Mitral Stenosis (MS) in Pregnancy and Anaesthesia Management

1. Introduction

• Creasy & Resnik's Maternal-Fetal Medicine, p. 1258

2. Pathophysiology of MS

• Reduced left ventricular filling - the LV is chronically under-loaded; stroke volume is reduced
• Elevated LA pressure - transmitted back to the pulmonary capillaries, causing pulmonary oedema
• Tachycardia worsens haemodynamics - faster heart rate = less diastolic filling time = higher LA pressure
• Atrial fibrillation (AF) - eventual complication; loss of atrial systole (which contributes 20-30% of ventricular filling) further raises the transvalvular gradient and drops cardiac output
• Pulmonary hypertension - chronic LA hypertension raises pulmonary vascular resistance (PVR), eventually causing right ventricular failure
• Thromboembolism - blood stasis in dilated LA (especially with AF) promotes clot formation and risk of embolic stroke
• Morgan & Mikhail's Clinical Anaesthesiology, 7e, p. 759

3. Effect of Pregnancy on MS

• ~50% of pregnant women with severe MS develop pulmonary oedema
• Maternal risk of death and heart failure is highest in the third trimester and puerperium (when cardiac output peaks)
• Long-standing MS causes right-sided heart failure, massive haemoptysis, pulmonary embolism, and infective endocarditis

• Severe MS (MVA < 1.0 cm²) in pregnancy is WHO Class IV - contraindicated
• Mild/moderate MS is WHO Class II-III depending on symptoms
• Creasy & Resnik's Maternal-Fetal Medicine, p. 1258-1259

4. Pre-conception Counselling and Antenatal Management

Pre-conception

• Women with significant MS should undergo percutaneous balloon mitral valvuloplasty (PBMV) before conception and delay pregnancy until fully recovered
• Women with severe MS and right-sided heart failure should avoid pregnancy until valvular disease is corrected

Antenatal management of MS in pregnancy

1. Activity restriction - bed rest, no strenuous activity
2. Salt restriction and diuretics - to control pulmonary congestion
3. Rate control - beta-blockers (metoprolol, atenolol), digoxin, or calcium-channel blockers (non-dihydropyridine) to maintain HR < 90 bpm
4. Atrial fibrillation management - if AF occurs: rate control with digoxin ± beta-blocker; anticoagulation (LMWH or UFH; warfarin only with caution in 2nd trimester)
5. Anticoagulation - recommended for significant MS with AF; heparin is preferred peripartum
6. Regular foetal surveillance - reduced uteroplacental flow can cause IUGR and foetal distress
7. PBMV during pregnancy - if heart failure is severe and refractory to medical therapy; should be done in 2nd trimester with abdominal/pelvic lead shielding (foetal mortality with PBMV is lower than open surgery; cardiac surgery on bypass carries a 20-30% foetal mortality rate)

• Creasy & Resnik's Maternal-Fetal Medicine, p. 1259, 1731

5. Obstetric Medications to Avoid

• Creasy & Resnik's Maternal-Fetal Medicine, p. 1730

6. Mode and Timing of Delivery

• Planned induction and vaginal delivery is generally recommended for most MS patients
• Caesarean section is reserved for obstetric indications (not cardiac alone), except in severe/critical MS where a controlled elective caesarean under optimised conditions may be preferred
• Multidisciplinary team approach is mandatory: cardiologist, MFM specialist, anaesthesiologist, cardiac surgeon on standby
• Patient should be admitted to hospital well in advance of expected labour

• Creasy & Resnik's Maternal-Fetal Medicine, p. 1729-1730

7. Anaesthesia Management

Haemodynamic Goals in MS (The "FAST" mnemonic)

• Morgan & Mikhail's Clinical Anaesthesiology, 7e, p. 760

A. Monitoring

• Invasive arterial line (beat-to-beat blood pressure, especially for caesarean)
• Central venous pressure (CVP) - a prominent cv wave indicates tricuspid regurgitation; monitor fluid loading carefully
• Pulmonary artery catheter / PA wedge pressure - in severe MS, PCWP reflects the transvalvular gradient rather than LV filling; a notched P wave on ECG and prominent a waves + decreased y descent on PCWP trace indicate sinus rhythm with MS
• TOE/TTE - can guide perioperative management; useful for detecting LA thrombus, assessing valve area, and fluid responsiveness
• Continuous ECG - monitor for AF and other SVTs
• Pulse oximetry, foetal heart rate monitoring

B. For Labour Analgesia (Vaginal Delivery)

• Provides excellent pain relief without tachycardia from pain
• Gradual onset of sympathetic blockade (unlike spinal) allows time to compensate
• Reduces catecholamine-driven tachycardia
• Can be extended for instrumental delivery or emergency CS

• Insert epidural catheter early in labour (before haemodynamic stress of active labour)
• Use low-concentration local anaesthetic (e.g., bupivacaine 0.1% + fentanyl) via slow titration
• Avoid rapid high-dose boluses that cause sudden drops in SVR
• Maintain left uterine displacement to avoid aortocaval compression
• Phenylephrine (not ephedrine) is the vasopressor of choice if hypotension occurs - ephedrine causes tachycardia

C. For Caesarean Section

Epidural Anaesthesia (preferred for CS in MS)

• Slow, titrated onset allows gradual SVR changes
• Maintains patient awake (early detection of decompensation)
• Less risk of GA-related tachycardia on intubation
• Epidural is preferred over single-shot spinal for severe MS

Spinal Anaesthesia

• Relative contraindication in severe/critical MS - sudden sympathectomy causes precipitous drop in SVR and preload, potentially catastrophic
• If used, "saddle block" (low-dose/limited dermatomal spread) is safer than a full T4 block
• Avoid in pulmonary hypertension or critical MS

"Severe aortic or mitral stenosis are relative contraindications to neuraxial anaesthesia; however, with close monitoring and control of the anaesthetic level, neuraxial anaesthesia can be performed safely, particularly if extensive dermatomal spread is not required."

• Morgan & Mikhail's Clinical Anaesthesiology, 7e, p. 1806

General Anaesthesia (GA)

• Uncontrolled AF or haemodynamic instability
• Contraindication to regional (coagulopathy, patient refusal, failed regional)
• Emergency CS with insufficient time

• Pre-oxygenation
• Induction: etomidate (haemodynamically neutral) preferred; avoid ketamine (causes tachycardia); thiopentone in cautious dosing
• Use opioids (fentanyl, remifentanil) for blunting laryngoscopy response to prevent tachycardia
• Avoid rapid sequence induction vasopressor responses causing HR surge
• Maintenance: volatile agents (isoflurane/sevoflurane in low concentrations) - avoid agents causing tachycardia or major vasodilation
• Opioid-based technique (high-dose fentanyl + lower volatile concentration) can be used to maintain HR control
• Intraoperative tachycardia: deepen anaesthesia with opioid (not meperidine/pethidine which causes tachycardia); or give esmolol/metoprolol IV
• Vasopressors: phenylephrine is preferred (pure alpha-agonist, maintains SVR without tachycardia); vasopressin or norepinephrine can also be used; avoid ephedrine
• Morgan & Mikhail's Clinical Anaesthesiology, 7e, p. 760-761

D. Intraoperative Haemodynamic Management Summary

8. Postpartum Management

• Immediate postpartum is a high-risk period - autotransfusion from uterine contraction raises preload acutely; LA pressure rises, risk of pulmonary oedema peaks
• Continue monitoring in HDU/ICU for 24-48 hours postpartum
• Restart diuretics and rate control medications
• Oxytocin infusion (slow, dilute) is acceptable; avoid bolus oxytocin
• Ergometrine/methylergonovine are contraindicated (raise PVR)
• Carboprost is contraindicated (raises pulmonary pressure)
• Misoprostol (PGE1) is relatively safer for postpartum haemorrhage management
• Restart anticoagulation as soon as haemostasis allows
• Breastfeeding compatible with most medications (beta-blockers - use propranolol or metoprolol cautiously)

9. Key Points Summary

• Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice (pp. 1258-1260, 1729-1731)
• Morgan & Mikhail's Clinical Anaesthesiology, 7e (pp. 759-761, 1806-1807)
• Fuster and Hurst's The Heart, 15th Edition
• Harrison's Principles of Internal Medicine, 22e