Evaluate and manage a patient with cardiac disease in pregnancy

In one line

Cardiac disease is the single most important non-obstetric cause of maternal death in South Africa, and the registrar's task is to risk-stratify before the haemodynamic load of pregnancy unmasks the lesion — using the modified WHO (mWHO) classification to decide who may proceed, who needs a pregnancy heart team, and who should be counselled against pregnancy altogether.

Two conditions that reliably accompany cardiac disease in our population have their groundwork at Intermediate level: anaemia in pregnancy, which removes the very reserve a failing heart depends on, and obesity in pregnancy, which multiplies the anaesthetic and thrombotic risk of every cardiac decision.

This chapter assumes the groundwork in the physiology of pregnancy and the murmur work-up taught at Intermediate; the consultant layer is classifying the lesion by how it fails under load, the named anticoagulation and PPCM regimens and exactly how they differ, the trial appraisal, and the judgement calls at the extremes of viability and at delivery.

Assessment

The Final candidate is expected to move beyond "murmur in pregnancy" to a structured risk assessment. Physiological pregnancy raises cardiac output ~40–50%, drops systemic vascular resistance and adds a hypercoagulable, volume-loaded state that peaks late in the second trimester, again at delivery and — dangerously — in the first 48 hours postpartum as the autotransfusion of uterine blood returns. A fixed-output lesion (severe mitral stenosis, pulmonary hypertension) cannot accommodate this and decompensates.

Classify the lesion by how it fails under load

The Intermediate list of "valve lesions and congenital defects" is assumed. Decompensation is predictable from the haemodynamic category, because pregnancy's three insults — a 40–50% rise in cardiac output, a fall in SVR, and the autotransfusion/diuresis of the early puerperium — each punish a different physiology. Sorting every patient into one of these categories sets the management:

• Fixed-output / inflow-obstructed lesions (severe mitral stenosis, severe aortic stenosis, pulmonary hypertension). These cannot raise stroke volume to meet the demand, so the body raises heart rate instead — and tachycardia is the enemy. In mitral stenosis the shortened diastole collapses transvalvular filling; in aortic stenosis the shortened diastole starves coronary perfusion of a hypertrophied ventricle; in pulmonary hypertension any fall in preload or rise in pulmonary resistance precipitates acute RV failure and a fatal low-output spiral. Management is therefore to rate-control, preserve preload and sinus rhythm, and guard against the fall in SVR (so regional anaesthesia must be incremental, never a single-shot spinal). Pulmonary arterial hypertension consequently sits in mWHO IV.
• Volume-overload / regurgitant lesions (mitral regurgitation, aortic regurgitation, most left-to-right shunts). The fall in SVR is protective — it reduces regurgitant fraction and afterload — so these are generally well tolerated, and the danger window is the postpartum SVR rebound and volume shift, not the antenatal period. These women usually reach term on surveillance and afterload-friendly drugs rather than intervention.
• Cyanotic / shunt lesions where SVR is load-bearing (Eisenmenger, uncorrected cyanotic CHD, systemic-RV physiology). Here the falling SVR worsens right-to-left shunting and deepens hypoxaemia, and the hypercoagulable state threatens paradoxical embolism. Management is to maintain afterload, give meticulous thromboprophylaxis, and avoid air in lines; Eisenmenger carries some of the highest maternal mortality of any lesion and belongs in the "advise against pregnancy" group.
• Aortopathy (Marfan, Loeys-Dietz, bicuspid-valve aortopathy, Turner syndrome). The lesion is the wall, not the valve: oestrogen-driven medial change plus the hyperdynamic circulation raise dissection risk, which clusters in the third trimester and early puerperium. Management is beta-blockade throughout, trimester-by-trimester aortic imaging, and mode-of-delivery decided by root diameter (see Management). Aortic dissection complicates roughly 3–5% of Marfan pregnancies.
• Pump-failure lesions (dilated/peripartum cardiomyopathy, severe LV impairment). A ventricle already at the limit of its Frank-Starling reserve cannot absorb a 50% output rise. The EF threshold drives everything (EF <30% is mWHO IV), and PPCM is its own diagnostic and therapeutic problem (below).

History. Establish the lesion, prior cardiac events, current NYHA functional class, exercise tolerance and arrhythmia. In the SA setting, actively seek rheumatic fever history and a previous diagnosis of peripartum cardiomyopathy (PPCM) — recurrence risk is substantial and worse if LV function has not normalised. SA maternal cardiac deaths are driven overwhelmingly by rheumatic disease (chiefly mitral stenosis) plus PPCM, the opposite mix to high-income registries dominated by congenital disease — so the index of suspicion for a tight, undiagnosed mitral valve in a late-booking patient must be high.

Examination. Distinguish the benign flow murmur of pregnancy from pathology. Red flags mandating echocardiography: a diastolic murmur, a loud or radiating systolic murmur, fixed splitting, signs of failure (raised JVP, basal crepitations, hepatomegaly), cyanosis or clubbing, and resting tachycardia disproportionate to gestation. Any woman presenting in pregnancy or up to ~6 months postpartum with dyspnoea or heart-failure symptoms should be "red-flagged" — orthopnoea and paroxysmal nocturnal dyspnoea are never physiological.

The atypical and subtle presentations that catch the unwary

The masked case is more dangerous than the classic one. Several traps recur:

• Decompensation that mimics normal late pregnancy. Ankle oedema, exertional breathlessness, a soft systolic flow murmur and a third heart sound are all physiological in the third trimester — which is exactly why a tight mitral stenosis or an early cardiomyopathy hides. The discriminators are orthopnoea, PND, a resting tachycardia that does not settle, a diastolic murmur, and a raised JVP — none of which are physiological. Treat new functional-class deterioration as cardiac until proven otherwise.
• PPCM presenting as something else. Because it strikes a young, previously well woman, PPCM is misattributed to chest infection, pulmonary embolism, "anxiety" or pre-eclampsia. The postpartum woman re-presenting with breathlessness, a cough (sometimes pink frothy sputum mistaken for infection) and fatigue needs an echo, not a course of antibiotics.
• The first presentation is the emergency. In a poorly resourced antenatal pathway, the lesion is often unmasked by acute pulmonary oedema in labour or by new atrial fibrillation — the "first contact" is a crisis, and the diagnosis is made retrospectively on the post-stabilisation echo.
• Functional class can lag the lesion. A woman may report NYHA I–II yet have severe stenosis because she has unconsciously limited her activity. Objective exercise tolerance and the echo, not the self-reported class alone, define risk.

Investigations. ECG and transthoracic echocardiography are the workhorses — echo defines lesion, valve area/gradients, LV ejection fraction and pulmonary pressures. NT-proBNP is useful: a level rising or >128 pg/mL around 20 weeks independently predicts adverse events. Chest radiography (shielded) is justified where failure is suspected. The output of assessment is a mWHO class, which drives everything downstream.

Reading the investigations like a consultant — where the numbers mislead

• Echocardiographic severity thresholds carry the diagnosis. Severe mitral stenosis is a valve area ≲1.0 cm²; the pregnant patient with an area in the 1.0–1.5 cm² range may look stable at booking and decompensate at 24–28 weeks as output peaks, so the gradient at rest in early pregnancy under-reads the risk — exercise or the natural haemodynamic stress test of advancing gestation reveals it. For aortic stenosis, a mean gradient is flow-dependent: the high-output pregnant state inflates the gradient, so do not over-call severity, but equally a "moderate" gradient in a symptomatic woman is severe physiology.
• NT-proBNP interprets in trend, not as a single value. Pregnancy modestly raises BNP/NT-proBNP versus the non-pregnant state, so a mildly raised level is not automatically failure; a level that rises serially or sits high around 20 weeks is the signal that predicts events, and a normal level is a useful negative. It does not distinguish lesion type.
• The ECG is for rhythm and strain, not diagnosis. New AF in a woman with a diastolic murmur is mitral stenosis until proven otherwise; right-axis deviation and RV strain point to pulmonary hypertension or a shunt.
• Pulse oximetry and the hyperoxia response matter in suspected shunt/cyanotic disease — resting desaturation, or a fall on exertion, reframes the risk entirely.
• What echo cannot give you is the trajectory. A reassuring booking echo does not license complacency; the assessment is repeated across gestation because the lesion's tolerance is being continuously tested by a rising load.