In 1931, Paul Dudley White stated, "There is no treatment for aortic stenosis." Even today the medical therapy of aortic stenosis has not significantly advanced (Fig. 32-1).1 Conversely, patients may tolerate aortic insufficiency for many years, but as the ventricle starts to dilate, a progressive downhill course begins and early operation is warranted.2 Definitive therapy for aortic valve disease was unavailable until the advent of cardiopulmonary bypass. Innovative cardiovascular surgeons then began to develop cardiac valve prostheses. Over the subsequent 50 years3 the variety of prostheses that have become available for use have expanded greatly. Available aortic valve substitutes include mechanical valve prostheses, stented biologic valve prostheses, stentless biologic valve prostheses, human homograft tissue (both as isolated valve replacement and aortic root replacement), percutaneous or transapical biologic valves and a combination of a biologic valve using a pulmonary autograft, and pulmonary outflow tract replacement with heterograft prostheses (Ross procedure). This chapter focuses on the use of mechanical valve replacement in the aortic position.
Survival of patients having aortic valve replacement compared to those not having valve replacement. (Reproduced with permission from Carabello BA: Clinical practice. Aortic stenosis. NEJM 2002; 346:677.)
In 1952, Hufnagel used an aortic valve ball and cage prosthesis heterotopically in the descending thoracic aorta to treat aortic insufficiency.4 After the advent of cardiopulmonary bypass, initial attempts at aortic valve replacement (AVR) consisted of replacement of the individual aortic cusps with Ivalon gussets sewn to the annulus. When successful, these prostheses often calcified and results were short lived. Shortly thereafter, surgical pioneers Starr, Braunwald, and Harkin began replacement of the aortic valve in the orthotopic position. First-generation aortic valve prostheses, the ball and cage, became the standard for AVR for more than a decade (Fig. 32-2). Many of these prostheses have remained durable for up to 40 years.5,6 Multiple modifications ensued, including changing the material of the ball from silastic to stellite, changes in the shape of the cage, depression of the ball occluder, the addition of cloth coating to the sewing ring and the cage, and changes in the sewing ring itself. These valves, however, required intense anticoagulation.7 Hemodynamic performance was compromised because there were three areas of potential outflow obstruction: (1) the annular size of the sewing ring (the effective orifice area of the valve); (2) the distance between the cage and the walls of the ascending aorta (particularly in the small aortic root); and (3) obstruction to outflow by the ball itself distal to the tissue annulus. Flow patterns were also abnormal (Fig. 32-3). These problems led to the development of the next generation of aortic valve prostheses—the tilting disc valve. Innovators such as Björk, Hall, Kaster, and Lillehei developed three models of tilting disc prostheses that became the second generation of commonly implanted aortic valve replacement devices ...