Abstract 16628: Threshold for Ascending Aorta Diameter for Clinical Management: An Assessment of the UK Biobank Population Based on Z-Scores

Abstract

Introduction: Ascending aortic diameter (AAoD) is commonly monitored to manage patients at risk of aortic dissection. Z-scores have also been proposed to identify at risk aortas, adjusting AAo for age, gender, and body surface area (BSA). Despite improved imaging and proven association of AAoD with age, sex and BSA, cutoff remains at 4.5 cm for monitoring and 5.5 cm for surgery in guidelines. However, studies like International Registry of Acute Aortic Dissection found that most aortic dissection had AAoD<5.5 cm. Aim: Identify AAoD in the UK Biobank population and compare current 4.5 cm cutoff with Z-scores to classify cases with dilated ascending aortas. Methods: Using cardiac magnetic resonance images of participants in the UK Biobank, we applied a pre-trained neural network to segment and quantify the AAoD. We also obtained demographics and clinical covariates for the participants with AAoD. Two common Z-scores were calculated using published equations including: (1) age, height, and sex (Z-HAS) and (2) age, BSA and sex (Z-BAS). We identified participants with AAoD>4.5 cm and compared them with Z>2 cutoff value that might require imaging follow-up for managing their dilated aortas. Results: AAoD diameter was calculated for 44,799 participants (22,983 females and 21,816 males). Common demographics in both groups are listed in the Table. Average AAoD was 3.15±0.32 cm in females and 3.44±0.35 cm in males. Diameter cutoff of 4.5 cm identified 15 females and 110 males with dilated aortas. On the other hand, Z-HAS classified 862 females and 674 males, while Z-BAS classified 583 females and 405 males (orange dots in the top and bottom panels of Figure, respectively) with higher aortic diameter that might require regular follow-up imaging. Conclusion: Z-Score might identify more people at dilated aortas as compared to the hard cutoff. Future work is needed to define whether Z scores are more sensitive means of identifying patients who might be at increased risk of aortic dissection.