How do you assess the severity of mitral stenosis?

Assessment of Mitral Stenosis Severity

Echocardiography is the preferred method for diagnosing mitral stenosis and assessing its severity, with valve area measurement by planimetry being the reference standard for determining severity. 1

Primary Echocardiographic Parameters for Severity Assessment

• Mitral valve area (MVA) is the most direct measure of stenosis severity:

  • Severe: MVA < 1.0 cm² 1
  • Moderate: MVA 1.0-1.5 cm² 1
  • Mild: MVA > 1.5 cm² 1

• Mean transmitral gradient is an important hemodynamic parameter:

  • Severe: > 10 mmHg at rest 1, 2
  • Moderate: 5-10 mmHg 1
  • Mild: < 5 mmHg 1

• Pulmonary artery systolic pressure (PASP) reflects hemodynamic consequences:

  • Severe: > 50 mmHg at rest 1
  • Moderate: 30-50 mmHg 1
  • Mild: < 30 mmHg 1

Imaging Techniques for Assessment

• Two-dimensional transthoracic echocardiography (TTE) should be used to:

  • Measure valve area by planimetry (reference standard) 1
  • Assess valve morphology including mobility, thickness, calcification, and subvalvular fusion 3
  • Calculate Wilkins' score (1-4 points for each: leaflet mobility, thickness, calcification, and subvalvular thickening) to determine suitability for intervention 3

• Doppler echocardiography should be used to:

  • Calculate mean transmitral gradient using continuous wave Doppler 1
  • Estimate valve area using pressure half-time method 3
  • Assess pulmonary artery pressure using tricuspid regurgitation velocity 1

Stress Echocardiography for Borderline Cases

• Exercise echocardiography is indicated in:

  • Asymptomatic patients with severe mitral stenosis (MVA < 1 cm²) 1
  • Symptomatic patients with non-severe mitral stenosis (MVA > 1.5 cm²) 1
  • Patients with discordant symptoms and resting hemodynamics 1

• Criteria for hemodynamically significant mitral stenosis during stress:

  • Mean gradient > 15 mmHg during exercise or > 18 mmHg during dobutamine infusion 1
  • PASP > 60 mmHg during exercise 1
  • Early increase in PASP at low-level exercise 1

Common Pitfalls and Caveats

• Heart rate effects: Tachycardia can artificially increase the gradient without changing the actual severity of stenosis 2
• Cardiac output effects: Low cardiac output states may result in low gradients despite severe stenosis 2
• Atrial fibrillation: Irregular rhythm can cause variable gradients; multiple measurements should be averaged 2
• Concomitant valve disease: Associated mitral regurgitation or aortic valve disease may affect assessment 1
• Body size considerations: Indexed valve area may be more appropriate in patients with large body surface area 1

Advanced Imaging Techniques

• Transesophageal echocardiography (TOE) is indicated:

  • To exclude left atrial thrombus before percutaneous mitral commissurotomy (PMC) 1
  • When TTE images are suboptimal 1
  • To assess suitability for percutaneous intervention 1

• 3D echocardiography provides:

  • More accurate planimetry of valve area 4
  • Better assessment of commissural fusion and subvalvular apparatus 1
  • Comprehensive evaluation of valve morphology from the "surgical view" 1

Remember that mitral stenosis severity assessment should integrate multiple parameters rather than relying on a single measurement, as discordance between valve area and gradient can occur due to various hemodynamic factors 2.