paul nolan, galway university hospitals. echo evaluation of as define aetiology quantitation of...
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AORTIC STENOSIS – WHEN ECHO AND CATH (OR EVEN ECHO AND ECHO) DON’T MATCH
Paul Nolan, Galway University Hospitals
Echo evaluation of AS
Define aetiology Quantitation of the severity Assessment of LV function Assessment of co-existing valvular
lesions Assessment of secondary effects
Pulmonary pressures Aortic dilatation
Quantification of AS by echo Peak velocity Mean velocity Peak gradient Mean gradient Aortic valve area
Continuity equation
Jet velocity – too simple?
Otto 1997 123 asymptomatic
patients End point
Death Aortic valve surgery
Jet velocity > 4m/s is an independent predictor of clinical outcome
Quantification of AS by Cardiac Cath Maximum
instantaneous gradient Equivalent to peak
gradient by echo Mean gradient
Equivalent to mean gradient be echo
Peak to peak gradient Not equivalent to any
echo measure ?not physiological
Quantification of the AVA in the Cath Lab Gorlin formula
AVA = Cardiac output
44.3 (SEP)(HR) √pressure gradient
So why sometimes do they not agree?
Technical sources of error in Echo Doppler angle
Technical sources of error in Echo Doppler angle Accuracy of the LVOT measurement
Any error is squared Average of a number of measurements Same measurement retained for serial echos
Placement of sample volume within LVOT Non-simultaneous measurement of Ao and
LVOT Doppler profiles Especially important in irregular rhythms
Average of number of beats Use max Ao and max LVOT velocities
The “Gold Standard”
Sources of error in the lab
Assessments of Cardiac Output can be prone to error
Common practice of comparing LV to femoral/radial pressure
Damped pressures Positioning of LV
catheter Alignment of LV and
Ao trace
Effect of incorrect alignment
Mean grad =47mmHg Mean grad =26mmHg
So where is the error?
“we are constantly seeing these discrepancies between Cath Lab and echo gradients
Consultant Cardiologist
“on occassion we see these discrepancies, particularly in asymptomatic patients”
Physiologist rebuttal
“Do not trust the echo report unless you have personally seen the quality of the study”
“In many patients, echo will provide discordant data necessitating confirmatory hemodynamics in the cath lab”
Susheel Kodali, Columbia Univ Medical Centre
Case 1
Case 1
Case 2AVA=0.8cm2
Mean grad=54mmHg
Pressure gradients are dependent on volume flow rate
When gradient and AVA don’t matchLow gradient, severe AVA
High gradient, moderate AVA
Poor LV systolic function
Small LV cavity Reduced SV Reduced flow
Concomitant significant MR
Significant AI Sepsis Anaemia High output states Pressure recovery
phenomenon
In theory the AVA should reflect the severity of the stenosis better than the gradient
AS and poor LV function
Reduced LV function Reduced cardiac output and stroke
volume Reduced volume flow rates Reduced gradient across aortic valve
Discordance between AVA and gradient
Severe AS by AVA but low gradient may reflect Truly severe AS Psuedo-severe AS
Role of dobutamine
Dobutamine Increase stroke volume
Gradual infusion of dobutamine (20ug/kg) Truly severe AS
LVOT and Aortic velocities increase proportionally
AVA remains constant Pseudo-severe AS
LVOT velocity increases disproportionally Ao velocity
AVA increases
Role of dobutamine
Main role is to assess for inotropic reserve Increase in stroke vol of
>20% with dobutamine Clinical question
Is the severe AS leading to poor LV function
Will replacing the valve improve function
Lack of inotropic reserve is an independent predictor of mortality post AVR
Small LV cavity
Newer concept Paradoxical low flow AS Low flow/low grad severe
AS with preserved EF Small LV cavity
Hypertrophy Reduced LV filling Reduced stroke volume
Discordance between gradient and AVA
PLF AS patients have worse outcome
We are measuring different things Cath lab and echo
measure different things
Doppler Max flow velocity at
the level of the vena contracta
Cath Net pressure
gradient between the LV and the aorta
Pressure recovery
Conservation of energy Blood flow decelerates
as it goes through valve Kinetic energy -
velocity is “lost” Converted into
potential energy – pressure
Therefore we get a recovery of Ao pressure distal to the valve
Pressure recovery
Extent of pressure recovery inv proportional to Ao CSA
Thus the max gradient by echo will over estimate the severity compared to the max grad by cardiac cath
Echo reflect the true valve orifice area
Cath reflects the physiological valve area
So where are we now
Is there anything extra that echo can add
Can we aid in the clarification of these discrepancies
Jet velocity – too simple?
Otto 1997 123 asymptomatic
patients End point
Death Aortic valve surgery
Jet velocity > 4m/s is an independent predictor of clinical outcome
Dimensionless Index
Potential error in echo calculation is determining LVOT diameter
Dimensionless index removes LVOT diameter from the assessment
DI= LVOT VTI/Ao VTI Value of less than 0.25 represents
severe AS
Indexed aortic valve area
Body size can lead to an incorrect classification of AS severity based on AVA
Has been demonstrated that an iAVA of <0.6cm/m2 is a marker of mortality
Guidelines classify severe AS as iAVA of <0.6cm/m2
Indexed aortic valve area
Case 1 AVA of 1.2 cm2
moderate BSA = 2.1 m2
iAVA=0.57 cm2/m2
Case 2 AVA of 0.9 cm2
Severe BSA= 1.3 m2
iAVA=0.7 cm2/m2
Remember Pressure recovery?
Cath reflects the physiological valve area
Can we somehow correct for pressure recovery
Energy loss index
[(AVA x Aa)/(Aa-AVA)]
BSA
Prognostic Value of Energy Loss Index in Asymptomatic Aortic Stenosis
Aortic valve events AVR, HFH, CV mortality
What about the third dimension? Continuity eqn
Assumption that LVOT is circular
LVOT more elliptical
3D TOE Allows direct
measurement of LVOT CSA
Conclusion
There are sources of error in echo assessment of AS Take care Averaged values for
LVOT
There are also sources of error in the Cath Lab
So be careful there too And try and get the
Consultants to be careful
What I would take away
Use the suite of measurements/assessments
Use new measurements Indexed AVA
Consider new techniques if available If your gradient and AVA don’t match
think about/explain why? Poor LV Small LV cavity/low stroke volume Concomitant AI or MR
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