Abstract Body (Do not enter title and authors here): Background: Discrepant transthoracic echocardiography (TTE) parameters are not infrequently observed in patients with significant aortic stenosis (AS), however, there is limited literature regarding their computed tomography (CT) characteristics and prognostic implications.

Aims: We compared the multi-modality imaging characteristics and outcomes in patients undergoing transcatheter aortic valve replacement (TAVR) by AS subtype.

Methods: Patients with severe AS (defined as aortic valve area <1.0 cm2 on TTE, n=906, age 79±9 years, 41.5% women) undergoing TAVR during 2019-2020 were classified by TTE as high-gradient (HG-AS, n=446, LVEF 61 ±8%), classical low-flow low-gradient (CLFLG-AS, n=121, LVEF 37 ±9%), paradoxical low-flow low-gradient (PLFLG-AS, n=261, LVEF 61 ±6%) and normal-flow low-gradient (NFLG-AS, n=78, LVEF 62 ±6%) AS. TTE and CT characteristics and all-cause mortality during follow-up were compared.

Results: Aortic valve area by TTE (continuity equation) and CT (planimetry) were lowest for HG-AS patients (means 0.70cm² and 1.04cm²), and highest for NFLG-AS patients (0.86cm² and 1.18cm²), while aortic valve calcium score (AVCa) on CT was higher for HG-AS patients than other groups (2471HU versus 2009-2180 HU). Kaplan-Meier survival curves by AS subgroup are shown in the figure. Low-gradient AS subgroups (compared with HG-AS) remained independently associated with worse survival with hazards ratio 2.04 (95% confidence interval 1.50-2.77) even after adjusting for other clinical and AS imaging parameters.

Conclusion: Characteristic TTE and CT features by AS subtypes are reported. TAVR patients with low-gradient AS (CLFLG-AS, PLFLG-AS and NFLG-AS) continue to have worse prognosis than HG-AS, highlighting the need for further research in these patients to improve their management and outcomes.