Mitral Stenosis: Causes, Pathophysiology, Symptoms, Diagnosis, Management and Prevention

Mitral Stenosis: Causes, Pathophysiology, Clinical Features, Diagnosis and Management

~Introduction

Mitral stenosis (MS) is a valvular heart disease characterized by the narrowing of the mitral valve orifice, which impedes blood flow from the left atrium (LA) to the left ventricle (LV) during diastole. This obstruction leads to increased pressure in the left atrium, pulmonary vasculature, and eventually the right heart chambers, resulting in pulmonary hypertension and right-sided heart failure if untreated.
Mitral stenosis remains an important cause of morbidity and mortality worldwide, particularly in developing countries where rheumatic fever continues to be prevalent. Although the incidence has declined in industrialized nations due to better control of rheumatic fever, it persists as a significant cardiovascular problem globally.

~Anatomy and Physiology of the Mitral Valve

The mitral valve, also known as the bicuspid valve, is located between the left atrium and left ventricle. It consists of two leaflets (anterior and posterior), chordae tendineae, papillary muscles, and the annulus. During diastole, the valve opens to allow blood flow from the left atrium to the left ventricle. During systole, it closes to prevent regurgitation of blood back into the atrium.

Normal mitral valve area (MVA) is approximately 4–6 cm². When the effective orifice area decreases below 2 cm², obstruction to left ventricular filling becomes hemodynamically significant, producing clinical symptoms.

~Etiology

The most common cause of mitral stenosis worldwide is rheumatic heart disease (RHD), which follows group A β-hemolytic streptococcal pharyngitis. Other rare causes include:

1. Congenital Mitral Stenosis – developmental anomalies of the mitral valve apparatus such as a parachute mitral valve or supravalvular mitral ring.

2. Degenerative (Calcific) Mitral Stenosis – due to senile calcification of the mitral annulus, seen in elderly individuals.

3. Collagen Vascular Disorders – such as systemic lupus erythematosus.

4. Infective Endocarditis – healing with scarring may rarely cause obstruction.

5. Carcinoid Heart Disease – involvement of the left side is rare but may occur in some cases.

6. Prosthetic Valve Obstruction – from pannus formation or thrombus after valve replacement.

~Pathophysiology

In rheumatic mitral stenosis, inflammatory processes following rheumatic fever cause thickening, fibrosis, and commissural fusion of the valve leaflets. Chordae tendineae become shortened, thickened, and fused, resulting in the characteristic “fish mouth” appearance of the mitral valve.

Hemodynamic Consequences

• Increased Left Atrial Pressure: Narrowing of the valve leads to elevated LA pressure to maintain forward flow.

• Pulmonary Venous Hypertension: Elevated LA pressure transmits backward into the pulmonary veins and capillaries, causing pulmonary congestion and dyspnea.

• Pulmonary Arterial Hypertension: Chronic pulmonary venous hypertension induces vasoconstriction and remodeling of pulmonary arterioles.

• Right Ventricular Hypertrophy and Failure: Persistent pulmonary hypertension increases the workload on the right ventricle, eventually leading to right-sided failure.

• Reduced Cardiac Output: As LV filling is impaired, cardiac output diminishes, especially during exertion.

~Severity Classification

Mitral stenosis is graded based on the mitral valve area and pressure gradients:

Severity	Valve Area (cm²)	Mean Gradient (mmHg)	Pulmonary Artery Pressure
Mild	>1.5	<5	Normal
Moderate	1.0–1.5	5–10	30–50 mmHg
Severe	<1.0	>10	>50 mmHg

~Clinical Manifestations

The onset of symptoms in mitral stenosis typically occurs years after the initial rheumatic insult. Symptoms may remain silent until the valve area is critically reduced.

Symptoms

1. Dyspnea on Exertion: Most common initial symptom due to elevated pulmonary venous pressure.

2. Orthopnea and Paroxysmal Nocturnal Dyspnea: Due to pulmonary congestion.

3. Fatigue: Result of decreased cardiac output.

4. Hemoptysis: Due to rupture of pulmonary bronchial veins.

5. Palpitations: Often due to atrial fibrillation secondary to left atrial enlargement.

6. Chest Pain: Occasionally due to pulmonary hypertension.

7. Hoarseness (Ortner’s Syndrome): Compression of the recurrent laryngeal nerve by an enlarged left atrium.

8. Thromboembolic Events: From left atrial thrombus in atrial fibrillation.

Signs

1. General Appearance: Malar flush (“mitral facies”) due to reduced cardiac output and peripheral vasodilation.

2. Pulse: Irregularly irregular in atrial fibrillation; small-volume pulse.

3. Apex Beat: Tapping in character due to palpable first heart sound (S1).

4. Heart Sounds:

   • Loud S1: Due to forceful closure of the mobile stenotic valve.

   • Opening Snap (OS): High-pitched sound after S2 due to abrupt halting of valve opening.

   • Mid-Diastolic Murmur: Low-pitched, rumbling murmur best heard at the apex with the patient in the left lateral position.

   • Presystolic Accentuation: Occurs in sinus rhythm due to atrial contraction.

5. Signs of Pulmonary Hypertension: Right ventricular heave, loud P2, tricuspid regurgitation murmur, peripheral edema, and ascites in advanced disease.

~Complications

1. Atrial Fibrillation (AF): Due to atrial dilatation.

2. Systemic Embolism: Commonly from left atrial thrombus.

3. Pulmonary Hypertension and Right Heart Failure.

4. Infective Endocarditis: Though rare, can occur in deformed valves.

5. Hemoptysis: Due to rupture of bronchial veins.

6. Pregnancy Complications: Worsened symptoms due to increased blood volume and cardiac demand.

~Diagnostic Evaluation

1. Electrocardiogram (ECG)

• P mitrale: Broad, notched P waves indicating left atrial enlargement.

• Atrial Fibrillation: Common in advanced cases.

• Right Ventricular Hypertrophy: May appear in long-standing pulmonary hypertension.

2. Chest X-Ray

• Left Atrial Enlargement: Double shadow of right heart border, straightening of left heart border.

• Pulmonary Venous Hypertension: Prominent pulmonary veins, Kerley B lines.

• Calcification: Of mitral valve in chronic cases.

3. Echocardiography

• Key Diagnostic Tool.

  • Assesses valve morphology, leaflet motion, commissural fusion, and subvalvular apparatus.

  • Measures mitral valve area by planimetry or pressure half-time method.

  • Evaluates transvalvular gradient and pulmonary artery pressure.

  • Detects left atrial thrombus and associated mitral regurgitation.

4. Cardiac Catheterization

• Used when echocardiographic findings are inconclusive or before intervention.

• Measures pressure gradients and pulmonary artery pressures directly.

5. Doppler Studies

• Quantify the severity of stenosis and presence of associated regurgitation.

~Management

The management of mitral stenosis depends on the severity of obstruction, symptom status, and the presence of complications such as atrial fibrillation or pulmonary hypertension.

1. Medical Management

Medical therapy is mainly supportive and aimed at symptom relief:

a. Diuretics

• Reduce pulmonary congestion and dyspnea by lowering left atrial pressure.

b. Beta-Blockers / Calcium Channel Blockers

• Control heart rate, especially in atrial fibrillation, allowing more time for ventricular filling.

c. Anticoagulation

• Warfarin indicated in patients with atrial fibrillation, history of embolism, or presence of left atrial thrombus.

• Maintains INR between 2.0–3.0.

d. Digoxin

• For rate control in atrial fibrillation, especially with right heart failure.

e. Antibiotic Prophylaxis

• For prevention of rheumatic fever recurrence and infective endocarditis in selected cases.

2. Interventional and Surgical Management

Definitive treatment aims to relieve obstruction and restore normal blood flow.

a. Percutaneous Transvenous Mitral Commissurotomy (PTMC)

• Procedure of choice for suitable patients (pliable valve, non-calcified, no thrombus, minimal regurgitation).

• Balloon catheter introduced via femoral vein and inflated across the mitral valve to separate fused commissures.

• Provides excellent symptomatic relief and long-term results.

b. Surgical Commissurotomy

• Closed Commissurotomy: Performed without cardiopulmonary bypass (less common now).

• Open Commissurotomy: Direct visualization and separation under cardiopulmonary bypass; indicated when PTMC is unsuitable.

c. Mitral Valve Replacement (MVR)

• Indicated for heavily calcified or deformed valves, or when PTMC/commissurotomy is contraindicated.

• Mechanical or bioprosthetic valves are used depending on patient profile and age.

~Prognosis

The natural history of mitral stenosis is variable. Patients may remain asymptomatic for decades after rheumatic fever. Once symptoms develop, progression can be rapid, especially with atrial fibrillation or pregnancy.
Without intervention, severe mitral stenosis leads to pulmonary hypertension, right heart failure, and death within 2–5 years. Successful balloon valvotomy or valve surgery markedly improves survival and quality of life.

~Mitral Stenosis in Pregnancy

Pregnancy increases cardiac output by 30–50%, which can exacerbate mitral stenosis symptoms.

• Mild cases: Managed conservatively with close monitoring and diuretics.

• Moderate to severe cases: PTMC may be safely performed in the second trimester if symptoms are refractory to medical therapy.

• Anticoagulation in AF requires careful adjustment due to teratogenic risk of warfarin.

~Prevention

1. Primary Prevention: Prompt diagnosis and treatment of streptococcal pharyngitis with penicillin to prevent rheumatic fever.

2. Secondary Prevention: Long-term antibiotic prophylaxis (benzathine penicillin every 3–4 weeks) in patients with a history of rheumatic fever.

3. Early Detection: Regular echocardiographic screening in high-risk populations.

4. Lifestyle Modifications: Avoid excessive salt, manage infections promptly, and maintain healthy physical activity.

~Recent Advances

• Three-Dimensional Echocardiography: Provides more accurate assessment of valve anatomy and suitability for PTMC.

• Transcatheter Mitral Valve Replacement (TMVR): An emerging alternative for high-risk surgical patients.

• Minimally Invasive and Robotic Surgeries: Offer reduced morbidity and faster recovery.

• Novel Anticoagulants: Being evaluated for use in rheumatic atrial fibrillation though warfarin remains standard.

~Conclusion

Mitral stenosis remains a major public health issue in developing regions despite global progress in healthcare. Rheumatic fever continues to be the predominant cause, making prevention and early intervention essential. Timely diagnosis through echocardiography, appropriate medical management, and interventional procedures like percutaneous balloon valvotomy have significantly improved outcomes. However, lifelong follow-up is required due to potential recurrence and associated complications. A multidisciplinary approach involving cardiologists, surgeons, and primary care physicians is crucial to ensure optimal patient care and long-term prognosis.