Transcript Evaluation of Prosthetic Valves

Echo Conference
3/16/11
Scott Midwall, MD
Objectives
Introduction to Prosthetic Valves (PV)
I.
Mechanical
II. Biological/Tissue
III. Appearance of Normally functioning Valves
I.
II. Approach to Evaluating PVs with echo and doppler
III. Evaluating Prosthetic Aortic Valves
IV. Echo Case/Questions (EchoSap)
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
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)
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
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->greater EOA
 Uses the patient’s own aortic root as the stent, absorbing
the stress induced during the cardiac cycle
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
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 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
 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 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
Evaluation of the Prosthetic Aortic
Valve (AV)
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
Doppler of Prosthetic AV
 Doppler velocity recordings across normal PVs usually
resemble those of mild native aortic stenosis
 Maximal velocity usually > 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
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 < 1
 DVI < 0.25 is highly suggestive of significant
obstruction
 DVI 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 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
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
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
Doppler Parameters of Prosthetic AV function in Mechanical and Stented
Biologic Valves in Conditions of Normal Stroke Volume
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
Patient-Prosthesis Mismatch (PPM)
 When the EOA of the inserted prosthesis is too small
in relation to the patient’s 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
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
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
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->
overestimation
Significant AI, AV Dehiscence
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:
 < 10% of sewing ring suggests mild
 10-20% suggests moderate
 > 20% suggests severe
 **Rocking of the prosthesis usually associated with
>40% dehisscence
Spectral Doppler and PVAI
 PHT is useful when the value is <200 ms, suggesting
severe AI, or > 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
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 (2664%)
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
Part II-Evaluation of Prosthetic
Mitral Valve
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
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
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
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
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 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
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: 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
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
Prosthetic MV and DVI
 DVI= 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
Doppler Parameters of Prosthetic MV
Function
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
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
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
Echo & Doppler Criteria for Severity of Prosthetic MR from TTE/TEE
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
TTE of Prosthetic MV
TEE of Same MV