Aortic stenosis is highly prevalent in advancing age. The prognosis of this disease has dramatically changed with the surgical replacement of the aortic valve and the trans catheter aortic valve re-placement (TAVI). The TAVI procedure is also successful in octogenarians and frail patients. However, the evaluation before the TAVI procedure requires a high dosage of iodinated contrast agent with, consequently, an increased risk for thyroid dysfunction. The primary endpoint of this study is to assess, prospectively, the incidence and the predictive factors (underlying thyroid disease, medication, food preservative, topical antiseptics) of hypothyroidism after a TAVI procedure. The secondary endpoint is the influence of the occurrence of hypothyroidism after the TAVI procedure on the geriatric assessment.