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Week 3: Mitral Stenosis > MVA Calculations > Flashcards

MVA Calculations Flashcards

1
Q

What are the three main parameters used to assess the severity of MS?

A
  1. Mitral valve area (MVA is the key parameter)
  2. Mean pressure gradient (mPG) (supportive)
  3. RVSP (supportive)
    - mPG and RVSP are supportive and cannot be used alone
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2
Q

What methods can be used in the calculation of MVA?

A
  1. 2D planimetry (note this calculates AOA not EOA; AOA>EOA)
  2. P1/2t
  3. SV Method
  4. PISA
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3
Q

MVA: Technique for 2D Planimetry?

A
  1. Zoomed PSAX view of MV
  2. From papillary muscle level, scan superiorly and medially to MV tips
  3. Scroll to mid-diastolic frame
  4. Trace inner margins of AVA (average 3 cycles)
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4
Q

MVA via 2D Planimetry Limitations?

A
  1. Angle of interrogation - need to measure MVA at leaflet tips
  2. Heavy calcification of MV - MV orifice not clearly seen
  3. Measures AOA - not comparable to other methods; EOA < AOA
    (3D echo method of choice to evaluate MVA)
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5
Q

Formula to calculate MVA via P1/2t?

A

MVA (cm2) = 220 / p½t (ms)

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6
Q

Significance of p½t in MVA?

A

P½t of 220ms = MVA < 1.0cm2

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7
Q

Technique for measuring p½t?

A
  1. Apical 4 chamber view
  2. CW doppler of mitral inflow
  3. Measure along early diastolic slope (E wave; like DT but not measured to baseline)
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8
Q

Limitations of p½t?

A
  1. Non-linear (curvilinear) diastolic slopes
  2. Significant AR
  3. Acute changes in LA compliance
  4. Rhythm disturbances (arrhythmias)
  5. Significant LV diastolic dysfunction
  6. Atrial septal defects
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9
Q

Limitations of p½t?

A
  1. Non-linear (curvilinear) diastolic slopes
  2. Significant AR
  3. Acute changes in LA compliance
  4. Rhythm disturbances (arrhythmias)
  5. Significant LV diastolic dysfunction
  6. Atrial septal defects
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10
Q

Which method is used to measure p½t?

A
  • 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)
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11
Q

Effect of significant AR on MVA calculation via p½t?

A
  • 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
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12
Q

How do changes in LA compliance affect MVA calculation via p½t?

A
  • Occurs immediately following PBMV; the relationship between p½t and MVA is altered
  • Accurate measurement by p½t can only be obtained 24-48hrs post valvuloplasty
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13
Q

Affect of ASD on MVA calculation via p½t?

A
  • 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
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14
Q

What is the continuity principle?

A
  • What flows in must flow out

- SV1 = SV2

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15
Q

Formula for MVA via Stroke Volume Method?

A

MVA = (LVOT area × LVOT VTI) / MV VTI

  1. Measure LVOT diameter
  2. Measure LVOT VTI
  3. Measure MV VTI (CW inflow trace)
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16
Q

Limitations of MVA via Stroke Volume Method?

A
  1. Under/overestimation of LVOTd (LVOT area)
  2. Poor sample volume placement (LVOT VTI)
  3. Poor alignment with MS jet (MV VTI)
    * Formula only valid in absence of significant AR or MR
17
Q

Calculation of MVA via Stroke Volume Method when there is significant AR will?

A

MVA will be overestimated

18
Q

Calculation of MVA via Stroke Volume Method when there is significant MR will?

A

MVA will be underestimated

19
Q

When only AR is present, what other formula can be used to calculate MVA using stroke volume method?

A

MVA = (RVOT area × RVOT VTI) / MV VTI

* Only valid when no significant MR, PR or intracardiac shunt)

20
Q

What is the key assumption of the PISA method?

A

Assumes volumetric flow rate proximal to a narrowed orifice (Q1) = volumetric flow rate through narrowed orifice (Q2)

21
Q

PISA Formula for MVA?

A

EROA = (2πr^2×VN) / MV Vmax

MV Vmax = peak E velocity on CW Doppler

22
Q

What is angle correction and when is it used in PISA?

A
  • 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
23
Q

PISA EOA Formula with angle correction factor (non-planar flow convergence)?

A

EOA corrected = EOA x 0.56

24
Q

PISA MVA Limitations

A
  1. Assumes EOA is constant over diastole
  2. Assumes EOA is circular
  3. Changes in PISA radius over diastole
  4. Need for angle correction (more measurements increase likelihood for error)
25
Q

Which is the preferred method for calculation of MVA?

A
  • PISA method can always be used

- Not affected by AR, so can be used irrespective of AR or MR

Week 3: Mitral Stenosis (3 decks)

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