM using CARTO-3, in both qualitative and quantitative methods. Methods Patients planned for first CARTO-based AF ablation, undergoing pre-ablation LGE-CMR. 3D substrate atrial maps were generated via ADAS based on LGE-CMR (CMR-fib) and via CARTO as EAM. Normal range LA voltage was defined by Image Intensity Ratio of 1.2-1.32 on ADAS and by 0.2-0.5mV on Carto. Comparison methods, qualitative segmentation and PBP quantitative, with EAM serving as the gold standard. Results 24 naive patients included in the study (mean age 63.5 ± 10.9 yrs; 7 females, 15 paroxysmal AF, 17 maps during sinus). Segmental qualitative analysis (384 segments) showed 77% scarred segments, predominantly small scars (up to ⅓ segment). Compared with EAM, the CMR had 68.4% agreement, with 80.4% sensitivity, 78% PPV, 36.6% specificity, 32.6% NPV , kappa 0.139 AUC 0.567. Better agreement was found for dense scar. PBP quantitative comparison (41,345 points) demonstrated 50% scarred points, with 89% accuracy between EAM and CMR, with 49.6% sensitivity, 99.7% specificity, 99.5% PPV, and 73.5% NPV kappa 0.53, AUC 0.747. In both methods, agreement was worse for LA roof and best for AP and septal wall. Conclusion LGE-CMR tends to underestimate scar presence in naive patients compared to EAM, potentially due to baseline voltage scars, which are less dense compared to iatrogenic scar, the voltage criteria for scar in literature. Sensitivity is higher in segmental comparison, while specificity is superior in PBP, consistent with expectations of minimizing the size of comparison (from a segment to point). Hence, qualitative segmental method is better when assessing overall scarring, while PBP for assessing smaller specific areas. PBP comparisons exhibit less bias than segmental comparisons, which are overly sensitive to small scars. The diminished reliability of the LA roof is probably due to the margin of the CMR scan. Our study result regarding low sensitivity and high specificity of PBP aligns with a prior study investigating naïve patients through PBP comparisons, highlighting the need for a larger-scale study to assess LGE-CMR accuracy, considering various wall thicknesses and establishing scar thresholds on ADAS and CARTO software, for ablation-naïve patients with LA body scars.PBP projection on LA bodyAUC for PBP comprasion

The correlation between left atrium voltage mapping and 3D late gadolinium enhancement cardiac magnetic resonance imaging findings in patients with known atrial fibrillation

Abstract Introduction The non-invasive cardiac magnetic resonance imaging-based late gadolinium enhancement (LGE-CMR) of the left atrium (LA) fibrosis distribution and degree can be utilized for preprocedural planning and real-time guidance of AF ablation. There is an ongoing discussion with somewhat conflicting results regarding the accuracy of LGE-CMR of the LA as compared with the invasive electroanatomical mapping (EAM). Earlier data mainly encompassed post-ablation patients with an EAM involving a relatively small number of acquired points. Aim To evaluate the accuracy of LGE-CMR-based LA fibrosis using the ADAS 3D LA software among ablation-naive AF patients as compared with EAM using the CARTO-3 navigation system. Methods Patients with non-permanent AF, naive to previous ablation/cardiac surgery, who underwent CARTO-based AF ablation with preceding LGE-CMR scan were selected for the study. The 3D substrate atrial maps were generated based on the LGE-CMR (CMR-fib) using the ADAS 3D LA software and the CARTO EAM (EAM-fib). A fibrosis threshold of 1.2-1.32 was established for the CMR-fib using the Image Intensity Ratio whereas a threshold of 0.2-0.5mV was applied for the EAM-fib. The two 3D-maps were assessed for fibrosis using anatomically synchronized quantitative point by point comparison. The EAM was set as the gold standard. Results The study included 26,777 points acquired from 17 patients (aged 65.8±7.92 yrs with 6 females and 10 paroxysmal AF cases). CMR-fib showed 22.0% of LGE, while the EAM-fib demonstrated 48.8% of low voltage areas. The CMR-fib vs. EAM-fib point by point comparison concluded with an agreement of 73.1% and interrater reliability of 0.45 (p<0.001). The sensitivity and specificity were 45.0% and 99.9%, respectively, while the PPV and NPV were 99.8% and 65.6%, respectively. The Area Under the Curve (AUC) was calculated as 72.4. Increase of the EAM-fib threshold for scar (to 0.5-1.5mV) led to a further decrease in the assessment diagnostic performance and the interrater reliability. The lowest agreement was tested in the LA roof segments and the higher in the inferoseptal and posterior walls. Conclusion The LGE-CMR underestimates the presence of scar as presented by the EAM, however, those detected are mostly accurate. The low sensitivity that was demonstrated between the two methods may be attributed to the lower spatial resolution of the CMR as well as the superficial subendocardial layer mapped by EAM as compared with the averaged transmural mapping of the CMR-fib. A follow-up larger-scale study is required to assess the accuracy of LGE-CMR-based assessment of fibrosis, considering various wall thicknesses and establishing the scar threshold on the ADAS software, particularly for ablation-naive patients.

Impact of iNAV and dNAV 3D LGE-CMR on the assessment of atrial fibrosis in atrial fibrillation patients

Abstract Background Late gadolinium enhanced (LGE) cardiac magnetic resonance (CMR) imaging serves as a valuable non-invasive tool for visualizing and quantifying left atrial (LA) fibrosis in atrial fibrillation (AF) patients. The extent of pre-procedural LA-LGE, indicative of native atrial fibrosis, has proven to be a predictor of AF recurrence risk following AF ablation. Consequently, assessing the LA fibrotic burden has emerged as a potential guide for personalized patient management. Currently, most centers engaged in LA-LGE image acquisition apply a scan protocol based on a diaphragmatic navigator-gated 3D image strategy (dNAV). Recently introduced image navigated (iNAV) 3D LGE strategies are proposed to outperform the dNAV strategy. This advancement involves the dynamic tracking of the heart's respiratory position with an image reconstruction algorithm, yielding motion-compensated images in significantly reduced and more consistent scan durations. We performed an evaluation of the novel image navigated (iNAV) 3D LGE-CMR imaging strategy in comparison to the conventional diaphragm navigated (dNAV) 3D LGE-CMR strategy. Methods In twenty-six consecutive AF patients, both imaging techniques (i.e. iNAV and dNAV) were performed subsequently, with equivalent spatial resolution and timing in the cardiac cycle. Patients were randomized in the acquisition order of iNAV and dNAV. LA fibrosis was quantified (percentage of atrial fibrosis using image intensity ratio threshold 1.2) and overlap in atrial fibrosis areas was tested between the two methods. Results Acquisition time of iNAV was significantly lower compared to dNAV (5±1 minutes vs. 12±4 minutes, p<0.001, respectively). There was a significant correlation between the iNAV and dNAV LA fibrotic burden (r=0.69, p<0.001). LA fibrosis scores were lower for iNAV compared to dNAV (12±8% vs. 20±12%, p<0.001, respectively). Spatial correspondence between the atrial fibrosis maps was modest (Dice similarity coefficient 0.43±0.15). Notably, 13/23 (56%) patients underwent a shift in their UTAH fibrosis stage classification, depending on the chosen imaging strategy. Conclusion iNAV acquisition was more than twice as fast as dNAV, and iNAV resulted in a lower atrial fibrosis score as compared to dNAV. More than half of the patients were reclassified into a different UTAH fibrosis stage depending on the employed imaging strategy. This underscores the critical importance of recognizing that the choice of imaging strategy significantly impacts the categorization of patients into their respective fibrosis stages. This distinction carries potential clinical implications when evaluating the utility of UTAH fibrosis stages in the context of AF management and therapeutic decision-making, as patients in lower fibrosis stages are generally regarded as more suitable candidates for ablation, while those categorized in higher fibrosis stages face an increased risk of arrhythmia recurrence following PVI.Figure 1Figure 2

Magnetic Resonance Imaging Features for Differentiating Low-Grade and High-Grade Malignant Peripheral Nerve Sheath Tumors.

This study aimed to assess the usefulness of magnetic resonance imaging (MRI) findings for differentiating low-grade and high-grade malignant peripheral nerve sheath tumors (MPNSTs). This study included 31 patients (onset age range, 19-83 years; mean onset age, 57 years; 9 men and 22 women) with 36 histopathologically proven MPNSTs (7 low-grade MPNSTs and 29 high-grade MPNSTs) who underwent preoperative MRI between December 2007 and October 2022. Quantitative and qualitative MRI findings were retrospectively evaluated and compared between the 2 subtypes. The maximum tumor diameter (106.1 ± 64.0 vs 54.9 ± 19.8 mm, P = 0.032) and tumor-to-muscle signal intensity ratio (SIR) of fat-suppressed gadolinium-enhanced T1-weighted images (2.69 ± 1.40 vs 1.62 ± 0.40, P = 0.005) were significantly higher in high-grade MPNSTs than in low-grade MPNSTs. The receiver operating characteristic analysis revealed that the tumor-to-muscle SIR of fat-suppressed gadolinium-enhanced T1-weighted images exhibited the highest area under the curve value (0.88), followed by the maximum tumor diameter (0.76). The sensitivity and specificity of the tumor-to-muscle SIR of fat-suppressed gadolinium-enhanced T1-weighted images for diagnosing high-grade MPNST at an optimal SIR threshold of greater than 1.73 were 90% and 83%, respectively. However, other MRI findings showed no significant differences between the 2 subtypes ( P = 0.16-1.00). Although the MRI findings of low-grade and high-grade MPNST overlapped considerably, the maximum tumor diameter and degree of contrast enhancement can be used to differentiate low-grade MPNST from high-grade MPNST.

Abstract 14746: Association of Left Atrial Late Gadolinium Enhancement With Electrogram Abnormalities, Tissue Impedance, and Proximity to the Aorta

Introduction: Left atrial (LA) late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) predominates near the aorta(AO); however, LGE does not equate fibrosis and may be artifactual or indicate expanded interstituim. Hypothesis: We sought to examine the association of LA LGE with proximity to the descending and ascending AO and use regional impedance and voltage measurements to dissect the mechanism of LGE . Methods: The retrospective cohort included consecutive patients who underwent pre-procedural CMR and atrial fibrillation (AF) ablation between January 2016 - 2021. The association of voltage amplitude, impedance, and image intensity ratio (IIR) at each electroanatomic map point with distance from the nearest AO point was examined after adjustment for age, sex, AF type, AO stenosis, LA volume, and AO diameter. Results: Included 63 patients (age 65.5±8.8 years, 33% female). Among 42 ablation naive patients, distance from AO was unassociated with bipolar and unipolar voltage amplitudes, but associated with impedance (+0.04 ohm/mm, P=0.011) and IIR (-0.03 /mm, P<0.001). Among 21 patients with prior ablation, distance from AO was unassociated with IIR, but associated with bipolar (+0.01 mV/mm, P<0.001) and unipolar (+0.01 mV/mm, P=0.001) voltage amplitudes and impedance (+0.03 ohm/mm, P=0.025). Conclusions: Given lower impedance but normal voltage, de novo peri-AO LA-LGE likely signifies expanded interstitium, rather than fibrosis or fat infiltration. Following ablation, peri-AO voltage and impedance are both decreased compared to other LA regions, suggesting that peri-AO lesion delivery is more effective, likely due to lower impedance at baseline.

Differences in atrial substrate localization using late gadolinium enhancement-magnetic resonance imaging, electrogram voltage, and conduction velocity: a cohort study using a consistent anatomical reference frame in patients with persistent atrial fibrillation.

Electro-anatomical voltage, conduction velocity (CV) mapping, and late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) have been correlated with atrial cardiomyopathy (ACM). However, the comparability between these modalities remains unclear. This study aims to (i) compare pathological substrate extent and location between current modalities, (ii) establish spatial histograms in a cohort, (iii) develop a new estimated optimized image intensity threshold (EOIIT) for LGE-MRI identifying patients with ACM, (iv) predict rhythm outcome after pulmonary vein isolation (PVI) for persistent atrial fibrillation (AF). Thirty-six ablation-naive persistent AF patients underwent LGE-MRI and high-definition electro-anatomical mapping in sinus rhythm. Late gadolinium enhancement areas were classified using the UTAH, image intensity ratio (IIR >1.20), and new EOIIT method for comparison to low-voltage substrate (LVS) and slow conduction areas <0.2 m/s. Receiver operating characteristic analysis was used to determine LGE thresholds optimally matching LVS. Atrial cardiomyopathy was defined as LVS extent ≥5% of the left atrium (LA) surface at <0.5 mV. The degree and distribution of detected pathological substrate (percentage of individual LA surface are) varied significantly (P < 0.001) across the mapping modalities: 10% (interquartile range 0-14%) of the LA displayed LVS <0.5 mV vs. 7% (0-12%) slow conduction areas <0.2 m/s vs. 15% (8-23%) LGE with the UTAH method vs. 13% (2-23%) using IIR >1.20, with most discrepancies on the posterior LA. Optimized image intensity thresholds and each patient's mean blood pool intensity correlated linearly (R2 = 0.89, P < 0.001). Concordance between LGE-MRI-based and LVS-based ACM diagnosis improved with the novel EOIIT applied at the anterior LA [83% sensitivity, 79% specificity, area under the curve (AUC): 0.89] in comparison to the UTAH method (67% sensitivity, 75% specificity, AUC: 0.81) and IIR >1.20 (75% sensitivity, 62% specificity, AUC: 0.67). Discordances in detected pathological substrate exist between LVS, CV, and LGE-MRI in the LA, irrespective of the LGE detection method. The new EOIIT method improves concordance of LGE-MRI-based ACM diagnosis with LVS in ablation-naive AF patients but discrepancy remains particularly on the posterior wall. All methods may enable the prediction of rhythm outcomes after PVI in patients with persistent AF.

Association between Left Atrial Late Gadolinium Enhancement and Atrial Fibrillation: The Multi-Ethnic Study of Atherosclerosis (MESA).

To determine the prevalence and correlates of left atrial (LA) late gadolinium enhancement (LGE) at cardiac MRI and its association with atrial fibrillation (AF) in a population-based sample from the Multi-Ethnic Study of Atherosclerosis (MESA). In this secondary post hoc analysis of the MESA cohort (ClinicalTrials.gov no. NCT00005487), participants without AF underwent LGE cardiac MRI at the fifth examination (2010-2012). LA LGE burden was quantified using the image intensity ratio technique on biplane long-axis two-dimensional (2D) LGE images without fat saturation. Survival analysis was performed with log-rank testing and Cox regression. Of 1697 participants (mean age, 67 years ± 9 [SD]; 872 men), 1035 (61%) had LA LGE, and 75 (4.4%) developed AF during follow-up (median, 3.95 years). At univariable analysis, LA LGE was associated with age (β = .010 [95% CI: .005, .015], P < .001), diastolic blood pressure (β = .005 [95% CI: .001, .009], P = .02), HbA1c level (β = .06 [95% CI: .02, .11], P = .009), heart failure (β = .60 [95% CI: .11, 1.08], P = .02), LA volume (β = .008 [95% CI: .004, .012], P < .001), and LA function (emptying fraction, LA global longitudinal strain, LA early diastolic peak longitudinal strain rate, and LA late diastolic peak strain rate; all P < .05). After adjusting for the variables in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) AF score, LA LGE independently helped predict incident AF (hazard ratio = 1.46 [95% CI: 1.13, 1.88], P = .003). The highest tertile (LGE > 2%) was twice as likely to develop AF. Although limited by the 2D LGE technique employed, LA LGE was associated with adverse atrial remodeling and helped predict AF in a multiethnic population-based sample.Clinical trial registration no. NCT00005487Keywords: MR Imaging, Cardiac, Epidemiology Supplemental material is available for this article. © RSNA, 2023.

In silico biatrial fibrosis ablation improves atrial fibrillation outcome

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Medical Research Council Fellowship Background In DECAAF II, left atrial (LA) fibrosis ablation plus PVI did not improve AF outcome compared to PVI alone across the study cohort. We hypothesize that biatrial fibrosis ablation could improve AF ablation therapy outcome in a subset of patients with properties identified through a large virtual in silico trial. Purpose To investigate the effects of anatomy, fibrosis distribution, and LGE-MRI threshold on ablation outcome using a virtual cohort of 4000 patients. Methods We constructed 1000 biatrial models from a statistical shape model and we mapped pectinate muscles, Bachmann’s bundle and fibers from an atlas. For each of the 1000 anatomies we applied a randomly selected fibrosis map from a library of 100 clinical maps. We then created four versions of each case by assigning one of four randomly selected right atrial (RA) fibrosis distributions with Utah grades 1-4 (Fig 1A), giving 4000 virtual patients. Four ablation approaches were applied to each patient model after 5 seconds of AF: PVI, PVI &amp; LA fibrosis, PVI &amp; RA fibrosis, PVI &amp; biatrial fibrosis. LGE-MRI was thresholded for fibrosis ablation at either 1.2 or 1.32 image intensity ratio (IIR). The outcome was classified 5 seconds post ablation. Results Biatrial fibrosis ablation is more effective than LA ablation. For patients with high (Utah 4) RA fibrosis, biatrial fibrosis ablation increases AF termination compared to LA fibrosis ablation (Figs 1B &amp; 2A: 62% vs 14%), this compares to cases with low (Utah 1) RA fibrosis (21% vs 14%). For patients with high LA (Utah 4) fibrosis, biatrial ablation is more effective than LA ablation (Fig 2B: 52% vs 19%), this compares to patients with low (Utah 1) LA fibrosis (17% vs 7%). Increasing IIR threshold for ablation decreases termination (LA fibrosis ablation: 15.8% termination at IIR 1.2, 11.0% at IIR 1.32; biatrial: 41.5% at IIR1.2; 20.3% at IIR1.32). Anatomy has a larger effect on biatrial ablation outcome (31.2% of outcomes change between anatomies) than on PVI only ablation outcome (20.0% change). Conclusion Biatrial fibrosis ablation is superior to LA fibrosis ablation for cases with high RA fibrosis. Biatrial fibrosis distribution should be considered when targeting AF ablation therapy.

Predictors of atrial flutter recurrence after atrial fibrillation ablation: the crucial role of structural and morphological left atrial remodeling

Abstract Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Unrestricted Grant - Abbott Medical Introduction Recurrence of supraventricular tachyarrhythmias after catheter ablation of atrial fibrillation (AF) is common, representing 30% of patients. Although AF recurrence occurs mostly, 10% of the patients face arrhythmia recurrence through atypical atrial flutter (AFL). The diagnostic and therapeutic management of atypical AFL is challenging. Predicting atypical AFL after AF catheter ablation is critical. Purpose To identify morphological and structural predictors of recurrence in the form of atypical AFL compared to AF based on Late Gadolinium Enhancement Cardiac Magnetic Resonance (LGE-CMR). Methods – From January 2013 to December 2021, 56 patients facing post AF-CA atypical AFL were included in the monocentric and retrospective cohort. 112 patients with AF recurrence were randomly included in the cohort from the general database. Pre-procedure LGE-CMR was post-processed for every patient to assess global and regional left and right atrial (LA, RA) fibrosis quantification using an image intensity ratio &amp;gt; 1.32 as fibrosis. Sphericity was calculated as the percentage of similarity with respect to a sphere, and the volume of LA and RA were calculated. Results – 168 patients who had faced supraventricular arrhythmia recurrence after AF-CA were included in the monocentric retrospective cohort. They were mainly male (72.1%), with a median CHADS-VASc score of 1.4 +/- 1.3, a number of previous CA of 2,2 +/- 0.4, and a biatrial dilation (LA volume index of 53.5 ml/m2, RA volume index of 59.6 ml/m2). An age superior to 65 (OR=6.61, CI95%:2.18-14.41, p&amp;lt;0.01), the number of previous CA procedures (OR=3.03, CI95%:1.17-7.81, p=0.02), a history of management of invasive additional lines (OR=2.48, CI95%:1.01-6.27, p=0.05), an elevated LA sphericity (OR=1.33, CI95%:1.11-1.59, p&amp;lt;0.01) and an increased LA fibrotic burden (OR=1.03, CI95%:1.00-1.07, p=0.04) independently predicted the occurrence of atypical AFL compared with AF recurrence after AF-CA (Figure 1). Specifically, an increased amount of fibrosis in the lateral LA zone area (OR=1.03, CI95%:1.01-1.04, p&amp;lt;0.01)] was an independent predictor of recurrence in the form of atypical AFL compared with AF recurrence (Figure 2). Conclusion The structural LA remodeling of AE, including LA fibrosis and LA sphericity, is a predictor of recurrence in the form of atypical atrial flutter compared with AF recurrence after AF-CA.

PO-01-151 DEGREE OF FIBROSIS REMODELING ALTERS ATRIAL FIBRILLATION INDUCIBILITY

Mechanistically, the role of remodeled substrate in atrial fibrillation (AF) inducibility is not well understood. Here we assess the changes in AF reentrant-drivers (RDs) based on different levels of fibrotic remodeling – as visualized by degree of enhancement in late gadolinium enhancement (LGE) MRI. We compare the inducibility of the native fibrotic substrates in patients undergoing first-time ablation (FtA) and in those of repeat ablation (ReA) and characterize the regions most involved in RD maintenance. To investigate how different levels of fibrotic remodeling (enhancement in LGE MRI) affect AF inducibility. Ten LGE MRIs were obtained from AF patients undergoing FtA (n=5) or ReA (n=5). Fibrotic tissue was differentiated using personalized image intensity ratio (IIR) threshold; for scar, we used IIR=1.61; and the IIR for dense fibrosis was the midpoint between the two (Fig. 1B). For each patient, two personalized bi-atrial models were constructed: baseline and multi-level fibrosis. The baseline model includes only two tissue types – normal myocardium and fibrotic tissue; the multi-level fibrosis model for FtA has the addition of dense fibrosis, and for ReA, dense fibrosis and scar (Fig. 1C). Each model was tested for AF inducibility by rapid pacing from 40 uniformly distributed bi-atrial sites (Fig. 1D). RD-harboring regions were “cut out” (Fig. 1E) and the volumetric fraction of each substrate in each region was calculated (Fig. 1F). The ReA group had on average more remodeled tissue (29.11%) than the FtA group (20.05%). While the ReA group did not have more RDs than the FtA group, their RDs were more frequently inducible (from different pacing sites) compared to the RDs in the FtA group (usually inducible from just one pacing site). In general, one model was not found to be more arrhythmogenic than the other. For 7/10 patients, the model-pair produced at least one common RD. In all models, RDs required at least 30% of remodeled tissue within the local RD region. In ReA multi-level fibrosis models, RD-harboring regions had tissue significantly more remodeled (72.34%) than RD-harboring regions in baseline models (36.59%; p<0.0001). Different levels of fibrotic remodeling result in different levels of AF inducibility. These insights might be important in predicting ablation targets in AF patients.

PO-02-197 PREDICTORS OF ATRIAL FLUTTER RECURRENCE AFTER ATRIAL FIBRILLATION ABLATION: THE CRUCIAL ROLE OF STRUCTURAL AND MORPHOLOGICAL LEFT ATRIAL REMODELING

Recurrence of supraventricular tachyarrhythmias after catheter ablation of atrial fibrillation (AF) is common, representing 30% of patients. Although AF recurrence occurs mostly, 10% of the patients face arrhythmia recurrence through atypical atrial flutter (AFL). The diagnostic and therapeutic management of atypical AFL is challenging. Predicting atypical AFL after AF catheter ablation is critical. To identify morphological and structural predictors of recurrence in the form of atypical AFL compared to AF based on Late Gadolinium Enhancement Cardiac Magnetic Resonance (LGE-CMR). From January 2013 to December 2021, 56 patients facing post-AF-CA atypical AFL were included in the monocentric and retrospective cohort. 112 patients with AF recurrence were randomly included in the cohort from the general database. Pre-procedure LGE-CMR was post-processed for every patient to assess global and regional left and right atrial (LA, RA) fibrosis quantification using an image intensity ratio > 1.32 as fibrosis. Sphericity was calculated as the percentage of similarity with respect to a sphere, and the volume of LA and RA were calculated. 168 patients who had faced supraventricular arrhythmia recurrence after AF-CA were included in the monocentric retrospective cohort. They were mainly male (72.1%), with a median CHADS-VASc score of 1.4 +/- 1.3, a number of previous CA of 2,2 +/- 0.4, and a biatrial dilation (LA volume index of 53.5 ml/m2, RA volume index of 59.6 ml/m2). An age superior to 65 (OR=6.61, CI95%:2.18-14.41, p<0.01), the number of previous CA procedures (OR=3.03, CI95%:1.17-7.81, p=0.02), a history of management of invasive additional lines (OR=2.48, CI95%:1.01-6.27, p=0.05), an elevated LA sphericity (OR=1.33, CI95%:1.11-1.59, p<0.01) and an increased LA fibrotic burden (OR=1.03, CI95%:1.00-1.07, p=0.04) independently predicted the occurrence of atypical AFL compared with AF recurrence after AF-CA (Figure). Specifically, an increased amount of fibrosis in the lateral LA zone area (OR=1.03, CI95%:1.01-1.04, p<0.01)] was an independent predictor of recurrence in the form of atypical AFL compared with AF recurrence (Table). The structural LA remodeling of AE, including LA fibrosis and LA sphericity, is a predictor of recurrence in the form of atypical atrial flutter compared with AF recurrence after AF-CA.

Quantitative late gadolinium enhancement cardiac magnetic resonance analysis of the relationship between ablation parameter and left atrial tissue lesion following pulmonary vein isolation.

The impact of ablation parameters on acute tissue lesion formation after pulmonary vein isolation (PVI) has not been sufficiently evaluated in patients with atrial fibrillation. Radiofrequency ablation lesion can be visualized by late gadolinium enhancement cardiac magnetic resonance (LGE-CMR). We sought to quantitatively analyze the relationship between ablation parameter and tissue lesion following PVI at different segments of pulmonary vein (PV) using LGE-CMR. Twenty-one patients with atrial fibrillation who underwent PVI procedure were retrospectively enrolled. All patients underwent LGE-CMR examination within 3 days after radiofrequency ablation. Ablation parameters during PVI were documented, including lesion size index (LSI), force-time integral (FTI), power, contact force, temperature, and time of duration. The ablation point was projected onto 3-dimensional (3D) left atrial shell constructed base on LGE-CMR and corresponding image intensity ratio (IIR) was calculated on the same shell. A tissue lesion point was defined when the LGE-CMR IIR was > 1.2. In total, 1,759 ablation points were analyzed. The ablation parameters and IIRs for each PV segment were significantly different (P < 0.0001). IIRs corresponding to ablation points at posterior of PV tended to be higher than those at non-posterior of PV when similar ablation parameters were applied during ablation. LSI was a better predictor of tissue lesion existence following PVI than FTI, contact force, power, temperature, and duration time at non-posterior wall of PV. The IIR showed positive correlation with LSI at non-posterior wall of PV (non-posterior of right PV, r = 0.13, P = 0.001, non-posterior of left PV, r = 0.26, P < 0.0001). When similar ablation parameters were applied during PVI, the posterior wall of PV had more severe tissue lesion than non-posterior wall of PV. Therefore, it was reasonable to decrease ablation energy at posterior wall of PV. Moreover, LSI was a better index to reflect tissue lesion quality following PVI at non-posterior of PV.

Elevated fibrosis burden as assessed by MRI predicts cryoballoon ablation failure.

Late-gadolinium enhancement magnetic resonance (LGE-MRI) imaging is increasingly used in management of atrial fibrillation (AFib) patients. Here, we assess the usefulness of LGE-MRI-based fibrosis quantification to predict arrhythmia recurrence in patients undergoing cryoballoon ablation. Our secondary goal was to compare two widely used fibrosis quantification methods. In 102 AF patients undergoing LGE-MRI and cryoballoon ablation (mean age 62 years; 64% male; 59% paroxysmal AFib), atrial fibrosis was quantified using the pixel intensity histogram (PIH) and image intensity ratio (IIR) methods. PIH segmentations were completed by a third-party provider as part of the standard of care at our hospital; Image intensity ratio(IIR) segmentations of the same scans were carried out in our lab using a commercially available software package. Fibrosis burdens and spatial distributions for the two methods were compared. Patients were followed prospectively for recurrent arrhythmia following ablation. Average PIH fibrosis was 15.6 ± 5.8% of the left atrial (LA) volume. Depending on threshold (IIRthr ), the average IIR fibrosis (% of LA wall surface area) ranged from 5.0 ± 7.2% (IIRthr = 1.2) to 37.4 ± 10.9% (IIRthr = 0.97). An IIRthr of 1.03 demonstrated the greatest agreement between the methods, but spatial overlap of fibrotic areas delineated by the two methods was modest (Sorenson Dice coefficient: 0.49). Fourty-two patients (41.2%) had recurrent arrhythmia. PIH fibrosis successfully predicted recurrence (HR 1.07; p = .02) over a follow-up period of 362 ± 149 days; regardless of IIRthr , IIR fibrosis did not predict recurrence. PIH-based volumetric assessment of atrial fibrosis was modestly predictive of arrhythmia recurrence following cryoballoon ablation in this cohort. IIR-based fibrosis was not predictive of recurrence for any of the IIRthr values tested, and the overlap in designated areas of fibrosis between the PIH and IIR methods was modest. Caution must therefore be exercised when interpreting LA fibrosis from LGE-MRI, since the values and spatial pattern are methodology-dependent.

The use of novel 3D dark-blood late gadolinium enhancement MRI to determine the optimal threshold for atrial scar after pulmonary vein isolation ablation

Abstract Background Dark-blood late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) is proved to be superior to bright-blood LGE MRI in localising subtle subendocardial scar in the ventricles, because of improved contrast between myocardial scar and blood. However, dark-blood LGE MRI has not yet been applied to identify atrial scar in the left atrium (LA) and therefore its threshold to determine scar is unknown. Purpose To determine the optimal intensity threshold for 3D dark-blood LGE MRI for atrial ablation scar after pulmonary vein isolation (PVI) Methods Twelve re-do PVI patients with symptomatic atrial fibrillation (AF) who underwent pre-procedural 3D dark-blood LGE MRI were included. The image intensity ratio (IIR = myocardial intensity normalized to the blood pool) from the LGE MRI were calculated using ADAS-AF. High-density bipolar voltages (BiV) maps were recorded during sinus rhythm prior to ablation. All BiV locations ≤5 mm from the ADAS LA anatomy were compared with the corresponding IIR, using custom-made software in MATLAB. To achieve an equal ratio between scar (BiV ≤0.15 mV) and non-scar (BiV &amp;gt;0.15 mV) for each patient, non-scar pairs were randomly resampled to the same number as scar pairs. This was repeated 10 times and for every random selection, receiver operating characteristics (ROC) analysis was performed to determine the optimal IIR threshold (provided by the Youden's index) for scar defined as BiV &amp;lt;0.15 mV (Figure 1). All IIR thresholds and areas under the curve were averaged to determine the overall performance and optimal IIR threshold. Results Of the 12 included patients, 8 had prior cryo PVI, 2 radiofrequency PVI, and 2 surgical/hybrid AF ablation. ROC curve analysis estimated the average optimal threshold for predicting BiV &amp;lt;0.15 mV to be an IIR of 1.106, with a mean area under the curve (AUC) of 0.73 (Figure 1). Figure 2 shows two examples of the IIR map (A), BiV map (B), and the correspondence map (C) providing information on spatial agreement between IIR and BiV. This individual qualitative assessment provides insight into the spatial variation between techniques and may facilitate future studies on the pathophysiological understanding of atrial ablation scarring. Conclusion This is the first study to use the novel 3D dark-blood whole heart LGE MRI to evaluate LA ablation scar after PVI. Based on the ROC analyses, an IIR of 1.106 is the optimal threshold for atrial ablation scar, defined as high density bipolar voltage &amp;lt;0.15 mV. Funding Acknowledgement Type of funding sources: None.

Cuantificación de la fibrosis auricular derecha mediante resonancia magnética cardiaca: verificación del método para la estandarización de umbrales

Introduction and objectivesLate 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. MethodsA 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. ResultsThe 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%. ConclusionsAn 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.

Assessment of left atrial fibrosis progression in canines following rapid ventricular pacing using 3D late gadolinium enhanced CMR images.

BackgroundAtrial fibrillation (AF) is associated with extracellular matrix (ECM) remodelling and often coexists with myocardial fibrosis (MF); however, the causality of these conditions is not well established.ObjectiveWe aim to corroborate AF to MF causality by quantifying left atrial (LA) fibrosis in cardiac magnetic resonance (CMR) images after persistent rapid ventricular pacing and subsequent AF using a canine model and histopathological validation.MethodsTwelve canines (9 experimental, 3 control) underwent baseline 3D LGE-CMR imaging at 3T followed by insertion of a pacing device and 5 weeks of rapid ventricular pacing to induce AF (experimental) or no pacing (control). Following the 5 weeks, pacing devices were removed to permit CMR imaging followed by excision of the hearts and histopathological imaging. LA myocardial segmentation was performed manually at baseline and post-pacing to permit volumetric %MF quantification using the image intensity ratio (IIR) technique, wherein fibrosis was defined as pixels > mean LA myocardium intensity + 2SD.ResultsVolumetric %MF increased by an average of 2.11 ± 0.88% post-pacing in 7 of 9 experimental dogs. While there was a significant difference between paired %MF measurements from baseline to post-pacing in experimental dogs (P = 0.019), there was no significant change in control dogs (P = 0.019 and P = 0.5, Wilcoxon signed rank tests). The median %MF for paced animals was significantly greater than that of non-paced dogs at the 5-week post-insertion time point (P = 0.009, Mann Whitney U test). Histopathological imaging yielded an average %MF of 19.42 ± 4.80% (mean ± SD) for paced dogs compared to 1.85% in one control dog.ConclusionPersistent rapid ventricular pacing and subsequent AF leads to an increase in LA fibrosis volumes measured by the IIR technique; however, quantification is limited by inherent image acquisition parameters and observer variability.

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

Introduction and objectivesLate 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. MethodsA 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. ResultsThe 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%. ConclusionsAn 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.

Atrial tissue characterisation using electroanatomic voltage mapping and cardiac magnetic resonance imaging

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Background Atrial voltage mapping and atrial cardiac magnetic resonance imaging are two contemporary methods for quantification of atrial fibrosis. However, the absence of a gold standard for measuring atrial fibrosis has precluded their direct comparison. Nevertheless, understanding the relative performance of voltage mapping and atrial late gadolinium enhancement for identification of atrial cardiomyopathy remains critical to correctly targeting clinical application of these techniques. Purpose To assess the relative performance of electroanatomic voltage mapping and atrial late gadolinium enhancement imaging using three surrogate markers chosen to distinguish pre-procedural utility (progression to recurrent atrial fibrillation following ablation) from potential utility for providing atrial fibrillation mechanistic insights (paroxysmal vs. persistent status of atrial fibrillation and relationship with co-morbidities associated with atrial fibrillation). Methods 123 patients underwent atrial late gadolinium enhancement imaging and electroanatomic voltage mapping prior to atrial fibrillation ablation. Atrial late gadolinium enhancement imaging was assessed with CEMRG software and electroanatomic voltage mapping processed with OpenEP software using previously published thresholds. Low voltage tissue was defined at (1) &amp;lt;0.5mV, (2) &amp;lt;1.17mV, and (3) &amp;lt;1.3mV. Atrial fibrosis using late gadolinium enhancement was defined using four thresholds (1) signal intensity &amp;gt;3.3 standard deviations above the blood pool mean; (2) image intensity ratio (IIR) 1.2x blood pool mean; (3) IIR 1.32x blood pool mean; and (4) IIR 0.97x blood pool mean. Results Patients with persistent atrial fibrillation and those with CHA2DS2VaSc &amp;gt;2 had increased low voltage area for each of the thresholds tested, but there was no increase in atrial late gadolinium enhancement area at any of the imaging thresholds tested. Increased atrial fibrosis using IIR&amp;gt;0.97 was independently associated with recurrence of atrial fibrillation (OR 1.05 (CI 1.01-1.09), p=0.009) in both univariate and multivariate analysis. Low voltage area &amp;lt;1.13mV and low voltage area &amp;lt;1.17mV were associated with increased risk of recurrence (OR 1.02 (CI 1.01-1.04), p=0.01, and OR 1.03 (CI 1.01-1.04), p=0.009) in univariate analysis but neither voltage threshold remained statistically significant in multivariate analysis controlling for clinical variables. Conclusion Increased fibrosis burden measured with atrial magnetic resonance imaging, but not with low voltage area, is independently associated with recurrence of atrial fibrillation following catheter ablation. However, increased low voltage area measured with electroanatomic mapping is associated with persistent atrial fibrillation status and CHADS2VaSc score. These findings support the use of magnetic resonance imaging for pre-procedure assessment and the use of electroanatomic mapping for intraprocedural mechanism-based assessment of atrial cardiomyopathy.

CA-537-02 MARKED DISCREPANCY IN LEFT ATRIAL LATE GADOLINIUM ENHANCMENT QUANTIFICATION BETWEEN TWO COMMONLY USED TECHNIQUES

Left atrial (LA) fibrosis, estimated by late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging (CMR), is a predictor of recurrent atrial fibrillation (AF) following catheter ablation. The two prevailing techniques for identification of LA LGE at present are 1) image intensity ratio (IIR) method, normalising intensity of the atrial wall by mean value of the atrial blood pool, and 2) standard deviation (SD) method analysing signal intensity distribution of the LA wall. However, there is a paucity of data comparing these techniques and no consensus exists as to the optimal quantification tool for LA LGE.