Prosthetic Valves

Basic Principles

▪ Evaluation of prosthetic valves by echocardiography is based on the same principles as evaluation of native valve disease.
▪ Fluid dynamics (and Doppler flows) depend on the specific valve type and size (Fig. 13.1).
▪ Dysfunction of mechanical valves usually is due to valve thrombosis resulting in systemic embolism, incomplete closure (regurgitation), or inadequate opening (stenosis) (Table 13.1).
▪ Dysfunction of bioprosthetic valves usually is due to leaflet degeneration (regurgitation) or calcification (stenosis).
▪ All prosthetic valves are at risk of endocarditis, which often primarily affects the annular ring rather than the valve leaflets.

Key Points

□ There are several types of surgically implanted bioprosthetic valves, which can be classified as stented, stentless, or combined valve-root prostheses (including homograft valves).
□ Most surgically implanted bioprosthetic valves have three struts (or “stents”) supporting the leaflets at the commissures.
□ Stentless surgical bioprosthetic valve may be indistinguishable from a normal native valve.
□ Transcatheter aortic valve implantation is usually performed via the femoral artery retrograde across the valve.
□ Transcatheter bioprosthetic valves currently include balloon expandable and self-expanding types, both with a trileaflet bioprosthetic valve mounted inside a metal mesh cage or “stent” (Fig. 13.2; see Fig. 13.1).
Fig. 13.1 Basic types of prosthetic valves.Examples of a bileaflet mechanical valve (A), surgical bioprosthetic valve (B), and transcatheter bioprosthetic aortic valve (C).
[A] From http://www.medtronic.com/us-en/healthcare-professionals/products/cardiovascular/heart-valves-surgical/open-pivot-mechanical-heart-valve.html. ©Medtronic 2018. [B] From https://www.edwards.com/eu/products/heartvalves/Pages/PERIMOUNTAortic.aspx. [C] From https://www.edwards.com/gb/devices/Heart-Valves/Transcatheter-Sapien-3.

TABLE 13.1

Prosthetic Valves: Clinical Echocardiographic Correlates
	Mechanical AVR	Surgical Bioprosthetic AVR	Transcatheter Bioprosthetic AVR	Mechanical MVR	Bioprosthetic MVR
Fluid dynamics	Complex fluid dynamics depending on valve type	Central orifice, laminar flow, blunt flow profile	Central orifice, laminar flow, blunt flow profile	Complex fluid dynamics depending on valve type	Central orifice, laminar flow, blunt flow profile
Echo imaging	Shadowing and reverberations limit valve imaging	Echogenic sewing ring and three struts Trileaflet porcine or pericardial tissue similar to that of a native aortic valve	Increased echogenicity of aortic sinuses and annulus due to supporting stent Biologic valve leaflets appear similar to a native aortic valve	Shadowing and reverberations limit valve imaging on TTE Valve occluder motion well seen on TEE	Stented valve, flow directed toward septum Trileaflet porcine or pericardial tissue similar to that of a native aortic valve
Normal Doppler findings	Antegrade velocity <3 m/s with triangular-shaped flow curve Mild eccentric AR due to occluder closure	Antegrade velocity <3 m/s with triangular-shaped flow curve No to trace central AR	Antegrade velocity <3 m/s with triangular-shaped flow curve Mild valvular or paravalvular AR	Antegrade velocity <1.9 m/s with short T½ Mild eccentric MR due to occluder closure	Antegrade velocity <1.9 m/s with short T½ No to trace central MR
Advantages/disadvantages	Excellent long-term durability Requires chronic anticoagulation	Variable durability, longer in older patients Does not require anticoagulation	Unknown long-term durability Currently recommended in high-risk patients Does not require anticoagulation	Excellent long-term durability Requires chronic anticoagulation	Variable durability, longer in older patients Does not require anticoagulation (unless needed for AF)
Complications	Valve thrombosis Pannus Paravalvular AR Endocarditis	Leaflet degeneration Stenosis Regurgitation Pannus Paravalvular AR Endocarditis	Leaflet degeneration Stenosis Regurgitation Pannus Paravalvular AR Endocarditis	Valve thrombosis Pannus Paravalvular MR Endocarditis	Leaflet degeneration Stenosis Regurgitation Pannus Paravalvular A Endocarditis
Echo follow-up (in addition to annual clinical evaluation)	Baseline post-operative Changing signs or symptoms	Baseline post-operative Changing signs or symptoms Annual starting 5 years after implantation	Baseline post-operative Changing signs or symptoms Annual exams recommended at this time	Baseline postoperative Changing signs or symptoms	Baseline post-operative Changing signs or symptoms Annual starting 5 years after implantation

From Otto CM: Textbook of clinical echocardiography, ed 6, Philadelphia, 2018, Elsevier.

□ The most common mechanical valve now implanted is a bileaflet design with two semicircular disks that open to form a central slit-like orifice and two larger lateral openings.
□ Other types of mechanical valves include single disk valves that “tilt” to open, either on a central strut or with hinges in the annular ring. Ball-cage valves may still be seen in some patients.
□ On echocardiography, mechanical valves result in ultrasound reverberations and shadowing that limit direct visualization of valve function.

Step-by-Step Approach

Step 1: Review Clinical and Operative Data

▪ Information on the operative procedure is reviewed before the echocardiographic examination.
▪ The valve type and size, obtained from the medical record or the patient’s valve ID card, are included on the echocardiographic report.
▪ Blood pressure and heart rate at the time of the echocardiogram are recorded.

Key Points

□ Information in the operative report helps guide the echocardiographic image acquisition and improves the final interpretation.
□ With aortic valve surgery, key features are valve replacement versus resuspension, concurrent replacement of the aortic root either above the sinotubular junction or including the sinuses of Valsalva, and surgical coronary reimplantation (with replacement of the aortic sinuses).
□ With mitral valve surgery, key features are valve repair or replacement, preservation of the mitral leaflets and chords with valve replacement, amputation of the left atrial (LA) appendage, and whether a concurrent atrial ablation (e.g., maze) procedure was done.
□ The valve type and size determine the expected hemodynamics and are important for distinguishing normal prosthetic Doppler data from prosthetic valve stenosis or regurgitation.
□ On early postoperative studies, unexpected findings are discussed directly with the surgeon to correlate with observations during the surgical procedure.

Step 2: Obtain Images of the Prosthetic Valve

▪ Prosthetic aortic valves are imaged in parasternal long- and short-axis views.
▪ Prosthetic mitral valves are imaged in parasternal long- and short-axis views and in apical 4-chamber and long-axis views (Fig. 13.3).
▪ Transesophageal echocardiography (TEE) imaging is needed to evaluate the left atrium (LA) side of mechanical mitral prosthetic valves, due to shadowing from the transthoracic approach, when valve dysfunction is suspected (Fig. 13.4).
▪ TEE also often provides better images of the posterior aspect of aortic valve prostheses.

Key Points

□ Transthoracic imaging of mechanical valves is limited by reverberations and shadowing. Even so, the leaflets and annular region may be adequately evaluated by this approach for most baseline or follow-up studies in clinically stable patients.
□ Three-dimensional (3D) TEE imaging of prosthetic valves provide better spatial resolution, albeit with lower temporal resolution (see Fig 13.4).
□ Bioprosthetic valves have a trileaflet structure similar to a native aortic valve. Mitral bioprosthetic valves are stented to provide support for the leaflets, with the leaflets well seen in both parasternal and apical views.
□ With aortic bioprosthetic valves, support is provided either by stents, by attachment directly to the aortic wall (stentless valves), or by implanting an intact valve and root (sometimes called a “mini-root” approach). The aortic bioprosthetic prosthesis is well seen in long- and short-axis views.
□ When prosthetic valve dysfunction is suspected on clinical grounds or based on transthoracic echocardiography (TTE) findings, both TTE and TEE are recommended.

Step 3: Record Prosthetic Valve Doppler Data

▪ Antegrade velocities across the prosthetic valve are recorded with pulsed and continuous-wave (CW) Doppler.
▪ Prosthetic valve regurgitation is evaluated using CW and color Doppler.

Key Points

□ Both bioprosthetic and mechanical valves are inherently stenotic compared with normal native valves.
□ The normal antegrade velocity and pressure gradient depends on the specific valve type, valve size, heart rate, and cardiac output.
□ Ideally, Doppler data are compared with the patient’s own baseline postoperative examination, done when the patient had fully recovered from surgery and was clinically stable.
□ If a baseline examination is not available, recorded data are compared with published data for that valve type and size.
□ A small amount of regurgitation is normal with most prosthetic valves.

Step 3A: Evaluate for Prosthetic Valve Stenosis (Table 13.2)

▪ Maximum and mean gradients are calculated with the Bernoulli equation from transvalvular velocities (Fig. 13.5).
▪ Continuity equation valve area can be calculated for aortic valve prostheses (Fig. 13.6).
▪ The mitral pressure half-time is measured for prosthetic valves in the mitral position (Fig. 13.7).

TABLE 13.2

Prosthetic Stenosis and Regurgitation: Findings Suggestive of Significant Valve Dysfunction with Stented Bioprosthetic and Mechanical Valves
	Severe Stenosis	Severe Regurgitation
AVR	V _max >4 m/s Mean ΔP >35 mm Hg Velocity ratio <0.25 Rounded, late peaking velocity curve shape EOA <0.8 cm²	LV dilation AR jet width ≥65% of LVOT diameter CW Doppler signal dense with T½ <200 ms Holodiastolic flow reversal in DA RV >60 mL RF >50%
MVR	V _max >2.5 m/s Mean ΔP >10 mm Hg T½ >200 ms VTI_mitral/VTI_LVOT >2.5 EOA <1.0 cm²	LV dilation Large central MR jet or variable size wall-impinging jet Large PISA with vena contracta ≥0.6 cm CW Doppler signal dense with triangular shape Pulmonary vein systolic flow reversal Pulmonary hypertension (esp. if new) RV ≥60 mL, RF ≥50%, EROA ≥0.50 cm²
PVR	V _max >3 m/s (or >2 m/s with a homograft) with a progressive increase in velocity on serial studies	RV dilation Jet width >50% of pulmonic annulus CW Doppler signal dense, steep deceleration, flow ends in mid- to late diastole Diastolic flow reversal in pulmonary artery RF >50%
TVR	V _max >1.7 m/s Mean ΔP ≥6 mm Hg T½ ≥230 ms	TR jet area >10 cm² Vena contracta width >0.7 cm CW Doppler signal dense with triangular shape Holosystolic flow reversal in hepatic veins Severe RA dilation

From Otto CM: Textbook of clinical echocardiography, ed 6, Philadelphia, 2018, Elsevier.

Summarized and modified from: Zoghbi WA, Chambers JB, Dumesnil JG, et al: Recommendations for evaluation of prosthetic valves with echocardiography and doppler ultrasound, J Am Soc Echocardiogr 22(9):975-1014, 2009.

Key Points

□ LV outflow tract diameter is measured from the two-dimensional (2D) images for calculation of valve area. The valve size may differ from the subaortic anatomy and so cannot be substituted for this diameter measurement.
□ When measurement of outflow tract diameter is difficult, the ratio of the velocity proximal to the valve and in the orifice is used as a measure of stenosis severity.
□ With bileaflet mechanical valves, the small central orifice often results in high velocities due to local acceleration, which should not be mistaken for prosthetic valve stenosis (see Fig. 13.5A)
□ The mitral pressure half-time is used to calculate valve area, as for native mitral stenosis. Often the pressure half-time itself is reported.
Fig. 13.6 Schematic drawing of the continuity equation with a stented bioprosthetic aortic valve replacement (AVR).Stroke volume (SV) proximal to the valve in the left ventricular outflow tract (LVOT) equals SV through the aortic valve replacement. SV at each site is equal to the cross-sectional area (CSA) of flow times the velocity-time integral (VTI) of flow at that site. LVOT flow is measured with pulsed Doppler from an apical approach. CSA_LVOT is calculated as a circle from a mid-systolic LVOT diameter measurement, and the VTI of flow through the valve prosthesis is measured with CW Doppler, usually from the apical approach. This equation then is solved for the aortic prosthetic effective orifice area (EOA).
□ “Patient-prosthesis mismatch” describes a normally functioning prosthetic valve that has a valve area inadequate for the patient’s body size (Fig. 13.8).

Step 3B: Evaluate for Prosthetic Valve Regurgitation

▪ Prosthetic valve regurgitation is evaluated using CW and color Doppler (Fig. 13.9).
▪ Evaluation of prosthetic mitral regurgitation requires TEE; transthoracic imaging is nondiagnostic due to shadowing and reverberation by the valve prostheses.
▪ A small amount of prosthetic regurgitation is normal; moderate to severe prosthetic regurgitation or any degree of paraprosthetic regurgitation is pathologic.

Key Points

□ Prosthetic regurgitation often is first detected with CW Doppler due to the high signal-to-noise ratio, excellent bioprosthetic penetration, and wide beam geometry of CW Doppler.
□ Normal prosthetic regurgitation has a weak CW Doppler signal and typically is brief in duration.
□ A dense regurgitant CW Doppler signal is an indication for further evaluation (Fig. 13.10).
□ Normal prosthetic regurgitation on color Doppler is spatially localized adjacent to the valve, has a small vena contracta and jet area, is through the prosthesis (not paravalvular), and is brief in duration.
Fig. 13.7 Transmitral pulsed Doppler flow.In the apical 4-chamber view (left), mitral inflow across a stented bioprosthetic valve is directed toward the ventricular septum, with a reversed direction of the normal LV diastolic flow vortex. Pulsed or CW Doppler (right) shows a normal inflow pattern with an E and A velocity (in sinus rhythm). The diastolic mean gradient and the pressure half-time are only slightly higher than expected for a normal native mitral valve.
□ The exact pattern of normal prosthetic regurgitation depends on the valve type—for example, central with bioprosthetic valves, two eccentric jets with bileaflet mechanical valves.
□ Pathologic prosthetic valve regurgitation on color Doppler often is paravalvular, has a larger vena contracta and jet area, and lasts longer during the cardiac cycle.
Fig. 13.8 Prosthetic valve effective orifice area.View of a bioprosthesis and a bileaflet mechanical valve with the leaflets in a fully open position. The area highlighted in pink is the effective orifice area. Patient–prosthesis mismatch is present when the effective orifice area is smaller than needed to maintain a normal cardiac output at rest and with exercise without an excessive increase in transvalvular pressure gradient.
From Pibarot P, Dumesnil JG: Prosthesis-patient mismatch: definition, clinical impact, and prevention, Heart 92:1022-1029, 2006.

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Apr 23, 2020 | Posted by admin in CARDIOLOGY | Comments Off

Key Points

Step-by-Step Approach

Step 1: Review Clinical and Operative Data

Key Points

Step 2: Obtain Images of the Prosthetic Valve

Key Points

Step 3: Record Prosthetic Valve Doppler Data

Key Points

Step 3A: Evaluate for Prosthetic Valve Stenosis (Table 13.2)

Key Points

Step 3B: Evaluate for Prosthetic Valve Regurgitation

Key Points

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Thoracic Key

Fastest Thoracic Insight Engine

Prosthetic Valves

Prosthetic Valves

Basic Principles

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Thoracic Key

Fastest Thoracic Insight Engine

Prosthetic Valves

Basic Principles

Key Points

Step-by-Step Approach

Step 1: Review Clinical and Operative Data

Key Points

Step 2: Obtain Images of the Prosthetic Valve

Key Points

Step 3: Record Prosthetic Valve Doppler Data

Key Points

Step 3A: Evaluate for Prosthetic Valve Stenosis (Table 13.2)

Key Points

Step 3B: Evaluate for Prosthetic Valve Regurgitation

Key Points

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Full access? Get Clinical Tree