How do you grade the severity of mitral stenosis using echocardiogram (echo)?

Echocardiographic Grading of Mitral Stenosis Severity

Mitral valve area (MVA) measured by 2D planimetry is the most direct and reliable parameter for grading mitral stenosis severity, with severe stenosis defined as MVA < 1.0 cm², moderate as 1.0-1.5 cm², and mild as > 1.5 cm². 1

Primary Severity Parameters

The severity classification relies on three key echocardiographic measurements that should be assessed together:

Mitral Valve Area (MVA)

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

Two-dimensional transthoracic echocardiography (TTE) with direct planimetry of the valve orifice is the reference standard method for measuring MVA. 1 This technique provides the most accurate assessment and should be prioritized over calculated methods. 2

Mean Transmitral Gradient

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

Measure the mean gradient using continuous wave Doppler across the mitral valve, ensuring maximal sweep speed and minimal velocity scale for optimal accuracy. 3

Pulmonary Artery Systolic Pressure (PASP)

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

PASP reflects the hemodynamic consequences of mitral stenosis and provides prognostic information beyond valve area alone. 1

Alternative Measurement Techniques

Pressure Half-Time Method

Doppler echocardiography can calculate MVA using the pressure half-time (PHT) method, though this has significant limitations in elderly patients and those with hemodynamic confounders. 2 The PHT-derived MVA should be used as a supportive measure rather than the primary determinant, as it can be affected by left atrial and left ventricular compliance, aortic regurgitation, and other conditions. 2

Three-Dimensional Echocardiography

3D echocardiography provides more accurate planimetry of valve area and better assessment of commissural fusion and subvalvular apparatus compared to 2D imaging. 1 When available, 3D imaging offers comprehensive evaluation of valve morphology from the "surgical view." 1

Stress Echocardiography for Discordant Cases

Exercise echocardiography is indicated when resting hemodynamics do not match clinical symptoms—specifically in asymptomatic patients with severe mitral stenosis (MVA < 1 cm²) or symptomatic patients with non-severe mitral stenosis (MVA > 1.5 cm²). 3, 1

During stress testing, hemodynamically significant mitral stenosis is defined by:

• Mean gradient > 15 mmHg during exercise 3, 1
• Mean gradient > 18 mmHg during dobutamine infusion 3, 1
• PASP > 60 mmHg during exercise 3, 1

Use supine bicycle exercise when possible to acquire images at baseline, low workload, and peak exercise, allowing assessment of both mitral valve gradient and PASP throughout the stress protocol. 3

Transesophageal Echocardiography (TEE) Indications

TEE should be performed when:

• TTE images are suboptimal or technically inadequate 1
• Excluding left atrial thrombus before percutaneous mitral commissurotomy 1
• Assessing valve suitability for percutaneous intervention 1
• Clinical findings are discordant with TTE results 3

Critical Pitfalls to Avoid

Always integrate clinical examination with echocardiographic findings—a high pre-test probability from physical examination (early diastolic opening snap, low-pitched diastolic rumble) should prompt additional investigation if echo results are discordant. 3 The echocardiogram can underestimate severity due to technical factors such as improper Doppler alignment or suboptimal imaging windows. 3

Specific Technical Considerations:

• Concomitant valve disease: Associated mitral regurgitation or aortic valve disease may affect gradient measurements and should be carefully evaluated. 1
• Body size: Consider indexed valve area (MVA/BSA) in patients with large body surface area, as absolute MVA may underestimate functional severity. 1
• Atrial fibrillation: When present, perform stress echo during continuation of rate control medication to avoid early rise in heart rate that confounds gradient assessment. 3
• Low flow states: In patients with reduced cardiac output, gradients may be falsely low despite anatomically severe stenosis—valve area by planimetry becomes even more critical in this setting. 3

Algorithmic Approach to Severity Assessment

1. Obtain 2D TTE with direct planimetry of MVA as the primary measurement 1
2. Measure mean transmitral gradient using continuous wave Doppler 1
3. Calculate PASP from tricuspid regurgitation velocity 1
4. Verify concordance between all three parameters 1
5. If discordant with symptoms: Proceed to exercise echocardiography 3, 1
6. If technically limited images: Consider TEE for definitive assessment 1