What are the three main parameters used to assess the severity of MS?
- Mitral valve area (MVA is the key parameter)
- Mean pressure gradient (mPG) (supportive)
- RVSP (supportive)
- mPG and RVSP are supportive and cannot be used alone
What methods can be used in the calculation of MVA?
- 2D planimetry (note this calculates AOA not EOA; AOA>EOA)
- P1/2t
- SV Method
- PISA
MVA: Technique for 2D Planimetry?
- Zoomed PSAX view of MV
- From papillary muscle level, scan superiorly and medially to MV tips
- Scroll to mid-diastolic frame
- Trace inner margins of AVA (average 3 cycles)
MVA via 2D Planimetry Limitations?
- Angle of interrogation - need to measure MVA at leaflet tips
- Heavy calcification of MV - MV orifice not clearly seen
- Measures AOA - not comparable to other methods; EOA < AOA
(3D echo method of choice to evaluate MVA)
Formula to calculate MVA via P1/2t?
MVA (cm2) = 220 / p½t (ms)
Significance of p½t in MVA?
P½t of 220ms = MVA < 1.0cm2
Technique for measuring p½t?
- Apical 4 chamber view
- CW doppler of mitral inflow
- Measure along early diastolic slope (E wave; like DT but not measured to baseline)
Limitations of p½t?
- Non-linear (curvilinear) diastolic slopes
- Significant AR
- Acute changes in LA compliance
- Rhythm disturbances (arrhythmias)
- Significant LV diastolic dysfunction
- Atrial septal defects
Limitations of p½t?
- Non-linear (curvilinear) diastolic slopes
- Significant AR
- Acute changes in LA compliance
- Rhythm disturbances (arrhythmias)
- Significant LV diastolic dysfunction
- Atrial septal defects
Which method is used to measure p½t?
- If there is a low EDV (small A wave), measure early diastolic slope (E wave)
- If high EDV (bigger A wave), measure mid-late diastolic slope (A wave)
Effect of significant AR on MVA calculation via p½t?
- In severe MS, LA-LV pressure gradient remains high throughout diastolic period
- With severe AR, the increase in LVEDP decreases the pressure gradient between the LA and LV at end-diastole
- Increase in LVEDP effectively reduces p½t resulting in overestimation of MVA
How do changes in LA compliance affect MVA calculation via p½t?
- Occurs immediately following PBMV; the relationship between p½t and MVA is altered
- Accurate measurement by p½t can only be obtained 24-48hrs post valvuloplasty
Affect of ASD on MVA calculation via p½t?
- MS and ASD: increased LAP due to MS with increased left-to-right shunt across ASD
- This reduced PG across MV during diastole
- MVA overestimated
- MS and ASD with L-R shunt = Lutembacher syndrome
What is the continuity principle?
- What flows in must flow out
- SV1 = SV2
Formula for MVA via Stroke Volume Method?
MVA = (LVOT area × LVOT VTI) / MV VTI
- Measure LVOT diameter
- Measure LVOT VTI
- Measure MV VTI (CW inflow trace)
Limitations of MVA via Stroke Volume Method?
- Under/overestimation of LVOTd (LVOT area)
- Poor sample volume placement (LVOT VTI)
- Poor alignment with MS jet (MV VTI)
* Formula only valid in absence of significant AR or MR
Calculation of MVA via Stroke Volume Method when there is significant AR will?
MVA will be overestimated
Calculation of MVA via Stroke Volume Method when there is significant MR will?
MVA will be underestimated
When only AR is present, what other formula can be used to calculate MVA using stroke volume method?
MVA = (RVOT area × RVOT VTI) / MV VTI
* Only valid when no significant MR, PR or intracardiac shunt)
What is the key assumption of the PISA method?
Assumes volumetric flow rate proximal to a narrowed orifice (Q1) = volumetric flow rate through narrowed orifice (Q2)
PISA Formula for MVA?
EROA = (2πr^2×VN) / MV Vmax
MV Vmax = peak E velocity on CW Doppler
What is angle correction and when is it used in PISA?
- In MS, can have non-planar flow convergence due to stenotic leaflets (angle assumed to be 100°)
- If flow convergence zone proximal to stenotic valve is flat then angle correction is not required
PISA EOA Formula with angle correction factor (non-planar flow convergence)?
EOA corrected = EOA x 0.56
PISA MVA Limitations
- Assumes EOA is constant over diastole
- Assumes EOA is circular
- Changes in PISA radius over diastole
- Need for angle correction (more measurements increase likelihood for error)
