Embolic myocardial infarction in a pregnant woman with a mechanical heart valve on low molecular weight heparin.

Even with continuing technical improvements in prosthesis design and the development of less thrombogenic materials, mechanical valve prostheses still carry a thromboembolic risk significant enough to warrant long-term anticoagulation therapy. Optimal anticoagulation is especially crucial during pregnancy due to the hypercoagulable state that rapidly develops after conception. Conventional anticoagulation therapy with coumarin derivatives is associated with risks of teratogenicity and hemorrhage for the fetus, and thromboembolic and hemorrhagic complications for the mother. As a result, other forms of anticoagulation, such as unfractionated or low molecular weight heparin, have been advocated as an alternative in selected cases. The present report describes a case of embolic myocardial infarction occurring in a pregnant woman with an aortic bileaflet mechanical valve prosthesis while on therapeutic low molecular weight heparin after only one dose was withheld before amniocentesis.