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Aims: Left atrial (LA) remodelling is a common feature of many cardiovascular pathologies and is a sensitive marker of adverse cardiovascular outcomes. The aim of this study was to establish normal ranges for LA parameters derived from coronary computed tomographic angiography (CCTA) imaging using a standardised image processing pipeline to establish normal ranges in a previously described cohort. Methods: CCTA imaging from 193 subjects recruited to the Budapest GLOBAL twin study was analysed. Indexed LA cavity volume (LACVi), LA surface area (LASAi), wall thickness and LA tissue volume (LATVi) were calculated. Wall thickness maps were combined into an atlas. Indexed LA parameters were compared with clinical variables to identify early markers of pathological remodelling. Results: LACVi is similar between sexes (31 ml/m2 v 30 ml/m2) and increased in hypertension (33 ml/m2 v 29 ml/m2, p = 0.009). LASAi is greater in females than males (47.8 ml/m2 v 45.8 ml/m2 male, p = 0.031). Median LAWT was 1.45 mm. LAWT was lowest at the inferior portion of the posterior LA wall (1.14 mm) and greatest in the septum (median = 2.0 mm) (p

The left atrium (LA) has a complex anatomy with heterogeneous wall thickness and curvature. The anatomy plays an important role in determining local wall stress; however, the relative contribution of wall thickness and curvature in determining wall stress in the LA is unknown. We have developed electromechanical finite element (FE) models of the LA using patient-specific anatomical FE meshes with rule-based myofiber directions. The models of the LA were passively inflated to 10mmHg followed by simulation of the contraction phase of the atrial cardiac cycle. The FE models predicted maximum LA volumes of 156.5 mL, 99.3 mL and 83.4 mL and ejection fractions of 36.9%, 32.0% and 25.2%. The median wall thickness in the 3 cases was calculated as $$1.32\, \pm \,0.78$$1.32±0.78 mm, $$1.21\, \pm \,0.85$$1.21±0.85 mm, and $$0.74\,\pm \,0.34$$0.74±0.34 mm. The median curvature was determined as $$0.159\,\pm \,0.080$$0.159±0.080 $$\hbox {mm}^{-1}$$mm-1, $$0.165\,\pm \,0.079\,\hbox {mm}^{-1}$$0.165±0.079mm-1, and $$0.166\,\pm \,0.077\,\hbox {mm}^{-1}$$0.166±0.077mm-1. Following passive inflation, the correlation of wall stress with the inverse of wall thickness and curvature was 0.55–0.62 and 0.20–0.25, respectively. At peak contraction, the correlation of wall stress with the inverse of wall thickness and curvature was 0.38–0.44 and 0.16–0.34, respectively. In the LA, the 1st principal Cauchy stress is more dependent on wall thickness than curvature during passive inflation and both correlations decrease during active contraction. This emphasizes the importance of including the heterogeneous wall thickness in electromechanical FE simulations of the LA. Overall, simulation results and sensitivity analyses show that in complex atrial anatomy it is unlikely that a simple anatomical-based law can be used to estimate local wall stress, demonstrating the importance of FE analyses.

Background: The Lesion Index (LSI) is a proprietary algorithm from Abbott Medical combining contact force, radiofrequency application duration, and radiofrequency current. It can be displayed during ablation with the TactiCath contact force catheter. The LSI Index was designed to provide real-time lesion formation feedback and is hypothesized to estimate the lesion diameter. Methods and Results: Before ablation, animals underwent cardiac computed tomography to assess atrial tissue thickness. Ablation lines (n=2–3 per animal) were created in the right atrium of 7 Göttingen mini pigs with point lesions (25 W). Within each line of ablation, the catheter tip was moved a prescribed distance (D/mm) according to 1 of 3 strategies: D=LSI+0 mm; D=LSI+2 mm; or D=LSI+4 mm. Two weeks after ablation, serial sections of targeted atrial tissue were examined histologically to identify gaps in transmural ablation. LSI-guided lines had a lower incidence of histological gaps (4 gaps in 69 catheter moves, 5.8%) than LSI+2 mm lines (7 gaps in 33 catheter moves, 21.2%) and LSI+4 mm lines (15 gaps in 23 catheter moves, 65.2%, P Conclusions: In this model of chronic atrial ablation, delivery of uninterrupted transmural linear lesions may be facilitated by using LSI to guide catheter movement. When ΔLSI between adjacent lesions is ≤1.5 mm, no gaps in atrial linear lesions should be expected.

BACKGROUND: Tissue thickness at the site of ablation is a determinant of lesion transmurality. We reported the feasibility, safety and efficacy of long-standing persistent atrial fibrillation (PsAF) ablation, incorporating deliberate LAA isolation and occlusion and identified systematic differences in ostial LAA tissue thickness in a matched cohort of cadaveric specimens. METHODS: Pre-procedural CCT scans were acquired from 22 patients undergoing LAA isolation and subsequent occlusion. Using a novel CCT wall thickness algorithm, LAA ostial wall thickness was assessed in vivo, compared with measurements from the cadaveric specimens and analysed for differences between regions that demonstrated acute electrical reconnection and those that did not. RESULTS: Mean tissue thickness calculated for each LAA ostial quadrant was 2.1(+/-0.6)mm (anterior quadrant), 1.9(+/-0.4)mm (superior quadrant), 1.5(+/-0.4)mm (posterior quadrant) and 1.8(+/-0.7)mm (inferior quadrant). Tissue was significantly thicker in the anterior (p = 0.004) and superior quadrants (p = 0.014) than the posterior quadrant. Higher thickness measurements were recorded from quadrants demonstrated to be thicker from histology. Tissue was significantly thicker in regions that demonstrated acute electrical reconnection (1.9(+/-0.6)mm) when compared with those that did not (1.6(+/-0.5)mm) (p = 0.008). CONCLUSIONS: CCT imaging may be used to detect differences in wall thickness at different atrial locations and success of LAA ablation may be affected by local tissue thickness. Atrial wall thickness may need to be considered as a metric to guide titration of radiofrequency (RF) energy for safe and successful ablation. This article is protected by copyright. All rights reserved.

Atrial fibrillation (AF) is a supraventricular tachyarrhythmia characterized by uncoordinated atrial activation with consequent deterioration of mechanical function. Personalized computational modeling provides a novel framework for integrating and interpreting the combined role of atrial electrophysiology and mechanics in AF development and sustenance. Coronary computed tomography angiography data were segmented using a threshold-based approach and the smoothed voxel representation was dis-cretized into a high-resolution tetrahedral finite element (FE) mesh. To estimate the complex left atrial fiber architecture, individual fiber fields were generated according to morphological data on the endo- and epicardial surfaces based on local solutions of Laplace's equation and trans-murally interpolated to all tetrahedral elements. Personalized geometrical models included the heterogeneous thickness distribution of the left atrial myocardium and subsequent discretization led to high-fidelity tetrahedral FE meshes. The novel algorithm for (automated) incorporation of the left atrial fiber architecture provided a realistic estimate of the atrial microstructure and was able to qualitatively capture all important fiber bundles. The established modeling pipeline provides a robust framework for the rapid development of personalized model cohorts and facilitates simulations of atrial electromechanics.