Prosthetic Valves

Question 1

Presentation of prosthetic valve

Answer 1

• Heart failure
• dysfunction of the valve
• endocarditis
• overanticoagulation
• undercoagulation causing emboli in mechanical valves
• anaemia and jaundice from intravascular haemolysis

Question 2

Signs (before auscultation)

Answer 2

1. Scars
   - median sternotomy (if vein harvesting scars also present it is suggestive of coexistent IHD)
   - small infraclavicular scar - May suggest tunnelled line as source of endocarditis or placement for treatment of endocarditis (long term abx) (although perc peripherally inserted central catheters (PICC) used now). Which would indicate cause if need for valve replacement
2. Stigmata of endocarditis
3. Bruising (anticoagukation due to AF or mechanical valve)
4. Anaemia
   - due to SA Bacterial endocarditis
   - due to intravascular mechanical haemolysis through or around dysfunctional prosthetic valve)
5. Jaundice (pre-hepatic due to haemolysis)
6. Signs of valve dysfunction esp valve regurgitation which may be due to endocarditis
7. Audible mechanical clicks

Question 3

Signs (auscultation)

Answer 3

• click from end of bed. Time with carotid pulse.
• if 2 clicks then likely aortic and mitral replacement

Biological valves - don’t click but create an abnormal timbre and are lower pitched than normal. a soft systolic murmur across a prosthetic aortic or pulmonary valve can be normal (Innocent turbulent flow) if no other signs of stenosis (which can occur). Regurgitant murmur is never normal and suggests valvular or paravalvular leak (could indicate endocarditis)

Mechanical valves

• often loud crisp metallic closure click
• Star-Edwards (ball and cage) aortic valves often have a series of additional systolic clicks due to the ball rattling in cage. If these are muffled or absent may suggest low cardiac output or clot formation on ball or cage struts
• single tilting or bileaflet mechanical valves may occasionally produce faintly audible opening click

systolic murmur across MV represents paravalvular leak. Even severe may be barely audible.if suspected listen to back of chest as may be conducted through aortic root.

Small paravalvular leaks are common I. Patients with calcific degenerative valve disease As difficult for sutures to take.

Bileaflet tilting-disc valves such as st Jude’s allow v small jets of turbulent flow to reduce thrombosis risk. These are inaudible and have no haemodynamic consequence. Therefore ifsigns if aortic regurgitation then paravalvular leak or endocarditis should be suspected.

Question 4

Investigations

Answer 4

• TTE - assess valve function, well-seated, pressure gradients, flow velocities, endocarditis
• TOE if endocarditis expected or particularly good for mitral mechanical valve assessment (but also others). Acoustic shadowing can make even substantial paravalvular leaks invisible in TTE

Question 5

Merits of biological valve

Answer 5

1. Don’t need long term anticoagulation. Warfarin normally given for first 3/12 as bioprosthesis becomes fully endothelialised
2. However higher incidence of degeneration and structural failure (aortic > mitral) so repeat surgery needed which is more risky than initial operation. Therefore generally only offered to those with 10-15 year life expectancy (over 70’s or over 60’s if comorbidities) (failure rate 30-60% in this time period)
3. Need at least annual follow-up/echo

Question 6

Mechanical valve

Answer 6

More durable so valve of choice if <60 and no contraindication to anticoagulation

Risk of thromboembolism is higher in mitral mechanical valve compared to aortic (lower flow rate)

Anticoagulation may be indicated anyway eg AF so may as well use mechanical valve as more durable

Question 7

Difficulty in pregnant or women of childbearing age requiring salve replacement

Answer 7

Mechanical valve risks fetal Malformation with warfarin or maternal osteoporosis with long term heparin.

Bioprosthetic valves are more likely to undergo calcific degeneration during pregnancy and require urgent reoperation

Question 8

Anticoagulation in mechanical prosthetic valves

Answer 8

• Starr-Edwards no longer in use (provides highest risk of thrombotic event)
• single and bileaflet tilting disc valves have better haemodynamic a and larger orifices. Designed to have small leaks / “washing jets” which along with less thrombogenic coatings mean less intense anticoagulation is required.
• bileaflet tilting-disc prosthesis in aortic position has target INR 2.5 (2-3)
• any prosthesis in mitral position, multiple valves replaced or concomitant AF should aim for 3.0 (2.5 to 3.5)

Question 9

How do you manage anticoagulation perioperatively?

Answer 9

• if bileaflet tilting-disc in aortic area and no other risks of thromboembolism then stop warfarin up to 72 hours before and restart 24 hours after. No need for bridging
• otherwise stop 48 hours or more before surgery and start heparin once INR<2. Stop heparin 4-6 hours before surgery and restart when practical until INR >2.5