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