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← Section III · Chamber Size and Function
III.J

Doppler Estimation of Volumetric Flow

6 cards

Notes

Fundamental formula

SV=CSA×VTISV = CSA \times VTI

  • Cross-sectional area (CSA) measured in cm², velocity-time integral (VTI) in cm → SV in cm³ (= mL).
  • CSA of a circular annulus = π × (d/2)² = 0.785 × d².

Common sites of measurement

  • LVOT: annulus CSA (mid-systole, inner-to-inner from PLAX) × VTI from LVOT PW (apical 5C).
  • Mitral annulus: MV annulus CSA × MV inflow VTI.
  • Pulmonary annulus: PV annulus CSA × RVOT VTI.
  • Ascending aorta or descending aorta at suprasternal notch, when other windows fail.

Cardiac output

  • CO = SV × HR (mL/min).
  • Normal CO: 4–8 L/min. Normal cardiac index (CO/BSA): 2.5–4.0 L/min/m².

Continuity equation

  • Applied at points where flow is conserved (before and after a stenosis, or between different valves without regurgitation).
  • Aortic valve area = (CSA_LVOT × VTI_LVOT) / VTI_AV.
  • Mitral prosthesis EOA = (CSA_LVOT × VTI_LVOT) / VTI_prosthesis (requires no significant AR/MR).

Shunt flow calculation (Qp:Qs)

  • Qp:Qs = SV_pulmonary / SV_systemic.
  • Qp = CSA_pulmonic valve × VTI_pulmonic.
  • Qs = CSA_LVOT × VTI_LVOT.
  • Qp:Qs > 1.5 typically indicates hemodynamically significant left-to-right shunt (candidate for closure).
  • Qp:Qs > 2 in unrepaired ASD/VSD strongly favors closure (in absence of Eisenmenger physiology).

Sources of error

  • Incorrect annulus diameter - small error is squared. Underestimating LVOT diameter by 10 % underestimates SV by ~20 %.
  • Poor Doppler alignment - underestimates velocity (cos θ error).
  • Off-axis (oblique) plane through the annulus - overestimates diameter.
  • Sample volume position - LVOT PW too close to valve captures acceleration; too far captures LV inflow.

Regurgitant volume by two-site method

  • MR volume = SV_mitral inflow − SV_LVOT (only if AV competent).
  • AR volume = SV_LVOT − SV_mitral inflow (only if MV competent).
  • Regurgitant fraction = RV / SV_regurg valve (in %).

Cards

  • clozeIII.J-001
    Volumetric flow by Doppler: SV = CSA × VTI. CSA of a circular annulus = 0.785 × d².
  • basicIII.J-002
    Formula for cardiac output and normal range?
    → CO = SV × HR. Normal 4–8 L/min. Cardiac index (CO/BSA) normal 2.5–4.0 L/min/m².
  • basicIII.J-003
    State the two components of Qp:Qs and the threshold typically considered hemodynamically significant.
    → Qp = CSA_pulmonic × VTI_pulmonic. Qs = CSA_LVOT × VTI_LVOT. Qp:Qs > 1.5 is hemodynamically significant; > 2.0 usually prompts closure in unrepaired shunts.
  • basicIII.J-004
    Why do small errors in LVOT diameter measurement produce large errors in stroke volume?
    → CSA = π × (d/2)². The diameter is SQUARED — a 10% underestimation of diameter underestimates CSA (and SV) by ~20%.
  • basicIII.J-005
    State the aortic valve area continuity equation.
    → AVA = (CSA_LVOT × VTI_LVOT) / VTI_AV.
  • basicIII.J-006
    When are regurgitant volumes computed by SV-difference INVALID?
    → When both valves being compared have significant regurgitation, or when either is stenotic. For MR: aortic valve must be competent. For AR: mitral valve must be competent.