Mitral Stenosis Rheumatic Legacy

1. Introduction

Mitral stenosis (MS) is one of the most characteristic and historically significant valvular heart diseases. It refers to the pathological narrowing of the mitral valve orifice, which impedes blood flow from the left atrium (LA) to the left ventricle (LV). Although the mitral valve may be affected by congenital, degenerative, or rare infiltrative processes, rheumatic heart disease (RHD) remains the predominant cause of mitral stenosis worldwide.

Mitral stenosis exemplifies the enduring impact of rheumatic fever, which often develops after an untreated streptococcal throat infection in childhood. Despite dramatic declines in rheumatic fever incidence in high-income countries due to improved hygiene, antibiotics, and healthcare access, mitral stenosis remains a major public health problem in low- and middle-income nations, where RHD continues to flourish.

This article explores mitral stenosis as a “rheumatic legacy”, delving into its epidemiology and historical context, hemodynamic consequences, symptoms and auscultatory findings, and the indispensable role of echocardiography in diagnosis and management.

2. Epidemiology and Historical Context

2.1 Historical Perspective

19th and early 20th centuries: Mitral stenosis was one of the most common valvular diseases in Europe and North America. Physicians like Laennec and Osler meticulously described the murmur of MS, highlighting its unique diastolic rumble.
Decline in developed countries: The introduction of penicillin in the mid-20th century led to a sharp reduction in acute rheumatic fever, and consequently, the incidence of rheumatic mitral stenosis plummeted in Western nations.
Persistence in developing nations: Today, MS continues to be a major cause of morbidity and mortality in South Asia, Sub-Saharan Africa, Latin America, and parts of the Middle East.

2.2 Global Burden

Prevalence: Around 33 million people globally suffer from rheumatic heart disease, and a large proportion of them have mitral stenosis.
Age distribution:
- In endemic regions: Often manifests in teens or young adults.
- In developed countries: Seen mainly in older immigrants or survivors of childhood rheumatic fever.
Gender predisposition: MS is more common in women (about 2:1 ratio).
Public health challenge: Contributes significantly to maternal mortality in countries with high RHD prevalence, as pregnancy exacerbates MS symptoms.

2.3 Etiology Beyond Rheumatic Fever

Congenital mitral stenosis: Rare; presents in childhood with other anomalies.
Degenerative mitral annular calcification: Can mimic MS in elderly populations.
Radiation-induced or drug-related (ergotamine, methysergide) cases are exceedingly rare.

Thus, the “rheumatic legacy” remains the principal explanation for most cases worldwide.

3. Hemodynamic Consequences of Mitral Stenosis

The mitral valve normally has an area of 4–6 cm². Symptoms typically develop when the orifice narrows to <2 cm², and severe stenosis is defined as ≤1.0 cm².

3.1 Pathophysiology

Obstruction of LA emptying → Left atrial pressure rises.
Elevated LA pressure → pulmonary venous hypertension → pulmonary congestion and dyspnea.
Chronic LA pressure overload → LA enlargement, increasing risk of atrial fibrillation and thromboembolism.
Transmission of high pressure to pulmonary circulation → pulmonary hypertension and eventual right ventricular (RV) strain.
Long-standing disease → right-sided heart failure (edema, hepatomegaly, ascites).

3.2 Stages of Hemodynamic Progression

Compensated stage: Mild narrowing, LA pressure slightly elevated, patients asymptomatic.
Decompensated LA stage: Marked LA dilation, atrial fibrillation, risk of emboli.
Pulmonary vascular disease: Pulmonary arteriolar changes cause fixed pulmonary hypertension.
RV failure stage: Tricuspid regurgitation, systemic congestion, poor prognosis.

3.3 Hemodynamic Parameters

Mitral valve gradient: The pressure difference between LA and LV rises as stenosis worsens.
Pulmonary artery pressure: Elevated in moderate-to-severe MS.
Cardiac output: Reduced during exercise, leading to exertional symptoms.

4. Symptoms and Murmur Characteristics

4.1 Clinical Presentation

The hallmark symptoms result from elevated LA pressure, pulmonary congestion, and reduced cardiac output.

Dyspnea: Initially exertional, later at rest; due to pulmonary venous congestion.
Orthopnea and paroxysmal nocturnal dyspnea: Result of redistribution of blood into pulmonary circulation when supine.
Fatigue and weakness: Due to low cardiac output.
Hemoptysis: From rupture of bronchial veins under high LA pressure.
Palpitations: Often due to atrial fibrillation.
Right heart failure symptoms: Edema, ascites, hepatomegaly in advanced disease.

4.2 Impact of Atrial Fibrillation

Common complication in MS (up to 50% of patients).
Leads to sudden worsening of symptoms due to loss of atrial contraction.
Increases risk of systemic embolism, particularly stroke.

4.3 Murmur Characteristics

Mitral stenosis produces one of the most distinctive murmurs in cardiology.

Auscultatory findings:
1. Opening snap (OS): High-pitched sound after S2, caused by sudden tensing of stenotic leaflets.
2. Diastolic rumble: Low-pitched, best heard with the bell of the stethoscope at the apex, in the left lateral decubitus position.
3. Presystolic accentuation: Intensification of murmur during atrial contraction (lost if atrial fibrillation develops).
Loud S1: Due to forceful closure of stiffened mitral valve.
Other signs:
- Pulmonary hypertension → loud P2.
- Right heart failure → tricuspid regurgitation murmur.

4.4 Clinical Staging by Symptoms

Mild MS: Symptoms only with exertion.
Moderate MS: Dyspnea on daily activity.
Severe MS: Symptoms at rest, RV failure signs.

5. Role of Echocardiography

Echocardiography is the gold standard for diagnosing and assessing the severity of mitral stenosis. It provides essential data on valve anatomy, hemodynamics, and complications.

5.1 Transthoracic Echocardiography (TTE)

Valve morphology: Thickened leaflets, commissural fusion, doming of anterior leaflet (“hockey-stick” appearance).
Mitral valve area: Measured by planimetry or Doppler pressure half-time method.
Pressure gradients: Peak and mean transmitral gradients using Doppler.
LA size: Enlargement is a common feature.
Pulmonary artery pressure: Estimated via tricuspid regurgitant jet velocity.

5.2 Transesophageal Echocardiography (TEE)

Superior for detecting LA thrombus, especially before balloon valvotomy.
Helps assess valve morphology for suitability of percutaneous mitral balloon valvuloplasty (PMBV).

5.3 3D Echocardiography

Provides detailed assessment of mitral valve anatomy.
Improves accuracy of valve area measurement.

5.4 Role in Management Decisions

Mild MS: Medical management and monitoring.
Moderate-to-severe MS: Assessment for PMBV or surgical intervention.
Complications: Guidance in detecting atrial thrombus, pulmonary hypertension, and RV dysfunction.

6. Additional Diagnostic Tools

Although echocardiography dominates, other modalities play supportive roles:

Chest X-ray: Shows LA enlargement, straightening of left heart border, pulmonary congestion, calcified mitral valve.
ECG: Left atrial enlargement (P mitrale), atrial fibrillation, RV hypertrophy in advanced cases.
Cardiac catheterization: Used when noninvasive data are inconclusive; directly measures transmitral gradient and pulmonary pressures.

7. Modern Management Overview (Brief Context)

While this article emphasizes causes and pathophysiology, a brief note on management contextualizes the importance of diagnosis.

Medical therapy: Diuretics for congestion, rate/rhythm control for AF, anticoagulation for embolism prevention.
Interventional therapy:
- Percutaneous balloon mitral valvotomy (PBMV): Preferred for suitable valve anatomy.
- Surgical commissurotomy or valve replacement: For unsuitable anatomy or failed PBMV.