Page 27 - ANZCP Gazette APRIL 2022

PERFUSION CONSIDERATIONS WHEN PERFORMING CARDIOPULMONARY BYPASS ON A PREGNANT PATIENT
James Holder CCP, FANZCP and John Fitzgerald CCP(UK), FANZCP
Wellington Regional Hospital, NZ
A pregnant patient requiring cardiac surgery with the involvement of cardiopulmonary bypass is an uncommon event since bypass can cause considerable complications for both the mother and fetus (1). In this case study, we discuss the replacement of the ascending aorta and aortic valve in a 14 weeks pregnant patient who presented with mixed valve disease and a dilated aorta. Surgery was performed at Wellington Regional Hospital (WRH).
Patient History and Aetiology
Pregnant patients requiring cardiac surgery often experience mitral valve issues (1) and are conservatively managed until the fetus has almost reached full term or when expedient intervention is indicated. The increased blood volume of the mother and the associated haemodynamic stresses of pregnancy can overwhelm a failing mitral valve (see Table 1). This could mean that a caesarean section is required, followed immediately by a mitral valve repair or replacement.
The cause of mitral valve insufficiency in women of childbearing age is often due to previous rheumatic fever which leads to rigidity and deformity of valve cusps, the fusion of the commissures, or shortening and fusion of the chordae tendineae (2).

However, in this case the patient presented with a bicuspid aortic valve with severe mixed aortic valve disease and a dilated ascending aorta. Due to the mother’s strong family history, her bicuspid valve had been identified and monitored for a number of years. She was otherwise fit, well and active. A cardiac MRI demonstrated dilatation of 53 mm in the mid-ascending aorta, with 62% preserved ejection fraction, moderate aortic stenosis with mild to moderate aortic regurgitation, a dilated
left ventricle and mild concentric left ventricular hypertrophy. Using the modified maternal cardiovascular risk assessment laid out by the World Health Organisation, these factors combined scored class 4 – extremely high risk. As such, the risk of a cardiac event during pregnancy was estimated to be >40%. In cases where the aortic dimension is greater than 50 mm, pregnancy should be avoided or discussions should be had with the mother regarding termination if she is already pregnant.
The patient was aware of her pre-existing cardiac condition, but the pregnancy was unplanned. The cardio-obstetric team decided that the risk of conservatively managing this pregnancy was unacceptably high, therefore surgery would be necessary in the very near future. One option considered was a termination of pregnancy, with subsequent surgery once she had recovered. The type of valve chosen could jeopardise her potential to conceive again in the future. A mechanical valve will typically last longer, meaning fewer cardiac interventions in the future, but its use would necessitate anticoagulation medications; which would add significant risk to any future pregnancies, and the associated pro-coagulable state.
Warfarin is the current drug of choice for preventing thromboembolic complications with a mechanical valve (4). Warfarin is teratogenic in the first trimester, but at 14 weeks this is no longer an issue as the first trimester organogenesis is complete. However, warfarin holds significant fetopathy risks in the second and third trimester, with approximately 30–50% risk of stillbirth or miscarriage depending on the dose required (5). Warfarin would need to be changed to Clexane in the third trimester to safely manage delivery. Clexane is not as efficacious in preventing thrombosis in the context of a mechanical valve, but it does not cross the placenta. Unfortunately, administration is twice daily by injection with regular monitoring of anti-Xa levels to ensure adequate anticoagulation. Reported rates of valve thrombus in pregnancy are often affected by poor adherence. With either form of anti-coagulation there is an increased risk of bleeding, including ante-natal and postpartum haemorrhage.
A tissue aortic valve does not require anticoagulation; however, it is likely to require a repeat operation in the near future, as pregnancy can accelerate the deterioration of tissue valves. In this case a strategy for a planned and controlled delivery was made, bridging with a heparin infusion pre and post delivery, establishing Warfarin post-delivery when the bleeding risk is acceptable.

APRIL 2022 | www.anzcp.org 24