Replacement of dysfunctional native cardiac valves is very common in the practice of congenital heart disease. A subset of patients with congenital heart disease will require multiple “re-replacements” of valvular prostheses secondary to growth or prosthesis degeneration. Therefore, appropriate longitudinal evaluation of prosthetic valves is critical to clinical practice. Transthoracic echocardiography is the most useful tool in the routine evaluation of valve prostheses, but transesophageal echocardiography, cardiac catheterization, and fluoroscopy are all important adjuncts to the clinical evaluation of a dysfunctional prosthesis. As a reference for longitudinal follow-up, a transthoracic echocardiogram should be obtained early after valve implantation in all patients.
Prosthetic valves can be divided into two large categories: tissue and mechanical. The tissue prostheses include porcine or bovine heterografts and human allografts/homografts (Fig. 31.1). The mechanical prostheses include tilting disc prosthetics (e.g., the St. Jude bileaflet and the Medtronic-Hall single disc) and the ball-cage prosthesis (e.g., the Starr-Edwards) (see Fig. 31.1). To accurately interpret echocardiographic findings, the exact type and size of the prosthesis should be known, as the various valve types demonstrate different hemodynamic profiles (Tables 31.1 through Table 31.4) and regurgitation characteristics. Prosthetic valve dysfunction may be caused by valve thrombosis, pannus formation, senescent changes (bioprostheses), and infection (Fig. 31.2).
EVALUATION OF THE MITRAL PROSTHESIS
Doppler interrogation of a mitral prosthesis is crucial in determining the functional status of the valve. However, the transthoracic echocardiographic evaluation of a mitral prosthesis should begin with a two-dimensional evaluation of valve stability and surrounding structures. A large vegetation, thrombus, or valve dehiscence can be identified. The leaflets of a bioprosthetic valve can be evaluated for symmetric excursion and evidence of calcification. The mechanical mitral prosthesis produces reverberation artifact, which limits the two-dimensional interrogation of the prosthesis itself and the surrounding structures, especially the left atrium (Fig. 31.3). Flow velocity through the prosthetic valve and determination of the maximal and mean pressure gradients should be obtained using continuous-wave Doppler interrogation. The pressure gradient can be elevated secondary to valve stenosis, regurgitation, or increased cardiac output. The pressure half-time measurement and the left ventricular outflow tract (LVOT) velocity can help distinguish between these two scenarios. The pressure half-time should be prolonged if the valve is obstructed, but normal or shortened if the increased pressure gradient across the valve is secondary to regurgitation. The LVOT velocity will be decreased if the increased velocity across the mitral prosthesis is secondary to severe regurgitation, as the forward flow across the LVOT will be decreased (Table 31.5). It is important to recall that the pressure half-time method used to determine the area of a native mitral valve will overestimate the area of a mitral prosthesis. If there is no significant aortic or mitral regurgitation, the continuity equation is a valid and more optimal method for determining the area of a mitral prosthesis. The continuity equation for this calculation is as follows:
MP area = LVOT area × ([LVOT TVI]/[MP TVI])
= LVOT diameter2 × 0.785 × ([LVOT TVI]/[MP TVI])
Figure 31.1. Prosthetic valves. A: St. Jude bileaflet mechanical prosthesis. B: Starr-Edwards prosthesis. C: Porcine bioprosthesis.
where MP is mitral prosthesis, LVOT TVI is the LVOT time-velocity integral, and MP TVI is the time-velocity integral of the mitral prosthesis inflow velocity obtained by continuous-wave Doppler.
Regurgitation should be evaluated with color flow imaging, spectral Doppler interrogation, and two-dimensional evaluation of the valve. If there is regurgitation, it is important to distinguish periprosthetic regurgitation from prosthetic regurgitation (Fig. 31.4), as the mechanism for each is different. The degree of regurgitation should then be assessed. The degree of prosthetic regurgitation can be assessed both by semiquantitative methods and quantitative methods (proximal isovelocity surface area [PISA]) if the jet is well seen. Severe regurgitation is indicated by the following:
1.Increased mitral inflow peak velocity 2.5 m/s or greater with normal mitral inflow pressure half-time (≤150 m/s)
2.Dense mitral regurgitant continuous-wave Doppler signal
3.Regurgitant fraction 55% or greater
4.Systolic Doppler flow reversals in the pulmonary vein
While prosthetic regurgitation can be detected by color flow imaging, the mechanical mitral prosthesis poses special challenges. The artifact produced in the left atrium may limit the ability to detect even significant degrees of prosthetic and periprosthetic regurgitation. In this situation, indirect indicators of significant regurgitation should be used. These include two-dimensional evidence of valve instability or periprosthetic tissue changes, increased left ventricular dimension, increased inflow gradient with a normal or reduced pressure half-time, and decreased LVOT velocity. Transesophageal echocardiography is very useful in defining the presence and degree of mechanical mitral prosthesis regurgitation (Fig. 31.5), as the posterior-to-anterior direction of the ultrasound beam allows visualization of the left atrium without imaging artifact.
When evaluating a prosthesis for regurgitation, it must be remembered that a small degree of prosthetic regurgitation is inherent for most mechanical prostheses. The Doppler fingerprint of this regurgitation varies by prosthesis type. A Medtronic-Hall prosthesis has one central jet of regurgitation, the St. Jude Medical mechanical prosthesis has two side jets and one central jet, the Starr-Edwards prosthesis has two curved side jets, and the Björk-Shiley prosthesis has two unequal side jets (Fig. 31.6). These normal regurgitant jets should be small, with a jet area <2 cm2 and a jet length <2.5 cm. Periprosthetic regurgitation is always abnormal. It may be a small amount of regurgitation related to a gap in the sutures placed at the anastomosis, or it may be secondary to an infectious process with perivalvular extension. Periprosthetic regurgitation that is significant may require treatment. Surgical intervention has traditionally been required, but transcatheter placement of devices to eliminate periprosthetic leakage is now possible in selected patients who are not surgical candidates without evidence of active infection (Fig. 31.7, Video 31.1).
EVALUATION OF THE AORTIC PROSTHESIS
An aortic valve prosthesis should be evaluated with an approach similar to the evaluation of the mitral prosthesis, with a few caveats. The spectral Doppler assessment of the left ventricular outflow tract and the aortic valve are usually best obtained with transthoracic imaging. Transesophageal imaging often does not allow optimal alignment of the Doppler beam to obtain the most accurate velocities through the valve and outflow tract. Left ventricular size, wall thickness, and function are also often most reliably measured during transthoracic imaging. Regurgitation can be demonstrated by both transthoracic and transesophageal imaging, but anterior periprosthetic jets are best seen on transthoracic images and posterior jets are best demonstrated by transesophageal images secondary to the location of the transducer and the artifact produced by the valve. Transesophageal images in general are better for the detection of a vegetation.
Obstruction of an aortic prosthesis results in increased flow velocity across the prosthesis and is best quantitated by Doppler echocardiography. Doppler interrogation should be performed in multiple imaging windows to obtain the maximal velocity across the prosthesis. To completely evaluate the prosthesis, continuous-wave Doppler should be obtained. From the highest velocity signal, a maximum instantaneous pressure gradient and a mean pressure gradient should be calculated. Pulsed-wave Doppler interrogation of the LVOT and measurement of the LVOT TVI is critical in determining the etiology of the increased blood flow velocity across the aortic prosthesis. Care should be taken to place the Doppler sample volume for this measurement below the area of flow acceleration. If the valve is truly obstructed, the LVOT velocity should not be increased. If the increased velocity across the valve is secondary to aortic regurgitation or a high output state, the LVOT velocity will be increased. The ratio of LVOT velocity or TVI versus AV velocity or TVI is helpful. If the prosthesis is obstructed, the ratio decreases (LVOT TVI/AV TVI ≤0.2 with normal 0.3; see Table 31.2).
Figure 31.2. Prosthetic valve dysfunction. A: Bioprosthetic valve with cusp perforation secondary to senescent changes. B: Bioprosthetic valve with severe cusp thickening. C: Mechanical valve compromised by pannus formation.
Figure 31.3. Apical four-chamber view showing reverberation artifact obscuring the left atrium in a patient with a mechanical mitral prosthesis.
The area of the aortic prosthesis can be estimated by the continuity equation as follows:
AP area = LVOT area × ([LVOT TVI]/[AP TVI])
= SROD2 × 0.785 × ([LVOT TVI]/[AP TVI])
where AP is aortic prosthesis and SROD is sewing ring diameter.
Evaluation of aortic prosthetic regurgitation should include two-dimensional evaluation of the valve and surrounding structures, color flow imaging to determine the jet characteristics and location (prosthetic versus periprosthetic), pressure half-time of the regurgitant jet, mitral inflow pattern, diastolic reversal flow in the descending thoracic aorta, and regurgitation fraction (if the jet is suitable for quantification). The normal regurgitation patterns of mechanical prosthetic valves should be kept in mind so as not to be confused with pathologic regurgitation. Severe aortic valve regurgitation is indicated by the following.
1.Pressure half-time of regurgitant jet of 250 ms or less
2.Restrictive mitral inflow pattern (if the aortic regurgitation is acute)
3.Holodiastolic flow reversal in the descending thoracic aorta Doppler signal
4.Regurgitant fraction of 55% or greater
EVALUATION OF TRICUSPID AND PULMONARY PROSTHESES
Tricuspid and pulmonary valve replacements are common in patients with congenital heart disease. The evaluation of these prostheses is analogous to the evaluation of the aortic and mitral prosthetic valves, with a few exceptions. The tricuspid and pulmonary valves are usually anterior structures. Therefore, imaging of these valves is often best with transthoracic imaging. The posterior location of the echo transducer in transesophageal imaging can diminish the ability to evaluate these anterior structures. If transesophageal imaging is used, transgastric images are usually best for evaluation.
Several forms of congenital heart disease require placement of an extraanatomic conduit and valve to establish continuity between the subpulmonary ventricle and the pulmonary arteries. These conduits are best evaluated with transthoracic images. Unique imaging windows must be obtained to completely determine the functional status of these prostheses. Imaging windows can often be found by palpation of the chest wall. Since the valve prosthesis is very close to the chest wall in these situations, flow through the valve is often felt as a vibratory sensation or “thrill.” Placing the transducer at the site of the thrill may provide the best visualization of the valve. Often, the valve prosthesis itself is not seen and one must rely on Doppler interrogation and other indirect findings to determine the status of the prosthesis. Indirect findings include calculation of the right ventricular systolic pressure from the tricuspid valve regurgitation velocity signal using the modified Bernoulli equation: Ρ = 4V2. The velocity (and hence the calculated pressure gradient) across the pulmonary conduit cannot exceed the velocity through the tricuspid valve. Other indirect findings include right ventricular size, wall thickness, and function. The interventricular septal motion may also provide clues to right ventricular pressure or volume overload. If the septum flattens only in diastole, volume overload should be suspected. Septal flattening in both systole and diastole is indicative of right ventricular pressure overload.
Figure 31.4. Transesophageal echocardiogram showing mechanical mitral prosthesis with both periprosthetic (white arrow) and prosthetic regurgitation (yellow arrows).
Pulmonary valve prosthetic regurgitation may be brief in duration. The spectral Doppler pattern may be helpful in determining the degree of regurgitation. Rapid equalization of pulmonary artery and right ventricular diastolic pressure will occur if the degree of regurgitation is severe. This will result in a Doppler pattern of regurgitation that returns to the baseline before the end of diastole (Fig. 31.8). This pattern does not always signify significant regurgitation, however. If the right ventricle has poor compliance, smaller volumes of regurgitation cause greater changes in the diastolic pressure and can lead to a similar Doppler pattern. Right ventricular noncompliance may result in diastolic forward flow with atrial contraction (Fig. 31.9).
Figure 31.5. Mechanical mitral prosthesis visualized by transesophageal echocardiography. Note that there is no artifact obscuring the left atrium (prosthesis (arrow)) (A), allowing better visualization of the periprosthetic regurgitation jet (B). MR (mitral regurgitation (arrow))
Figure 31.6. Appearance of normally functioning mechanical mitral prosthesis. A: Medtronic-Hall prosthesis with a single central jet (arrow) of normal regurgitation. B: St. Jude prosthesis with three jets of normal regurgitation.
Tricuspid prosthetic valves are often large and have lower flow velocity across them. Therefore, a lower calculated pressure gradient is expected compared with the mitral valve prosthesis. Respiratory variation in transtricuspid flow is greater than that in transmitral flow. Flow is increased across the tricuspid prosthesis during inspiration and decreased during expiration. Measurement of the prosthetic gradient should be obtained over several cardiac cycles and then averaged, or it should be obtained during held expiration.
Tricuspid valve prosthetic regurgitation, when severe, may be laminar. Systolic flow reversals in the hepatic veins are a marker of severe tricuspid prosthetic regurgitation but are not always present. If the right atrium is very large, the systolic flow reversals in the hepatic veins are diminished or absent.
PERCUTANEOUS VALVE IMPLANTATION
The first transcatheter pulmonary valve was implanted in 2000 in France. A redesigned version of the original valve was subsequently used in Europe and Canada for several years. The Melody valve (Medtronic Corporation, Minneapolis, MN) underwent clinical trials in the United States starting in 2007. It was FDA approved in 2010. Since then, over 5,000 valves have been implanted worldwide. The valve was primarily indicated for replacement of right ventricle to pulmonary artery conduits and it subsequently has been utilized in pulmonary valve bioprostheses. Since 2010, application of the Melody valve has broadened and it is successfully used, in an “off-label” manner, in tricuspid and mitral bioprostheses.
Figure 31.7. Three-dimensional echocardiogram image of a mitral prosthesis. A: Color Doppler demonstrates a periprosthetic regurgitation (arrow). B: Images after a closure device (arrow) has been placed to eliminate the periprosthetic regurgitation.
Figure 31.8. Spectral Doppler pattern consistent with severe pulmonary prosthetic regurgitation. Note the diastolic signal returns to the baseline prior to the start of systole.
The Melody valve is a three cusp bovine jugular venous valve mounted within a platinum iridium stent (Fig 31.10). The use of percutaneous valves has saved many patients from recurrent valve replacement surgery. Two-dimensional and Doppler echocardiography have played an important role in the serial follow-up of patients after Melody valve insertion. Recurrent pulmonary valve regurgitation is rare during follow-up; however, progression of Melody valve stenosis is important. If one notices an increase in the mean gradient through a Melody valve, one has to be suspicious of a stent fracture. Stent fractures occurred in as many as 20% of patients who had implantation of a Melody valve without pre-stenting of the right ventricle to the pulmonary artery conduit (Fig. 31.11). Stent fracture when the Melody is used in a “valve-in-valve” manner (within an existing bioprosthesis) has been exceedingly rare.
Figure 31.9. Spectral Doppler pattern through the pulmonary valve consistent with right ventricular noncompliance. Note the diastolic forward flow through the pulmonary valve with atrial contraction.
Figure 31.10. Photograph of MelodyTM valve. The valve is constructed by sewing a segment of bovine jugular vein to a platinum iridium stent. The stent is then mounted over an 18, 20, or 22 mm balloon-in-balloon delivery catheter. (Medtronic Corporation, Minneapolis, MN. Copyright 2014 Medtronic, Inc.)
Implantation criteria for a transcatheter pulmonary valve include objective evidence of right ventricular to pulmonary artery conduit dysfunction defined as moderate or more valve regurgitation and/or conduit valve stenosis with a mean gradient ≥35 mm Hg. The patient has to be large enough to accommodate the 22 French delivery system and the right ventricle to pulmonary artery conduit needs to be greater than 16 mm in dimension at time of original surgical implant. Currently, patients who have acute endocarditis or native right ventricular outflow tract regurgitation/stenosis are not candidates for transcatheter pulmonary valves. The valve is expanded over a balloon-in-balloon system to 18, 20, or 22 mm in maximum dimension (Video 31.2). Conduits/bioprostheses with inner diameters >22 mm will not be acceptable landing zones for the current Melody system.
Videos 31.3 to 31.8 demonstrate the use of a percutaneous Melody valve that was implanted within a 31 mm Carpentier-Edwards (CE) bioprosthesis in the tricuspid position. The patient was a teenager with Ebstein anomaly who had a tricuspid valve replacement. In this patient, successful placement of the Melody valve within the bioprosthesis obviated the need for re-operation. Videos 31.3 and 31.4 are intracardiac echocardiography (ICE) images demonstrating the CE valve with a mean inflow gradient of 15 mm Hg. The valve leaflets were thickened with a large coaptation defect and consequent severe regurgitation. Videos 31.6 and 31.7, after Melody implantation, demonstrate the coaptation provided by the Melody valve. There is mild central regurgitation and the mean gradient was reduced to 5 mm Hg. Videos 31.5 and 31.8 demonstrate the valve-in-valve implantation procedure.
Figure 31.11. Fluoroscopic image of Melody valve stent fracture. When the mean gradient through a Melody valve increases, stent fracture, especially in a conduit that was not pre-stented, must be suspected. (Property of Mayo Clinic.)
The intermediate term follow-up of the Melody valve has been good. Surface echocardiography plays an important role in the serial assessment of these patients. ICE and TEE have roles during implantation in select patients. ICE has aided the interventionalist during Melody valve placement in the tricuspid position (see Videos 31.3 and 31.6). TEE with 3D imaging has been used for Melody valve placement within mitral bioprostheses. Another percutaneous valve, the Sapien valve (Edwards Life Science Corporation), has been utilized in native aortic valves. Its applicability for congenital cardiac disease is beginning in the United States. In the coming years we will see greater use and redesign of both of these valves as their applicability in patients with congenital heart disease expands. The echocardiographer should remain cognizant of these novel innovations in percutaneous valve technology.
Prosthetic valves are manufactured in multiple different diameters. At surgery, the largest possible prosthesis should be implanted to provide the largest effective orifice area. If a prosthesis has an effective orifice area that is too small in relation to the patient’s body surface area, an increased gradient will be present without inherent stenosis of the valve. This is known as patient–prosthesis mismatch. Patient–prosthesis mismatch is determined by calculating the effective orifice area of the prosthesis and dividing that area by the body surface area of the patient to obtain an indexed effective orifice area. If the indexed effective orifice area is greater than 0.85 cm2/m2, the degree of mismatch is mild. Severe patient–prosthesis mismatch is defined as an indexed effective orifice area of 0.6 cm2/m2 or less. Patient–prosthesis mismatch has been shown in several studies to correlate with poor patient outcomes.
Flow dynamics and function of a prosthetic valve can be described in terms of potential energy (pressure) and kinetic energy (blood velocity). The maximal gradient across a prosthetic valve occurs at the vena contracta where kinetic energy is largest and potential energy (pressure) is lowest. As blood moves “downstream” from the vena contracta, some kinetic energy will revert to potential energy (i.e., pressure increases). Therefore at a point downstream from an obstruction, pressure is “recovered” and the pressure gradient from that point compared to the pressure proximal to the valve is lower than the pressure gradient between the proximal pressure and the pressure at the vena contracta. Evaluation of prosthetic aortic valve function by Doppler echocardiography utilizes the highest obtained velocity through the valve (velocity at the vena contracta) to calculate the pressure gradient across the valve from the Bernoulli equation. Pressure gradients obtained in the catheterization laboratory involve direct measurement of pressure in the aorta distal to valve. Therefore, evaluation of the pressure gradient across an aortic prosthetic valve by Doppler echocardiography can predict a gradient higher than the gradient measured in the cath lab if there is significant pressure recovery in the aorta. This phenomenon is most prevalent clinically in patients with small aortic valve area. If pressure recovery is suspected in a patient with a large calculated gradient by Doppler but a normal appearing prosthesis, an energy loss coefficient can be calculated from echocardiographic parameters that may more accurately reflect the effective orifice area of the prosthesis obtained during catheterization:
ELCo = EOADop × Area Aorta
Area Aorta - EOADop
(ELCo = energy loss coefficient, Area Aorta = cross-sectional area of the aorta at the sinotubular junction, EOADop = effective orifice area measured by Doppler echocardiography)
Brown DW, McElhinnery DB, Araoz PA, et al. Reliability and accuracy of echocardiographic right heart evaluation in the U.S. Melody Valve Investigational Trial. J Am Soc Echocardiogr. 2012;25:383–392.
Connolly HM, et al. Doppler hemodynamic profiles of 82 clinically and echocardiographically normal tricuspid valve prostheses. Circulation. 1993;88:2722–2727.
Garcia D, Dumesnil J, Durand L, et al. Discrepancies between catheter and Doppler estimates of valve effective orifice area can be predicted from the pressure recovery phenomenon. J Am Coll Cardiol. 2003;41:435–442.
Lengyel M, et al. Doppler hemodynamic profiles in 456 clinically and echo-normal mitral valve prostheses [abstract]. Circulation. 1990;82(suppl 3):III–43.
Miller F, et al. Normal aortic valve prosthesis hemodynamics: 609 prospective Doppler examinations [abstract]. Circulation. 1989;80(suppl 2):II-169.
Mohr-Kahaly S, et al. Regurgitant flow in apparently normal valve prostheses: improved detection and semiquantitative analysis by transesophageal two-dimensional color-coded Doppler echocardiography. J Am Soc Echocardiogr. 1990;3: 187–195.
Novaro GM, et al. Doppler hemodynamic of 51 clinically and echocardiographically normal pulmonary valve prostheses. Mayo Clin Proc. 2001;76:155–160.
Rahimtoola SH. The problem of valve prosthesis-patient mismatch. Circulation. 1978;58:20–24.
Sorajja P, et al. Successful percutaneous repair of perivalvular prosthetic regurgitation. Cathet Cardiovasc Interv. 2007;70: 815–823.
1.Which of the following options describes the most accurate measurement of the left ventricular outflow tract diameter after implantation of an aortic prosthesis?
A.Junction of the anterior sewing ring with septum to junction of the posterior sewing ring with the anterior mitral leaflet
B.Sewing ring leading edge to leading edge
C.Reported prosthesis size
D.Sewing ring inner edge to inner edge
E.Sinotubular junction leading edge to leading edge
2.To obtain the left ventricular outflow tract TVI (time velocity integral) for evaluation of aortic prosthesis stenosis, which of the following is the proper position of the pulsed waved (PW) Doppler sample volume?
A.Just below the prosthesis sewing ring
B.In the aorta just distal to the prosthesis
C.½ cm to 1 cm below the prosthesis sewing ring
D.2 cm below the prosthesis sewing ring
3.Which of the following conditions invalidates the standard continuity method for measuring the aortic valve prosthesis area?
B.Severe aortic valve regurgitation
D.Dynamic left ventricular outflow tract obstruction
E.Severe mitral valve regurgitation
4.Which measurement is consistent with severe regurgitation in a patient with a mechanical mitral prosthesis?
A.Mitral E velocity 1.2 m/s
B.Mitral inflow pressure half time 200 ms
C.Increased mitral valve TVI:LVOT TVI ratio
D.Diastolic mean Doppler gradient through the prosthesis of 3 mmHg.
5.Which of the following is indicative of a thrombosed mechanical mitral prosthesis?
A.Progressive left ventricular enlargement
B.Increased tricuspid regurgitation velocity
C.Increased LVOT TVI
D.Systolic flow reversal in the pulmonary vein
6.A patient with a 23 mm mechanical aortic prosthesis presents with heart failure symptoms and is found to have a left ventricular ejection fraction of 25% and a mean systolic gradient across the aortic prosthesis of 30 mmHg. On an echo one year ago, the left ventricular ejection fraction was reported as 55% and the mean systolic gradient was 12 mmHg. What is the next most appropriate step?
A.Fluoroscopy of the valve
B.Initiate heart failure medical therapy and re-evaluate in 4 weeks
7.A patient with a mechanical 21 mm aortic prosthesis is noted to have a systolic mean Doppler gradient of 42 mmHg across the prosthetic valve on a post-operative transthoracic echocardiogram. Fluoroscopy demonstrates normal leaflet motion. Cardiac catheterization is performed and a peak-to-peak gradient of 20 mmHg from the left ventricle to the aorta is reported. What likely explains the discrepancy between the two measurements?
A.There is no discrepancy. Peak-to peak catheter gradients cannot be compared to Doppler mean gradients.
B.The prosthesis is too small for this patient (prosthesis-patient mismatch).
C.The patient is anemic postoperatively so Reynolds number is increased making the echo derived gradient higher.
D.Pressure recovery phenomenon led to the higher Doppler gradient.
E.The patient has sub-aortic stenosis.
8.A patient with repaired Tetralogy of Fallot who has a valved conduit from the right ventricle to the pulmonary artery presents for evaluation. Echocardiographic windows are challenging and the conduit valve is not well visualized. What ancillary data are suggestive of severe conduit valve regurgitation?
A.Systolic flattening of the ventricular septum
B.Tricuspid regurgitation velocity = 4.2 m/s
C.Spectral Doppler through the conduit demonstrating cessation of diastolic flow before atrial contraction
D.Holosystolic flow reversals in the hepatic veins
9.Which condition renders calculation of mitral prosthetic valve area by the continuity equation invalid?
A.Moderate aortic valve regurgitation
B.Aortic valve stenosis
C.Pannus formation on the mitral prosthesis
D.Left ventricular diastolic dysfunction
10.Which of the following is true regarding echocardiographic evaluation of a tricuspid prosthesis?
A.Diastolic gradients through the prosthesis are higher in expiration.
B.Transesophageal images are often needed to visualized these prostheses.
C.Systolic flow reversals in the hepatic veins are an ancillary sign of significant prosthetic regurgitation.
D.Pressure half time cannot be used to assess valve area.
1.Answer: A. The left ventricular outflow tract is best measured from the septum to the anterior mitral leaflet. The valve size or valve sewing ring diameter does not accurately reflect the anatomic LVOT diameter. The sinotubular junction is in the aorta so it would not reflect the LVOT dimension.
2.Answer: C. The pulsed wave Doppler signal best representing the left ventricular outflow tract (LVOT) TVI is obtained ½ cm to 1 cm below the prosthesis sewing ring where flow is still laminar. As the flow approaches the prosthesis, there is a zone of flow convergence, where velocity is higher. TVI measured in the zone of flow convergence will be larger than the TVI that accurately reflects flow in the LVOT. If this larger measurement is used in the continuity equation, the calculated aortic valve area will be too large.
3.Answer: D. The standard continuity method for measuring aortic valve prosthesis area involves measurement of the left ventricular outflow tract diameter, the left ventricular outflow tract (LVOT) TVI, and the aortic valve TVI. Therefore, dynamic left ventricular outflow tract obstruction would alter measurement of the LVOT TVI and render the calculation invalid. The mitral valve TVI is not involved in the calculation, so mitral regurgitation or stenosis would not interfere with an accurate calculation. Likewise, pulmonary hypertension would not invalidate any measurement in the continuity equation.
4.Answer: C. Severe mitral regurgitation results in increased volume that must cross the mitral prosthesis in diastole. Therefore, an increase in the mitral E velocity is expected and the diastolic gradient is expected to be higher than normal. With regurgitation, but not stenosis, the pressure half time should be normal (< 150 m/s). Because the mitral valve TVI reflects both effective cardiac output and regurgitation volume, the ratio of mitral valve TVI to LVOT TVI is expected to be increased.
5.Answer: B. A thrombosed mechanical prosthesis results in mitral valve stenosis. The left ventricle would not be expected to enlarge in that hemodynamic setting. The cardiac output would decrease, so the LVOT TVI would decrease. Systolic flow reversals in the pulmonary veins are indicative of mitral regurgitation, not stenosis. With mitral stenosis, the left atrial pressure increases leading to increased pulmonary artery pressure and therefore an increase in tricuspid regurgitation velocity.
6.Answer: A. Dysfunction of an aortic prosthesis resulting in obstruction increases ventricular afterload and can result in reduction of left ventricular systolic function. The gradient across an aortic prosthesis may not be severely elevated even with severe obstruction when the left ventricular systolic function is reduced and the cardiac output is low. The increase in the gradient in this scenario despite a decrease in LV systolic function should prompt concern for aortic prosthesis obstruction. The best method of evaluating disc motion of a mechanical prosthesis is fluoroscopy.
7.Answer: D. The pressure recovery phenomenon can be seen in small (19 mm and 21 mm) aortic prostheses. This results in a higher echo gradient compared to a catheter-measured gradient. While prosthesis-patient mismatch can also occur with a small prosthesis, the catheter gradient and the echo gradient would be concordant. The gradients would also be concordant with sub-aortic stenosis. The increase in gradient seen with anemia is unlikely to be this high on echocardiography. Catheter peak-to-peak gradients can be compared to Doppler mean gradients.
8.Answer: C. Severe conduit valve regurgitation would result in volume loading of the right ventricle, producing diastolic, but not systolic flattening of the ventricular septum. An elevated tricuspid regurgitation velocity is more consistent with obstruction in the conduit. Holosystolic flow reversals in the hepatic veins would be seen with severe tricuspid regurgitation rather than severe pulmonary conduit regurgitation. The Doppler hallmark of severe pulmonary conduit regurgitation is cessation of diastolic flow (indicating equalization of pulmonary artery and right ventricular pressures) prior to the end of diastole. This is analogous to the short-pressure, halftime of severe aortic regurgitation.
9.Answer: A. Calculation of the mitral valve prosthetic area by the continuity equation requires measurement of the left ventricular outflow (LVOT) TVI, the mitral prosthesis TVI, and the LVOT diameter; flow across the aortic valve is assumed to be the flow that must cross the mitral valve. If there is moderate aortic valve regurgitation, the LVOT TVI will be elevated and not indicative of effective cardiac output (flow across the mitral valve), rendering the continuity equation invalid. In aortic valve stenosis, the LVOT TVI is not altered (the aortic valve TVI would be altered). Pannus formation of the mitral prosthesis can increase the mitral gradient, but does not invalidate the equation. Left ventricular diastolic dysfunction can result in lower cardiac output and LVOT TVI, but the equation is still valid.
10.Answer: C. Flow across the tricuspid valve increases in diastole with inspiration. The tricuspid valve is anterior and usually best imaged with transthoracic imaging. Systolic flow reversals, when present, correlate with severe tricuspid regurgitation. Pressure halftime is useful in the assessment of valve gradient and area.