Background: Severe aortic valve stenosis (AS) is the commonest valve disease. Aortic valve replacement (AVR) is primarily indicated when symptoms occur and/or when there is a drop in left ventricular ejection fraction. However, irreversible myocardial damage, such as replacement fibrosis, leads to increased morbidity and mortality despite treatment. Improved patient selection and timely treatment is thus warranted. T1 mapping, a non-invasive method to quantify myocardial fibrosis by cardiac magnetic resonance (CMR), could be a marker to guide treatment.

Aims: To investigate the change of myocardial fibrosis\* in AS patients following AVR and if these changes are associated with disease and/or procedural characteristics.

Methods: This is an observational clinical trial. Approximately 60 patients with severe AS planned to undergo AVR (either surgical or transcatheter) at Rigshospitalet, Denmark will be included. Participants will undergo CMR before surgery and at a 1-year follow-up. Other assessments include clinical evaluation and blood sampling. The primary end-point is change in T1 values after AVR. Hypotheses and perspectives: The investigators hypothesize that (1) myocardial fibrosis\* will regress in patients undergoing AVR as a group, (2) the degree of myocardial fibrosis is positively correlated with the degree of symptoms, (3) the regression of myocardial fibrosis is greater in patients undergoing TAVR compared to SAVR, and (4) the regression of myocardial fibrosis is greater in patients with tricuspid aortic stenosis compared to bicuspid aortic stenosis. Ultimately, T1 mapping is a potential marker for improved patient selection for the timing of AVR. \* Estimated by T1 mapping