When is mitral regurgitation considered severe?

Definition of Severe Mitral Regurgitation

Severe mitral regurgitation is defined by an effective regurgitant orifice area (EROA) ≥0.4 cm² for primary MR and ≥0.2 cm² for secondary MR, regurgitant volume (RVol) ≥60 mL for primary MR and ≥30 mL for secondary MR, regurgitant fraction (RF) ≥50%, and vena contracta width ≥7 mm. 1

Primary vs. Secondary Mitral Regurgitation

The definition of severe MR differs based on whether the MR is primary (degenerative) or secondary (functional):

Primary MR (valve abnormality causes leakage)

• EROA ≥0.4 cm²
• RVol ≥60 mL/beat
• RF ≥50%
• Vena contracta ≥7 mm

Secondary MR (ventricular dysfunction causes normal valve to leak)

• EROA ≥0.2 cm²
• RVol ≥30 mL/beat
• RF ≥50%
• Vena contracta ≥7 mm

Integrated Assessment Approach

It's crucial to understand that no single parameter should be used in isolation. Guidelines emphasize integrating multiple parameters to grade MR severity 1:

• Qualitative measures:

  • Pulmonary vein systolic flow reversal or minimal to no systolic flow
  • Central large jet >50% of left atrial area
  • E-wave dominant mitral inflow (>1.2 m/s)
  • PISA radius ≥1.0 cm at Nyquist limit

• Supporting findings:

  • Left atrial and left ventricular dilatation
  • TVI mitral/TVI aortic >1.4

Important Physiological Considerations

The relationship between EROA and regurgitant volume is complex and depends on multiple factors 1:

1. Left ventricular end-diastolic volume (LVEDV): An EROA of 0.2 cm² can be associated with RF >50% when LVEDV is normal, but typically requires 0.3 cm² at moderately dilated LVEDV values (220-240 mL).

2. Pressure gradient between LV and LA: Higher EROA values occur in decompensated heart failure patients with hypotension and elevated LA pressure compared to hypertensive patients with normal LA pressure.

3. Left ventricular ejection fraction (LVEF): It's virtually impossible to have a 60 mL regurgitant volume unless LVEF is >40% and the LV is significantly dilated.

Limitations of PISA Method

The PISA (proximal isovelocity surface area) method commonly used to calculate EROA has important limitations 1:

• Underestimates true EROA in secondary MR due to the crescentic shape of the proximal convergence
• Cannot be performed in the absence of a defined proximal convergence zone
• May be difficult to measure in mild MR

Clinical Implications

The distinction between primary and secondary MR thresholds is critical because:

1. In secondary MR, the LV is already damaged, and even lesser degrees of MR can have adverse hemodynamic effects 1

2. The prognostic influence of MR severity is more important early in the disease course, and less important later when LV dilation is extreme and advanced heart failure is established 1

3. Treatment approaches differ significantly between primary and secondary MR 2

Remember that severe MR by itself may be considered an indication for repair in primary MR, while the indications for intervention in secondary MR are less certain and require consideration of multiple factors 2.