hemodynamics and general principles in valve...

Hemodynamics and General Principles in Valve DiseaseFederico M Asch MD, FASE

MedStar Heart and Vascular InstituteGeorgetown University

Washington, DC

• I have no financial disclosures related to this presentation

Outline

• Flow• Pressure Gradients• Meaningful Calculations in VHD• Application in Specific conditions

Basic General Concepts


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

• Cross Sectional Area (CSA)– Mathematically calculated area of a circle.– CSA = r2

– CSA = 0.785 d2

Volumetric Flow

2.1 cm

CSA = (3.14)(1.05)2

CSA = 0.785(2.1)2= 3.46 cm2

• Stroke Volume– The amount of blood pumped out of the heart with each beat.– Calculated as the CSA x TVI

Volumetric Flow

2.1 cm TVIX = Stroke Volume

cm2 X cm = cm3 (cc, ml)

LV Stroke Volume LVOT CSA x TVI LVOT

Cardiac Output = SV x HR/1000Cardiac Index = CO/BSA

SV = (0.785)(LVOT Diameter2) x TVI LVOT

Cardiac Output = SSSSVVV x HR/10

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


• Flow• Pressure Gradients / PHT• Meaningful Calculations in VHD• Application in Specific conditions

Pressure Gradients

The Bernoulli Equation

P = ½ (v22 – v1

2) +2 v

t s + R( V )

Convective Acceleration

Flow Acceleration

Viscous Friction

The forces of viscous friction in the normal clinical setting are negligible and can be

removed from the equation.


P = ½ (v22 – v1

2) +2 v

t s


Flow Acceleration

The forces of flow acceleration in the normal clinical setting are negligible and can be

removed from the equation.


P = ½ (v22 – v1

2)


If V1 values are

- <1 m/s V1 can be removed from the equation.

- 1-1.5 acceptable

- > 1.5 cannot use simplified equation

Where:

½ = mass density for blood = 4

V1 = Flow velocity proximal to the valve

V2 = Flow velocity distal to the valve

P = 4 (v22)

The Simplified Bernoulli EquationP = 4 (v2

2)• 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

PR

TR

VPR Early VPR End

VTR

PA Diastolic PressureVPR End

2+ RA Pressure

PA Systolic PressureVTR

2+ RA Pressure

Mean GradientAverage of all instantaneous (4 x V2) over the flow period

Apical 3 ch Apical 5 chical 3 ch Apical 5 ch

Gradients in Aortic Stenosis

Pressure Half Time (PHT)Time for peak gradient to decrease to half

Mitral Stenosis:

MVA= 220/PHT

Longer PHT, More Severe MS

CW

Pressure Half Time (PHT)Time for peak gradient to decrease to half

Regurgitation:

Shorter PHT= More severe Regurg

CW




• 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

2)( Va)

Peak Velocity

EROA = Regurgitant Flow / MR Peak VelRegurgitant 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.

SVAO = CSAAO X TVIAO

SVMV = CSAMV X TVIMV

Regurg Vol = Mitral SV - Aortic SV

Regurg Vol = Mitral SV - Aortic SV



• MV Regurgitant Volume (RV)– SVMV – SVAV

• AV (RV)– SVAV – SVMV

Regurg Fraction (RF) = RV / SV



• MV Regurgitant Fraction (RV)RVMV – SVMV

• AV RF– RVAV / SVAV

Mitral RegurgitationQuantitative Hemodynamics

120 cc

70 cc50cc

R volume = 120 - 70 = 50 ccR fraction = 50/120 = 42%

Systole Diastole

RV / RF (Doppler)What to measure?

AV annulus DiameterLong Axis View, end systole

Aortic Valve TVI PW at the annulus

MV Annulus Diameter4 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 (PISA)

• 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

Feigenbaum’s Echocardiography, 6th ed. 2005

Evaluation of MR by PISA method

PISA

• Information Needed – The radius of the aliased region (r)– The aliasing velocity (VA)– The MR Peak Velocity (MRVEL)

Copyright ©2008 American College of Cardiology Foundation. Restrictions may apply.

O'Gara, P. et al. J Am Coll Cardiol Img 2008;1:221-237

Principles of the PISA Method of MR Quantitation

• R= 0.72cm• PISA= 2 x (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 CSATVILVOT x CSALVOT = TVIAV x CSAAV

Continuity Equation

TVILVOT x CSALVOT = TVIAV x CSAAV

TVIVILVOT T x CSAALVOT

TVIVIAV

CSAAAAV

TV V =

AVA = CSAAALVOT T x TVIVILVOT

TVIVIVIVIAV

LVOT 1.98 cm LVOT TVI = 28 cm Vmax = 30 cm

AVA = 3.08 x = 2.8 cm228 cm30 cm

Aortic Valve Area (AVA)


LVOT Diameter2.15 cm


• LVOT– TVI – 22.47 cm– Velocity – 93.0 cm/s

• Aortic– TVI – 70.8 cm– Velocity – 2.86 cm/s



• Pitfalls– Accuracy of the LVOT Diameter measurement

• Right View (Parasternal Long Axis)• End systole

– Angle 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

hemodynamics and general principles in valve...

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