Download Hemodynamics and General Principles

Hemodynamics and General Principles
in Valve Disease
Federico M Asch MD, FASE
MedStar Heart and Vascular Institute
Georgetown University
Washington, DC
• I have no financial disclosures related to this presentation
Outline
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Flow
Pressure Gradients
Meaningful Calculations in VHD
Application in Specific conditions
Basic General Concepts
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Flow
Pressure Gradients
Meaningful Calculations in VHD
Application in Specific conditions
Volumetric Flow
• Time Velocity Integral (TVI)
– The integrated area under a curve over a period of
time.
– Represents the distance (cm) that blood travels
with each stroke.
Time
TVI
Velocity
Volumetric Flow
• Cross Sectional Area (CSA)
– Mathematically calculated area of a circle.
– CSA = Ʌ r2
– CSA = 0.785 d2
CSA = (3.14)(1.05)2
2.1 cm
CSA = 0.785(2.1)2
= 3.46 cm2
Volumetric Flow
• Stroke Volume
– The amount of blood pumped out of the heart with each beat.
– Calculated as the CSA x TVI
2.1 cm
X
TVI
= Stroke Volume
cm2
X
cm
= cm3 (cc, ml)
LV Stroke Volume
LVOT CSA x TVI LVOT
SV = (0.785)(LVOT Diameter2) x TVI LVOT
Cardiac Output = SSV
V x HR/1000
HR/10
Cardiac Index = CO/BSA
Cardiac Output (C.O.)
• The amount of blood pumped out of the heart every minute
(Liters/minute)
• Calculated as the Stroke Volume x Heart Rate
• CO = SV (cc/beat) x HR (beats/minute)
• cc/minute
• Divide by 1000 to convert to Liters/minute
Cardiac Index (C.I.)
• The Cardiac Output (CO) indexed to Body Surface Area (BSA).
• Calculated as CO/BSA
• Units are L/min/m2
Volumetric Flow
• Pitfalls
– Inadequate Doppler / beam alignment.
– Inadequate sample volume placement.
– Inadequate tracing of TVI.
– Not valid with mod-severe aortic stenosis or regurgitation.
– Diameter and TVI measurements must be taken from the same
space.
– Diameter measurement errors are squared:
• small diam variation = large flow error
Qp/Qs
Pulmonic CO/Systemic CO
Qp =RVOT CSA x TVI
Qs = LVOT CSA x TVI
Basic General Concepts
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Flow
Pressure Gradients / PHT
Meaningful Calculations in VHD
Application in Specific conditions
Pressure Gradients
The Bernoulli Equation
ǻP = ½ ȡ (v22 – v12)
+
Convective
Acceleration
ȡ 2ƅv
ƅt
ǻs + R( V )
Flow
Acceleration
Viscous
Friction
The forces of viscous friction in the normal
clinical setting are negligible and can be
removed from the equation.
The Bernoulli Equation
ǻP = ½ ȡ (v22 – v12)
Convective
Acceleration
+
ȡ 2ƅv
ƅt
ǻs
Flow
Acceleration
The forces of flow acceleration in the normal
clinical setting are negligible and can be
removed from the equation.
The Bernoulli Equation
ǻP = ½ ȡ (v22 – v12)
Convective
Acceleration
Where:
½ ȡ = mass density for blood = 4
V1 = Flow velocity proximal to the
valve
V2 = Flow velocity distal to the
valve
If V1 values are
- <1 m/s V1 can be removed from the equation.
-
1-1.5 acceptable
-
> 1.5 cannot use simplified equation
ǻP = 4 (v22)
The Simplified Bernoulli Equation
ǻP = 4 (v22)
• RV or PA Systolic Pressure
– 4(TR Velocity)2 + RA Estimated Pressure
• PA Diastolic Pressure
– 4(End PR Velocity)2 + RA Estimated Pressure
• LA Pressure
– Systolic BP – 4(MR Systolic Velocity) 2
• RV Systolic Pressure (if VSD)
– Systolic BP – 4(VSD velocity)2
The Modified Bernoulli Equation
• Pitfalls
– Large angle 0 (beam not parallel to jet)
– Long tubular stenosis
– Changes in blood viscosity
– V1 > 1.5 m/s
Effect of incident angle
on recorded peak velocity
Feigenbaum’s Echocardiography, 6th Ed.
Calculation of PA Pressure
PA Diastolic Pressure
VPR End 2
VPR Early
+
RA Pressure
VPR End
PR
PA Systolic Pressure
TR
VTR2
+
RA Pressure
VTR
Mean Gradient
Average of all instantaneous (4 x V2) over the flow period
Gradients in Aortic Stenosis
Apical
ical 3 ch
Apical 5 ch
Pressure Half Time (PHT)
Time for peak gradient to decrease to half
CW
Mitral Stenosis:
MVA= 220/PHT
Longer PHT, More Severe MS
Pressure Half Time (PHT)
Time for peak gradient to decrease to half
CW
Regurgitation:
Shorter PHT= More severe Regurg
Basic General Concepts
•
•
•
•
Flow
Pressure Gradients
Meaningful Calculations in VHD
Application in Specific conditions
Basic General Concepts
• Flow
• Pressure Gradients
• Meaningful Calculations in VHD
– Regurgitant Volume and Fraction
– PISA / EROA
– Valve Area – Continuity equation
• Application in Specific conditions
Regurgitant Flow (PISA)
Va = 35 cm/sec
PISA Radius
Peak Velocity
ZĞŐƵƌŐŝƚĂŶƚ&ůŽǁс;ϮͿ;ʋͿ;ƌ2)( Va)
EROA = Regurgitant Flow / MR Peak Vel
Regurgitant Volume = (EROA)(TVI)
Regurgitant fraction (PISA) = Regurgitant
Volume/ SVLVOT + Regurgitant Volume
Regurgitant Volume
• Regurgitant Volume
– The amount of blood (volume) that passes through an incompetent
valve.
Regurg Vol = Mitral SV - Aortic SV
SVAO = CSAAO X TVIAO
SVMV = CSAMV X TVIMV
Regurg Vol = Mitral SV - Aortic SV
• AV (RV)
– SVAV – SVMV
SVAO = CSAAO X TVIAO
SVMV = CSAMV X TVIMV
• MV Regurgitant Volume (RV)
– SVMV – SVAV
Regurg Fraction (RF) = RV / SV
• AV RF
– RVAV / SVAV
SVAO = CSAAO X TVIAO
SVMV = CSAMV X TVIMV
• MV Regurgitant Fraction
(RV)RVMV – SVMV
Mitral Regurgitation
Quantitative Hemodynamics
70 cc
50
cc
120 cc
Systole
Diastole
R volume = 120 - 70 = 50 cc
R fraction = 50/120 = 42%
RV / RF (Doppler)
What to measure?
AV annulus Diameter
Long Axis View, end systole
Aortic Valve TVI
PW at the annulus
MV Annulus Diameter
4 chamber view, mid diastole
MV TVI
PW at the annulus
Pitfalls of RV/RF
• PW Sample Volume location
– Must be at valve annulus
• Diameter Measurements
– Error is squared
• Arrhythmias
– Measure 5-10 beats and average
• Multivalvular lesions
– Invalid with shunt
– Invalid with > mild regurgitation of non-measured valve
Proximal Isovelocity Surface Area
• Used to assess the severity of Regurgitation
• Information Needed
– Zoomed image of Valvular Annulus
– Clear Color Doppler Image
• Lower Aliasing Velocity (shift baseline down)
– CW of Valvular Regurgitation
• TVI and Peak Velocity
(PISA)
Evaluation of MR by PISA method
Feigenbaum’s Echocardiography, 6th ed. 2005
PISA
• Information Needed
– The radius of the aliased region (r)
– The aliasing velocity (VA)
– The MR Peak Velocity (MRVEL)
Principles of the PISA Method of MR Quantitation
O'Gara, P. et al. J Am Coll Cardiol Img 2008;1:221-237
Copyright ©2008 American College of Cardiology Foundation. Restrictions may apply.
• R= 0.72cm
• PISA= 2ʌx (0.72cm)2 = 3.26 cm2
• Flow rate = PISA x Vn
• Flow rate= 3.26 cm2 x 30 cm/s = 97.8 cm3/s
• ERO= Flow rate / Vmax
• ERO= 97.8 cm3/s / 489 cm/s = 0.20 cm2
Regurgitant Flow (PISA)
Regurgitant Volume =
EROA X TVI
Continuity Equation
• Conservation of Flow
What goes in, must come out.
Flow LVOT = Flow AV
Continuity Equation
• Flow LVOT = Flow AV
• Flow = TVI x CSA
TVILVOT x CSALVOT = TVIAV x CSAAV
Continuity Equation
TVILVOT x CSALVOT = TVIAV x CSAAV
CSA
AAVV =
TVI
T
VILVOTT x CSA
ALVOT
TVI
VIAV
AVA = CSA
ALVOTT x
TVI
VILVOT
TVI
VIAV
Aortic Valve Area (AVA)
LVOT 1.98 cm
LVOT TVI = 28 cm
28 cm
AVA = 3.08 x 30 cm
= 2.8 cm2
Aortic Valve Area (AVA)
„
LVOT Diameter
‰
2.15 cm
Vmax = 30 cm
Aortic Valve Area (AVA)
• LVOT
– TVI – 22.47 cm
– Velocity – 93.0 cm/s
Aortic Valve Area (AVA)
• Aortic
– TVI – 70.8 cm
– Velocity – 2.86 cm/s
Aortic Valve Area (AVA)
• Pitfalls
– Accuracy of the LVOT Diameter measurement
• Right View (Parasternal Long Axis)
• End systole
– Angle ɽ of LVOT Velocity
– Perform CW from multiple views, use maximum
– Arrythmias (5-10 beats and average)
– Confusing MR with Aortic Flow
• MR often has higher velocity
• MR extends through IVRT
Summary
• Hemodynamics are key for understanding Cardiac physiology
• Pitfalls have to be considered and avoided
• Calculations have inherent limitations.
• All these considered, Comprehensive Valvular evaluation must
include pertinent hemodynamics