Cardiac bioprostheses in the 1990s.

T he first successful heart valve replacements were carried out in 1960 with the use of mechanical prostheses.1-3 Because of the risk of throm-boembolism that is inherent to all mechanical prosthe-ses and the hazards of continuous anticoagulation, fewer thrombogenic tissue valves were developed.4,5 In the early 1960s, homograft replacement of the aortic valve was reported,6'7 and shortly thereafter, valve replacements with porcine bioprostheses were used.8'9 The adequate hemodynamic properties, low thrombo-genicity, and freedom from substantial structural de-generation during the first years after implantation made the bioprostheses a very attractive alternative to mechanical valves.10-12 The absence of the need for anticoagulation appeared to be of particular advantage for valve replacement in patients engaged in competitive sports, women wishing to become pregnant, and elderly patients, in whom bleeding complications are most likely to occur. A true consensus about the indications for bioprosthetic valve replacement was, however , never reached in the debate between enthusiastic supporters of tissue valves and skeptical surgeons who were concerned about the long-term durability of the bioprostheses. Nevertheless, bioprostheses were implanted with increasing frequency from the 1970s until the early 1980s, and they were the standard valve substitutes for aortic, mitral, and tricuspid valves in many institutions. After the mid 1980s, the use of bioprostheses decreased due to growing concern about long-term durability of these valves. In the United Kingdom, 1984 was the peak year for use of tissue valve implants; almost 50% of all cardiac valve replacements were with bioprostheses. Over the next 5 years, use of bioprostheses decreased to less than one third of the total.13 Types of Bioprostheses During the past two decades, the largest experience with prosthetic valve replacement has been with the glutaraldehyde-fixed, frame-mounted Hancock and Carpentier-Edwards porcine valves. Over time, modifications of valve design have been accomplished in both prostheses. In 1976, the Hancock modified orifice bio-prosthesis was developed to improve hemodynamic performance in the small aortic root.14 This prosthesis features a composite design that removes one coronary cusp and its flow-impeding muscle shelf and replaces it with a cusp from a second larger valve. The probability of freedom from structural valve dysfunction and reop-eration at 10 years is similar to that of the Hancock standard valve.14 Similarly, in the early 1980s, the Car-pentier-Edwards supra-annular prosthesis was developed to improve hemodynamic properties and durability of the valve. However, the long-term performance of the supra-annular type was not better than that of the …