Anticoagulant management of patients with mechanical prosthetic valves undergoing non-cardiac surgery: Indications and unresolved issues

A wide array of recommendations is available for the management of anticoag ulation in patients with a prosthetic heart valve scheduled for non-cardiac surgery, ranging from avoidance of replacement anticoagulant therapy in al l cases (excluding those with a recent thromboembolic event), to replacemen t anticoagulant therapy in all, without risk stratification. These guidelin es are derived from only a few small-to medium-sized, non-randomized and of ten methodologically flawed studies conducted during the late 1970s, and ap plies mainly to caged-ball and caged-disc valves. Furthermore, extrapolatio n of the thromboembolic risk from data on patients not receiving oral antic oagulants at all is based on assumptions that are not necessarily valid. In this review, the direct and indirect evidence on which these guidelines ar e based is examined critically. Their applicability to the newer, less thro mbogenic valve models is questionable. The need for further prospective, ra ndomized studies is emphasized by the failure of existing studies to adjust properly for the main known or presumed thromboembolic risk factors, and t heir low statistical power to detect significant differences between protoc ols in an intention-to-treat manner. The evaluation of obstructive and non- obstructive thrombosis should serve as a secondary outcome measure in the a ssessment of anticoagulation management before non-cardiac surgery.