Echocardiography of Prosthetic Valves Dr. Tehrani

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