Mitral Stenosis: Comprehensive Clinical Overview
Definition and Anatomy
Mitral stenosis is a pathologic narrowing of the mitral valve orifice that may be congenital or acquired, resulting in obstruction to blood flow from the left atrium to the left ventricle 1. The mitral valve apparatus consists of four interconnected structures: the mitral annulus, the anterior and posterior leaflets, the chordae tendineae, and the papillary muscles—abnormalities in any component can result in stenosis 2.
Etiology and Pathophysiology
Primary Causes
Rheumatic mitral stenosis accounts for 85% of all cases worldwide and involves commissural fusion with thickening at the leaflet tips 2. This remains the predominant etiology globally despite declining incidence in developed nations 3.
Degenerative mitral stenosis results from mitral annular calcification (MAC) with progressive calcium deposition, valve thickening, and chordal shortening—notably without commissural fusion 2. This form is increasingly identified in developed countries, particularly in elderly patients 3.
Congenital mitral stenosis includes several subtypes: mitral annular hypoplasia (incomplete development resulting in abnormally small annulus), subvalvular mitral stenosis (stenosis of chordae tendineae and/or papillary muscles including parachute mitral valve, mitral arcade, and hammock mitral valve), and supravalvular or intravalvular mitral ring (ridge of tissue attached to the atrial side of leaflets) 1.
Hemodynamic Consequences
Reduced mitral valve orifice area causes elevation of left atrial pressure and pulmonary artery systolic pressure, with severity determined by the valve area and transvalvular gradient 2.
During exercise, increased cardiac output acutely increases the transvalvular gradient and left atrial pressure in stenotic valves, precipitating pulmonary edema and potential vascular rupture 4.
Pregnancy represents a critical stress period, as plasma volume increases 40% and cardiac output increases 30-50% during gestation, with maximal stress on stenotic valves occurring between weeks 24-32 4.
Severity Classification
Severe mitral stenosis is defined as a mitral valve area (MVA) ≤1.0 cm² with a mean transmitral gradient ≥10 mmHg 2. For clinical decision-making, intervention should be considered when MVA is <1.5 cm² with clinically significant symptoms 2, 5.
Signs and Symptoms
Clinical Presentation
Marked dyspnea on mild exertion, dyspnea at rest, or pulmonary edema indicate severe disease requiring intervention 5.
Hemoptysis occurs from rupture of pulmonary vessels due to elevated left atrial and pulmonary venous pressures, particularly during exercise or pregnancy 4.
Atrial fibrillation develops from chronic left atrial enlargement and pressure elevation 5.
Recurrent systemic emboli result from left atrial thrombus formation, particularly in the setting of atrial fibrillation 5.
Right ventricular failure manifests in advanced disease with chronic pulmonary hypertension 5.
Physical Examination Findings
- Auscultation reveals a characteristic opening snap followed by a diastolic rumble, best heard at the apex with the patient in the left lateral decubitus position 6.
Electrocardiographic Findings
- Bimodal P waves (P mitrale) indicate left atrial hypertrophy secondary to mitral valve obstruction 4.
Diagnosis and Evaluation
Echocardiography (Primary Diagnostic Modality)
Echocardiography is the preferred method for diagnosing mitral stenosis and assessing severity, with valve area by planimetry serving as the reference measurement 2, 7.
Transthoracic echocardiography must demonstrate: decreased mitral valve area, commissural fusion, valve thickening, and mean gradient >10 mmHg in severe stenosis 4.
Pulmonary artery systolic pressure quantification is essential, as it likely exceeds 50 mmHg in symptomatic patients 4.
Transesophageal echocardiography is required to exclude left atrial thrombi before any intervention, particularly percutaneous procedures 6.
Three-dimensional echocardiography provides enhanced anatomic visualization and improved assessment of valve morphology 7.
Additional Diagnostic Studies
Electrocardiography identifies atrial fibrillation and left atrial enlargement (P mitrale) 4.
Chest radiography may show left atrial enlargement and pulmonary congestion in advanced disease 6.
Cardiac catheterization is reserved for cases where non-invasive assessment is inconclusive or when coronary artery disease evaluation is needed before surgery 6.
Interventions and Treatments
Medical Management
Diuretics provide symptom relief when edema or pulmonary congestion is present, while heart rate control is essential in patients with atrial fibrillation 2.
Beta-blockers (metoprolol or atenolol preferred over propranolol in postpartum women) optimize diastolic filling through heart rate control 4.
Anticoagulation is mandatory in patients with atrial fibrillation to prevent thromboembolic complications 5.
Indications for Intervention
Intervention should be limited to patients with clinically significant (moderate to severe) mitral stenosis with valve area <1.5 cm² 2.
NYHA class II-IV symptoms with severe MS (MVA ≤1.5 cm²) warrant intervention 2.
Asymptomatic patients with very severe stenosis (MVA ≤1.0 cm²) and pulmonary hypertension (PASP >50 mmHg at rest or >60 mmHg with exercise) should be considered for intervention 2.
Percutaneous Balloon Mitral Commissurotomy (PBMC)
Percutaneous mitral balloon commissurotomy is the first-line intervention for symptomatic severe rheumatic MS with favorable valve morphology 2, 3.
The Inoue technique displays the most advantages: the balloon is short, soft, and its special unfolding character enables secure placement without risk of ventricular perforation 6.
Favorable valve morphology includes: minimal calcification, pliable leaflets, minimal subvalvular disease, and absence of significant mitral regurgitation 6.
Expected results include MVA increase from 1.0 to 1.8 cm² with significant reduction in mean gradient 6.
Complications occur in <10% of cases: mortality <1%, severe mitral regurgitation in 5%, thromboembolic events (preventable with TEE screening), and hemodynamically significant atrial septal defect (rare) 6.
Mid-term results (5-10 years) and low restenosis rates are comparable to surgical commissurotomy in patients with suitable valve morphology 6.
PBMC is indicated for NYHA class III-IV symptoms refractory to medical management when valve anatomy is favorable 4.
Surgical Intervention
Mitral valve replacement should be considered as the primary surgical option for degenerative MS 2.
Open commissurotomy may be performed in patients with no significant calcification and no major concomitant mitral regurgitation, preserving the subvalvular apparatus and left ventricular geometry 5.
Mitral valve replacement is indicated when: marked valve calcification is present, significant mitral regurgitation coexists, extensive degenerative destruction of subvalvular apparatus exists, or PBMC has failed 6.
Valve replacement entails lifelong anticoagulation in the majority of patients 5.
Special Clinical Scenarios
Young patients with severe mitral stenosis yet few symptoms may benefit from early PBMC to prevent progressive left atrial and pulmonary vascular changes 6.
Pregnant females with symptomatic severe MS should undergo PBMC as it avoids the risks of cardiopulmonary bypass 6.
Emergency situations with acute decompensation warrant urgent PBMC when anatomically feasible 6.
Patients with Grade II mitral stenosis and intermittent atrial fibrillation may benefit from intervention to prevent progression and thromboembolic complications 6.
Potential Complications
Disease-Related Complications
Pulmonary hypertension develops from chronic elevation of left atrial pressure, leading to increased pulmonary vascular resistance 1, 2.
Right ventricular failure occurs in advanced disease with severe pulmonary hypertension 5.
Atrial fibrillation results from chronic left atrial enlargement and increases thromboembolic risk 5.
Systemic thromboembolism, particularly stroke, occurs from left atrial thrombus formation 5.
Hemoptysis from pulmonary vessel rupture can be life-threatening 4.
Pulmonary edema develops acutely with increased cardiac output demands (exercise, pregnancy, fever, anemia) 4.
Intervention-Related Complications
PBMC complications include: severe mitral regurgitation (5%), thromboembolic events, atrial septal defect, and mortality <1% 6.
Surgical complications include: perioperative mortality, prosthetic valve complications, requirement for lifelong anticoagulation, and prosthesis-patient mismatch 1, 5.
Restenosis after PBMC occurs within 1-5 years in older patients with calcified, fibrotic valves 6.
Surveillance and Follow-up
Asymptomatic severe mitral stenosis requires echocardiographic assessment every 2-3 years, with more frequent monitoring for very severe stenosis or borderline hemodynamics 2.
Yearly monitoring is appropriate for patients with very severe stenosis (MVA ≤1.0 cm²) 2.
Post-intervention surveillance includes: assessment for restenosis, prosthetic valve function, and development of complications 7.
Relevant Red Flags and CVICU Tips
Critical Red Flags
Acute hemoptysis in a postpartum woman (within 3 months) should immediately raise suspicion for mitral stenosis, as symptoms may be erroneously attributed to physiologic pregnancy changes or asthma 4.
New-onset atrial fibrillation with rapid ventricular response in a patient with mitral stenosis can precipitate acute pulmonary edema and requires urgent rate control 4, 5.
Sudden neurologic deficits suggest systemic embolism from left atrial thrombus and warrant immediate anticoagulation and TEE 5.
Worsening dyspnea with hemodynamic instability indicates acute decompensation requiring urgent intervention 5.
CVICU Management Pearls
Aggressive heart rate control is paramount: maintain heart rate 60-80 bpm to optimize diastolic filling time, using beta-blockers as first-line agents 4.
Avoid tachycardia at all costs: fever, pain, anxiety, and hypovolemia must be aggressively managed as increased heart rate dramatically worsens hemodynamics 4.
Preload management requires careful balance: diuretics relieve pulmonary congestion but excessive diuresis reduces cardiac output 2.
Screen for left atrial thrombus with TEE before any intervention, even in patients without atrial fibrillation, as thrombus can form in sinus rhythm with severe stenosis 6.
Pulmonary artery catheterization may be necessary in critically ill patients to guide hemodynamic management and assess response to therapy 6.
Anticoagulation is mandatory in atrial fibrillation and should be initiated urgently after excluding contraindications 5.
Post-PBMC monitoring includes: serial echocardiography to assess for acute mitral regurgitation, hemodynamic monitoring for 24 hours, and observation for thromboembolic events 6.