Prosthetic Valves Flashcards
What is the difference between tissue and mechanical prosthetic valves?
- Tissue valves are biological, coming from humans or animals
- Mechanical valves are non-biological
What are the four types of tissue valves?
- Allograft (human)
- Autograft (Ross procedure)
- Bioprosthetic (animal/heterograft - can be stented or stentless)
- Percutaneous
What are the three types of mechanical valve?
- Bileaflet tilting disc
- Single tilting disc
- Ball-cage
What is the design of allograft (human) valves?
- Aortic valve from human donor
- Only used in aortic position
- Stentless
- Typically harvested as a block of tissue including aortic valve and ascending aorta
What are the flow characteristics of allograft (human) valves?
- Similar flow characteristics to native valve
- Central flow
- Trivial or no regurgitation
- Low stenosis rate
- Low thrombosis rate
What is the Ross Procedure?
- Native pulmonary valve resected and sewn into aortic position (autograft)
- Allograft then placed in pulmonary position
- Coronary arteries re-implanted to autograft
What are the flow characteristics for autografts (Ross Procedure)?
- Native valve flow characteristics for both valves
- Central flow
- Trivial or no regurgitation
What is the design of stented biological valves?
- Created from porcine pericardium and mounted on metallic stent
- May be an entire valve from a single pig or a composite from 2 or 3 individual pigs
- Stented pericardial valves usually bovine in origin (may be porcine or equine)
What are the flow characteristics of stented biological valves?
- Central flow dynamics
- Trivial or no regurgitation
- Relatively stenotic in smaller sizes
- Failure due to leaflet degeneration such as leaflet thickening, calcification and tearing resulting in stenosis and regurgitation
What is the design of stentless biological valves?
- Aortic position only
- Usually consist of a portion of porcine aorta
- Aortic segment may be relatively long or may be sculpted to fit under the coronary arteries
What are the flow characteristics of stentless biological valves?
- Central flow
- Improved flow characteristics compared to stented valves (larger valve area for given annulus size)
- Trivial or no regurgitation
What is the design of percutaneous (transcatheter) valves?
- Bovine or porcine tissue
- Variable design
- Commonly mounted on a balloon-expandable or self-expandable stent
- Placed within an existing valve
- Majority placed within aortic position; TAVR/TAVI instead of conventional surgical AVR
What are the flow characteristics of percutaneous valves?
- Central flow
- Small central regurgitant jets are common
- Paravalvular regurgitation is common (but not normal) in the aortic valves
- Long term durability uncertain
Characteristics of a CoreValve?
- Type of percutaneous tissue valve
- 3 valve leaflets and a skirt made from a single layer of porcine pericardium
- Attached to a self-expanding multi-level radiopaque frame made of Nitinol
Characteristics of an Edwards Sapien TAVR?
- Type of percutaneous tissue valve
- Bovine pericardial valve
- Attached to balloon-expandable, cobalt-chromium frame
Characteristics of a Melody Valve?
- Type of percutaneous tissue valve
- Bovine jugular vein valve attached to a platinum-iridium stent
- Balloon-expandable
- Most commonly implanted in pulmonary position for repaired congenital heart lesions and PS/PR
- Less commonly implanted in tricuspid position
What is a Valve-in-Valve Procedure?
- Placement of transcatheter valve into the orifice of a failed surgical valve; pushes old valve leaflets aside
- May be performed for mitral, tricuspid, aortic or pulmonary valves
What is the design of the bileaflet tilting disc mechanical valve?
- Two equal-sized semi-circular discs attached to a central hinge
- Open valve consists of three orifices; 1 small, slit-like central orifice between open discs and 2 larger, semi-circular lateral orifices
What are the flow characteristics of the bileaflet tilting disc valve?
- Complex flow dynamics with 2 large lateral orifices and 1 smaller central orifice
- Higher velocities reported in central orifice
- Normal leakage volume regurgitation common: appears as 3 jets - 2 peripheral and 1 central
What is normal leakage volume?
- Normal leakage volume = in-built regurgitation
- Aims to prevent thrombus formation at potential points of stasis by ‘washing out’ mechanism
- ‘Washing jets’ appear at hinge points
What is the design of the single tilting disc valve?
- Single hinged circular disc within rigid annulus
- Open valve consists of 2 distinct orifices of different sizes
- Variable opening angle of disc (ranges from 60° to 80°)
What are the flow characteristics of the single tilting disc valve?
- Flow through a major and minor orifice (semi-central flow)
- Leakage and closing volume regurgitation common around central strut and between disc and sewing ring (peripheral jets)
What is the design of Ball-Cage Valves?
- Silastic ball (poppet) within alloy cage
2. Rarely implanted nowadays
What are the flow characteristics of ball-cage valves?
- Non-central flow dynamics (lateral flow diverging around ball)
- ‘Stenotic’, especially in small sized valves
- Closing volume regurgitation common
- True valvular (leakage) regurgitation uncommon
What is the purpose/importance of a baseline study?
- Acquire haemodynamic data of ‘normal’ functioning valve (reference for future studies)
- Recognition of PPM (PPM occurs when EOA to small for patient)
- Useful to follow progression of PrV dysfunction
- Identify IE (then vs now)
- Monitoring of: 1) Regression of hypertrophy, 2) recovery of LV function and 3) reduction in RVSP (pre-op PHTN)
Aims of the 2D Echo Exam in the Baseline PrV Study?
- Assess appearance and the opening and closing motion of the valve
- Evaluate the valve bed (stable sewing ring, well-seated PrV)
- Identify any extraneous echoes e.g. appearance of valve calcification/densities near PrV
What are microbubbles due to degassing?
- Commonly seen downstream to mechanical PrV
- Created by degassing which occurs as blood flows through mechanical valve
- Normal phenomenon (not to be confused with SEC)
What is Spontaneous Echo Contrast (SEC)?
- Caused by Rouleaux effect
- RBCs stacked on top of each other
- Occurs when velocity of blood flow decreases, RBCs form rouleaux so easily detected via echo
Caviation vs. Degassing: Mechanism
Caviation: Evaporation of blood; Due to dramatic transient local drop in pressure
Degassing; Separation of gas contained in blood; Due to a transient drop in pressure
Caviation vs. Degassing: Size
Caviation: Very small (<1mm); Appear as a fine cloud rather than bubbles
Degassing: Bigger; Appears as true microbubbles
Caviation vs. Degassing: Duration
Caviation: Lasts for several milliseconds only
Degassing: May last for several seconds
What are the parameters considered in the haemodynamic assessment of AVR?
- Max and mean pressure gradients
- DPI/DVI
- Effective orifice area
Significance of acceleration time (AT) and contour of AVR signal?
- Normally: triangular in shape, AT < 100ms (max velocity in early systole)
- Clue to stenosis: rounded, AT > 100ms
When do you need to use the corrected maximum and mean AV gradients?
Required when LVOT velocity ≥ 1.2m/s
Corrected Maximum AV Gradient Formula?
Corrected maximum PG = AVRmax – LVOTmax
Corrected Mean AV Gradient Formula?
Corrected mean PG = AVRmean – LVOTmean
Formula for AVR EOA (VTI Method)?
EOA = (LVOT area × LVOT VTI) / (AV VTI)
Formula for AVR EOA (Vmax Method)?
- EOA = (LVOT area × LVOT Vmax) / (AV Vmax)
- EOA Vmax and VTI methods should not vary by more than 0.2cm2
What EOA formula is used when LVOT flow is non-laminar?
- EOA (cm^2) = (RVOT area × RVOT VTI) / AVR VTI
- Substitute RVOT SV for LVOT SV (providing < ¼AR and/or PR, and no shunt)
Formula for indexing EOA and when is this value useful?
- iEOA = EOA / BSA (cm2/m2)
- iEOA useful identifying prosthetic-patient mismatch
How is LVOTd/VTI measured in TAVI?
- LVOTd measured pre-stent (use amvl as a guide)
- LVOT VTI measured pre-stent to avoid flow acceleration
- Both measurements above need to be in at the same location
- Exception: low-sitting TAVI (CoreValve), LVOTd measured in-stent, proximal to PrV cusps
Doppler Velocity Ratio (DVI) Fomulae for AVR?
DVI = LVOT VTI / AV VTI DVI = LVOT Vmax / AV Vmax
Normal/abnormal DVI values for AVR?
- DVI considered fingerprint for individual’s prosthesis (serial studies)
- DVI > 0.30 = normal
- DVI < 0.25 = highly suggestive of stenosis
What are the parameters considered in the haemodynamic assessment of MVR?
- Mean pressure gradient
- Pressure half time
- Doppler velocity index
- Effective orifice area
When can the mean mitral gradient be elevated?
- Abnormal MVR:
1. Stenosis
2. Regurgitation - Normal MVR:
1. Hyperdynamic states
2. Tachycardia
3. Prosthesis-patient mismatch (PPM)
Can the p1/2t method be use to calculate MVA in PrV?
- P1/2t method for MVR tends to grossly overestimate the in-vitro MVA in the bioprosthesis and St Jude MVR
- P1/2t does however provide information regarding normality of the valve
What is the DVI formula for MVR?
DVI = MVR VTI / LVOT VTI (not calculated)
Values for a normal functioning MV PrV?
- Peak E velocity < 1.9m/s
- DVI < 2.2
- P1/2t < 130ms
EOA Formula for MVR?
EOA = (LVOT area x LVOT VTI) / MVR VTI
EOA Formula for MVR Using RVOT? When is this used?
- EOA = (RVOT area x RVOT VTI) / MVR VTI
- Used when AR
- Assumes SV RVOT = SV MVR (when no MR, PR or intracardiac shunt)
What are the parameters considered in the haemodynamic assessment of TVR?
- Mean pressure gradient
- P1/2t
- DVI
- EOA
Formula for TVR DVI?
DVI = TVR VTI / LVOT VTI
EOA TVR Formula?
- EOA= (LVOT area × LVOT VTI) / TVR VTI
- Assumes LVOT SV = TVR SV (no TR, AR or intracardiac shunt)
Values for a normal function TVR?
- E velocity (TV inflow) < 2.1m/s
- DVI < 3.3
- P1/2t < 200ms
What are the parameters considered in the haemodynamic assessment of PVR?
- Maximum and mean pressure gradients
2. EOA
Formula for EOA in PVR?
- EOA = (LVOT area x LVOT VTI) / PVR VTI
- Assumes LVOT SV = PVR SV (no AR, PR or shunt)
General PrV Formula for EOA?
EOA = (LVOT area x LVOT VTI) / PrV VTI
