Pathophysiology & How Pregnancy Aggravates MS
Consequences of the fixed mitral obstruction
Narrowed mitral valve → obstruction to LV filling
↓ Cardiac outputFixed, cannot rise with demand → fatigue, syncope
↑ Left atrial pressurePulmonary congestion → dyspnoea, orthopnoea, haemoptysis, pulmonary oedema
LA enlargementAF · thromboembolism · Ortner's syndrome (LA compresses recurrent laryngeal nerve)
Pulmonary hypertensionRV hypertrophy → RV failure (↑ CVP, hepatomegaly, ascites, oedema)
Loss of atrial kick matters: the stiff, hypertrophied left atrium contributes a disproportionate share of LV filling. When atrial fibrillation supervenes, filling falls and the patient may decompensate acutely — so maintaining sinus rhythm is a priority.
🤰 How pregnancy aggravates mitral stenosis
- ↑ Blood volume 30–50% (peaks ~28–32 weeks; the "second-trimester surge" 20–24 weeks) → ↑ pulmonary capillary hydrostatic pressure → pulmonary oedema.
- Progesterone → ↓ SVR and a ↑ heart rate → shorter diastole → ↓ LV filling across a fixed valve.
- NYHA class typically worsens by one grade during pregnancy.
- Autotransfusion during delivery (uterine contraction + relief of aortocaval compression) suddenly loads the left atrium → highest risk of pulmonary oedema is during labour and the immediate post-partum period.
- ↑ Coagulability → thromboembolic risk (compounded by AF and LA stasis).