Aortic stenosis – when echo and cath (or even echo and echo) don’t matcH

1. Paul Nolan, Galway University Hospitals Aortic stenosis – when echo and cath (or even echo and echo) don’t matcH

2. 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

3. Quantification of AS by echo • Peak velocity • Mean velocity • Peak gradient • Mean gradient • Aortic valve area • Continuity equation

4. 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

5. 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

6. Quantification of the AVA in the Cath Lab • Gorlin formula • AVA = Cardiac output • 44.3 (SEP)(HR) √pressure gradient

7. So why sometimes do they not agree?

8. Technical sources of error in Echo • Doppler angle

10. 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

11. The “Gold Standard”

12. 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

13. Effect of incorrect alignment Mean grad =47mmHg Mean grad =26mmHg

14. 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” SusheelKodali, Columbia Univ Medical Centre

15. Case 1

16. Case 1

18. Case 2 AVA=0.8cm2 Mean grad=54mmHg

20. Pressure gradients are dependent on volume flow rate

21. When gradient and AVA don’t match Low 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. So where are we now • Is there anything extra that echo can add • Can we aid in the clarification of these discrepancies

30. 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

31. 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

32. 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 asiAVA of <0.6cm/m2

33. 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

34. Remember Pressure recovery? • Cath reflects the physiological valve area • Can we somehow correct for pressure recovery

35. Energy loss index • [(AVA x Aa)/(Aa-AVA)] • BSA

36. Prognostic Value of Energy Loss Index in Asymptomatic Aortic Stenosis • Aortic valve events • AVR, HFH, CV mortality

37. What about the third dimension? • Continuity eqn • Assumption that LVOT is circular • LVOT more elliptical • 3D TOE • Allows direct measurement of LVOT CSA

38. 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

39. 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