Prosthetic Valves

• Prosthetic valves are used when severe valvular dysfunction is not repairable, especially stenotic lesions.
• No perfect prosthetic valve exists; prostheses are prone to degeneration, thrombus formation, and infection, causing dysfunction.
• Echocardiography is the main tool for evaluation and follow-up.
• Two main categories: mechanical and tissue valves.

Mechanical valves:

• Starr-Edwards caged-ball valve
  • Metal U-shaped cage attached to a sewing ring.
  • Silastic ball moves forward during systole, allowing antegrade flow around the ball; moves backward to occlude the sewing ring.
  • No regurgitation except the closing volume.
  • No longer implanted due to poor hemodynamics, but high durability means occasional patients are still encountered.
• Tilting-disc valve
  • Single disc secured by metal struts.
  • Opens at 60–80°, creating major and minor orifices.
  • Single jet exits the larger orifice; multiple jets exit the smaller orifice due to struts.
  • Small backflow regurgitation around the disc perimeter is normal.
• Bileaflet valve
  • Two semicircular leaflets open via a hinge mechanism at an angle approaching 90°.
  • Produces three orifices: two larger side orifices and one small central orifice.
  • Two washing regurgitation jets are normally seen at pivot points and around leaflet rims.
  • Better hemodynamics and larger effective orifice area than a single tilting-disc valve.

• Stented bioprosthesis
  • Three biologic leaflets from porcine aortic valve or bovine pericardium mounted on a stented ring.
• Stentless bioprosthesis
  • Made of intact porcine aortic valve or bovine pericardium.
  • Implanted only in the aortic position; may involve total root replacement.
  • Very difficult to differentiate from native valve; excellent hemodynamic profile.
• Aortic homograft
  • Treated and preserved human valve consisting of part of the interventricular septum, part of the anterior mitral leaflet, aortic root, aortic valve, and ascending aorta.
  • Typically used for total root replacement with coronary reimplantation.
  • If sub-coronary implantation is performed, native aortic root remodeling occurs with significant aortic regurgitation in a substantial number of patients.
• Pulmonary autograft (Ross procedure)
  • Harvests the pulmonary valve, annulus, and proximal pulmonary artery into the aortic position with coronary reimplantation.
  • A homograft is implanted in the pulmonary position.
  • Hemodynamics similar to native aortic valve.
  • Advantages: ability to grow, non-thrombogenic, resistance to infection.
  • Requires long cardiopulmonary bypass time; reserved for children and young adults.
• Transcatheter bioprosthetic valves
  • Increasingly used as an alternative to surgical replacement.
  • Aortic position is the main target; other positions have been performed.
  • Two main types: balloon-expandable and self-expanding valves.

Required clinical data:

• Prosthetic valve type
• Prosthetic valve size
• Date of implantation
• Baseline echocardiographic data
• Patient body surface area

Each valve has reference data for peak gradient, mean gradient, and effective orifice area, so valve type, manufacturer, and size are needed. Baseline data help detect degeneration over time.

2D imaging points:

• Valve type
  • Mechanical valves produce marked shadowing and reverberation artifacts from fixed and moving parts.
  • Bioprosthetic valves have minimal artifact at the sewing ring/supporting structure, not at moving leaflets.
  • Moving artifacts = mechanical valve; stationary artifacts = bioprosthetic valve, except a dysfunctional mechanical valve with a nonmoving occluder.
  • Stentless valves mimic native valves; look for a bright area at the sewing area.
  • Stented bioprostheses have three struts seen in short-axis.
  • Mechanical subtypes are better assessed in apical views because parasternal views shadow moving parts.
• Opening and closing motion
  • Bioprostheses: moving parts are leaflets.
  • Mechanical valves: moving part is the occluder—one disc, two discs, or ball.
  • Motion is classified as normal, reduced, or fixed.
  • TEE is superior to TTE for 2D/3D prosthetic imaging.
  • 3D TEE is best from the LA perspective, especially for mitral prostheses.
  • TTE of a prosthetic mitral valve obscures the LA; TEE obscures the LV but gives good LA visualization.
• Abnormal masses and calcifications
  • Examine leaflets, occluder, and sewing ring for calcifications, thrombi, or vegetations.
  • Describe mass location, shape, size, echogenicity, and motion.
  • Thrombi and vegetations are indistinguishable echocardiographically; clinical correlation is required.
  • If prosthetic endocarditis is suspected, TEE is necessary because TTE may miss vegetations.
• Sewing ring evaluation
  • Inspect for gaps and rocking movement indicating significant dehiscence.
• Cavitation
  • Microbubbles generated by rapid pressure drop, like turbine blades.
  • Frequently seen in mechanical valves, especially mitral position during leaflet closure.
  • Seen in the LV at the closure site.
  • Clinical significance is not established; in vitro bubble collapse may cause valve erosions.

• Color flow Doppler
  • Prosthetic valves, especially mechanical, cause distal shadowing.
  • Significant mechanical mitral regurgitation may be missed on TTE due to LA shadowing; TEE from the opposite side visualizes it.
  • Prosthetic valves are inherently stenotic, especially mechanical valves, so some turbulent flow is expected.
  • Significant turbulence may indicate stenosis, prosthesis-patient mismatch, or increased flow from regurgitation.
• Regurgitant flow
  • Physiologic trivial regurgitation is normal in almost all mechanical valves.
  • Closing volume: short-lived regurgitation at closure site caused by occluder motion.
  • Washing jet: true regurgitation at hinges and disc-sewing ring meeting points; helps prevent thrombus formation.
  • Biological valves may have a trivial central regurgitant jet.
  • Abnormal jets:
    • Valvular regurgitation: within the sewing ring; causes include thrombus, infective endocarditis, pannus, degeneration.
    • Paravalvular regurgitation: outside the sewing ring; due to partial dehiscence with or without infection.
• Valve gradient
  • High gradients are expected because prostheses are inherently stenotic.
  • Gradient depends on valve size relative to BSA, flow, and valve function.
  • Pressure recovery overestimates gradient and underestimates EOA, especially in 19 mm bileaflet valves with CW through the central orifice.
• Effective orifice area
  • Most important parameter for prosthetic stenosis.
  • Calculated by continuity equation and compared with manufacturer-specific EOA.
  • High gradient + small/decreasing EOA: dysfunctional stenosis, pressure recovery, or EOA measurement error. Normal moving leaflets rule out stenosis. Compare EOA to baseline using the same area, e.g., same LVOT area.
  • High gradient + normal EOA: high flow state or prosthesis-patient mismatch. High flow increases both LVOT and prosthetic flow, resulting in normal DVI.
• Prosthesis-patient mismatch
  • Normally functioning valve that is too small for the patient’s body size.
  • Defined by EOA indexed to BSA.
  • Aortic EOA index: Mild/not significant >0.85, Moderate 0.85–0.66, Severe ≤0.65 cm²/m².
  • Mitral EOA index: Mild/not significant >1.2, Moderate 1.2–0.91, Severe ≤0.9 cm²/m².
• Doppler clicks
  • Mechanical opening and closing clicks are like native valve clicks but higher amplitude.
  • Absence of opening or closing clicks in a mechanical valve should alert for prosthetic dysfunction.

Early complications:

• Most early postoperative valve dysfunction is technical.
• Most common early complication: paravalvular leak, usually not clinically significant.
• Paravalvular leak frequency increases with:
  • Calcium debridement
  • Redo valve surgery
  • Reconstruction of valvular annulus
• Early prosthesis thrombosis and acute endocarditis are rare.

Late complications:

• Thromboembolism
  • Mechanical valves are associated with much more thromboembolism than biological valves.
  • Risk factors:
    • LV dysfunction
    • Atrial fibrillation
    • LA enlargement
    • Mitral position
  • Most common cause: inadequate anticoagulation.
• Pannus formation
  • Fibrous ingrowth from host-prosthesis interaction.
  • Missed on 2D echo in 30% of cases, but its hemodynamic effect should not be missed.
  • Affects mechanical and biological valves.
  • May range from insignificant to severe dysfunction, including obstruction and regurgitation.
• Infective endocarditis
  • Hallmark: vegetations composed of fibrin, platelets, inflammatory cells, and infectious organisms.
  • Echocardiographically: irregularly shaped, independently mobile, low echogenicity.
  • Prosthetic valve vegetations form in the ring region and may spread to leaflets/structures.
  • Can impair mechanical valve opening/closing and cause leaflet destruction/perforation in biological valves.
  • Complications:
    • Abscess: echo-lucent space in the valve ring area.
    • Abscess may progress to pseudoaneurysm with characteristic to-and-fro flow on color Doppler.
    • May further open into another cardiac chamber causing a fistula.
  • Vegetations cannot be differentiated from thrombus or sutures without clinical information.
  • In high suspicion of aortic abscess, combined TTE and TEE is recommended because of shadowing of the posterior aortic root on TTE and anterior aortic root on TEE.

Prosthetic AV stenosis parameters:

Prosthetic AV regurgitation severity:

Shared mitral prosthetic parameters reflecting LA pressure:

• Peak mitral early velocity (E): <1.9 m/s is likely normal.
• Higher E occurs when LA pressure is elevated, including mitral regurgitation or stenosis.
• DVI = CW prosthetic MV inflow VTI / PW LVOT VTI
  • <2.2: prosthetic MV likely normal.
  • Higher DVI suggests stenotic prosthetic MV or significant regurgitation.

Prosthetic MV stenosis parameters:

Findings suggesting significant prosthetic mitral regurgitation in mechanical valve with normal PHT:

• Peak velocity ≥1.9 m/s
• Mean gradient ≥5 mmHg
• LV stroke volume by 2D/3D is >30% higher than LVOT stroke volume
• TR jet velocity >3 m/s

Prosthetic MV regurgitation severity:

Mitral annuloplasty:

• Successful MV repair usually shows restricted posterior leaflet motion.
• Ring annuloplasty appears as a bright ring in the mitral annulus.
• Mean gradient across repaired MV is typically <3 mmHg.

Prosthetic PV stenosis — suspicious findings:

• Cusp or leaflet thickening or immobility
• Narrowing of the forward color map
• Peak velocity >3 m/s, or >2 m/s through a homograft
• Increasing peak velocity on serial studies
• Impaired RV function or elevated RV systolic pressure

Prosthetic PV regurgitation severity:

Prosthetic TV stenosis — suspicious findings:

• Peak velocity >1.7 m/s
• Mean gradient ≥6 mmHg
• PHT ≥230 msec

Prosthetic TV regurgitation severity:

Normal values are manufacturer- and size-specific. Key examples from the appendix include:

Prosthetic mitral valve normal values include: