Echo Conference 3/16/11

Scott Midwall, MD

ObjectivesI. Introduction to Prosthetic Valves (PV)

I. MechanicalII. Biological/TissueIII. Appearance of Normally functioning Valves

II. Approach to Evaluating PVs with echo and doppler

III. Evaluating Prosthetic Aortic ValvesIV. Echo Case/Questions (EchoSap)

OverviewProsthetic Valves are classified as tissue or mechanical Tissue:

Actual valve or one made of biologic tissue from an animal (bioprosthesis or heterograft) or human (homograft or autograft) source

MechanicalMade of nonbiologic material (pyrolitic carbon,

polymeric silicone substances, or titanium)Blood flow characteristics, hemodynamics, durability,

and thromboembolic tendency vary depending on the type and size of the prosthesis and characteristics of the patient

ValvesBiologic (Tissue) Mechanical Stented

Porcine xenograftPericardial xenograft

StentlessPorcine xenograftPericardial xenograftHomograft Autograft

Ball and cage (Starr-Edwards)

Single tilting disc (Medtronic-Hall)

Bileaflet (St. Jude, CarboMedics)

Mechanical ValvesExtremely durable with overall survival rates

of 94% at 10 yearsPrimary structural abnormalities are rareMost malfunctions are secondary to

perivalvular leak and thrombosisChronic anticoagulation required in all With adequate anticoagulation, rate of

thrombosis is 0.6% to 1.8% per patient-year for bileaflet valves

Biological ValvesStented bioprostheses

Primary mechanical failure at 10 years is 15-20%Preferred in patients over age 70Subject to progressive calcific degeneration &

failure after 6-8 yearsStentless bioprostheses

Absence of stent & sewing cuff allow implantation of larger valve for given annular size->greater EOA

Uses the patient’s own aortic root as the stent, absorbing the stress induced during the cardiac cycle

Biologic Valves ContinuedHomografts

Harvested from cadaveric human heartsAdvantages: resistance to infection, lack of

need for anticoagulation, excellent hemodynamic profile (in smaller aortic root sizes)

More difficult surgical procedure limits its useAutograft

Ross Procedure

Caged-Ball Valve

Single-Leaflet Valve

Bileaflet Valve

Stentless Aortic Graft Valve

Stented Biologic Mitral Valve

Approach to Valve Evaluation Clinical data including reason for the study and

the patient’s symptomsType & size of replacement valve, date of

surgeryBP & HR

HR particularly important in mitral and tricuspid evaluations because the mean gradient is dependent on the diastolic filling period

Patient’s height, weight, and BSA should be recorded to assess whether prosthesis-patient mismatch (PPM) is present

Echo Imaging of Prosthetic Valves Valves should be imaged from multiple views,

with attention to:Opening & closing motion of the moving parts

(leaflets for bioprosthesis and occluders for mechanical ones)

Presence of leaflet calcification or abnormal echo density attached to the sewing ring, occluder, leaflets, stents, or cage

Appearance of the sewing ring, including careful inspection for regions of separation from native annulus & for abnormal rocking motion during the cardiac cycle

Echo ImagingMild thickening is often the 1st sign of

primary failure of a biologic valveOccluder motion of a mechanical valve may

not be well visualized by TTE because of artifact and reverberations

Imaging ConsiderationsIdentify the sewing ring, valve or occluder

mechanism, and surrounding areaBall or disc is often indistinctly imaged,

whereas leaflets of normal tissue valves should be thin with an unrestricted motion

Stentless or homograft may be indistinguishable from native valves

One can use modified views (lower parasternal) to keep the artifact from the valve away from the LV outflow tract

Doppler of Prosthetic AVDoppler velocity recordings across normal

PVs usually resemble those of mild native aortic stenosisMaximal velocity usually > 2 m/s, with

triangular shape of the velocity contourOccurrence of maximal velocity in early systole

With increasing stenosis, a higher velocity and gradient are observed, with longer duration of ejection and more delayed peaking of the velocity during systole

Doppler Velocity Index (DVI)Dimensionless ratio of the proximal velocity in

the LVO tract to that of flow velocity through the prosthesis: DVI= VLVO/ VPrAV

DVI is calculated as the ratio of respective VTIs and can be approximated as the ratio of respective peak velocities

Incorporates the effect of flow on velocity through the valve and is much less dependent on valve size

DVI Helpful measure to screen for valve

dysfunction, particularly when the CSA of the LVO tract cannot be obtained or valve size is unknown

DVI is always < 1DVI < 0.25 is highly suggestive of significant

obstructionDVI is not affected by high flow conditions

through the valve, including AI

Doppler & Prosthetic AV High gradients may be seen with normal

functioning valves with:Small sizeIncreased stroke volumePPMValve obstruction

Conversely, a mildly elevated gradient in the setting of severe LV dysfunction may indicate significant stenosis

Thus, the ability to distinguish malfunctioning from normal PVs in high flow states on the basis of gradients alone may be difficult

Doppler ContinuedOther qualitative and quantitative indices

that are less dependent on flow should be evaluated

Contour of the velocity:In a normal valve, even in high flow, there is a

triangular shape, with early peaking of the velocity and short acceleration time (AT)

With PV obstruction, a more rounded velocity contour is seen, with velocity peaking almost in mid-ejection, prolonged AT

Cutoff of AT of 100 ms differentiates well between normal and stenotic PVs

Effective Orifice Area (EOA)EOA PrAV = (CSA LVO x VTI LVO) / VTI PrAV EOA is dependent on size of inserted valve

Should be referenced to the valve size of a particular valve type

For any size valves, significant stenosis is suspected when valve area is < 0.8 cm2

However, for the smallest size valve, this may be normal because of pressure recovery

Largest source of variability is measurement of the LVO tract

Parameter Normal Possible Stenosis

Suggests Significant Stenosis

Peak Velocity (m/s)

<3 3-4 >4

Mean Gradient (mmHg)

<20 20-35 >35

DVI ≥0.30 0.29-0.25 <0.25

EOA (cm2) >1.2 1.2-0.8 <0.8

Contour of Jet velocity in PV

Triangular, early

peaking

Triangular to

intermediate

Rounded, symmetrical

AT (ms) <80 80-100 >100

Doppler Parameters of Prosthetic AV function in Mechanical and Stented Biologic Valves in Conditions of Normal Stroke

Volume

Patient-Prosthesis Mismatch (PPM)When the EOA of the inserted prosthesis is

too small in relation to the patient’s BSAA given valve area acceptable for a small,

inactive person may be inadequate for a larger physically active individual

Main consequence is the generation of higher than expected gradients through a normally functioning valve

PPM ContinuedCommonly seen in:

Patients with small aortic annulus sizes, particularly women

Patients whom indication for AVR was AS as opposed to AI

Young patients, who outgrow their initially inserted prosthesis

Failure of post-op regression of LV mass index at 6 months may be clue to presence of PPM

For patients with exertional symptoms without evidence of primary valve dysfunction, stress echo should be entertained to further evaluate

Evaluation of Prosthetic AIWith color doppler, one can evaluate the

components of the color AI jetFlow convergence, vena contracta, extent in

the LVO tract and LVNormal “physiologic” jet are usually low in

momentum, depicted by homogenous color jets that are small in extent

Ratios of jet diameter/LVO diameter from parasternal long-axis imaging and Jet area/LVO area from parasternal short-axis imaging are best applied for central jets

Prosthetic Valve AIWith eccentric AI

jets, measurement of jet width perpendicular to the LVO tract will cut the jet obliquely and risk overestimation

Entrainment of jet in the LVO tract may lead to rapid broadening of the jet just after the vena contracta-> overestimation

Significant AI, AV Dehiscence

AI in PVsContrary to native valves, the width of the vena

contracta may be difficult to accurately measure in the long-axis in the presence of a prosthesis

Imaging of the neck of the jet in short-axis, at the level of the sewing ring allows determination of the circumferential extent of the regurgitation

Approximate guide:< 10% of sewing ring suggests mild10-20% suggests moderate> 20% suggests severe**Rocking of the prosthesis usually associated

with >40% dehisscence

Spectral Doppler and PVAIPHT is useful when the value is <200 ms, suggesting

severe AI, or > 500 ms, consistent with mild AIIntermediate ranges may reflect other hemodynamic

variables such as LV compliance and are less specificHolodiastolic flow reversal in the descending thoracic

aorta is indicative of at least moderate AISevere is suspected when the VTI of the reverse flow

approximates that of the forward flowHolodiastolic flow reversal in the abdominal aorta is

usually indicative of severe AI

Parameter Mild Moderate Severe

Valve Structure/Function

Normal Abnormal Abnormal

LV size Normal Normal or Mild Dilation

Dilated

Jet width (%LVO diameter)

Narrow (≤25%)

Intermediate (26-64%)

Large (≥ 65%)

Jet density (CW doppler)

Incomplete or Faint

Dense Dense

PHT, ms (CW doppler)

>500 Variable (200-500)

Steep (< 200)

Diastolic Flow Reversal (Descending

Aorta)

Absent or Brief early

diastolic

Intermediate Prominent, holodisatolic

Regurgitant Volume (ml/beat)

< 30 30-59 >60

Regurgitant Fraction (%)

<30 30-50 >50

Evaluation of Prosthetic MVA major consideration with echo is the effect of

acoustic shadowing by the prosthesis on assessment of MRProblem is worse with mechanical valves

On TTE, LV function is readily evaluated, but the LA is often obscured for imaging and doppler interrogationTEE provides visualization of the LA and MR but

shadowing limits visualization of the LVThus, comprehensive assessment of PMV requires

both TTE & TEE when valve dysfunction is suspected

Prosthetic MV Imaging Considerations

In the parasternal long-axis view, the prosthesis may obscure portions of the LA and its posterior wallMR may be difficult to evaluate

Parasternal long-axis views allows visualization of the LVO tract, which can be impinged by higher profile prostheses

Apical views allow visualization of leaflet excursion for both bioprosthetic and mechanical valvesMay allow detection of thrombus or pannusVegetations can be seen but are often masked by

acoustic shadowing

Doppler Evaluation of PMVComplete exam should include:

Peak early velocityEstimate of mean pressure gradientHeart RatePressure half-time (PHT)Determination of whether regurgitation is

presentDVI and/or EOA as neededLV/RV size and functionLA size if possiblePA systolic pressure

Peak Early Mitral VelocityPeak E velocity is easy to measure

Provides simple screen for prosthetic valve dysfunction

Can be elevated in: hyperdynamic states, tachycardia, small valve size, stenosis, or regurgitation

Inhomogeneous flow profile across caged-ball and bileaflet prostheses can lead to doppler velocity measurements that are elevated out of proportion to the actual gradient

For normal bioprosthetic MVs, peak velocity can range from 1.0 to 2.7 m/s

MV Peak Velocity In normal bileaflet mechanical valves, peak

velocity is usually < 1.9 m/s but can be up to 2.4 m/s

As a general rule, peak velocity < 1.9 m/s is likely to be normal in most patients with mechanical valves unless there is markedly depressed LV function

Mean Gradients of MVNormally less than 5-6 mm HgValues up to 10-12 mm Hg have been

reported in normally functioning mechanical valves

High gradients can be due to: hyperdynamic states, tachycardia or PPM, regurgitation, or stenosis

MV Pressure Half-time (PHT)A large rise in PHT on serial studies or a markedly

prolonged single measurement (>200 ms) may be a clue to the presence of:obstructionPHT seldom exceeds 130 ms across normal pv

Minor changes in PHT occur as a result of nonprosthetic factors including:Loading conditionsDrugsAI

PHT should not be obtained in tachycardic rhythms or 1st degree blocks when the E & A velocities are merged or the diastolic filling period is short

EOA of PMVCalculation from PHT, as traditionally applied

in native MS, is not valid in prosthetic valves due to its dependence on LV and LA compliance and initial LA pressure

EOAPrMV= stroke volume/VTIPrMV

Usually reserved for cases of discrepancy between information obtained from gradients and PHT

Prosthetic MV and DVIDVI= VTIPrMV/ VTILVO

DVI can be elevated with stenosis or regurgitation

For mechanical valves, a DVI < 2.2 is most often normal

Higher values should prompt consideration of prosthesis dysfunction

Parameter Normal Possible Stenosis Suggests Significant Stenosis

Peak Velocity (m/s)

<1.9 1.9-2.5 ≥2.5

Mean Gradient (mm Hg)

≤5 6-10 >10

DVI <2.2 2.2-2.5 >2.5

EOA (cm2) ≥2 1-2 <1

PHT (ms) <130 130-200 >200

Doppler Parameters of Prosthetic MV Function

Prosthetic MV RegurgitationSince direct detection of prosthetic MR is often not

possible with TTE, particularly with mechanical valves, one must rely on indirect signs suggestive of significant MR

Such signs include:Hyperdynamic LV with low systemic outputElevated mitral E velocityElevated DVIDense CW regurgitant jet with early systolic maximal

velocityLarge zone of systolic flow convergence toward the

prosthesis seen in the LVClinical symptoms & presence of the above findings

represents a clear indication for TEE

Prosthetic MV RegurgitationAssessment of severity of prosthetic MR can

be difficult at times because of the lack of a single quantitative parameter that can be applied consistently in all patients

Currently, best method is to integrate several findings from both TTE and TEE that together suggest a given severity of regurgitation

Parameter Mild Moderate Severe

LV size Normal NL or Dilated

Usually Dilated

Valve Usually Normal Abnormal Abnormal

Color Flow Jet Area

Small, central jet (usually <4 cm2

or <20% of LA area)

Variable Large, central jet

(usually >8cm2 or

>40% of LA area)

Flow Convergence

None or Minimal Intermediate

Large

Jet Density: CW Incomplete/Faint Dense Dense

Jet Contour: CW Parabolic Usually Parabolic

Early peaking,

triangular

Pulm Vein Flow Systolic Dominance

Systolic Blunting

Systolic Flow Reversal

VC Width (cm) <0.3 0.3-0.59 ≥0.6

R vol (ml/beat) <30 30-59 ≥60

RF (%) <30 30-49 ≥50

EROA (cm2) <0.2 0.20-0.49 ≥0.50

Echo & Doppler Criteria for Severity of Prosthetic MR from TTE/TEE

TTE of Prosthetic MV

TEE of Same MV