Echocardiographic Evaluation of Prosthetic Valves, Part I

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Echocardiographic Evaluation of Prosthetic
Valves, Part I

• Echo Conference
• 3/16/11
• Scott Midwall, MD

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Objectives

• Introduction to Prosthetic Valves (PV)
• Mechanical
• Biological/Tissue
• Appearance of Normally functioning Valves
• Approach to Evaluating PVs with echo and doppler
• Evaluating Prosthetic Aortic Valves
• Echo Case/Questions (EchoSap)

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Overview

• Prosthetic 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
• Mechanical
• Made 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

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Valves

• Biologic (Tissue)

• Mechanical

• Stented
• Porcine xenograft
• Pericardial xenograft
• Stentless
• Porcine xenograft
• Pericardial xenograft
• Homograft
• Autograft

• Ball and cage (Starr-Edwards)
• Single tilting disc (Medtronic-Hall)
• Bileaflet (St. Jude, CarboMedics)

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Mechanical Valves

• Extremely durable with overall survival rates of
  94 at 10 years
• Primary structural abnormalities are rare
• Most malfunctions are secondary to perivalvular
  leak and thrombosis
• Chronic anticoagulation required in all
• With adequate anticoagulation, rate of thrombosis
  is 0.6 to 1.8 per patient-year for bileaflet
  valves

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Biological Valves

• Stented bioprostheses
• Primary mechanical failure at 10 years is 15-20
• Preferred in patients over age 70
• Subject to progressive calcific degeneration
  failure after 6-8 years
• Stentless bioprostheses
• Absence of stent sewing cuff allow implantation
  of larger valve for given annular size-gtgreater
  EOA
• Uses the patients own aortic root as the stent,
  absorbing the stress induced during the cardiac
  cycle

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Biologic Valves Continued

• Homografts
• Harvested from cadaveric human hearts
• Advantages resistance to infection, lack of need
  for anticoagulation, excellent hemodynamic
  profile (in smaller aortic root sizes)
• More difficult surgical procedure limits its use
• Autograft
• Ross Procedure

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Caged-Ball Valve
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Single-Leaflet Valve
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Bileaflet Valve
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Stentless Aortic Graft Valve
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Stented Biologic Mitral Valve
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Approach to Valve Evaluation

• Clinical data including reason for the study and
  the patients symptoms
• Type size of replacement valve, date of surgery
• BP HR
• HR particularly important in mitral and tricuspid
  evaluations because the mean gradient is
  dependent on the diastolic filling period
• Patients height, weight, and BSA should be
  recorded to assess whether prosthesis-patient
  mismatch (PPM) is present

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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

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Echo Imaging

• Mild thickening is often the 1st sign of primary
  failure of a biologic valve
• Occluder motion of a mechanical valve may not be
  well visualized by TTE because of artifact and
  reverberations

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Evaluation of the Prosthetic Aortic Valve (AV)
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Imaging Considerations

• Identify the sewing ring, valve or occluder
  mechanism, and surrounding area
• Ball 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

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Doppler of Prosthetic AV

• Doppler velocity recordings across normal PVs
  usually resemble those of mild native aortic
  stenosis
• Maximal velocity usually gt 2 m/s, with triangular
  shape of the velocity contour
• Occurrence 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

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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

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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 lt 1
• DVI lt 0.25 is highly suggestive of significant
  obstruction
• DVI is not affected by high flow conditions
  through the valve, including AI

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Doppler Prosthetic AV

• High gradients may be seen with normal
  functioning valves with
• Small size
• Increased stroke volume
• PPM
• Valve 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

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Doppler Continued

• Other 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

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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 lt 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

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Doppler Parameters of Prosthetic AV function in
Mechanical and Stented Biologic Valves in
Conditions of Normal Stroke Volume
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Patient-Prosthesis Mismatch (PPM)

• When the EOA of the inserted prosthesis is too
  small in relation to the patients BSA
• A 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

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PPM Continued

• Commonly 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

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Evaluation of Prosthetic AI

• With color doppler, one can evaluate the
  components of the color AI jet
• Flow convergence, vena contracta, extent in the
  LVO tract and LV
• Normal 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

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Prosthetic Valve AI

• With 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-gt overestimation

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Significant AI, AV Dehiscence
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AI in PVs

• Contrary 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
• lt 10 of sewing ring suggests mild
• 10-20 suggests moderate
• gt 20 suggests severe
• Rocking of the prosthesis usually associated
  with gt40 dehisscence

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Spectral Doppler and PVAI

• PHT is useful when the value is lt200 ms,
  suggesting severe AI, or gt 500 ms, consistent
  with mild AI
• Intermediate ranges may reflect other hemodynamic
  variables such as LV compliance and are less
  specific
• Holodiastolic flow reversal in the descending
  thoracic aorta is indicative of at least moderate
  AI
• Severe is suspected when the VTI of the reverse
  flow approximates that of the forward flow
• Holodiastolic flow reversal in the abdominal
  aorta is usually indicative of severe AI

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Part II-Evaluation of Prosthetic Mitral Valve
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Evaluation of Prosthetic MV

• A major consideration with echo is the effect of
  acoustic shadowing by the prosthesis on
  assessment of MR
• Problem is worse with mechanical valves
• On TTE, LV function is readily evaluated, but the
  LA is often obscured for imaging and doppler
  interrogation
• TEE provides visualization of the LA and MR but
  shadowing limits visualization of the LV
• Thus, comprehensive assessment of PMV requires
  both TTE TEE when valve dysfunction is suspected

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Prosthetic MV Imaging Considerations

• In the parasternal long-axis view, the prosthesis
  may obscure portions of the LA and its posterior
  wall
• MR 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
  valves
• May allow detection of thrombus or pannus
• Vegetations can be seen but are often masked by
  acoustic shadowing

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Doppler Evaluation of PMV

• Complete exam should include
• Peak early velocity
• Estimate of mean pressure gradient
• Heart Rate
• Pressure half-time (PHT)
• Determination of whether regurgitation is present
• DVI and/or EOA as needed
• LV/RV size and function
• LA size if possible
• PA systolic pressure

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Peak Early Mitral Velocity

• Peak 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

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MV Peak Velocity

• In normal bileaflet mechanical valves, peak
  velocity is usually lt 1.9 m/s but can be up to
  2.4 m/s
• As a general rule, peak velocity lt 1.9 m/s is
  likely to be normal in most patients with
  mechanical valves unless there is markedly
  depressed LV function

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Mean Gradients of MV

• Normally less than 5-6 mm Hg
• Values 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

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MV Pressure Half-time (PHT)

• A large rise in PHT on serial studies or a
  markedly prolonged single measurement (gt200 ms)
  may be a clue to the presence of obstruction
• PHT seldom exceeds 130 ms across normal pv
• Minor changes in PHT occur as a result of
  nonprosthetic factors including
• Loading conditions
• Drugs
• AI
• 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

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EOA of PMV

• Calculation 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

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Prosthetic MV and DVI

• DVI VTIPrMV/ VTILVO
• DVI can be elevated with stenosis or
  regurgitation
• For mechanical valves, a DVI lt 2.2 is most often
  normal
• Higher values should prompt consideration of
  prosthesis dysfunction

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Doppler Parameters of Prosthetic MV Function
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Prosthetic MV Regurgitation

• Since 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 output
• Elevated mitral E velocity
• Elevated DVI
• Dense CW regurgitant jet with early systolic
  maximal velocity
• Large zone of systolic flow convergence toward
  the prosthesis seen in the LV
• Clinical symptoms presence of the above
  findings represents a clear indication for TEE

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Prosthetic MV Regurgitation

• Assessment 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

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