Matthew Tsu-En Lee ¹ Vincenzo Martorana ² Rafizul Islam Md ³ Raphael Sivera ⁴ Andrew C. Cook ⁴ Leon Menezes ⁵ Gaetano Burriesci ^1,6 Ryo Torii ¹ Giorgia M. Bosi ^1*

• ¹ Department of Mechanical Engineering, Faculty of Engineering Sciences, University College London, London, England, United Kingdom
• ² Department of Economics, Business and Statistics, University of Palermo, Palermo, Sicily, Italy
• ³ Department of Medical Physics and Biomedical Engineering, Faculty of Engineering Sciences, University College London, London, England, United Kingdom
• ⁴ Institute of Cardiovascular Science, Faculty of Population Health Sciences, University College London, London, England, United Kingdom
• ⁵ NIHR Biomedical Research Centre, University College London Hospitals NHS Foundation Trust, London, England, United Kingdom
• ⁶ Ri.MED Foundation, Palermo, Sicily, Italy

Introduction: Statistical shape analysis (SSA) with clustering is often used to objectively define and categorise anatomical shape variations. However, studies until now have often focused on simplified anatomical reconstructions, despite the complexity of studied anatomies. This work aims to provide insights on the anatomical detail preservation required for SSA of highly diverse and complex anatomies, with particular focus on the left atrial appendage (LAA). This anatomical region is clinically relevant as the location of almost all left atrial thrombi forming during atrial fibrillation (AF). Moreover, its highly patient-specific complex architecture makes its clinical classification especially subjective. Methods: Preliminary LAA meshes were automatically detected after robust image selection and wider left atrial segmentation. Following registration, 4 additional LAA mesh datasets were created as reductions of the preliminary dataset, with surface reconstruction based on reduced sample point densities. Utilising SSA model parameters determined to optimally represent the preliminary dataset, SSA model performance for the 4 simplified datasets was calculated. A representative simplified dataset was selected, and clustering analysis and performance were evaluated (compared to clinical labels) between the original trabeculated LAA anatomy and the representative simplification. Results: As expected, simplified anatomies have better SSA evaluation scores (compactness, specificity and generalisation), corresponding to simpler LAA shape representation. However, oversimplification of shapes may noticeably affect 3D model output due to differences in geometric correspondence. Furthermore, even minor simplification may affect LAA shape clustering, where the adjusted mutual information (AMI) score of the clustered trabeculated dataset was 0.67, in comparison to 0.12 for the simplified dataset. Discussion: This study suggests that greater anatomical preservation for complex and diverse LAA morphologies, currently neglected, may be more useful for shape categorisation via clustering analyses.