Prosthetic Valves

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8 Prosthetic Valves

Scanning Issues

The expected appearance and hemodynamics of prostheses differ widely for different sizes and models of valve prostheses. Interpretation of appearance and hemodynamics requires knowing the specific size and design of the prosthesis. Therefore, know (and record) the following parameters of each prosthetic valve you scan:

Type, including model and year

Size

Notes

Use zoom views liberally.

Recall that the correlation of pressure half time (PHT) to mitral valve effective oriface area is poor for all forms of mechanical mitral valve replacement (MVR), and that the PHT method should not be emphasized for the assessment of mechanical MVRs.

Diastolic turbulent flow into the left ventricular outflow tract in the presence of a mechanical MVR suggests mechanical MVR obstruction.

The presence of a bileaflet occluder mechanical prosthesis requires the attempt to visualize the motion of both occluders. Prosthesis thrombosis usually occurs with one leaflet more frozen and one leaflet less so—so do not extrapolate the impression of one occluder to the other. Visualize both.

The range of design of valve prostheses is extensive, and familiarity with their design and components is essential to analysis of the two-dimensional and Doppler findings of prostheses, and also to the fluoroscopic findings. The range of mechanical prosthesis design (e.g., ball-in-cage, single tilting disk occluder, and bileaflet occluder designs) is generally understood in simplified terms. However, important design details that influence normal findings—such as the strut penetration into the single disk of the Medtronic Hall prosthesis (which normally emanates a central jet of insufficiency), and the variable profile of mechanical prosthesis sewing rings and of their occluders (which account for the variable visualization of occluder elements above and below the ring)—often are underappreciated.

Bioprostheses are just as variable in design: some have no struts or stents (the stentless aortic root models); some have wire, plastic sewing rings, or struts; some have the struts under and some have the struts over the leaflets; some use actual porcine or cadaveric aortic valves; and some have constructed bovine pericardial leaflets.

Reporting Issues

Know (and record) the type, model, size, and year of the valve you are scanning.

The effect of valve type (P = 0.0003)¹ and size (P = 0.01)¹ on gradient and area is considerable; therefore, it is necessary to know the type and size of the prosthesis. This will facilitate interpretation and imaging recognition of abnormalities.

Clearly state whether the recorded gradient is expected or greater than expected for that type of prosthesis.

Clearly state whether any insufficiency present is within the expected amount or of either pathologic quantity or pathologic origin (paravalvar is always pathologic).

Terminology

If there is a severe gradient across a mechanical MVR, use the term obstruction.

Leakage across the prosthesis is transvalvar.

Leakage beside the prosthesis is paravalvar.

If there is ≥3+ paravalvar insufficiency, and rocking, use the term dehiscence.

The moving mechanical elements of prostheses are occluders or hemi-disk occluders, depending on their geometry.

The implanted ring is the sewing ring.

Soft tissue on the sewing ring may be thrombus, pannus, or vegetations—or a combination. There is little ability case-by-case to accurately resolve (by echocardiography alone) which it is, or whether multiple causes are present.

Flail bioprosthetic leaflets may be reasonably referred to as torn.

Use of the term retroverted leaflet is questionable, because it is difficult to be certain, short of surgical inspection.

Do not state “normal appearance” for a mechanical prosthesis, because mechanical prostheses are so poorly visualized that such a phrase says little, especially for bileaflet occluders, and may easily be wrong. Most of the “appearance” of mechanical prostheses is artifact.

When describing by transesophageal echocardiography (TEE) the position(s) of paravalvar leaks, use a clock-face numeric system, with 12 o’clock at the top, 6 o’clock at the bottom, and the left atrial appendage at about 10 o’clock.

Describe the location of all paravalvar leaks, not only the largest. If the patient is submitted to surgical repair, all leaks will need to be addressed.

Gradient Issues

Important issues to understand include the following:

Correlation versus accuracy

Pressure recovery

Localized gradient

Net (peak or mean) gradient

Potential and kinetic energy

Spatial distribution of energy loss and gradient

Correlation of mean gradient is generally good for simultaneous comparisons of the following:

Bioprosthesis: r = 0.93; standard error of estimate (SEE) = 3 mm Hg²

Mechanical: r = 0.93; SEE = 3 mm Hg² or better ^2,³

Mitral prostheses: r = 0.93; SEE = 3 mm Hg²

Aortic prostheses: r = 0.94; SEE = 3 mm Hg²

However, overestimation may occur while the correlation is good, especially for the following:

Bileaflet occluder mechanical prostheses ³

Ball-in-cage mechanical prostheses ³

Older bioprostheses: Hancock and Ionescu-Shiley ¹

Nonsimultaneous correlation of mean gradient is less, as would be expected:

Bioprosthesis: r = 0.85 SEE or greater

Mechanical: r = 0.87 SEE or greater

Mechanical prosthetic valve gradients are flow dependent. In the case of very small prostheses in the aortic position, gradients rise very rapidly and conspicuously as flow increases beyond resting state flow (90 mm Hg peak for SJM and Hancock valves).³ Therefore, be attentive to anything likely to be causing increased cardiac output (e.g., anemia, fever, pregnancy, thyrotoxicosis).

Recall the significant 5-, 10-, and 15-year incidence of structural valve failure for older designs of bioprostheses (Table 8-2).⁴

Pressure Recovery Phenomenon

The pressure recovery phenomenon is a fascinating occurrence of hydrodynamics in which a localized gradient develops within a smooth-walled restrictive orifice. Bileaflet occluders are the most common cause of localized gradients and pressure recovery.

The pressure recovery phenomenon is well described for bileaflet occluder prostheses in the aortic position, and for the ball-in-cage Starr-Edwards prosthesis. The phenomenon is described in vitro, but probably does account for some patient discrepancies with catheterization. The pressure recovery is greatest for the central orifice. The pressure loss coefficient for the continuity relation has been shown in vitro to be K = 0.64. As much as 40% of the initial pressure loss is recovered by the end of the leaflets in the central orifice, and another 20% within another 5 cm. The pressure recovery of the side orifices is less (30%), and occurs further downstream. Side orifice velocities are 85 ± 4% of the center orifice velocity.⁵

Overestimation of peak and mean trans–aortic valve replacement (AVR) gradient is described for the St. Jude prostheses and for the Starr-Edwards prosthesis (with gradient differences as great as 44 mm Hg), but not for the Medtronic Hall tilting disk prosthesis.³

The pressure recovery phenomenon also may occur for mitral prostheses.⁵

A smooth-walled flaring restrictive orifice may establish pressure recovery: some of the kinetic energy recovers to potential energy (pressure).⁵ The pressure recovery phenomenon is greater for small valve prostheses (26-mm valve: 167 ± 52% vs. 31-mm valve: 123 ± 41%), and for the centerline gradients than the side orifice gradients (13 ± 12 mm Hg vs. 6 ± 4 mm Hg).⁵ Although there is good correlation of valve gradient by Doppler and catheterization, the Doppler estimates experimentally are significantly higher. A total pressure loss coefficient² for bileaflet occluder devices of 0.64 (±0.04) can be used.⁵

Within a nonplanar, smooth-walled orifice such as the central (minor) orifice of a bileaflet occluder valve prosthesis, a localized gradient can occur within the length of the smooth-walled orifice (“early” or “valvular” recovery). There is a small amount of subsequent recovery of pressure (“late” or “post-valvular” recovery). Within a few centimeters of the tip of the occluders, the total pressure recovery has occurred.

The magnitude of the pressure-recovery phenomenon is greater within the central orifice (15%) than the side orifices.

The pressure-recovery phenomenon is seen with both mechanical AVRs and MVRs. The late or post-valvular pressure recovery is greater in the case of AVRs, probably due to aortic root effects. (A narrow sinotubular junction, <30 mm diameter, appears to facilitate pressure recovery in vivo.)

Patient–Prosthesis Mismatch

Cardiac output and stroke volume are related to body size. Therefore, larger patients need larger valves and larger valve prostheses, or the larger flow in a larger patient will generate a high gradient across an undersized prosthesis. However, the aortic root in particular may have variable size with regard to body size, and the annular size ultimately determines the largest prosthesis size that can be inserted.

When a prosthesis is so small (i.e., its EOA is so small) that it is conferring a large gradient that may fall within the severe range, patient prosthesis mismatch (PPM) is said to exist. PPM is likely to occur with an EOA of <0.9 cm²/m².⁶ Surgeons insert the largest prosthesis than can be fitted into the annulus, to minimize the frequency of this complication, but ultimately, the annulus size may be small (mismatched) for the size of the patient.

Smaller prostheses produce higher gradients ^3,⁶ in the resting state, and especially with exercise or any context of increased flow. With exercise gradients not only rise, but rise very steeply.³ For example a small St. Jude prosthesis in the aortic position may produce a 90-mm Hg peak gradient with exercise levels of flow.³ Therefore, when interrogating a prosthesis, it is imperative to know the size of the prosthesis and type, and to anticipate its gradients. For smaller prostheses, where there are symptoms and a somewhat elevated gradient, mild exercise may bring out the degree of gradient and pulmonary hypertension in such states.

Assumptions Inherent in the Modified Bernoulli Equation

That a blood viscosity effect is negligible (as boundary layer formation is negligible other than against the walls to flow)

That inertial issues are negligible for an orifice restrictive to flow (as the amount of weight of blood involved is very small)

That most energy proximal to the orifice is potential, and can be omitted

That V₁ can be omitted

That there is no pressure recovery (i.e., all kinetic energy developed is lost to friction, heat, and vortices).⁵

A subvalvar gradient may be present in some cases of (native valve) AS cases ⁷; therefore, the omission of V1 from the modified Bernouilli equation may be a relevant problem in a clinically meaningful number of cases.

Area Issues

General Issues of Correlation

When comparing to Gorlin-derived areas, the factors most commonly influencing Doppler EOA and Gorlin area are difference in cardiac output and difference in AVG.⁸ It has been shown that there is flow dependence and pressure dependence of the Gorlin and continuity equations.⁹

Flow and Pressure Dependence of Gorlin and Continuity

In a pulse duplicator system, Gorlin overall yields slightly higher bioprosthetic valve areas (1–2%) for AVRs and moderately greater areas for MVRs (12–13%).⁹

For any given size and type of bioprosthesis, areas calculated by both formulas increase with increasing flow: up to 20% for bioprosthetic AVRs and 35% for bioMVRs.⁹

Bioprosthetic Mitral Valve Replacements

The PHT method for mitral valve area (MVA) determination for bioprosthetic MVR correlates poorly with in vitro (r = 0.15; P > 0.3) and continuity methods (r = 0.23; P > 0.2), and yields an MVA above predicted in 70% of cases.¹⁰ Therefore, its use should be avoided. In most hearts, PHT represents LV filling characteristics more than transmitral flow characteristics, unless the transmitral flow is markedly abnormal.

Bioprosthetic MVR area by continuity correlates well (r = 0.82; SEE = 0.1) with in vitro areas.¹⁰ For any given size and type of bioprosthesis, areas calculated by both formulas increase with increasing flow: up to 35% for bioprosthetic MVRs.⁹

MVR area by continuity is only feasible if there is no MR and no aortic insufficiency (or if amounts of MR and aortic insufficiency are equal).¹⁰

Mechanical Mitral Valve Replacements

The pressure recovery phenomenon can occur for mechanical mitral prostheses.⁵

PHT is better suited to describe mechanical MVR obstruction than for normal MVR function.¹¹

Bioprosthetic Aortic Valve Replacements

The continuity relation is accurate for bioprosthetic AVRs, as is well shown for the porcine Hancock bioprostheses.³

The Gorlin equation is accurate for assessment of bioprosthetic AVRs. One study demonstrated with a pulse duplicator system that Gorlin overall yields only slightly higher bioprosthetic valve areas (1–2%) for AVRs ⁹; whereas another study determined that for Hancock and Bjork-Shiley AVRs, the mean AVA error by Gorlin is 0.36 ± 0.32 cm². Gorlin overestimated AVA by >0.25 cm² in 32% of cases, and underestimated by >0.25 cm² in 21%.¹²

For any given size and type of bioprosthetic AVR, areas calculated by both formulas increase (up to 20%) with increasing flow.⁹

Mechanical Aortic Valve Replacements

Underestimation of area is described for the St. Jude prostheses and for the Starr-Edwards prosthesis, but not for the Medtronic Hall tilting disk prosthesis.³

Prosthetic Valve Dysfunction

Bioprosthetic valves

Insufficiency due to

• Expected small volume of central insufficiency

• Leaflet tear (sterile)

• Periprosthetic leak (sterile)

• Leaflet destruction from infective endocarditis

• Periprosthetic insufficiency owing to infective endocarditis

Stenosis due to

• Leaflet fibrosis

• Large bulky vegetations

• Thrombosis

Mechanical prostheses

Insufficiency due to

• Expected small volume of insufficiency at hinge points or strut insertions

• Occluder entrapment

• Periprosthetic insufficiency (sterile)

• Periprosthetic insufficiency owing to infective endocarditis

• Periprosthetic dehiscence (sterile)

• Periprosthetic dehiscence owing to infective endocarditis

Stenosis due to

• Obstruction from thrombus

• Obstruction from pannus

• Obstruction from pannus and thrombus

• Occluder entrapment in an adjacent structure

• Large vegetations

Bioprosthesis stenosis is established by the presence of an abnormally high gradient (in the absence of factors that would be expected to provoke a higher gradient by increasing the follow across the prosthesis) and reduced leaflet motion.

Bioprosthetic and mechanical prosthesis obstruction is established by the presence of an abnormally high gradient across the prosthesis, reduced leaflet or occluder motion, and the presence of soft tissue mass within the orifices of the prosthesis (e.g., vegetations, thrombus, pannus).

The role of TEE in prosthesis evaluation cannot be overstated, particularly for prostheses in the mitral position, whose vulnerable undersurfaces are seen perfectly “en-face” and for which almost all relevant lesions (e.g., thrombus, pannus, vegetations, transvalvar and periprosthetic leaks) can be directly visualized. As the prosthesis orifice is viewed directly, the only lesions that can remain hidden are minuscule thrombus within the flange or hinge grooves. Prostheses within the aortic position present more of a challenge to TEE, as a tall sewing ring obscures the orifice and the presence of material or occluder motion within it. If the occluders are high profile, then their motion may be evident as the upper or lower surfaces of the occluders move out of the orifice to emerge above or below the ring. The wire struts (stents) of bioprostheses in the aortic position may also shadow findings of relevance although generally to a much lesser degree than a sewing ring.

The ACC/AHA recommendations regarding prosthetic valve thrombosis are presented in Box 8-3.

Summary

The diverse engineering of prosthetic heart valves, and the many problems that they are susceptible to, render assessment of prosthetic valves by echocardiography a challenge.

The different hydrodynamic properties of different valves confer differing transvalvar flow patterns, and different gradients.

Shadowing by the sewing ring and/or occluders greatly compromises echocardiographic evaluation of both anatomic and functional consequences of prosthesis dysfunction.

The pressure recovery phenomenon is an issue for the Doppler assessment of AVRs in a small aorta.

BOX 8-1 Update on Valvular Heart Disease: Focused Update on Infective Endocarditis: ACC/AHA 2006 Recommendations

Class IIa

Prophylaxis against infective endocarditis is reasonable for the following patients at highest risk for adverse outcomes from infective endocarditis who undergo dental procedures that involve manipulation of either gingival tissue or the periapical region of teeth or perforation of the oral mucosa.

Patients with prosthetic cardiac valves or prosthetic material used for cardiac valve repair. (Level of evidence: B)

From ACC/AHA 2006 guidelines for the management of patients with valvular heart disease. J Am Coll Cardiol. 2006;48(3):e1–e148.

BOX 8-2 Selection of a Mitral Valve Prosthesis: ACC/AHA 2006 Recommendations

Class I

A bioprosthesis is indicated for mitral valve (MV) replacement in a patient who will not take warfarin, is incapable of taking warfarin, or has a clear contraindication to warfarin therapy. (Level of evidence: C)

Class IIa

1. A mechanical prosthesis is reasonable for MV replacement in patients under 65 years of age with long-standing atrial fibrillation. (Level of evidence: C)

2. A bioprosthesis is reasonable for MV replacement in patients 65 years of age or older. (Level of evidence: C)

3. A bioprosthesis is reasonable for MV replacement in patients under 65 years of age in sinus rhythm who elect to receive this valve for lifestyle considerations after detailed discussions of the risks of anticoagulation versus the likelihood that a second MV replacement may be necessary in the future. (Level of evidence: C)

From ACC/AHA 2006 guidelines for the management of patients with valvular heart disease. J Am Coll Cardiol. 2006;48(3):e1–e148.

BOX 8-3 Thrombosis of Prosthetic Heart Valves: ACC/AHA 2006 Recommendations

Class I

1. Transthoracic and Doppler echocardiography are indicated in patients with suspected prosthetic valve thrombosis to assess hemodynamic severity. (Level of evidence: B)

2. Transesophageal echocardiography and/or fluoroscopy are indicated in patients with suspected valve thrombosis to assess valve motion and clot burden. (Level of evidence: B)

Class IIa

1. Emergency operation is reasonable for patients with thrombosis of a left-sided prosthetic valve and New York Heart Association (NYHA) functional class III–IV symptoms. (Level of evidence: C)

2. Emergency operation is reasonable for patients with thrombosis of a left-sided prosthetic valve and a large clot burden. (Level of evidence: C)

3. Fibrinolytic therapy is reasonable for thrombosis of right-sided prosthetic heart valves with NYHA class III–IV symptoms or a large clot burden. (Level of evidence: C)

Class IIb

1. Fibrinolytic therapy may be considered as a first-line therapy for patients with thrombosis of a left-sided prosthetic valve, NYHA functional class I–II symptoms, and a small clot burden. (Level of evidence: B)

2. Fibrinolytic therapy may be considered as a first-line therapy for patients with thrombosis of a left-sided prosthetic valve, NYHA functional class III–IV symptoms, and a small clot burden if surgery is high risk or unavailable. (Level of evidence: B)

3. Fibrinolytic therapy may be considered for patients with an obstructed, thrombosed left-sided prosthetic valve who have NYHA functional class II–IV symptoms and a large clot burden if emergency surgery is high risk or unavailable. (Level of evidence: C)

4. Intravenous unfractionated heparin (UFH) as an alternative to fibrinolytic therapy may be considered for patients with thrombosis of a valve who are in NYHA functional class I–II and have a small clot burden. (Level of evidence: C)

From ACC/AHA 2006 guidelines for the management of patients with valvular heart disease. J Am Coll Cardiol. 2006;48(3):e1–e148.

BOX 8-4 Appropriateness Criteria and Indications for Cardiac Imaging Modalities for the Assessment of Prosthetic Heart Valves

Transthoracic Echocardiography

ACCF/ASE/AHA/ASNC/HFSA/HRS/SCAI/SCCM/SCCT/SCMR 2011 Appropriate Use Criteria for Echocardiography ¹⁴

ACC/AHA/ASE 2003 Guideline Update for the Clinical Application of Echocardiography

Recommendations for Echocardiography in Interventions for Valvular Heart Disease and Prosthetic Valves

Class I

• Assessment of the timing of valvular intervention based on ventricular compensation, function, and/or severity of primary and secondary lesions

• Selection of alternative therapies for mitral valve disease (such as balloon valvuloplasty, operative valve repair, valve replacement)^*

• Use of echocardiography (especially TEE) in guiding the performance of performing interventional techniques and surgery (e.g., balloon valvotomy and valve repair) for valvular disease

• Postintervention baseline studies for valve function (early) and ventricular remodeling (late)

• Re-evaluation of patients with valve replacement with changing clinical signs and symptoms; suspected prosthetic dysfunction (e.g., stenosis, regurgitation) or thrombosis ^*

Class IIa

• Routine re-evaluation study after baseline studies of patients with valve replacements with mild-to-moderate ventricular dysfunction without changing clinical signs or symptoms

Class IIb

• Routine re-evaluation at the time of increased failure rate of a bioprosthesis without clinical evidence of prosthetic dysfunction

Class III

• Routine re-evaluation of patients with valve replacements without suspicion of valvular dysfunction and with unchanged clinical signs and symptoms

• Patients whose clinical status precludes therapeutic interventions

ACC/AHA 2006 Recommendations for Follow-Up Visits ¹⁵

Class I

• For patients with prosthetic heart valves, a history, physical examination, and appropriate tests should be performed at the first postoperative outpatient evaluation 2–4 weeks after hospital discharge. This should include a transthoracic Doppler echocardiogram if a baseline echocardiogram was not obtained before hospital discharge. (Level of evidence: C)

• For patients with prosthetic heart valves routine follow-up visits should be conducted annually, with earlier re-evaluations (with echocardiography) if there is a change in clinical status. (Level of evidence: C)

Class IIb

• Patients with bioprosthetic valves may be considered for annual echocardiograms after the first 5 years in the absence of a change in clinical status. (Level of evidence: C)

Class III

• Routine annual echocardiograms are not indicated in the absence of a change in clinical status in patients with mechanical heart valves or during the first 5 years after valve replacement with a bioprosthetic valve. (Level of evidence: C)

ACC/AHA 1997 Guidelines for the Clinical Application of Echocardiography ¹⁶

Indications for Echocardiography in Interventions for Valvular Heart Disease and Prosthetic Valves

Class I

• Assessment of the timing of valvular intervention based on ventricular compensation, function, and/or severity of primary and secondary lesions

• Selection of alternative therapies for mitral valve disease (such as balloon valvuloplasty, operative valve repair, valve replacement). (TEE may offer incremental value in addition to information obtained by TTE)

• Use of echocardiography (especially TEE) in performing interventional techniques (e.g., balloon valvotomy) for valvular disease

• Postintervention baseline studies for valve function (early) and ventricular remodeling (late)

• Re-evaluation of patients with valve replacement with changing clinical signs and symptoms; suspected prosthetic dysfunction (stenosis, regurgitation) or thrombosis (TEE may offer incremental value in addition to information obtained by TTE.)

Class IIa

• Routine re-evaluation study after baseline studies of patients with valve replacements with mild to moderate ventricular dysfunction without changing clinical signs or symptoms

Class IIb

• Routine re-evaluation at the time of increased failure rate of a bioprosthesis without clinical evidence of prosthetic dysfunction

Class III

• Routine re-evaluation of patients with valve replacements without suspicion of valvular dysfunction and unchanged clinical signs and symptoms

• Patients whose clinical status precludes therapeutic interventions

ACC/AHA 2006 Guidelines for the Management of Patients with Valvular Heart Disease ¹⁷

Transesophageal Echocardiography

ACCF/ASE/AHA/ASNC/HFSA/HRS/SCAI/SCCM/SCCT/SCMR 2011 Appropriate Use Criteria for Echocardiography ¹⁴

TEE as Initial or Supplemental Test—Valvular Disease

Evaluation of valvular structure and function to assess suitability for, and assist in planning of, an intervention

Appropriateness criteria: A; median score: 9

ACC/AHA 2003 Guideline Update for the Clinical Application of Echocardiography ¹⁸

Class I

• Use of echocardiography (especially TEE) in guiding the performance of interventional techniques and surgery (e.g., balloon valvuloplasty and valve repair for valvular diseases)

Cardiac Computed Tomography

ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac CT ¹⁹

Characterization of prosthetic cardiac valves

Suspected clinically significant valvular dysfunction

Inadequate images from other noninvasive methods

Appropriateness criteria: A; median score: 8

^* TEE may provide incremental value in addition to information obtained by TTE.

TABLE 8-1 Electrocardiographic and Fluoroscopic Findings of Prosthetic Heart Valves

TABLE 8-2 Freedom from Failure for Two Types of Valves

TABLE 8-3 Utility of Different Imaging Modalities and Cardiac Catheterization in the Assessment of Valve Prostheses

MODALITY	PROS	CONS/CAVEATS
Transthoracic Echocardiography	2D echocardiography • By TTE, most stented bioprostheses are readily recognizable, but most mechanical prostheses are more vaguely seen, due to the prominent artifact. Sometimes, particularly for high profile mechanical prostheses, the occluders can be visualized in the open phase. • Rocking of a prosthesis, often seen in dehiscence, is usually obvious.

• Some bioprostheses are not stented, and are thereby not apparent on echocardiography.

• Vegetations and pannus are less likely to be seen on mechanical prostheses by TTE than by TEE.

Color Doppler echocardiography: TTE is able to determine the degree of insufficiency of aortic valve prostheses because alignment from the apex usually is adequate and devoid of ring shadowing of spectral signal.

• Shadowing of (a smaller) left atrium by a mechanical mitral prosthesis renders exclusion or assessment of MR severity (by color Doppler flow mapping) inherently incomplete.

• Distinguishing transvalvar from perivalvar insufficiency may be difficult if the valve ring depiction is unclear.

Spectral Doppler echocardiography: TTE is able to determine the gradient across both aortic and mitral valve prostheses because alignment from the apex usually is adequate and devoid of ring shadowing of spectral signal.

• Pulmonary venous pulsed-wave sampling is limited and tends to be incomplete in the presence of a mechanical mitral prosthesis.

Transesophageal Echocardiography

• For MVR (especially for mechanical MVRs),

• TEE is the single best test to identify

• Perivalvular leaks of mechanical MVRs

• Left atrial side vegetations of mechanical MVRs—TEE is the single best test for the assessment of mitral prosthesis endocarditis

• Pannus/thrombus of mechanical MVRs

• Torn leaflets of bioprostheses are also better identified by TEE than by TTE

• TEE is useful to identify restricted mechanical MVR occluder motion, but this is subjective.

• By TEE, the characteristic patterns of expected transvalvar insufficiency of mechanical prostheses (unique to the type of prosthesis) can be recognized.

• TEE is significantly handicapped in the assessment of mechanical AVR because

• The occluders of mechanical prostheses are not seen “face-on” and are generally shadowed by the valve ring.

• Paravalvar leaks on the far side of sewing rings are invariably shadowed.

• Small vegetations within a sewing ring may also be shadowed by the ring.

• A mitral MVR may additionally shadow the inferior aspect of an AVR.

Cardiac CT

• Cardiac CT using helical scanning is able to depict

• Occluder opening and closing positions (is the single best test to do so, as measurement of the angles is possible)

• Thrombus/pannus

• The metallic components of prosthetic sewing rings produce prominent streaking, blooming, and partial volume artifacts that require optimal filtering to enable visualization of soft tissue lesions such as vegetations and pannus.

• Atrial fibrillation and other irregular heart rhythms are a technical problem

• Higher heart rates (>75 bpm) are often still a technical problem.

Cardiac MRI

SSFP sequences: Useful to quantify LV and RV function

• The paramagnetic influence of metallic components in valve prostheses generates significant signal “void” artifacts.

• CMR is contraindicated for ball-in-cage prostheses.

Velocity-encoded phase contrast sequences: Useful to quantify AI and PR

Nuclear

RNA: Useful to determine ventricular function in the context of perivalvular insufficiency

Chest Radiography

• Enables identification of most prostheses as long as

• They contain radiopaque material. Note that some bioprosthetic AVRs are stentless and without radiopaque material.

• Penetration is optimal.

• The prosthesis does not project over the spine and a large heart on the frontal radiograph.

• The lateral view is by far the most useful to identify and recognize prostheses.

• Can depict the presence of left heart failure from left heart valve prostheses dysfunction

Cardiac Catheterization

• Cine fluoroscopy is the standard by which to observe the occluder motion of mechanical prostheses.

• The reference standard for the determination of filling pressures and hemodynamics

• The reference standard for coronary angiography

• Mechanical prostheses should not be crossed by a catheter, reducing the yield of hemodynamics in certain situations. The presence of mechanical aortic and mitral prostheses renders assessment of the LV pressures problematic.

AI, aortic insufficiency; AVR, aortic valve replacement; bpm, beats per minute; CMR, cardiac magnetic resonance; LV, left ventricle; MR, mitral regurgitation; MVR, mitral valve replacement; PR, pulmonary regurgitation; RV, right ventricle; SSFP, steady-state free precession; TEE, transesophageal echocardiography; TTE, transthoracic echocardiography.

Figure 8-1 The pressure recovery phenomenon is most commonly encountered through the central orifice of a mechanical bileaflet (hemidisk) prosthesis where the smooth and gently flaring sides to the orifice are permissive. At the level of the prosthesis, between the hemidisks, the pressure has fallen maximally. This phenomenon is localized to the site between the occulders. Subsequently, shortly downstream, the pressure gradient partly recovers, resulting in a net gradient. Catheterization records the net gradient. Continuous wave Doppler imaging may record the higher localized gradient

(From Vandervoort PM, Greenberg NL, Powell KA, et al: Pressure recovery in bileaflet heart valve prostheses. Localized high velocities and gradients in central and side orifices with implications for Doppler-catheter gradient relation in aortic and mitral position. Circulation. 1995;92[12]:3464–3472. Used with permission.)

Figure 8-2 Top left: Pressure profiles through central (solid) and side (dotted) orifices obtained from the numerical simulations illustrating the marked pressure drop in the central orifice, located slightly more proximal than the side orifices. Top right: Illustration of the differences in pressure profiles obtained through the central orifice of a St. Jude valve no. 23 in a mitral (solid) and aortic (dotted [26 mm aorta]) configuration in vitro. Pressure recovery within the central orifice is similar for mitral and aortic positions. In the aortic configuration, however, additional pressure recovery occurs further downstream in the aorta. Bottom left: Correlation between catheter transvalvular pressure gradients and Doppler-derived pressure gradients without and with incorporating the pressure loss coefficient K = 0.64 in the simplified Bernoulli equation. AVR, aortic valve replacement; MVR, mitral valve replacement.

(From Vandervoort PM, Greenberg NL, Powell KA, et al. Pressure recovery in bileaflet heart valve protheses. Localized high velocities and gradients in central and side orifices with implications for Doppler-catheter gradient relation in aortic and mitral position. Circulation. 1995;92[12]:3463–3472. Used with permission.)