Emergency redo mitral valve replacement in a 27-year-old pregnant female with a clotted prosthetic mitral valve, preoperative fetal demise and postoperative ventricular assist device: a case report

Anticoagulation in Pregnant Women With Prosthetic Heart Valves

Background: Pregnancy is associated with an increased risk of thrombosis in women with mechanical prosthetic heart valves. Effective anticoagulation is therefore critical in such patients but remains problematic, since oral anticoagulation and both unfractionated and low-molecular-weight heparin may be associated with important fetal and maternal side effects.

Purpose: To review information related to the use of anticoagulation with both warfarin and heparin and reassess the safety and efficacy of these therapies in pregnant women with mechanical prosthetic heart valves.

Data source and selection: A MEDLINE search from 1966 to October 2003 for English and non-English language articles that reported the use of anticoagulation in pregnancy was conducted. Articles were included if they reported use of anticoagulation in pregnancy with emphasis on those that included women with mechanical prosthetic heart valves.

Conclusions: Anticoagulation prophylaxis with both warfarin and heparin (unfractionated heparin and low-molecular-weight heparin) may be associated with important fetal and maternal side effects. Optional regimens for the treatment of low-risk and high-risk patients are proposed to minimize potential complications.

MECHANICAL HEART VALVES AND PREGNANCY

Mechanical heart valves pose a particular challenge in pregnancy, as the primary agent used to prevent valve thrombosis, coumadin (warfarin), is a known teratogen. Alternatives to coumadin, such as unfractionated heparin (UFH) and low-molecular weight heparin (LMWH) are safer for the fetus, particularly during the first trimester of pregnancy, but expose the mother to potential valve failure. This review will examine these controversies and the complex literature regarding management in pregnancy.

Low-molecular-weight heparin for thromboprophylaxis in pregnant women with mechanical heart valves

BACKGROUND

Pregnancy in a woman with a mechanical heart valve is a life-threatening situation. Due to the inability of unfractionated heparin to prevent valvular thromboses, warfarin or other vitamin K antagonists have been the preferred anticoagulants for the mother. They are, however, potentially harmful to the fetus. With the advent of low-molecular-weight heparins, clinicians were hopeful for an alternative that was safe for the fetus, but more effective than unfractionated heparin, which carries a 29-33% risk of life-threatening thromboses and a 7-15% chance of mortality. Unfortunately, fatal thromboses have occurred with low-molecular-weight heparin as well.

METHODS

We searched the MEDLINE database and other sources to identify cases of the use of low-molecular-weight heparin for thromboprophylaxis in women with mechanical heart valves.

RESULTS

We found 73 cases and added three of our own for a total of 76. There were 17 thrombotic events (22%). Thirteen were valve thromboses, two were strokes, and two were myocardial infarctions. There were three deaths (4%).

CONCLUSIONS

While pregnant women with mechanical heart valves who receive low-molecular-weight heparin for thromboprophylaxis are at extremely high risk of life-threatening thromboses, there is no evidence that low-molecular-weight heparin is inferior to unfractionated heparin.

Cardiopulmonary bypass and mitral valve replacement during pregnancy

Gravid patient cardiopulmonary bypass remains a high-risk procedure with regard to fetal preservation. Maternal mortality is similar to that of the nonpregnant female at 1.5-5%. However, fetal mortality remains high at 16-33%, with an average of 19% over the past 25 years, with no correlation to gestational age. Teratogenesis is a major consideration in the first trimester. Variations in the timing of surgical intervention, gestational age, maternal health status, type of procedure, pre- or postorganogenesis, perfusion protocol, and pharmaceutical therapy are all factors that can influence fetomaternal outcome. In this report, we present a literature review along with our experience of a 26-year-old female who developed complications with her pregnancy at approximately 17 weeks gestation, with adverse neurological sequelae. The patient was 152 cm in height and weighed 48 kg, with a calculated body surface area of 1.40 M2. She had no prior history of cardiac disease and, upon admission to our institution, presented with a declining health status in pulmonary edema and was treated medically, with an ultimate requirement for mitral valve replacement. The total cardiopulmonary bypass time was 99 min with an aortic crossclamp time of 83 min. The literature, as expected, is limited to case reports and reviews since a controlled clinical trial during pregnancy is nonexistent, using extracorporeal circulation. This greatly challenges the medical staff in managing such difficult cases, with an incidence of heart disease during pregnancy of 1.2-3.7%.

Low-molecular-weight heparins for thromboprophylaxis and treatment of venous thromboembolism in pregnancy: a systematic review of safety and efficacy

To assess the safety and efficacy of low-molecular-weight heparins (LMWHs) for thromboprophylaxis and treatment of venous thromboembolism (VTE) in pregnancy, a systematic review of studies to the end of 2003 was undertaken. Data on VTE recurrence and side effects were extracted and cumulative incidences of VTE and adverse effects calculated. Of 81 reports identified, 64 reporting 2777 pregnancies were included. In 15 studies (174 patients) the indication for LMWH was treatment of acute VTE, and in 61 studies (2603 pregnancies) it was thromboprophylaxis or adverse pregnancy outcome. There were no maternal deaths. VTE and arterial thrombosis (associated with anti-phospholipid syndrome) were reported in 0.86% (95% confidence interval [CI], 0.55%-1.28%) and 0.50% (95% CI, 0.28%-0.84%) of pregnancies, respectively. Significant bleeding, generally associated with primary obstetric causes, occurred in 1.98% (95% CI, 1.50%-2.57%), allergic skin reactions in 1.80% (95% CI, 1.34%-2.37%), heparin-induced thrombocytopenia in 0%, thrombocytopenia (unrelated to LMWH) in 0.11% (95% CI, 0.02%-0.32%), and osteoporotic fracture in 0.04% (95% CI, < 0.01%-0.20%) of pregnancies. Overall, live births were reported in 94.7% of pregnancies, including 85.4% in those receiving LMWH for recurrent pregnancy loss. LMWH is both safe and effective to prevent or treat VTE in pregnancy.

Low molecular weight heparin in pregnancy: current issues

Low molecular weight heparin (LMWH) is now the most commonly used anticoagulant for prophylaxis and treatment of venous thromboembolism in pregnancy and the puerperium in the UK. The reliable pharmacokinetics of LMWHs and their long half-life, resulting in the need for less frequent injections than unfractionated heparin (UFH), makes them attractive for practical use in the 9 months of pregnancy. Widespread use over the last 10 years has shown that LMWHs are safer than UFH in pregnancy. There is, however, poor consensus and wide disparity of views among experts with regard to the appropriate dose for the varying indications, the duration of treatment, and whether and how LMWH should be monitored because of the lack of an evidence base. These areas of uncertainty reflect the fact that clinical practice has grown largely through the publication of small trials, observational studies, personal experience and anecdote. Good clinical trials are urgently required.