Mechanical heart valve (MHV) + Pregnancy (BSH 2023)

Intro

Estimated incidence of MHV in pregnancy = 3.7 per 100,000 pregnancies

High maternal risks associated with MHV in pregnancy

  • 9% maternal mortality

  • 41% severe morbidity

  • 16% valve thrombosis

  • 9% Stroke

High foetal risks associated with MHV in pregnancy

  • Miscarriage, stillbirth, foetal haemorrhage, warfarin-induced teratogenicity

Above data from UK Obstetric Surveillance System

  • Estimate only 28% of pregnancies have a good maternal + foetal outcome

MHV thrombosis risk

Higher risk valves: Starr-Edwards, Lillehei-Kaster, Bjork-Shiley, other ‘titling-disc’ valves

Medium risk valves: Other ‘bi-leaflet’ valves

Lower risk valves: Carbomedics, Medtronic, St Jude Medical, On-X

Other contributing risk factors

  • Mitral, tricuspid or pulmonary valves

  • Previous VTE

  • Valve dysfunction/mismatch

  • Left ventricular impairment

  • AF

  • Poor anticoagulation adherence

choice of anticoagulant

Warfarin from positive pregnancy test until 36 weeks —> LMWH

  • Lowest maternal mortality and composite maternal risk

  • Highest foetal loss and composite foetal risk

  • Live birth rate higher when daily dose <5mg/day

Combination (LMWH —> Warfarin weeks 13-36 —> LMWH)

  • Most risks/outcomes sit between Warfarin and LMWH alone

LMWH alone

  • Highest maternal mortality and composite maternal risk

  • Lowest foetal loss and composite foetal risk

Unfractionated heparin rarely used.

DOACS are inferior to warfarin for MHVs, and cross the placenta

(See Table 2 in BSH guideline for detailed stats on risks)

Warfarin Teratogenicity

(also applies to other VKA’s)

Pathophysiology

  • Osteocalcin carboxylation for bone formation is a vitamin K dependent process

  • Warfarin has low molecular weight —> easy transfer across the placenta —> foetus more anticoagulated than the mother due to immature foetal liver enzymes

 

First Trimester - Foetal Warfarin Syndrome (FWS)

  • Occurs following warfarin exposure during gestational weeks 6-12

  • Affects ~10% of foetuses exposed. Possible dose-response relationship.

  • 6% congenital abnormalities

  • Nasal hypoplasia —> neonatal respiratory distress

  • Stipling of vertebrae & epiphyses —> hypoplasia of extremities

 

Second and third trimester risks

  • Risk of foetal, placental and neonatal haemorrhage

  • Other reported adverse outcomes from warfarin use in pregnancy

    • CNS – microcephaly, hydrocephalus, Dandy-Walker malformation

    • Eyes – blindness

    • Still birth, neonatal death, premature delivery

    • Others – scoliosis, developmental delay, deafness, CHD, seizures

Breastfeeding

  • Warfarin is safe in breast feeding

Antenatal care

Specialist team should include obstetrics, cardiology and haematology as a minimum

Care throughout pregnancy should be provided at a specialist tertiary centre

Counselling should start prior to cardiac surgery in individuals of childbearing age

Pre-pregnancy counselling/history

  • Indication, type, number and age of MHV’s

  • Cardiac symptoms, cardiac function, valve function

  • Adherence with current/previous anticoagulation

  • Discussion of risks in pregnancies, pros and cons of each management strategy

  • Warfarin teratogenicity from 6 weeks gestation —> importance of early pregnancy tests

  • Plus general preconception care - medication review, supplements, lifestyle etc

Anticoagulant Monitoring During Pregnancy

Warfarin

  • European guidelines (ESC) recommend using the same INR range as outside of pregnancy

  • Monitor every 1-2 weeks

  • Avoid high INRs (greater anticoagulation in the foetus, see above)

  • Do not reduce dose to reduce teratogenic risks as evidence for this dose relationship is not secure

LMWH

  • Switch from warfarin to LMWH very high risk period for valve thrombosis

  • Switch to LMWH the day of stopping warfarin. INR does not need to be in normal range.

  • Use twice daily dosing

  • Use higher dose of LMWH compared to outside of pregnancy

    • 2.5mg/kg/day enoxaparin

    • 250 IU/kg dalteparin and tinzaparin

  • Monitor Anti-Xa levels (Most individuals require a dose increase during treatment)

    • Peak Anti-Xa target 1.0-1.4 IU/ml

    • Weekly until target achieved then every 2-4 weeks

aspirin

Add Aspirin 75mg daily if no contraindications

Increase to 150mg daily at 12 weeks in patients at increased risk of pre-eclampsia

valve thrombosis

Diagnosis

Low index of suspicion

Signs/Symptoms include:

  • Loss valve clicking sound

  • Left sided obstructive symptoms - SOB, heart failure, syncope, cardiogenic shock

  • Right-sided obstructive symptoms - loss of appetite, peripheral oedema, ascites

  • Left-sided non-obstructive symptoms - Stroke, renal infarct, splenic infarct

  • Right-sided non-obstructive symptoms - Pulmonary embolism

Mangement

Specialist care, see guideline for details

peri-partum anticoagulation

High risk period

Risk of PPH and wound haematomas

MDT should prepare written management plan in advance

Anticoagulation

  • Switch to LMWH at 36 weeks

  • Aim to give last dose of LMWH >24hours prior to delivery

  • Consider stopping aspirin 3 days prior to delivery

Neuroaxial anaesthesia

  • 24-hour interval required from time of last treatment dose LMWH to spinal procedures

  • If prophylactic dose LMWH given whilst spinal catheter in situ, then 12-hour interval required from time of last dose to removal of catheter.

post-partum anticoagulation

High risk period for major bleeding

—> This also increases thrombotic risk through delays to re-introduction of anticoagulants

BSH recommends prophylactic-intermediate dose LMWH for first 24-48 hours post-delivery

Treatment dose LMWH from 48 hours onward

Re-introduce warfarin from 5-7 days post-delivery

(Note other national guidelines recommend therapeutic dose LMWH from 6-8 hours post-delivery).