Severity Classification of Mitral Stenosis
Mitral stenosis is classified as severe when the mitral valve area (MVA) is ≤1.0 cm², mean transmitral gradient is >10 mmHg, and pulmonary artery systolic pressure (PASP) is >50 mmHg. 1
Diagnostic Parameters for Severity Classification
The severity of mitral stenosis is determined using three key parameters:
| Severity | MVA (cm²) | Mean Gradient (mmHg) | PASP (mmHg) |
|---|---|---|---|
| Mild | >1.5 | <5 | <30 |
| Moderate | 1.0-1.5 | 5-10 | 30-50 |
| Severe | <1.0 | >10 | >50 |
Hemodynamic Assessment
The hemodynamic severity is best characterized by:
- Planimetered mitral valve area - Direct measurement of the valve orifice
- Calculated mitral valve area from the diastolic pressure half-time (PHT)
- MVA (cm²) = 220/PHT (ms)
- PHT ≥150 ms suggests severe stenosis 2
The mean pressure gradient is highly dependent on:
- Transvalvular flow
- Diastolic filling period
- Heart rate variations
Dynamic Assessment of Severity
Exercise or stress echocardiography provides valuable information about the hemodynamic significance of mitral stenosis:
- MS is diagnosed as severe if the mean gradient is >15 mmHg on exertion or >18 mmHg during dobutamine infusion 2
- PASP >60 mmHg on exertion is another marker of hemodynamically significant MS 2
Important Clinical Considerations
- A noncompliant mitral valve may be moderately stenotic at rest but hemodynamically severely stenotic during stress, as it fails to open further to accommodate increased flow 2
- Mean gradient <10 mmHg does not exclude severe MS, particularly in patients with:
- Atrial fibrillation
- Enlarged left atrium
- Impaired left ventricular diastolic function 1
Discrepancies in Guidelines
While most guidelines agree on the definition of severe MS as MVA ≤1.0 cm², there are some variations:
- The European Society of Cardiology (ESC) and American College of Cardiology/American Heart Association (ACC/AHA) guidelines define severe MS as MVA ≤1.5 cm² for intervention purposes 2
- The diastolic pressure half-time threshold of ≥150 ms is used inconsistently across guidelines 2
Intervention Considerations
Intervention is typically considered for:
- Symptomatic patients with severe MS (MVA ≤1.0 cm²)
- Moderate MS (MVA 1.0-1.5 cm²) with evidence of hemodynamic significance:
- Mean gradient >15 mmHg during exercise
- PASP >60 mmHg during exercise 2
Conclusion
When evaluating mitral stenosis severity, it is essential to integrate multiple parameters including MVA, mean gradient, and PASP. In cases of discrepancy between resting measurements, stress echocardiography provides crucial information about the hemodynamic significance of the stenosis, which better reflects the true functional severity of the condition.