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Pregnancy in women with mechanical prosthetic valves is associated with a high risk of maternal mortality due to valve thrombosis if anticoagulant use is irregular.
While cardiac surgical maternal risks are approximately the same as those in non-pregnant women, fetal mortality associated with cardiopulmonary bypass (CPB) can be up to 19%.
Fetal heart rate (FHR) monitoring using transesophageal echocardiography (TEE) has been reported in our institution, and end-diastolic velocity (EDV) is a more sensitive peri-operative fetal monitor than FHR.
A 27-year-old patient (G5P0) at 30 weeks-of-gestation presented with severe aortic stenosis. She had undergone aortic valve replacement and ventricular septal defect (VSD) repair 15 years previously. She took warfarin irregularly, and had stopped taking all medications 10 months previously to conceive. She refused termination of pregnancy and was scheduled for aortic valve replacement.
Baseline blood pressure was 102/57 mmHg, heart rate was 84 beats/min. After positioning supine with left-lateral tilt of 30 degrees, general anesthesia was induced with 150 mg propofol, 70 mg rocuronium and 50 μg sufentanil. Anesthesia was maintained by continuous intravenous infusion of 4 mg/kg/h propofol, 3 μg/kg/min of cisatracurium, 0.4 μg/kg/min remifentanil and intermittent sufentanil when anesthesia depth decreased. A TEE probe was inserted, positioned at the deep gastric level and rotated until the placenta was seen and the umbilical artery was identified using color Doppler (Fig. 1a). Fetal heart rate was calculated and positive EDV could be observed by using the pulsed-wave Doppler signal (Fig. 1b).
Fig. 1aPlacenta seen and umbilical artery identified
Heparin was administered to achieve an active clotting time >480 s and normothermic CPB was established, at which point maternal blood pressure was 92/56 mmHg, heart rate was 85 beats/min while FHR was 120 beats/min with a positive EDV. As pump flow increased, EDV gradually disappeared, FHR remained unchanged, while maternal blood pressure was 79/45 mmHg and heart rate was 91 beats/min (Fig. 2a).
Fig. 2aAs cardiopulmonarey bypass was initiated, the end-diastolic volume gradually disappeared while fetal heart rate was approximately unchanged
The fetal heart rate (FHR) significantly decreased following aortic-cross clamping since the pump flow was temporarily decreased (Fig. 2b). As mean arterial pressure (MAP) increased (from 54 to 74 mmHg), FHR also increased but with absence of end-diastolic velocity (AEDV) that persisted throughout the rest of the operation.
Fig. 2bFetal heart rate dropped abruptly and significantly at the very beginning of aortic-cross clamping
The operation continued without incident. As CPB was terminated, the patient’s blood pressure was 100/60 mmHg and heart rate was 98 beats/min, the FHR had increased to 133 beats/min. The hemodynamic changes are summarized in Fig. 3.
Fig. 3Maternal and fetal hemodynamic changes. Where “+” means end-diastolic volume (EDV) was present and “−” means absence of end-diastolic volume (AEDV). CPB: cardiopulmonary bypass. FHR: fetal heart rate
The patient was then transferred to the cardiac intensive care unit where she stayed for one night with continuous cardiotocography monitoring and intermittent transabdominal ultrasound examination. Fetal heart rate was sustained at 140–150 beats/min and the EDV reappeared 4 h postoperatively. She was subsequently transferred to the general ward where she remained for another four days, with three-day continuous cardiotocography monitoring and intermittent FHR monitoring on the last day. She was then discharged home in good condition using warfarin for anticoagulation. Follow-up three days later was unremarkable, and cardiotocography monitoring was normal.
She was re-admitted at 34+2 weeks-of-pregnancy with decreased fetal movements for 15 hours. She underwent emergency cesarean delivery. Severely meconium-stained amniotic fluid was found and the fetus was born with Apgar scores of 2, 4, 4 at 1, 5 and 10 min respectively. Intracranial hemorrhage was confirmed by ultrasound on the neonatal intensive care unit and the baby died 20 h later.
For pregnant women undergoing non-obstetric surgery, fetal heart rate monitoring is recommended
In this case, TEE in real time was used to detect changes in umbilical artery blood flow Doppler signals. Results were interpreted by a multi-disciplinary team including ultrasound physicians, obstetricians and fetal medicine specialists. Arterial flow waveform depends on the forward ejection of blood from the fetal heart, vessel elasticity and blood viscosity. During systole, blood velocity reaches a maximum after valve opening, whereas during diastole flow decelerates to the nadir (the EDV) when the cardiac contraction can no longer maintain forward flow against the elastic properties of the downstream vascular bed and the viscosity of the blood.
Umbilical arteries represent the downstream resistance of the placental circulation, since no somatic arteries arise from their origin, and their resistance is normally low. Placental dysfunction increases resistance and umbilical artery flow will fall and ultimately cease. If resistance rises further, the rigid placental circulation recoils after distension by pulse pressure and reversed end-diastolic flow occurs; fetal compromise increases as placental resistance increases. Absence of end-diastolic volume is a sign of fetal compromise and it may precede abnormal cardiotocography by up to 24 days.
We found EDV measured using TEE may be a useful intra-operative monitor of fetal blood supply. Although FHR was within the normal range, AEDV was present (Fig. 2a, Fig. 2b). Management included increasing maternal temperature and perfusion pressure, but although FHR increased, EDV did not recover. The association between decreased or absent EDV and short- or long-term fetal prognosis is unknown but AEDV is associated with intrauterine growth retardation
Risk of fetal death in growth-restricted fetuses with umbilical and/or ductus venosus absent or reversed end-diastolic velocities before 34 weeks of gestation: a systematic review and meta-analysis.
Transesophageal echocardiography may represent a supplemental peri-operative fetal monitor, and EDV monitoring may detect abnormalities with the potential to improve fetal outcome in cardiac surgery during pregnancy.
References
Chan W.S.
Anand S.
Ginsberg J.S.
Anticoagulation of pregnant women with mechanical heart valves: a systematic review of the literature.
Risk of fetal death in growth-restricted fetuses with umbilical and/or ductus venosus absent or reversed end-diastolic velocities before 34 weeks of gestation: a systematic review and meta-analysis.
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