No long-term survival benefit of allografts over xenografts has been demonstrated. Autografts have proven durability and have the potential to grow in situ. They are thus increasingly being used in the management of pediatric and adolescent patients with aortic valve disease. Both allografts and autografts have a low reinfection rate when used in the treatment of prosthetic aortic endocarditis and are considered the valve replacement of choice for this condition. The incidence of thromboembolic events is lowest in patients younger than 50 years, lower with aortic prostheses than with mitral or multiple prostheses, and lower with bileaflet disk valves than with single-leaflet valves.
Hemorrhagic events are more common in older patients.
Recent studies have indicated that the level of anticoagulation required to prevent thromboembolism is less than was previously thought. A recent large study of anticoagulation in mechanical prostheses has suggested that an international normalized ratio of between 2.5 and 4.0 is desirable in most instances and minimizes hemorrhagic and thromboembolic complications. The appropriate international normalized ratio for an individual patient will vary depending on past history of embolic or bleeding events, age, and type, position, and number of prostheses. Thromboembolic risk with xenografts is greatest in the first three months after surgery. Valvular Thrombosis Acute thrombosis of a mechanical valve is more common with a single tilting-disk valve.