Is it the time to reconsider the choice of valves for cardiac surgery: mechanical or bioprosthetic?

Valvular heart disease is a pathologic process involving one or more of the four valves (aortic, pulmonary, mitral and tricuspid) of the heart typified by stenosis or regurgitation and leading to patient symptoms. The most common causes are tissue degeneration, rheumatic fever and congenital heart diseases. Aortic valve replacement (AVR) using either mechanical or bioprosthetic (tissue) valves via open-heart surgical AVR (SAVR) is the most widely accepted standard treatment. The choice of which valve type to be used depends on patient age, disease nature and other comorbidities. A study conducted by Khan and colleagues compared outcomes of mechanical and tissue cardiac valves and found that tissue and mechanical valve recipients have similar survival over 20 years of follow-up. However, differences were found: there is an increased risk of hemorrhage in patients receiving mechanical valve replacements and an increased risk of late reoperation in all patients receiving tissue valve replacements. Randomized trials show more midterm morbidity with mechanical valves when compared to bioprosthetic valves (Table 1). The major argument against the use of bioprosthetic valves in young and middle aged patients is the inevitability of reintervention for structural valve failure. On the other hand, mechanical valves are heralded as a life-long solution. Current literature suggests that most patients receiving tissue valves do not have a reoperation. This is supported by life-table analysis of large data sets which suggest that the average life-expectancy of a 60 year-old after AVR is about 12 years. Because most bioprosthetic valves are free from structural deterioration for 12 –15 years, many patients will die before the valves degenerate. The risk of tissue valve reoperation increases progressively with time, especially in younger patients. The American College of Cardiology/American Heart Association (ACC/AHA) recommends that a bioprosthetic valve be indicated for in patients of any age for whom anticoagulant therapy is contraindicated, cannot be managed appropriately, or is not desired and a mechanical prosthesis is reasonable for AVR or mitral valve replacement (MVR) in patients less than 60 years of age who do not have a contraindication to anticoagulation. Up to now, clinical practice has largely followed this recommendation. During the last two decades, there has been an increasing trend for surgeons to implant a bioprosthetic as opposed to a mechanical valve. This trend has greatly accelerated in the last few years with the approval and broad adoption of transcatheter aortic valves. As a result, an increasing incidence of patients requiring reoperation for failing bioprosthetic valves is to be expected. While the current guidelines are clear that patient choice and willingness to take anticoagulation are critical driving factors in valve choice, the fact is that presently older patients preferentially receive bioprosthetic valves while younger patients receive mechanical valves. We believe that there is considerable evidence