There is controversy as to the best timing for surgery. Patients presenting with acute severe mitral regurgitation are generally critically ill and require urgent surgery. However, in patients with chronic mitral regurgitation, the timing is more uncertain.
In the past, cardiologists recommended waiting until severe symptoms developed before proceeding to surgery. However, waiting often was associated with a bad outcome, and left ventricular function did not respond well to the sudden change in afterload imposed by putting an artificial valve in a patient who had severe regurgitation. Now, many recommend operating as soon as significant symptoms develop. Some, in fact, even recommend that these patients not be treated with medication so as not to mask symptoms and that surgery be done as soon as any symptom presents.
However, replacement of a native valve with a prosthetic one is not a cure for the patient, but rather a shift to a new set of problems associated with the prosthetic valve. Newer forms of therapy include valve repair with an annular ring and valve reconstruction and appear to provide better and more natural results in patients while avoiding the use of anticoagulant medications. Long-term follow-up of this procedure from multiple surgical sites is not yet available.
When is a mechanical prosthesis preferred over a bioprosthetic valve?
Bioprosthetic valves in the aortic position may not require anticoagulation, whereas mechanical valves always require such therapy. Bioprosthetic valves are therefore preferred in patients for whom anticoagulation poses additional risks or problems: young vigorous patients whose occupations or sports activities present risks of trauma, patients who have clotting disorders or bleeding problems (e.g., peptic ulcer disease), and patients who are unable to follow instructions or have appropriate monitoring of clotting factors. Mechanical prostheses may be preferred in young patients with expected considerable longevity, those for whom anticoagulation is not difficult to manage, those who may calcify tissue excessively (e.g., patients with renal failure), and those who may have already failed a bioprosthetic implant.
Which type of valve has a lower incidence of bacterial endocarditis? Which has a lower overall complication rate?
Bacterial endocarditis (or, more broadly, infective endocarditis to include fungal organisms) occurs in about 1% of valve replacement per year of implant. The incidence is approximately the same for bioprosthetic and mechanical valves. When infection occurs on a bioprosthetic valve, cure with antibotics alone is feasible in many cases, especially when the infection is on the leaflet. When infection is present in mechanical prostheses, the valve ring is always involved, and therefore medical cure is extremely difficult (though not impossible). Surgical therapy is usually required, with valve replacement.
The complication rate is somewhat lower with bioprosthetic valves than mechanical valves, but when the decreased long-term survival of the bioprosthetics is considered, the overall patient survival and requirement for reoperation are about the same for both types.