What are the requirements for mitral stenosis in terms of Mitral Valve Area (MVA) by Pressure Half-Time (PHT) and mean gradient?

Requirements for Mitral Stenosis Diagnosis Based on MVA by PHT and Mean Gradient

Mitral stenosis is defined as severe when the mitral valve area (MVA) is <1.0 cm² and the mean transmitral gradient is >10 mmHg, with moderate stenosis defined as MVA 1.0-1.5 cm² and mean gradient 5-10 mmHg. 1

Classification of Mitral Stenosis Severity

Severity	MVA by PHT (cm²)	Mean Gradient (mmHg)	Pulmonary Artery Systolic Pressure (mmHg)
Mild	>1.5	<5	<30
Moderate	1.0-1.5	5-10	30-50
Severe	<1.0	>10	>50

Diagnostic Considerations

Pressure Half-Time (PHT) Method

• PHT measures the time required for the peak transmitral pressure gradient to decrease by half
• MVA (cm²) = 220/PHT (ms)
• A PHT ≥150 ms suggests severe stenosis 1

Important Limitations of PHT Method

• PHT may be inaccurate in patients with:
  • Abnormal left atrial or left ventricular compliance
  • Associated aortic regurgitation
  • Previous mitral valvotomy
  • Atrial fibrillation 1, 2
  • Older patients (≥60 years) show weak correlation between PHT and actual MVA 2

Mean Gradient Assessment

• Accurately measured from continuous-wave Doppler signal across mitral valve using modified Bernoulli equation
• Mean gradient >15 mmHg during exercise or >18 mmHg during dobutamine infusion indicates hemodynamically significant mitral stenosis 1
• Mean gradient is flow-dependent and may be lower than expected in severe MS with:
  • Low cardiac output states
  • Significant left atrial enlargement
  • Atrial fibrillation with slow ventricular response 3

Clinical Correlation

The relationship between MVA and mean gradient is not always straightforward:

• Patients with severe MVA (<1.0 cm²) may have mean gradients <10 mmHg (low-gradient severe MS) 3, 4
• Mean gradient reflects not only stenosis severity but also hemodynamic conditions:
  • Heart rate (higher with tachycardia)
  • Cardiac output
  • Left atrial compliance
  • Associated valvular lesions 3

Diagnostic Algorithm

1. Measure MVA by planimetry (most accurate reference method)
2. Calculate MVA by PHT method
3. Measure mean transmitral gradient
4. If discrepancy between MVA and gradient:
   • Consider exercise or dobutamine stress echocardiography
   • Look for PASP >60 mmHg on exercise (marker of significant MS) 1
   • Consider cardiac catheterization for direct hemodynamic assessment 1

Pitfalls to Avoid

• Relying solely on PHT for MVA calculation, especially after percutaneous mitral commissurotomy, in older patients, or those with atrial fibrillation 2
• Interpreting mean gradient in isolation without considering heart rate, rhythm, and cardiac output 3
• Failing to recognize that a mean gradient <10 mmHg does not exclude severe MS, particularly in patients with atrial fibrillation, enlarged left atrium, or impaired left ventricular diastolic function 4

When evaluating mitral stenosis, always correlate echocardiographic findings with clinical symptoms, as discordance may require further hemodynamic assessment during exercise to determine the true functional significance of the stenosis 1.