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Echocardiography of Prosthetic Valves
Dr. Tehrani
Different Types of Valves
Homografts (allograft)Cadaveric human aortic and pulmonary valves
Heterograft (Xenograft)Prosthetic Valves
Bioprosthetic valvesPig aortic valve Bovine pericardial (other)
MechanicalUrethane ball in a cageSingle or multiple discs
Homografts (allograft)
Homografts
Homograft ValvesHarvested soon after death w/ the endothelium still viablePreparation for implantation
Storage in ABXCryopreservation (more recently)
No anticoagulationLow incidence of endocarditisFailure due to gradual aortic incompetence
Homografts
PositionMitral
Fitted w/ stent, not proved successful (high failure rate at 5 years)Stentless grafts not an option for MVR
AorticStentless
Subcoronary Root Replacement
Echocardiography of Stentless Aortic Homografts
Doppler flow characteristics similar to native valve.Only 2-D evidence: Increased Echo intensity, and Thickness of aortic annulus.
Stentless Heterografts (Xenograft)
Stentless Heterografts (Xenograft)
Same utility as allografts for AVR:
Subcoronary implantation, andRoot replacement
Advantage over allografts is wider availabilityDurability is at least as good as allografts
Prosthetic Valves
Prosthetic Valves
All ProstheticProsthetic valves valves have a sewing ring anchored to the native tissue with sutures
The occluding portion of the valve:Tissue leaflets Bio-ProstheticProstheticSingle or multiple discs/ Urethane ball in a cage Mechanical Prosthetic
Bio-Prosthetic and Mechanical Prosthetic
Bio-prosthetic Valves
Bioprosthetic Valves
Two types, of occluding mechanism1.Porcine aortic
valve (the valve size of the biggest pig is limiting)
Hancock, andCarpentier-Edwards bioprosthesis
Carpentier-Edwards bioprosthesis
Bioprosthetic valves
2. Bovine Pericadium leaflets are shaped to size.
More choices
Echocardiographiaclly these two valves types are indistinguishable.
Ionescu-Shiley
(1976)
Bioprosthetic valvesMitral Position
2-D ECHOCARDIOGRAPHIC APPEARANCE
Bioprosthetic valvesAortic Position
2-D ECHOCARDIOGRAPHIC APPEARANCE
Bioprosthesis
Used extensively in a variety of sites:AorticMitralTricuspid
Advantage:Low thrombogenicity => No anticoagulation
Bioprosthesis
Disadvantages:Less durable than mechanical prosthesisMitral position worse
Due to greater backpressure gradientDysfunction:
Leaflet thickening, and Ca++ Fracture, tears, or progressive stenosis
In vivo, roughly 10% of normal bioprosthetic valves have some leakage.
Overview of Various Devices
Bio-Prosthetic Valves
Mechanical Prosthetic Valves
Mechanical Vlaves
Ball-and-Cage ValvesTilting disc Prosthesis
Single diskBileaflet
Mechanical Prosthesis
The occluding mechanism dictates both: The echocardiographic appearance of the valve, andThe flow pattern through the valve
To assess performance, the type of valve implanted must be known
Ball-and-Cage Valves
First implanted by starr and Harken in 1960.
Ball-and-Cage Valves
Opening and closure of the ball-valve
Ball-and-Cage Valves
Axisymmetric flow around the valve.Stagnant flow in the shadow of the ball.
Ball-and-Cage Valves
Doppler assessment at the margins of the ball
Ball-and-Cage Valves
M-Mode assessment of Ball-Cage Valve
Ball-and-Cage Valves
DurableMitral position
Satisfactory profile with the largest size (34 or 32 mm diameter devices)Can affect the interventricular septum
Aortic positionSmall prosthesis required, which can be associated with significant gradient
Regurgitation limited to closure backflow.
Tilting Disc Prosthesis
All essentially similar consisting of Circular prosthetic material, andOne or two hinged and mobile disc(s)
Disc attachment to the ring is eccentric
Closure occurs by backpressure on the largest portion of the disk
Single Disc Prosthesis
Single Disc devices:Hall-Medtronics monostrutBjork-Shiley
Opening arch is 55-70 degreesFlow orifice:
Major and minor flow orificesStreamlines of flow passing through the sewing ring and then laterally out and around the prosthetic disc
Single Disc Prosthesis
Bjork-Shiley StandardConvex-concave
Many other variations in the marketAll of these devices have a zone of stagnation behind the disc thrombus formation
Single Disc Prosthesis
Bjork-Shiley in the Mitral position
Single Disc Prosthesis
Leak around: Central strut
Dominant jetBetween the occluding disc and sewing ring.
Two smaller peripheral jets
Normal hemodynamicsReg.Frac. approx. 12%
Tachycardia, and low outputReg.Frac. upto 37%
Single Disc Prosthesis
Single Disc Prosthesis
Dysfunction
Gradual ingrowth of fibrous tissue (panus)
Flow obstructionIntermittent sticking of the valve with associated flash pulmonary edema
Bileaflet Mechanical Prosthesis
St. Jude prosthesisThe most commonly used.
Two equal sized semi-circular leaflets attached by a midline hinge.Discs can tilt in excess of 80 degrees, resulting in larger:
Orifice area
Bileaflet Mechanical Prosthesis
St. Jude prosthesisThe most commonly used.
Two equal sized semi-circular leaflets attached by a midline hinge.Discs can tilt in excess of 80 degrees, resulting in larger:
Orifice area
Regurgitant back flow
Bileaflet Mechanical Prosthesis
Regurgitation occurs at the disc marginsThe regurgitant jets converge toward the center of the valve
Bileaflet Mechanical Prosthesis
St. Jude valve in the mitral position.
Imaging of Prosthetic Valves
Special Problems of 2-D Imaging Artificial Valves
Echocardiographs are calibrated to measure distance based on the speed of sound in tissue.
Prosthetic valves have different acoustic properties than tissue. Hence, distortion of:
SizeLocation, andAppearance, of the prosthesis.
Special problems of artificial valves
Intense reverberation, andShadowingLess gain leads to less:
Reverberation, and Shadowing, as well asBetter visualization of non-biologic components of the valve HOWEVER Decreased definition of cardiac
structures
Special problems of artificial valves
First image at normal settings, then Reduce the gain to interrogate the leaflets of Bio-prosthetic valves.
Utilize multiple views.
Prosthetic Valve Pathology
Prosthetic Valve Stenosis Aortic Mitral
Prosthetic Valve Regurgitation Aortic Mitral
G E N E R A L L Y
Prosthetic Stenosis (and Regurgitation) is:
A question of degree,
Not a question of whether.
Prosthetic Valve Stenosis
Determinants of gradients across normal prosthetic valves include:
Valve type, i.e., ManufacturerValve sizeFlow through the valve
Wide range of “Normals”
Aortic Prosthesis Gradients as a Function of Valve TYPE and SIZE
No.21
No.27
Dependence on:
Valve type, and
Size
Gradient as a Function of Valve Type
Normal Dopplar data in patients with various types of prosthetic valves in the Aortic Position
Gradient as a Function of Valve Size
Valve specifications and doppler echocardiographic data in 67 St. Jude medical valves in the Aortic position
Chafizadeh ER, Circ. 83:213, 1991
Gradient as a Function of Flow
No.21
I. Valve type, i.e., Manufacturer
II. Valve size
III. Flow through the valve
Indicies of Valve Stenosis which are Less Flow Depenent
A. Contour of jet velocityB. Doppler velocity indexC. Effective orifice areaD. Valve resistance
A-Contour of the jet velocity
With prosthetic obstruction there is:
Late peaking of the velocity,More rounded contour,Prolonged ejection.
B-Doppler Velocity Index
DVI= Pk VelLVOT/Pk Veljet
Flow independent 0.2 – 0.27 cutoff for critical stenosis
Caveat: Pressure recoveryTo be discussed …
C-Effective Orifice Area
Continuity Eqn.
Caveat: Pressure recoveryTo be discussed …
jetLVOTLVOT TVITVICSAEOA
D-Valve resistance
At cutoff of 280 dynes.sec.cm5, best at differentiating AS, from NL (Zoghbi et al.)
1.33 x SEPGrad.VR
Special Caveats Re:Overestimation of Gradients
Two scenarios:
I. The velocity upstream from the valve is not negligible in application of the Bernoulli Eqn.
Usually in AV when proximal velocity on the LVOT is > 1.5 m/s
2 2
21 4V V P
…Overestimation of Gradients
II. Central acceleration with the St. Jude valve:
Increase of velocities (and gradients) is created at the level of the valve through the smaller central orifice.Most significant with:
High flow states Small valves
…Overestimation of Gradients
Central acceleration with the St. Jude valve:
CW Doppler records these high velocities.
Catheter-derived gradients show pressure recovery at 30mm downstream from the valve.
Indicies which are LessFlow Dependent, BUT…
A. Contour of jet velocityB. Doppler velocity indexC. Effective orifice areaD. Valve resistance
Clearly, both ofThese ParametersWill be Affected byThe PressureRecovery Phenomenon.
Prosthesis-Patient Mismatch
Mismatch
Rahimtoola 1978: “Mismatch is present when the effective
prosthetic valve area, after insertion into the patient, is less than that of a normal human valve.”
By definition: Some such “mismatch” will almost always be
present.
Mismatch
Literature identifies the above as a cut-off for mismatch
22Index /mcm 0.85 EOA
Mismatch
0.007184 x hgt.wt.BSA 0.7250.425
Next locate the publishedin-vivo EOA of the valve used.
This is the EOA that The patient physiologicallyNeeds.
Mismatch
JACC Review Article, 10/2000
Not the company reported data
Prosthetic Valve Pathology
Prosthetic Valve Stenosis Aortic Mitral
Mitral Prosthesis Stenosis
Parameters used for assessment of function:
A. PHT/Area by PHTB. Effective Orifice Area by
continuityC. Mean gradient
Mitral Prosthesis Stenosis
A-PHT/Area by PHTNot expected to yield accurate valve area
The empiric constant of 220 validated for the geometry of rheumatic MS
Useful in longitudinal follow-up of valve FxShould not be used when diastolic filling period is short (fusion of E and A)
TachycardiaLong first degree block
Mitral Prosthesis Stenosis
B-Effective Orifice Area by continuity Eqn.
One underlying assumption is absence of significant AI or MR
Physiologic prosthetic MR 10-30% (Medtronic-Hall, significant central MR, specific design feature less thrombogenic)
Mitral Prosthesis Stenosis
C-Mean gradient, function of:
SizeType of prostheticFlow
Heart rate (should also bereported when evaluating MVA)
Prosthetic Valve Pathology
Prosthetic Valve Stenosis Aortic Mitral
Prosthetic Valve Regurgitation Aortic Mitral
Prosthetic Valve Regurgitatoin
Two issues:
Physiologic v.s. Pathologic regurgitationTTE v.s. TEE for assessment of regurgitation
Prosthetic Valve Regurgitation
Physiologic Regurgitation
Early onsetEarly onset and brief durationReflects backflow from closing movement of occluding device
Tilting disc and bileaflet valves have additional late backflowlate backflow leakage
Intended to reduce risk of thrombosis
Aortic Prosthesis Regurgitation
Criteria similar to grading native valve AI:
Jet widthPHT < 350Holodiastolic flow reversalRegurgitant fraction>40%
Mitral Prosthesis Regurgitation
TTE of limited value in assess MR due to acoustic shadowing of the LA
Doppler findings suggestive of severe MRE wave > 1.9 m.sPISAShort isovolumetic relaxation timeTVILVOT/TVIPr-MV < 0.4