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Week 10: Prosthetic Valves > Prosthetic Valves > Flashcards

Prosthetic Valves Flashcards

1
Q

What is the difference between tissue and mechanical prosthetic valves?

A
  • Tissue valves are biological, coming from humans or animals
  • Mechanical valves are non-biological
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2
Q

What are the four types of tissue valves?

A
  1. Allograft (human)
  2. Autograft (Ross procedure)
  3. Bioprosthetic (animal/heterograft - can be stented or stentless)
  4. Percutaneous
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3
Q

What are the three types of mechanical valve?

A
  1. Bileaflet tilting disc
  2. Single tilting disc
  3. Ball-cage
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4
Q

What is the design of allograft (human) valves?

A
  1. Aortic valve from human donor
  2. Only used in aortic position
  3. Stentless
  4. Typically harvested as a block of tissue including aortic valve and ascending aorta
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5
Q

What are the flow characteristics of allograft (human) valves?

A
  1. Similar flow characteristics to native valve
  2. Central flow
  3. Trivial or no regurgitation
  4. Low stenosis rate
  5. Low thrombosis rate
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6
Q

What is the Ross Procedure?

A
  1. Native pulmonary valve resected and sewn into aortic position (autograft)
  2. Allograft then placed in pulmonary position
  3. Coronary arteries re-implanted to autograft
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7
Q

What are the flow characteristics for autografts (Ross Procedure)?

A
  1. Native valve flow characteristics for both valves
  2. Central flow
  3. Trivial or no regurgitation
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8
Q

What is the design of stented biological valves?

A
  1. Created from porcine pericardium and mounted on metallic stent
  2. May be an entire valve from a single pig or a composite from 2 or 3 individual pigs
  3. Stented pericardial valves usually bovine in origin (may be porcine or equine)
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9
Q

What are the flow characteristics of stented biological valves?

A
  1. Central flow dynamics
  2. Trivial or no regurgitation
  3. Relatively stenotic in smaller sizes
  4. Failure due to leaflet degeneration such as leaflet thickening, calcification and tearing resulting in stenosis and regurgitation
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10
Q

What is the design of stentless biological valves?

A
  1. Aortic position only
  2. Usually consist of a portion of porcine aorta
  3. Aortic segment may be relatively long or may be sculpted to fit under the coronary arteries
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11
Q

What are the flow characteristics of stentless biological valves?

A
  1. Central flow
  2. Improved flow characteristics compared to stented valves (larger valve area for given annulus size)
  3. Trivial or no regurgitation
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12
Q

What is the design of percutaneous (transcatheter) valves?

A
  1. Bovine or porcine tissue
  2. Variable design
  3. Commonly mounted on a balloon-expandable or self-expandable stent
  4. Placed within an existing valve
  5. Majority placed within aortic position; TAVR/TAVI instead of conventional surgical AVR
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13
Q

What are the flow characteristics of percutaneous valves?

A
  1. Central flow
  2. Small central regurgitant jets are common
  3. Paravalvular regurgitation is common (but not normal) in the aortic valves
  4. Long term durability uncertain
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14
Q

Characteristics of a CoreValve?

A
  • 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
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15
Q

Characteristics of an Edwards Sapien TAVR?

A
  • Type of percutaneous tissue valve
  • Bovine pericardial valve
  • Attached to balloon-expandable, cobalt-chromium frame
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16
Q

Characteristics of a Melody Valve?

A
  • 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
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17
Q

What is a Valve-in-Valve Procedure?

A
  • 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
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18
Q

What is the design of the bileaflet tilting disc mechanical valve?

A
  1. Two equal-sized semi-circular discs attached to a central hinge
  2. Open valve consists of three orifices; 1 small, slit-like central orifice between open discs and 2 larger, semi-circular lateral orifices
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19
Q

What are the flow characteristics of the bileaflet tilting disc valve?

A
  1. Complex flow dynamics with 2 large lateral orifices and 1 smaller central orifice
  2. Higher velocities reported in central orifice
  3. Normal leakage volume regurgitation common: appears as 3 jets - 2 peripheral and 1 central
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20
Q

What is normal leakage volume?

A
  • 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
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21
Q

What is the design of the single tilting disc valve?

A
  1. Single hinged circular disc within rigid annulus
  2. Open valve consists of 2 distinct orifices of different sizes
  3. Variable opening angle of disc (ranges from 60° to 80°)
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22
Q

What are the flow characteristics of the single tilting disc valve?

A
  1. Flow through a major and minor orifice (semi-central flow)
  2. Leakage and closing volume regurgitation common around central strut and between disc and sewing ring (peripheral jets)
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23
Q

What is the design of Ball-Cage Valves?

A
  1. Silastic ball (poppet) within alloy cage

2. Rarely implanted nowadays

24
Q

What are the flow characteristics of ball-cage valves?

A
  1. Non-central flow dynamics (lateral flow diverging around ball)
  2. ‘Stenotic’, especially in small sized valves
  3. Closing volume regurgitation common
  4. True valvular (leakage) regurgitation uncommon
25
Q

What is the purpose/importance of a baseline study?

A
  • 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)
26
Q

Aims of the 2D Echo Exam in the Baseline PrV Study?

A
  1. Assess appearance and the opening and closing motion of the valve
  2. Evaluate the valve bed (stable sewing ring, well-seated PrV)
  3. Identify any extraneous echoes e.g. appearance of valve calcification/densities near PrV
27
Q

What are microbubbles due to degassing?

A
  • 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)
28
Q

What is Spontaneous Echo Contrast (SEC)?

A
  • 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
29
Q

Caviation vs. Degassing: Mechanism

A

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

30
Q

Caviation vs. Degassing: Size

A

Caviation: Very small (<1mm); Appear as a fine cloud rather than bubbles

Degassing: Bigger; Appears as true microbubbles

31
Q

Caviation vs. Degassing: Duration

A

Caviation: Lasts for several milliseconds only

Degassing: May last for several seconds

32
Q

What are the parameters considered in the haemodynamic assessment of AVR?

A
  1. Max and mean pressure gradients
  2. DPI/DVI
  3. Effective orifice area
33
Q

Significance of acceleration time (AT) and contour of AVR signal?

A
  • Normally: triangular in shape, AT < 100ms (max velocity in early systole)
  • Clue to stenosis: rounded, AT > 100ms
34
Q

When do you need to use the corrected maximum and mean AV gradients?

A

Required when LVOT velocity ≥ 1.2m/s

35
Q

Corrected Maximum AV Gradient Formula?

A

Corrected maximum PG = AVRmax – LVOTmax

36
Q

Corrected Mean AV Gradient Formula?

A

Corrected mean PG = AVRmean – LVOTmean

37
Q

Formula for AVR EOA (VTI Method)?

A

EOA = (LVOT area × LVOT VTI) / (AV VTI)

38
Q

Formula for AVR EOA (Vmax Method)?

A
  • EOA = (LVOT area × LVOT Vmax) / (AV Vmax)

- EOA Vmax and VTI methods should not vary by more than 0.2cm2

39
Q

What EOA formula is used when LVOT flow is non-laminar?

A
  • EOA (cm^2) = (RVOT area × RVOT VTI) / AVR VTI

- Substitute RVOT SV for LVOT SV (providing < ¼AR and/or PR, and no shunt)

40
Q

Formula for indexing EOA and when is this value useful?

A
  • iEOA = EOA / BSA (cm2/m2)

- iEOA useful identifying prosthetic-patient mismatch

41
Q

How is LVOTd/VTI measured in TAVI?

A
  • 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
42
Q

Doppler Velocity Ratio (DVI) Fomulae for AVR?

A 
DVI = LVOT VTI / AV VTI
DVI = LVOT Vmax / AV Vmax
43
Q

Normal/abnormal DVI values for AVR?

A
  • DVI considered fingerprint for individual’s prosthesis (serial studies)
  • DVI > 0.30 = normal
  • DVI < 0.25 = highly suggestive of stenosis
44
Q

What are the parameters considered in the haemodynamic assessment of MVR?

A
  1. Mean pressure gradient
  2. Pressure half time
  3. Doppler velocity index
  4. Effective orifice area
45
Q

When can the mean mitral gradient be elevated?

A
  • Abnormal MVR:
    1. Stenosis
    2. Regurgitation
  • Normal MVR:
    1. Hyperdynamic states
    2. Tachycardia
    3. Prosthesis-patient mismatch (PPM)
46
Q

Can the p1/2t method be use to calculate MVA in PrV?

A
  • 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
47
Q

What is the DVI formula for MVR?

A

DVI = MVR VTI / LVOT VTI (not calculated)

48
Q

Values for a normal functioning MV PrV?

A
  1. Peak E velocity < 1.9m/s
  2. DVI < 2.2
  3. P1/2t < 130ms
49
Q

EOA Formula for MVR?

A

EOA = (LVOT area x LVOT VTI) / MVR VTI

50
Q

EOA Formula for MVR Using RVOT? When is this used?

A
  • EOA = (RVOT area x RVOT VTI) / MVR VTI
  • Used when AR
  • Assumes SV RVOT = SV MVR (when no MR, PR or intracardiac shunt)
51
Q

What are the parameters considered in the haemodynamic assessment of TVR?

A
  1. Mean pressure gradient
  2. P1/2t
  3. DVI
  4. EOA
52
Q

Formula for TVR DVI?

A

DVI = TVR VTI / LVOT VTI

53
Q

EOA TVR Formula?

A
  • EOA= (LVOT area × LVOT VTI) / TVR VTI

- Assumes LVOT SV = TVR SV (no TR, AR or intracardiac shunt)

54
Q

Values for a normal function TVR?

A
  1. E velocity (TV inflow) < 2.1m/s
  2. DVI < 3.3
  3. P1/2t < 200ms
55
Q

What are the parameters considered in the haemodynamic assessment of PVR?

A
  1. Maximum and mean pressure gradients

2. EOA

56
Q

Formula for EOA in PVR?

A
  • EOA = (LVOT area x LVOT VTI) / PVR VTI

- Assumes LVOT SV = PVR SV (no AR, PR or shunt)

57
Q

General PrV Formula for EOA?

A

EOA = (LVOT area x LVOT VTI) / PrV VTI

Week 10: Prosthetic Valves (1 decks)

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