16 Prosthetic heart valves

Question 1

What are the 3 types of mechanical valves?

Answer 1

Ball and cage valves include a silastic ball occluder which moves up and down within the cage retainer.

Tilting disc valves include one disc occluder which tilts within its occluder.

Bileaflet valves (common) include two semicircular disc occluders which open and close on its hinges.

Question 2

Describe the structure of a mechanical valve.

Answer 2

Mechanical valves are constructed from artificial materials and consist of the sewing ring (the “annulus” - to sew the valve into position), the occluder (“leaflets” - open and close) and the retainer (the part attached to the sewing ring to keep the occluder in position).

Question 3

What are the types of biological valves?

Answer 3

Xenograft valves are created from a porcine valve or bovine.

Homograft valves are valves from cadavers.

Autograft valves are valves from the patient. In the ross procedure, the AV is replaced with the patient’s PV and the PV is replaced with a xenograft valve or homograft valve.

Stented biological prosthetic valves partially obstruct the forward flow.

Stentless biological prosthetic valves offer a bigger EOA with lower velocities and gradients.

Question 4

Describe the structure of a biological valve.

Answer 4

Biological valves are constructed from the native valve or the pericardium and consist of the sewing ring (“annulus” - to sew the valve into position), the stents (the struts attach the leaflets to the sewing ring) and the leaflets.

Question 5

What are the advantages and disadvantages of biological and mechanical valves?

Answer 5

Biological valves degenerate faster but mechanical valves require life long anticoagulation.

Biological valves degenerate due to fibrosis and calcification and mechanical stress.

Mechanical valves increase the risk of thrombosis.

Question 6

Describe the assessment of replacement prosthetic valves.

Answer 6

Describe the valve movement (well seated or rocking indicating dehiscence), the leaflet or occluder movement (obstruction indicates degeneration or masses), the presence of masses (thrombi and vegetations are acute and mobile and pannus are chronic and immobile) and the presence of bubbles (mechanical prosthetic valves cause cavitation causing bubbles).

Question 7

Describe the assessment of prosthetic valve stenosis.

Answer 7

Assess the mean PG, maximum PG, EOA and PHT (MV).

Do not measure the EOA in the presence of moderate + AR or MR.

Question 8

What is patient prosthesis mismatch?

Answer 8

The valve EOA is too small for the patient’s body size but the valve function is normal. This increases forward flow velocities and gradients.

Question 9

What are the 3 causes of high forward velocities and gradients of prosthetic valves?

Answer 9

Patient prosthetic mismatch, central jet artefact and leaflet degeneration/occluder obstruction.

Question 10

How are the causes of high forward velocities and gradients of prosthetic valves differentiated?

Answer 10

In patients with prosthetic valves, the measured pressure gradients are falsely high, therefore, the EOA is more important than the gradients, in the assessment.

Predicted indexed EOA (based on normal reference value, not TTE measurement) and DVI (TTE measurement).

For prosthetic AVs, an EOA indexed of <0.85cm²/m² indicates patient prosthesis mismatch (<0.65 is severe).
For prosthetic MVs an EOA indexed of <1.2cm²/m² indicates patient prosthesis mismatch (<0.9 is severe).
If the EOA is normal, valve dysfunction may be due to abnormal valve structure and/or mobility.

DVI = (LVOT VTI) / (prosthetic AV VTI)
For prosthetic AVs, a DVI of <0.3 indicates central jet artefact in a bi-leaflet AV with normal mobility, or valve dysfunction in a non-bi-leaflet AV.
DVI = (prosthetic MV VTI) / (LVOT VTI)
For prosthetic MVs, a DVI of >2.2 indicates central jet artefact in a bi-leaflet MV with normal mobility, or valve dysfunction in a non-bi-leaflet MV.

If the DVI is normal, valve dysfunction may be due to a high flow state or LVOT flow acceleration.

Question 11

What is pressure recovery?

Answer 11

Pressure increases downstream of a stenotic valve because of the conversion of kinetic energy to potential energy (recovery).

Question 12

Describe the assessment of normal and abnormal prosthetic AV, MV, PV and TV function.

Answer 12

In high flow states, the maximum velocity and mean PG are increased but the AT is normal.

In patients with patient prosthesis mismatch, the EOA is decreased, the maximum velocity and mean PG increase and the AT is normal or increased.

AV
A Vmax >3m/s, mean PG >20mmHg, AT >100ms and EOA (<1cm2) indicate stenosis.
An EOA indexed <0.85cm2/m2 indicates patient prosthesis mismatch and a DVI <0.3 indicates central jet artefact or valve dysfunction.

MV
A Vmax >2.5m/s, mean PG >5mmHg, PHT >200ms and EOA (<1cm2) indicate stenosis.
An EOA indexed <1.2cm2/m2 indicates patient prosthesis mismatch and a DVI >2.2 indicates central jet artefact or valve dysfunction.

TV
A Vmax >1m/s and mean PG >20mmHg indicate stenosis.

PV
A Vmax >3m/s and mean PG >20mmHg indicate stenosis.

Question 13

What is central jet artefact?

Answer 13

In patients with bileaflet prosthetic valves, 3 forward flow jets are present. However, the central jet causes a high velocity (central jet artefact).

Question 14

Describe the assessment of prosthetic valve artefacts.

Answer 14

Mechanical prosthetic valves cause acoustic shadow artefacts because the metal reflects the ultrasound and creates a shadow on the other side of the valve.

Mechanical prosthetic valves cause reverberation artefacts because the metal causes the ultrasound to bounce between the valve and create false images.

Question 15

Describe the assessment of prosthetic valve masses.

Answer 15

Thrombi and vegetations are acute and mobile.

Pannus (fibrous scar tissue) are chronic and immobile.

If a mass is visualised, a TOE is required.

Question 16

What are the causes of normal and abnormal transvalvular and paravalvular regurgitation?

Answer 16

Typically, transvalvular regurgitation is small and central and paravalvular regurgitation is small and eccentric.

In mechanical valves, there is normal trace regurgitation when the occluder closes and forces blood back and when the occluder is closed and blood flows over the valve to wash it (decrease the risk of thrombosis).

In mechanical valves, abnormal transvalvular regurgitation is due to obstruction of the occluder by a mass or mechanical failure of the occluder.

In biological valves, abnormal transvalvular regurgitation is due to fibrosis and calcification or rupture of the leaflets.

Abnormal paravalvular regurgitation is due to dehiscence.

Question 17

In patients with prosthetic valves, when are follow up TTEs required?

Answer 17

3-12 weeks post-surgery (to allow anaemia and LV function to normalise).

For mechanical valves, routine TTEs are not normally required.

For biological valves, annual routine TTEs are required after 5 years.

Question 18

How are valves repaired?

Answer 18

Valve repair is indicated for regurgitant valves.

The valve is surgically repaired by resecting the tissue and, if required, inserting an annuloplasty ring to reinforce the annulus.

Question 19

When is a ballon valvuloplasty indicated, how is performed, and how is it assessed?

Answer 19

Valvuloplasty is indicated for stenotic valves and contraindicated for severe MR, bilateral commissural calcification and/or an IAS thrombus.

The balloon is passed into the RA via the femoral vein, into the LA via the IAS, and across the stenotic MV. The ballon is inflated to widen the MV via commissural splitting.

In the 72 hours post-valvuloplasty, do not assess the MS using PHT.

Question 20

What are the two methods to predict valvuloplasty success?

Answer 20

The Wilkins score is based on leaflet mobility, valvular thickening, subvalvular thickening and valvular calcification. A Wilkins score of >8 indicates a low probability of success.
Leaflet mobility (mobile = 1; immobile = 4), valvular thickening (normal (<5mm) = 1; severe thickening (8–10 mm) = 4), subvalvular thickening (normal thickening = 1; global thickening = 4), valvular calcification (low echogenicity = 1; high echogenicity = 4).

The commissural calcification score is based on the level of calcification of the anterolateral commissure and posteromedial commissure. A commissural calcification score of ≥2, out of 4, indicates a low probability of success.
0 = no calcification, 1 = calcification of half a commissure, 2 = calcification of the whole commissure.

Question 21

When is a mitraclip indicated, how is performed, and how is it assessed?

Answer 21

Mitraclip is indicated in older patients with severe MR.

The mitraclip is passed to the RA via the femoral vein, into the LA via the IAS, and across the MV. The Mitraclip attaches the A2 and P2 MV scallops of the anterior and posterior MV leaflets to create a double orifice.

The normal quantitative methods are not accurate so semi-quantitative methods and 3D TTE are used to assess the MR.

Question 22

When is a TAVI indicated, how is performed, and how is it assessed?

Answer 22

TAVI is indicated for older patients with multiple comorbidities.

The TAVI valve is inserted via the femoral artery or via LV apex puncture. The balloon is inflated to widen the stenotic AV and the TAVI valve, within a stent, is deployed, alone or using a ballon, to widen the AV.

Post-TAVI, assess the complications (pericardial effusion and/or cardiac tamponade), stenosis and regurgitation.