1. Echocardiographic Evaluation of Prosthetic Heart Valves
Patricia Tung, M.D.
February 10, 2010

2. Objectives Types of prostheses Prosthetic dysfunction
Echocardiographic surveillance of prostheses

3. Types of Prostheses Mechanical valves Tissue valves Homograft valves
Major differences related to risk of thromboembolism (higher for mechanical) and risk of deterioration (higher for bioprosthetic).
Durability of mechanical valves unsurpassed but inherent risks of thromboembolism
Bioprostheses developed primarily to overcome the risk of thromboembolism and inconvenience of anticoagulation therapy. Major drawback is durability.

4. Mechanical Valves
A, The Starr-Edwards caged-ball valve. B, The Omniscience valve. C, The Medtronic-Hall valve. D, The St. Jude bileaflet valve. E, The CarboMedics bileaflet valve.
3 main categories: tilting disk, bileaflet, and ball-cage
Tilting disk - opens at an angle to the annulus plane, constrained by a strut, cage or slanted slot
Bileaflet: 2 semicircular disks that form 2 large lateral openings and a smaller central opening
St. Jude’s: 1. Does not require supporting struts and 2. has favorable flow characteristics ->causes lower transvalvular pressure gradient at any outer diameter and cardiac output than caged-ball or tilting disc valves. Therefore favorable hemodynamics in smaller sizes; ideal for children.

5. Tissue Valves
-3 biologic leaflets and similar anatomic structure to native aortic valve
Stented valve leaflets are usually porcine or bovine/equine pericardium mounted on rigid cloth support with stent at each commissure
Stentless valves use flexible fabric or tissue cuff, often attached to aortic root graft

6. Homograft Valves
Aortic or pulmonic cadaver valve -> preserved, treated with antibiotics and frozen
Usually the valve and great vessel preserved as a block; ideal when there is also aortic root pathology

7. Objectives Types of prostheses Prosthetic dysfunction
Echocardiographic surveillance of prostheses

8. Mechanisms of Prosthetic Valve Dysfunction
Structural failure
Stenosis
Regurgitation
Thromboembolic complications
Endocarditis
Patient Prosthesis Mismatch
Structural failure = failure of a prosthetic valve to open or close properly

9. Structural Failure Bioprosthetics
Structural failure result from progressive tissue degeneration. Fibrocalcific changes to leaflets -> 1. increased resistance to opening (stenosis) or failure to coapt (regurgitation)
Usually occurs 10 or more years after implantation; acute stenosis rare. Acute regurgitation can occur with a leaflet tear; often adjacent to an area of calcification
A – valve failure secondary to mineralization and collagen degeneration
B – Cuspal tears and perforations
Structural failure of current generation mechanical valves is rare; valve stenosis or regurgitation often due to thrombus or pannus ingrowth.

10. Cohn et al. Ann Thorac Surg, 1998.
Estimates of freedom from structural valve deterioration (SVD) stratified by age.
Porcine AVR
Bovine pericardial AVR
The rate of structural valve failure is age-dependent, and is significantly lower in patients older than 65 years (Fig A Braunwald).
In patients over 65 undergoing AVR with a porcine bioprosthesis, the rate of structural deterioration is less than 10 percent at 10 years.
Valve failure is prohibitively rapid in children and in adults under 35 to 40 years of age; bioprostheses are avoided unless circumstances dictate.
Cohn et al.
Ann Thorac Surg,
1998.

11. Homograft Dysfunction
Subject to severe tissue calcification
Usually reserved for complex aortic root abscesses
Hyperlipidemia accelerates prosthesis calcification
Secondary prevention may slow this process
Similar progressive deterioration as tissue valves.
Nollert G, Miksch J, Kreuzer E, et al:  Risk factors for atherosclerosis and the degeneration of pericardial valves after aortic valve replacement.   J Thorac Cardiovasc Surg   2003; 126:965.
Farivar RS, Cohn LS:  Hypercholesterolemia is a risk factor for bioprosthetic valve calcification and explantation.   J Thorac Cardiovasc Surg   2003; 126:969.

12. Physical Exam Findings
Subtle findings especially if no baseline PE. Requires high suspicion for PV malfunction.

13. Echocardiographic Evaluation
TTE
valve area and regurgitation
exclude significant obstruction
Flow velocity is crucial measurement
Often inadequate for infection or small structural changes (strut fracture, small vegetation, paravalvular leak)
TEE
inspection of valve apparatus and seating
may not accurately quantify valve flow velocities
Major challenges:
1. Distinguish normal from pathologic fluid dynamics of prosthetic valve
2. Acoustic shadowing from sewing rings of bioprosthetic and mechanical -> shadow and reverberations that obscure motion of valve structures and block Doppler signal
TEE particularly useful for mitral valves b/c allows visualization from the LA side of valve
TEE also reliably distinguishes transprosthetic from paraprosthetic regurgitation.
TEE less helpful for aortic valves b/c posterior portion sewing ring shadows valve leaflets

14. Normal Appearance PV
Left: TTE PSL of bileaflet mechanical aortic valve; leaflets obscured by shadowing from sewing ring
Right: TEE bileaflet mechanical mitral valve a) diastole – sewing ring and 2 open leaflets; b) systole shadowing from sewing ring and reverb from leaflets obscures LV side of valve

15. Normal Doppler Clicks
Normal motion of mechanical occluder or bioprosthetic leaflets creates a Doppler signal.
Analogous to auscultatory click except both opening and closing create Doppler signal.

16. Normal Doppler Flow Patterns
PSL view of stented mitral bioprosthetic valve.
Left: stents protrude into ventricular chamber
Right: antegrade flow into LV
Bioprosthetics have flow profile similar to native Ao valve with 3 leaflets and a central orifice -> provides laminar antegrade flow with a blunt flow profile
In the mitral position, orientation of bioprosthesis results in anteromedially directed inflow toward the septum instead of toward the apex (as for normal valves). This causes a reversed vortex of blood flow in mid-diastole as seen in an apical 4C view.

17. Fluid Dynamics and Velocities
Flow profiles of different valves vary substantially; none is analogous to flow across a native valve.

18. Normal Finding: Regurgitation
Small amount regurgitation in nearly all mechanical and 30-50% of bioprosthetic prostheses
Can be difficult to separate normal from pathologic regurgitation, particularly in the mitral position
TEE indicated if pathologic regurgitation is suspected
TEE of bileaflet mitral valve
Bileaflet mechanical – 2 crisscross jets of regurgitation parallel to leaflet opening plane
Tilting disk – regurg at closure line with major jet directed away from sewing ring

19. Pathologic Regurgitation
Characterized by:
An eccentric or large jet
Marked variance on the color flow display
A jet that originates around the valve sewing ring
Visualization of a proximal flow acceleration region on the LV side of the mitral valve
In addition to Doppler eval of regurgitation
- Shape, origin, and orientation of the regurgitant jet
- Vena contracta diameter
- Intensity and shape of the continuous wave Doppler signal
- Evidence of distal flow reversal
- LV size, hypertrophy, and systolic function

20. Prosthetic Valve Regurgitation
For aortic valves, TTE color flow imaging in parasternal and apical views can be helpful b/c the Doppler signal reaches the LVOT w/o intercepting the valve prosthesis (no shadowing).
For mitral valves, parasternal can be helpful if view can be obtained where the LA side is not shadowed by prosthesis.

21. Prosthetic Valve Stenosis
Pressure gradients
Calculated using the Bernoulli equation (4v2)
Good correlation when validated against invasive pressure measurements
mechanical valves, especially bileaflet, result in overestimation of the gradient due to differing fluid dynamics
Sig variation in normal prosthetic valve velocities, gradients and areas. However, all prostheses are inherently stenotic compared to a native valve.
Mitral prostheses have lower velocities and gradients than aortic prostheses 2/2 passive flow at lower pressures; generally true for larger vs smaller prostheses.
Although max velocity across PV > native, shape of velocity curve is triangular vs rounded for native stenosis. Therefore, mean gradient PV usu less than native valve with SAME max antegrade velocity

22. The most complex fluid dynamics are from bileaflet mechanical valves
- Flow velocity profile shows three peaks corresponding to each opening, with higher velocities in the center of the orifice
- Local high pressure gradient in the central orifice that is often significantly greater than the overall pressure gradient across the valve.
Within narrow central stream, acceleration forces result in localized high pressure gradient and velocity with pressure recovery distal to the valve (i.e. pressure difference b/t upstream to valve > valve to downstream. Because CW Doppler records highest velocity along a length of the beam, the higher upstream velocity is recorded. Whereas gradient of interest is the upstream to downstream gradient.
Because of pressure recovery, Doppler overestimates transvalvular gradient, especially in bileaflet valves.

23. Prosthetic Aortic Valve Area
Velocities across PVs vary with volume flow rate for a given orifice area. Therefore, normally functioning prosthesis may have high velocities and gradients secondary to increased CO (sepsis, pregnancy) OR a low transvalvular velocity with depressed CO.
Therefore, a flow independent measure of PV function is more useful clinically > valve area
Continuity equation for aortic (and pulmonic) valves
LVOT velocity recorded from apical approach with pulsed Doppler proximal to PV, avoid region of flow acceleration immediately adjacent to valve
CSA LVOT = pi(D/2)2
Aortic jet veloicty recorded with CW from whichever window provides highest velocity signal
LVOT diameter PSL midsystole immed adjacent to Ao valve\
*****direct measurement of outflow tract preferred to valve size since size relates to external diameter of sewing ring, not effective diameter of subvalvular flow region

24. Prosthetic AVA: Velocity Ratio
Measure velocity increase across valve
Ratio of outflow tract velocity/aortic jet velocity reflects degree of stenosis
Ratio = 1 if no obstruction present
Given inherent stenosis, normal range is 0.35 to 0.5 for aortic prosthesis
Advantages: takes volume flow rate into account; does not require outflow tract diameter measurement
As stenosis increases, aortic jet velocity will increase without change in the outflow tract velocity
for normal valve

25. Prosthetic Mitral Valve Area
Can be estimated using the pressure half-time approach as for native mitral valve stenosis.
The expected half-time for a PV is longer than with a native valve.
Pressure half time for mitral and tricuspid valve areas
Bileaflet valves affect accuracy of pressure gradient but the T1/2 less affected b/c depends on time course of velocity decline rather than absolute velocity itself

26. Incidence of Thromboembolic Complications
Fatal Complication
Non-Fatal Complication
Valve Thrombosis
Aortic
0.2 per 100 patient years
1.0 to 2.0 per 100 patient years
0.1 percent per year
Mitral -
2.0 to 3.0 per 100 patient years
0.35 percent per year
Thrombosis in tricuspid position extremely high; therefore bioprostheses preferred at this site.

27. Prosthetic Valve Thrombosis
TEE is often negative if the thrombi are small or if new thrombus has not formed since the initial embolic event.
Thus an embolic event in a patient with a prosthetic valve (esp mechanical) must be presumed to be related to the PV even if the TEE is negative.
Echo evaluation, especially in mechanical valves, is limited due to shadowing and reverberations unless very large thrombus. Echo cannot definitively exclude thrombus.
Clinical events often occur with clots smaller than the detection limit for ultrasound
Prosthetic valve itself is a cardiac source of embolus
Infected pannus cannot be differentiated from thrombus with ultrasound.

28. Prosthetic Valve Endocarditis
Difficult to detect with TTE
Often involves sewing ring and annulus, resulting in paravalvular abscess rather than a discrete vegetation
Features that increase suspicion for PV endocarditis on TTE:
Regurgitation or stenosis due to infected pannus on inflow surface
Valve instability or rocking
Unexplained change in chamber dimensions

29. Prosthetic Valve Endocarditis
Often involves the sewing ring and annulus resulting in formation of a paravalvular abscess rather than the typical vegetation.
TTE – LA masked by valve from parasternal and apical windows. TEE generally required.

30. Patient Prosthesis Mismatch
Size of prosthesis results in inadequate blood flow given metabolic demands
Prosthesis itself functions well
Indexed effective orifice area < or = 0.85cm2/m2
Predicts high transvalvular gradients, persistent LVH and increased rate of cardiac events following AVR
Estimates vary between 20-70% of AVR affected
PPM can result in hemodynamics consistent with stenosis even with a normally functioning prosthesis.

31. Objectives Types of prostheses Prosthetic dysfunction
Echocardiographic surveillance of prostheses

32. Recommended Surveillance
Baseline echocardiogram 6-8 weeks postoperatively
Routine echocardiographic surveillance annually thereafter
Evaluate for
Regression of hypertrophy or dilation
Recovery of LV systolic function
Changes in PA pressures

34. Summary
Prosthetic valve dysfunction is well detected by echocardiography
Dysfunction includes
Structural failure
Thromboembolic complications
Endocarditis
PPM
Distinguishing normal from pathologic function can be challenging; most useful is comparison to baseline post-prosthesis
Other means of assessing prosthetic valve function include:
Fluoroscopy - useful with mechanical valves. Good for assessing mechanical leaflet motion due to outstanding spatial and temporal resolution and stability of valve ring with the cardiac cycle (i.e. rocking of the base).
MRI - safely in all valves except Starr-Edwards (early 60’s). Can visualize mechanical valves, but lacks the temporal resolution and Doppler capabilities of echocardiography. Shows gross valve position, function, and regurgitation.
Cardiac catheterization - Aortogram/LV gram can evaluate regurgitation.

35. References
Otto, C. Textbook of Clinical Echocardiography, Fourth Edition 2009.
Libby et al. Braunwald’s Heart Disease. Eighth Edition 2008.
Pibarot, P and Dumesnil JG. Prosthesis-patient mismatch: definition, clinical impact, and prevention. Heart 2006;92:
Bonow RO, Carabello BA, Chatterjee K, et al:  ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (writing committee to revise the 1998 Guidelines for the Management of Patients with Valvular Heart Disease): Developed in collaboration with the Society of Cardiovascular Anesthesiologists: endorsed by the Society for Cardiovascular Angiography and Interventions and the Society of Thoracic Surgeons.   Circulation   2006; 114:e84.