Prosthetic valve thrombosis caused by heparin-induced thrombocytopenia thrombosis during pregnancy.

eparin is commonly used as a bridge before surgery in patients who are treated with oral anticoagulants to prevent thromboembolic complications. In addition, heparin is also indicated as an alternative to warfarin during the first trimester of pregnancy to avoid the risk of fetal embryopathy.1 Risk of thromboembolism, however, may be increased by the use of heparin compared with continuous use of warfarin.1,2 Thromboembolic events may be caused not only as a result of insufficient anticoagulation on heparin, but also by heparin-induced thrombocytopenia thrombosis. Although heparin-induced thrombocytopenia thrombosis is a possible cause of catastrophic venous or arterial thromboembolism during i.v. heparin,3 its incidence may be underestimated.4,5 A 33-year-old woman with mechanical prosthetic valve (SJM 27 mm) in the mitral position was admitted to hospital due to pregnancy. She had been well-controlled on warfarin. Transthoracic echocardiography on admission showed normal prosthetic valve motion (Figure 1). After admission, i.v. heparin (20,000 IU/day) was started and warfarin was discontinued. Activated partial thromboplastin time was maintained at around 50 s. Seven days after admission, the patient suddenly developed dyspnea, and chest X-ray showed pulmonary congestion. On physical examination, diastolic rumble was audible, suggesting the presence of prosthetic valve stenosis. Transesophageal echocardiography indicated severely stenotic mitral prosthetic valve with thrombus formation (Figure 2A). After thrombolytic therapy using tissue plasminogen activator followed by increased dose of heparin, the size of the thrombosis had increased (Figure 2B). Heparin-induced thrombocytopenia thrombosis was suspected and heparin was replaced with argatroban (0.7 μg · kg–1 · min–1). Mitral valve replacement was then performed (Figure 2C) and the pregnancy terminated. The patient was found to be positive for HIT (heparininduced thrombocytopenia) antibodies and was diagnosed as H