Prosthetic valves

TypesSelectionComplications

Types • Bioprosthetic valves

– Heterograft (xenograft)• Bovine• porcine

– Homograft (allograft)– Autograft

• Pericardial• Pulmonary (Ross)

• Mechanical– Caged ball valve– Tilting disc valve– Bileaflet valve

Heterografts(xenografts)

• Stentless– Porcine

• Toronto SPV valve, medtronic freestyle valve

• Stented - facilitate implant, maintain 3D

relationship,more physiological flow

– Porcine• Hancock , carpenteir

edward s, medtronic – Bovine

• Stented bovine p prosthesis

The Hancock M.O. II aortic bioprosthesis (porcine)

Carpentier-Edwards Duralex mitral bioprosthesis

Tissue heterograft• Advantages

- No need of anticoagulation after 1st 3 m

– Little hemolysis

• Disadvantages

– Limited ,uncertain durability• Cuspal tear• Perforation• degeneration

– Rapid deterioration esp children• Fibrin depostn• Ca++• 10-30% need re op in 10 yr• 30-60% need re op in 15 yr

– Small size have poor hemodynamics

Bioprosthetic valve

Preferred in • Pregnancy• Bleeding Diathesis• Age> 70 years• Poor compliance

Mechanical valves

– Caged ball valveAdvantages

• Oldest • durabilty upto 40 yr

Disadvantages • high profile• hemolysis • high thrombogenecity• Poor hemodynamics in

small sizes

Unique features

• Occluder travels completely out of the orifice, reduces thrombus & pannus growing from the sewing ring

• Continuously changing points of contact of the ball reduces the wear & tear in any one area

• Thrombogenic risk 4-6% / year

Starr Edwards Valve

• not suitable - for the mitral position in patients with a small left

ventricular cavity - for the aortic position in those with a small aortic

annulus - those requiring a valve-aortic arch composite graft

Tilting disc valve- monoleaflet

• - Medtronic Hall valve - Omnicarbon (Medical CV) - Monostrut (Alliance Medical

Technologies) - Bjork-Shiley valves

– Adv • low profile• Good hemodynamics even in

small sizes• Excellent durability• Permit central laminar flow

• Medtronic hall valve– Titanium housing– teflon sewing ring– carbon coated disc

– disadv –• Anticoagulation mandatory • higher risk of thrombosis

than cage ball v• sudden catastrophic valve

thrombosis

Bileaflet valveAdv –• Low bulk - flat profile • Less thrombogenicy • Central laminar flow• two semicircular discs that

pivot between open and closed positions

• No need for supporting struts

• Good hemodynamics even in small sizes

• 2 lat ,1 central minor orifice , no chance of sudden catastro thrombosis

Disadv-

• Anticoagulation mandatory

• risk of thrombosis

St. Jude Medical mechanical heart valve

CarbomedicsTitanium housing Pyrolytic carbon

Types of prosthetic valves and thrombogenicity

Type of valve Model Thrombogenicity

Mechanical

Caged ball Starr-Edwards ++++

Single tilting disc Bjork-Shiley,Medtronic Hall +++

Bileaflet St Jude Medical,Sorin Bicarbon,Carbomedics

++

Bioprosthetic

Heterografts Carpentier-Edwards,Tissue Med (Aspire), Hancock II

+ to ++

Homografts +

TTK chitra

• tilting disc valve - metallic housing (cobalt based wrought alloy) - circular disc high molecular weight polyethylene - A polyester suture ring

• Hemodynamically comparable to other mechanical valves

• valve related complications are similar

Characteristics of Various prosthetic valves

Flow Dynamics

Desired valves• Mechanical valves - preferred in young patients who have a life expectancy of more than 10 to 15 years

who require long-term anticoagulant therapy for other reasons (e.g., atrial fibrillation)

• Bioprosthetic valves preferred in patients who are elderly have a life expectancy of less than 10 to 15 years who cannot take long-term anticoagulant therapy • A bileaflet-tilting-disk or homograft prosthesis is most suitable

for a patient with a small valvular annulus in whom a prosthesis with the largest possible effective orifice area is desired.

algorithm for choice of prosthetic heart valve

Radiologic Identification

Starr-Edwards caged ball valve

Radiopaque base ring Radiopaque cage Three struts for the aortic

valve; 4 struts for the mitral or tricuspid valve

Silastic ball impregnated with barium that is mildly radiopaque (but not in all models)

TTE – stenosis

Valve area calculations• Continuity equation Area Ao prosthesis =

(diameter sewing ring)² x 0.785xLVOT VTI/ Ao prosthesis VTI

Area mitral prosthesis= (diameter LVOT)²x 0.785xLVOT VTI/ VTI mitral prosthesis

• Pressure Half time ( mitral valve prosthesis) • Dimensionless index- LVOT velocity/ aortic prosthesis velocity < 0.23 indicates prosthetic valve stenosis

Prosthetic Valve regugitation

• Mitral – velocity2.5m/sec - jet area 2cm²• Aortic -- aortic PHT≤ 250m/sec -- flow reversal in aorta

Normal Doppler Values of Prosthetic Valves

Aortic Position Velocity Mean Gr Starr Edward 3.1±0.5 24±4 St Jude 3.0±0.8 11±6Medtronic Hall 2.6±0.3 12±3Aortic Homograft 0.8±0.4 7±3Hancock 2.4±0.4 11±2Carpentier’s 2.4±0.5 14±6

Mitral Position Velocity MeanGrStarr Edward 1.8±0.5 7±2 St Jude 1.5±0.3 5±2 Medtronic Hall 1.6±0.3 5±2Aortic Homograft 1.5±0.4 4±2Hancock 1.5±0.3 5±2Carpentier’s 1.5±0.3 5±2

Importance of TEE

• higher-resolution image than TTE • size of vegetation defined more precisely• peri annular complications indicating a locally

uncontrolled infection (abscesses, dehiscence, fistulas) detected earlier

• limitation -inability to detect aortic prosthetic-valve obstruction or regurgitation, especially when a mitral prosthesis is present

Mitral Bileaflet

Cinefluoroscopy

• Structural integrity • Motion of the disc or poppet• excessive tilt ("rocking") of the base ring -

partial dehiscence of the valve• Aortic valve prosthesis - RAO caudal - LAO cranial Mitral -- RAO cranial

Fluoroscopy of a normally functioning CarboMedics bileaflet prosthesis in mitral position

A=opening angle B=closing angle

• St. Jude medical bileaflet valve – Mildly radiopaque

leaflets are best seen when viewed on end

– Seen as radiopaque lines when the leaflets are fully open

– Base ring is not visualized on most models

MRI

• Not useful in assessing prosthetic-valve structure

• used only when prosthetic-valve regurgitation or para valvular leakage is suspected but not adequately visualized by echocardiography

Cardiac Catheterization

• measure the transvalvular pressure gradient, from which the EOA can be calculated

• can visualize and quantify valvular or paravalvular regurgitation

Valve dysfunction complication example Role of echo

Primary mechanical failure Ball varianceStrut fracture

Visualize structure, assess gradient & regurgitation

Nonstructural dysfunction Pt- prosthesis mismatchpannus

Gradient, visualize tissue in & around the sewing ring

Bleeding event Intracranial hge Source of embolus, presence & mobility of masses

Endocarditis Vegetation, abcess, dehiscence

Visualize area around the sewing ring, echo dense / lucent area, perivalvular regurgitation

Thrombosis Thrombus impedes opening &closing of occluder mechanism

Localize mass, assess gradient, detect regurgitation

Embolism stroke Identify & characterize the source of emboli

patient-prosthesis mismatch• When the effective prosthetic valve area, after insertion into the

patient less than that of a normal valve (Rahimtoola in 1978)• EOA indexed to BSA is less than 0.85 cm2/m2

• EOA (echo) differs from geometric orifice area (measured directly)• EOA for each prostheses type & size obtained in literature from pts

normally functioning prostheses• Average if > 1 value

-- mild (0.9 - 1 cm² /m² -- moderate (0.6 - 0.9 cm2/m² -- severe (iEOA < 0.6cm²/m² (Rahimtoola)

• in-vitro area of the majority of valve prostheses ( int diameter <23 mm) < that of the normal human valve area

• the in-vivo prosthetic area further reduced by IVS hypertrophy, progressive endothelialization and tissue ingrowth

(Aortic prosthetic devices may be functionally stenotic)

three-step algorithm

• Step 1: Calculation of the patient BSA. Step 2: Reference to the specific table for identification of the

adequate valvular EOA according to the patient BSA. Step 3: Selection of the most appropriate type and size of

valve prosthesis according to the target iEOA

Valve Thrombosis Incidence of 0.1 to 5.7 % per patient-year

<0.2% per year for mech valves<0.1% bioprosthetic valves

• small thrombus, at the hinge portion of a bileaflet valve obstruct the mechanism

• tilting disk -- a much larger thrombus to prevent function

• Ball and cage valves – less susceptible occluder has no

contact at all with the valve housing for a portion of every cycle

Clinical– Non obstructive- incidental/embolic phenomenon– Partial obstruction- dyspnea,systemic embolism , fever– Severe obstruction- overt heart failure

• Fibrinolytic therapy - Rt sided thrombosis 80-100% success rate• Surgery for fibrinolysis failure/symptoms > 3 wk

• Surgery – Lt sided thrombosis, large clot burden

FIBRINOLYTIC PROTOCOLheart 2007;93:137-142

• 2 types of protocol -rescue fibrinolysis (short protocol for unstable pt) - long protocol for stable pt

• Short protocol - r tPA 10 mg bolus + 90 mg in 90 min or - SK 15lac in 60 min• Long protocol -- SK- 5lac u in 20 min f/b 15lac u for 10 hr -- rtPA -- 10 mgbolus f/b 90mg/hr for 9 hrs

• Urokinase– High dose: 4,500 IU/kg/h for 12 h without heparin– Low dose: 2,000 IU/kg/h with heparin for 24 h

Embolisation

• cerebral embolization CT normal/infarctwarf & heparin – 72 hrs APTT lower therapeutic level till the desired INR

• anticoagulantion delayed for at least 7 to 14 days - ICH, extensive cerebral infarction OAC

If embolic event occurs while the patient is on adequate antithrombotic therapy

• If on warfarin with INR of 2.0 to 3.0: increase dose to achieve INR of 2.5 to 3.5

• If on warfarin with INR of 2.5 to 3.5: add aspirin 50 to 100 mg/d

• If on warfarin with INR of 2.5 to 3.5, plus aspirin 80 to 100 mg/d: aspirin dose may also need to be increased to 325 mg/d

• If on aspirin 325 mg/d: switch to warfarin with goal INR of 2.0 to 3.0

Excessive Anticoagulation

• vit K 2.5 mg daily until the INR is acceptable

• fresh frozen plasma

• Human recombinant factor VIIa, 15 to 19 g/kg (INR >10.0 with bleeding)

Structural Failure of Bioprosthetic Valves

• About 30 % of heterograft bioprosthetic valves and 10 to 20 % of homograft valves require replacement within 10 to 15 years because of structural failure

• severe regurgitation due to a tear or rupture of one or more of the valve cusps

• calcified and rigid valves• Rarely severe valvular stenosis

Structural deterioration

• Higher incidence patients <40 years & with mitral prostheses

• gradual onset of dyspnea and other symptoms of heart failure

• Bioprosthetic-valve regurgitation or stenosis can be detected by auscultation

• valve dysfunction assessed by echocardiography or catheterization

Failure of Bio prosthetic Valves

Hemolysis• Incidence - 6%• Subclinical intravascular hemolysis • severe hemolytic anemia uncommon & suggests

paravalvular leakage due to partial dehiscence of the valve or infection

• Patients with a caged-ball valve / multiple prosthetic valves have an increased incidence & severity of hemolysis.

Hemolysis

• Pts with hemolytic anemia treated with iron & folate supplements or blood transfusion

- decreased blood viscosity & increased COP a/w anemia increase the hemolysis

• Paravalvular leakage & severe hemolysis – valve replacement or repair

Para valvular leak• improper implantation of a valve • A heavily calcified annulus is a risk factor for

paravalvular leaks -- incomplete debridement of calcium compromises both suture placement and valve seating

• Active endocarditis is also a risk factor• Late paravalvular leaks are suggestive of prosthetic

valve endocarditis• generally result in hemolysis• In the absence of a paravalvular leak, a normally

functioning modern valve should not result in hemolysis

Paravalvular Regurgitation

• mild or moderate paravalvular leakage - asymptomatic , may have only a mild hemolytic anemia

- can be observed carefully with serial echo • severe paravalvular leakage - usually have symptoms

of heart failure or severe anemia - should be treated with surgical repair or

replacement of the valve

PVE(2-6%) salient features

• Endovascular, microbial infection occurring on parts of a valve prosthesis or on reconstructed native heart valves , with or without implantation of an annular ring

• early PVE is 5% higher in surgery during active IE • Diagnostic approach, surgical indications same

PVE how diff from native?PVE NVE

• Early- nosocomial• Late- comm acquired• Mech prosthesis -originate from

the sewing cuff /from nearby located thrombi → periprosthetic leaks, ring abscesses, invasion of adjacent tissue

• Bioprosthesis infections mostly restricted to the cusps → secondary bioprosthetic failure

• Staphylococci, HACEK group, fungi occur more frequently in PVE

• Strepto & enterococci found more frequently in native valve endocarditis

• vegetations larger• irreversible adhesion

production of a biofilm, inhibit the host defence mechprotects against antimicrobial Tt

• Duration of Tt longer

• Smaller• No such biofilm

Pannus Valve obstruction occurs 5-10% of mechanical valves per year

Thrombus • mobile, somewhat less

echo-dense, associated with spontaneous contrast

Pannus• Pannus formation -more

common in aortic position • fibrous tissue ingrowth• highly echogenic• usually firmly fixed to the

valve apparatus• Pre valve jet suggests

pannus

MCQ

1.Factors favouring bioprostheses include all except

a. Age > 70 yrs b. Bleeding diathesis c. Combined multivalvular placement d. Poor compliance

2. Which of the following favours valve repair?

a. RHD b. Endocarditis c. Extensive leaflet destruction d. MVP

3. Which is the most durable mechanical prosthesis?

a. St Jude medical b. Medtronic Hall c. Starr- Edwards d. Bjork Shiley

4. Indication for long term anticoagulation in aortic bioprosthesis include all except

a. Prior embolic events b. Atrial fibrillation c. Ventricular tachycardia d. LV dysfunction

5. 55yr male, s/p AVR for BAV , SR, good LV function, Dental prophylaxis needed, anti thrombotic therapy would be the following

a. Stop warf 72 hrs before procedure, restart after control of bleeding

b. Stop warf 72 hrs before procedure, start heparin 48hrs before procedure

c. Stop warf 1wk before procedure

d. Continue warf

6 . Heparin alone regimen in a pregnant lady on OAC, s/p MVR , thrombo embolic complications would be

a. 25%b. 33%c. 43%d. 45%

7. Ideal anti thrombotic therapy in a 45 yr female, s/p MVR for RHD, with h/o embolic stroke would be the following

a. Warfarin INR 2.5- 3.5, aspirin 50- 100mg

b. Warfarin INR 2.0 - 3.0, aspirin 50- 100mg

c. Warfarin INR 2.5- 3.5, aspirin 75- 150mg

d. Warfarin INR 2.0 - 3.0, aspirin 75- 150mg

8. Prosthetic valve thrombosis would be catastrophic in the following

a. Bioprosthesisb. Tilting disc valvec. Bileaflet valved. Starr- Edwards valve

9. Mitral prostheses best assessed by

a. RAO cranialb. RAO caudalc. LAO craniald. LAO caudal

10. Clinical hemolysis is maximum with

a. Caged ballb. Bioprosthesisc. Tilting discd. Bileaflet