Aortic stenosis is a common heart valve disease in older adults. It occurs when the aortic valve becomes narrowed, making it harder for blood to flow from the heart to the rest of the body. Without treatment, this condition can lead to serious complications and reduced survival. A widely used treatment is transcatheter aortic valve implantation (TAVI), a minimally invasive procedure that replaces the diseased valve and improves blood flow.

Recent research suggests that heart diseases, including aortic stenosis, may affect the gut (intestinal) environment. The gut contains trillions of microorganisms (called the gut microbiota) that play an important role in digestion, immunity, and overall health. In patients with heart conditions, reduced blood flow may impair the intestinal barrier and alter the balance of these microorganisms. This imbalance may contribute to inflammation and other complications.

This study aims to better understand how aortic stenosis and its treatment with TAVI influence the gut microbiota and intestinal health. Researchers will measure specific substances produced by gut bacteria (called metabolites) in blood and stool samples. These include bile acids, trimethylamine N-oxide (TMAO), tryptophan-related compounds, and short-chain fatty acids.

Samples will be collected before and three months after the TAVI procedure. In addition, genetic analysis of stool samples will be performed to identify and compare the types of bacteria present before and after treatment.

The goal is to determine whether improving heart function with TAVI can restore a healthier gut environment. This may help identify new ways to improve outcomes and reduce complications in patients with aortic stenosis.

Inclusion Criteria:

• • 18 years or older

  • Hospitalized for TAVI or investigations before TAVI for significant aortic valve disease

    • Severe CAS is defined as: high flow gradient with normal CO (mean gradient ≥40mmHg, Vmax≥4m/s, valve area ≤ 1cm² or ≤0,6cm/m²) or low flow low gradient (mean gradient<40mmHg, Vmax <4m/s, valve area ≤ 1cm² or ≤0,6cm/m², stroke volume < 35ml/m², LVEF<40%) confirmed by low dose dobutamine echo or high calcium score (> 1200 in women and > 2000 in men), paradoxical low-gradient CAS: LVEF > 55%, Vmax< 4m/s, mean gradient < 40mmHg, area < 1cm²)
    • Combined aortic stenosis and aortic regurgitation, considered as severe valvular heart disease with a need for TAVI.

  • Written informed consent

Exclusion Criteria:

• - Treatment interfering with the composition of the intestinal microbiota: local or systemic corticosteroids within the last 3 months, antibiotics within the last 3 months, antiretrovirals, bile acid chelators (questran and colesevelam), HIV-targeted antiretroviral therapies, selective serotonin reuptake inhibitor-type antidepressants
• Clinical criteria: history of cholecystectomy, documented chronic liver disease in the patient, failure to fast on the day of the blood test, inflammatory bowel disease
• Valve in valve TAVI.
• LVEF < 20%
• Patients requiring emergency intervention (myocardial infarction, acute aortic or mitral regurgitation, cardiogenic shock).
• AS of rheumatic origin, infective endocarditis.

Adult patients with severe aortic valve disease referred for transcatheter aortic valve implantation (TAVI) at a single tertiary care center. Patients are enrolled prospectively and undergo evaluation of gut microbiota composition and metabolomic profiles before and after TAVI.

The plan for sharing individual participant data is currently under evaluation. Data sharing will be considered in compliance with institutional guidelines, ethical approvals, and applicable data protection regulations.