Presentation on theme: "Echocardiography of Prosthetic Valves Dr. Tehrani."— Presentation transcript:
Echocardiography of Prosthetic Valves Dr. Tehrani
Different Types of Valves Homografts (allograft) Cadaveric human aortic and pulmonary valves Heterograft (Xenograft) Prosthetic Valves Bioprosthetic valves Pig aortic valve Bovine pericardial (other) Mechanical Urethane ball in a cage Single or multiple discs
Homografts Homograft Valves Harvested soon after death w/ the endothelium still viable Preparation for implantation Storage in ABX Cryopreservation (more recently) No anticoagulation Low incidence of endocarditis Failure due to gradual aortic incompetence
Homografts Position Mitral Fitted w/ stent, not proved successful (high failure rate at 5 years) Stentless grafts not an option for MVR Aortic Stentless Subcoronary Root Replacement
Echocardiography of Stentless Aortic Homografts Doppler flow characteristics similar to native valve. Only 2-D evidence: Increased Echo intensity, and Thickness of aortic annulus.
Prosthetic valves All Prosthetic valves have a sewing ring anchored to the native tissue with sutures The occluding portion of the valve: Prosthetic Tissue leaflets Bio-Prosthetic Single or multiple discs/ Urethane ball in a cage Mechanical Prosthetic Bio-Prosthetic and Mechanical Prosthetic
Bioprosthetic Valves Two types, of occluding mechanism 1. Porcine aortic valve (the valve size of the biggest pig is limiting) Hancock, and Carpentier- Edwards bioprosthesis
Bioprosthetic valves 2. Bovine Pericadium leaflets are shaped to size. More choices Echocardiographiaclly these two valves types are indistinguishable. Ionescu-Shiley (1976)
Bioprosthetic valves Mitral Position 2-D ECHOCARDIOGRAPHIC APPEARANCE
Bioprosthetic valves Aortic Position 2-D ECHOCARDIOGRAPHIC APPEARANCE
Bioprosthesis Used extensively in a variety of sites: Aortic Mitral Tricuspid Advantage: Low thrombogenicity => No anticoagulation
Bioprosthesis Disadvantages: Less durable than mechanical prosthesis Mitral position worse Due to greater backpressure gradient Dysfunction: Leaflet thickening, and Ca++ Fracture, tears, or progressive stenosis In vivo, roughly 10% of normal bioprosthetic valves have some leakage.
Overview of Various Devices Bio-Prosthetic Valves Mechanical Prosthetic Valves
Mechanical Vlaves Ball-and-Cage Valves Tilting disc Prosthesis Single disk Bileaflet
Mechanical Prosthesis The occluding mechanism dictates both: The echocardiographic appearance of the valve, and The flow pattern through the valve To assess performance, the type of valve implanted must be known
Ball-and-Cage Valves First implanted by starr and Harken in 1960.
Ball-and-Cage Valves Opening and closure of the ball-valve
Ball-and-Cage Valves Axisymmetric flow around the valve. Stagnant flow in the shadow of the ball.
Ball-and-Cage Valves Doppler assessment at the margins of the ball
Ball-and-Cage Valves M-Mode assessment of Ball-Cage Valve
Ball-and-Cage Valves Durable Mitral position Satisfactory profile with the largest size (34 or 32 mm diameter devices) Can affect the interventricular septum Aortic position Small prosthesis required, which can be associated with significant gradient Regurgitation limited to closure backflow.
Tilting Disc Prosthesis All essentially similar consisting of Circular prosthetic material, and One or two hinged and mobile disc(s) Disc attachment to the ring is eccentric Closure occurs by backpressure on the largest portion of the disk
Single Disc Prosthesis Single Disc devices: Hall-Medtronics monostrut Bjork-Shiley Opening arch is 55-70 degrees Flow orifice: Major and minor flow orifices Streamlines of flow passing through the sewing ring and then laterally out and around the prosthetic disc
Single Disc Prosthesis Bjork-Shiley Standard Convex-concave Many other variations in the market All of these devices have a zone of stagnation behind the disc thrombus formation
Single Disc Prosthesis Bjork-Shiley in the Mitral position
Single Disc Prosthesis Leak around: Central strut Dominant jet Between the occluding disc and sewing ring. Two smaller peripheral jets Normal hemodynamics Reg.Frac. approx. 12% Tachycardia, and low output Reg.Frac. upto 37%
Dysfunction Gradual ingrowth of fibrous tissue (panus) Flow obstruction Intermittent sticking of the valve with associated flash pulmonary edema
Bileaflet Mechanical Prosthesis St. Jude prosthesis The most commonly used. Two equal sized semi-circular leaflets attached by a midline hinge. Discs can tilt in excess of 80 degrees, resulting in larger: Orifice area
Bileaflet Mechanical Prosthesis St. Jude prosthesis The most commonly used. Two equal sized semi-circular leaflets attached by a midline hinge. Discs can tilt in excess of 80 degrees, resulting in larger: Orifice area Regurgitant back flow
Bileaflet Mechanical Prosthesis Regurgitation occurs at the disc margins The regurgitant jets converge toward the center of the valve
Bileaflet Mechanical Prosthesis St. Jude valve in the mitral position.
Special Problems of 2-D Imaging Artificial Valves Echocardiographs are calibrated to measure distance based on the speed of sound in tissue. Prosthetic valves have different acoustic properties than tissue. Hence, distortion of: Size Location, and Appearance, of the prosthesis.
Special problems of artificial valves Intense reverberation, and Shadowing Less gain leads to less: Reverberation, and Shadowing, as well as Better visualization of non-biologic components of the valve HOWEVER Decreased definition of cardiac structures
Special problems of artificial valves First image at normal settings, then Reduce the gain to interrogate the leaflets of Bio-prosthetic valves. Utilize multiple views.
G E N E R A L L Y Prosthetic Stenosis (and Regurgitation) is: A question of degree, Not a question of whether.
Prosthetic Valve Stenosis Determinants of gradients across normal prosthetic valves include: Valve type, i.e., Manufacturer Valve size Flow through the valve Wide range of “Normals”
Aortic Prosthesis Gradients as a Function of Valve TYPE and SIZE No.21 No.27 Dependence on: Valve type, and Size
Gradient as a Function of Valve Type Normal Dopplar data in patients with various types of prosthetic valves in the Aortic Position
Gradient as a Function of Valve Size Valve specifications and doppler echocardiographic data in 67 St. Jude medical valves in the Aortic position Chafizadeh ER, Circ. 83:213, 1991
Gradient as a Function of Flow No.21 I.Valve type, i.e., Manufacturer II.Valve size III.Flow through the valve
Indicies of Valve Stenosis which are Less Flow Depenent A.Contour of jet velocity B.Doppler velocity index C.Effective orifice area D.Valve resistance
A-Contour of the jet velocity With prosthetic obstruction there is: Late peaking of the velocity, More rounded contour, Prolonged ejection.
B-Doppler Velocity Index DVI= Pk Vel LVOT /Pk Vel jet Flow independent 0.2 – 0.27 cutoff for critical stenosis Caveat:Pressure recovery To be discussed …
C-Effective Orifice Area Continuity Eqn. Caveat:Pressure recovery To be discussed …
D-Valve resistance At cutoff of 280 dynes.sec.cm 5, best at differentiating AS, from NL (Zoghbi et al.)
Special Caveats Re: Overestimation of Gradients Two scenarios : I.The velocity upstream from the valve is not negligible in application of the Bernoulli Eqn. Usually in AV when proximal velocity on the LVOT is > 1.5 m/s
…Overestimation of Gradients II.Central acceleration with the St. Jude valve: Increase of velocities (and gradients) is created at the level of the valve through the smaller central orifice. Most significant with: High flow states Small valves
…Overestimation of Gradients Central acceleration with the St. Jude valve: CW Doppler records these high velocities. Catheter-derived gradients show pressure recovery at 30mm downstream from the valve.
Indicies which are Less Flow Dependent, BUT… A.Contour of jet velocity B.Doppler velocity index C.Effective orifice area D.Valve resistance Clearly, both of These Parameters Will be Affected by The Pressure Recovery Phenomenon.
Mismatch Rahimtoola 1978: “Mismatch is present when the effective prosthetic valve area, after insertion into the patient, is less than that of a normal human valve.” By definition: Some such “mismatch” will almost always be present.
Mismatch Literature identifies the above as a cut-off for mismatch
Mismatch Next locate the published in-vivo EOA of the valve used. This is the EOA that The patient physiologically Needs.
Mismatch JACC Review Article, 10/2000 Not the company reported data
Mitral Prosthesis Stenosis Parameters used for assessment of function: A.PHT/Area by PHT B.Effective Orifice Area by continuity C.Mean gradient
Mitral Prosthesis Stenosis A-PHT/Area by PHT Not expected to yield accurate valve area The empiric constant of 220 validated for the geometry of rheumatic MS Useful in longitudinal follow-up of valve Fx Should not be used when diastolic filling period is short (fusion of E and A) Tachycardia Long first degree block
Mitral Prosthesis Stenosis B-Effective Orifice Area by continuity Eqn. One underlying assumption is absence of significant AI or MR Physiologic prosthetic MR 10-30% (Medtronic-Hall, significant central MR, specific design feature less thrombogenic)
Mitral Prosthesis Stenosis C-Mean gradient, function of: Size Type of prosthetic Flow Heart rate (should also be reported when evaluating MVA)
Prosthetic Valve Regurgitatoin Two issues: Physiologic v.s. Pathologic regurgitation TTE v.s. TEE for assessment of regurgitation
Prosthetic Valve Regurgitation Physiologic Regurgitation Early onset Early onset and brief duration Reflects backflow from closing movement of occluding device late backflow Tilting disc and bileaflet valves have additional late backflow leakage Intended to reduce risk of thrombosis
Mitral Prosthesis Regurgitation TTE of limited value in assess MR due to acoustic shadowing of the LA Doppler findings suggestive of severe MR E wave > 1.9 m.s PISA Short isovolumetic relaxation time TVI LVOT /TVI Pr-MV < 0.4