Transcatheter Aortic Valve Replacement
Aortic stenosis (AS) is the most common form of acquired degenerative heart valve disease in developed countries, with increasing prevalence with age. An estimated 300,000 patients have severe AS in the United States, with more than 60,000 undergoing surgical aortic valve replacement (SAVR) every year. These numbers are growing rapidly, with the US census predicting approximately 84 million citizens will be 65 years and older by 2050. Medically treated, symptomatic, severe AS carries a poor prognosis with 1- and 5-year survival rates of 60% and 32%, respectively. Historically, SAVR has been the treatment of choice for AS, producing excellent results with low morbidity, mortality and excellent long-term results. Despite these favorable results, at least 30% of patients with severe symptomatic AS were not referred for SAVR due to reluctance by referring physicians and patients. These were usually older frail patients with multiple comorbidities and are likely the impetus for the emergence of transcatheter aortic valve replacement (TAVR).
Transcatheter treatment of aortic valve disease dates back to 1965 when Davies devised a catheter-mounted valve for the treatment of aortic insufficiency (AI),  which spurred the development of several experimental catheter-based devices for treating AI over the next 15 to 20 years., In 1989, Anderson implanted an original model of a balloon-expandable, catheter-mounted stented valve within pig aortas. Anderson used a hand-made mesh containing a porcine valve. Although this important development and others in the 1990s provided great insight, none were followed by human applications. In 2000, Bonhoeffer performed the first human implantation of a stented valve made of bovine jugular vein into a right ventricle-to-pulmonary artery conduit. Two years following that, Cribier performed the first TAVR in a human by using a bioprosthetic valve made of equine pericardium mounted on a balloon-expandable stainless steel stent and delivered in an antegrade fashion through a transeptal approach.  In the 15 years following the first TAVR, the field has seen a rapid evolution of knowledge, technology, and operative techniques.This chapter will address this evolution with the main emphasis on the status of TAVR today.
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