Hypothyroidism After the TAVI Procedure in Elderly Patients

Overview

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.

Aortic stenosis is highly prevalent in advancing age. The prevalence is 2.5% at an age of 75 years and 8.1% at an age of 85 years. The estimated mortality after onset of symptoms (dizziness, syncope, thoracic pain and dyspnea) with conventional medical treatment is 75% after 3 years follow up. The prognosis of this disease has dramatically changed with the surgical replacement of the aortic valve. However, an open surgical procedure is not always possible in high risk patients for anatomical reasons (sternotomy, radiation and chest deformation) or comorbidities defined by the Euroscore and the Society of Thoracic Surgeons' risk score (STS score). Trans-catheter aortic valve replacement (TAVI) is becoming the standard care of patients suffering of non-operable, high risk severe and symptomatic aortic stenosis. The TAVI procedure is associated with immediate hemodynamic improvement characterized by a decreased aortic valve mean pressure gradient, an improved left ventricular end systolic volume and mass, a decreased end ventricular diastolic volume and a better ejection fraction. This hemodynamic improvement translates into better clinical outcomes. Mortality rates (2.2% and 6.7% at one month and at one year) and long term stroke rate are similar after TAVI or surgical replacement. The TAVI procedure is also successful in octogenarian and in frail patients. Consequently, patient's frailty is a growing argument to refer the patient for a percutaneous treatment of valve disease instead of a conventional surgical approach. The standard evaluation before the TAVI procedure comprises some radiologic studies with iodinated contrast agent (coronarography, thoracic CT scanner and the TAVI procedure itself). Furthermore, some patients require a treatment with Amiodarone® because of the occurrence of atrial fibrillation during the procedure. A typical iodinated contrast study confers 13500 µg of free iodine and 15-60g of bound iodine (several hundred thousand times above the recommended daily intake). An excess of iodium expo-sure can lead to thyroid dysfunction: * Hyperthyroidism particularly in patients with underlying nodular thyroid disease (Jod-Basedow effect). * Hypothyroidism in patients with underlying thyroid disease or in patients who are taking medication (lithium, amiodarone) which can lead to thyroid dysfunction. The mechanism of iodinated contrast agent hypothyroidism is the failure to escape of the acute Wolf-Chaikoff effect. Amiodarone confers 3-21 mg iodine daily and can also lead to thyroid dysfunction particularly in patients with underlying thyroid disease because of the failure to escape of the acute Wolf-Chaikoff effect. An autoimmune mechanism is also described. Epidemiology In our recent clinical practice (geriatric day hospital UZ Brussel), an increased incidence of hypothyroidism in elderly patients after a TAVI procedure has been observed. In our knowledge, there are no data about the incidence of hypothyroidism and what could be the impact for elderly patients after a TAVI procedure.