Assessment of Prosthetic Heart Valves

  • Key Points

  • Cardiac CT is able to image both biologic and mechanical cardiac valve prostheses.

  • Helical CCT scanning enables recognition of normal or impaired occluder motion.

  • Thrombus or pannus on mechanical valves can be depicted by CCT scanning.

  • Atrial fibrillation is more common in patients with mitral prostheses, making CCT scanning less useful in such cases.

  • Hemodynamic limits of patients with prosthetic valve dysfunction will preclude many from undergoing CCT scanning.

Currently, only preliminary data are available on the evaluation of prosthetic cardiac valves by CCT, although contemporary CCT, if cardiac gated, can yield excellent images of many prosthetic valves. Prosthetic valve disease, though, is prone to many of the factors that pose significant technical limitations or usual exclusions to cardiac CT, such as a high incidence of atrial fibrillation associated with prostheses in the mitral valve position, in particular.

Retrospectively gated helical imaging is the best means to assess prosthetic, especially mechanical, valves, and contrast enhancement improves image quality and diagnostic confidence.

Prosthetic Valves

Transthoracic echocardiography (TTE) and especially transesophageal echocardiography (TEE) have been the mainstays of bioprosthetic and mechanical prosthetic valve assessment, by virtue of the combination of two-dimensional imaging and spectral and color Doppler modalities. However the limitations of echocardiography are real, and these limitations are regularly encountered in busy laboratories and hospitals:

  • Inability to resolve transvalvular versus paravalvular insufficiency

  • Inability to image thrombus or pannus within the valve ring of a mechanical aortic valve prosthesis

  • Inability to distinguish thrombus from pannus

  • Inability to image an abscess on the far side of an aortic valve replacement (AVR) ring because shadowing or reverberation from the ring is projected onto the far root

  • Inability to image an AVR well because of a mechanical mitral valve replacement (MVR) projecting reverberation artifact and shadowing onto the AVR

  • Inability to adequately image the occluders of an AVR to determine their excursion

  • Inability to distinguish postoperative inflammatory changes and hematomas from early infection-related changes

  • Inability to assess the pulmonic valve by TEE due to near-field shadowing and reverberations from an AVR

Among a series of 170 patients with 208 mechanical prostheses who underwent surgery, echocardiographic diagnostic errors were encountered in 7% of MVRs and 15% of AVRs. The most common mistakes were the following :

  • Lack of surgical confirmation of paravalvular insufficiency: 36% of errors

  • Failure to identify pannnus overgrowth: 4% of errors

  • Failure to identify thrombus/pannus overgrowth: 4% of errors

  • Failure to identify vegetations: 4% of errors

  • Failure to identify ball variance: 4% of errors

  • Erroneous diagnoses: 28% of errors

  • AVR misclassification of aortic insufficiency (AI) as transvalvular: 28% of errors

  • AVR misclassification of AI as paravalvular: 8% of errors

Although the primary means of assessing valve prostheses remains echocardiographic, there appears to be a complementary role for CCT, because most prosthetic valves are well imaged by CCT, which is not necessarily the case with TTE and TEE. Some very old models of mechanical prostheses contain a large amount of ferrous metal that generates prohibitive artifact. Most contemporary bileaflet occluder “mechanical“ valves are so well seen that it is necessary to have a high degree of familiarity with the structure and motion of different models to understand the imaging findings.

Assessing the opening angle of the occluder elements of a mechanical prosthesis is one of the traditional means of establishing the normality of mechanical prosthesis function, or, alternatively, obstruction by thrombus, pannus, or both; vegetations; tissue; or primary mechanical failure. Fluoroscopy or cineradiology can measure the opening angle accurately (difference between real and measured opening angles: –0.7 ± 1.8 degrees) and with high reproducibility (to within –0.1 ± 0.8 degrees). Pressure gradient recording or Doppler calculations of gradients by TTE or TEE are complementary to two-dimensional imaging findings by CT.

The opening and closing angles of mechanical prosthesis occluder motion can be accurately assessed or measured using CCT.

Obstructing pannus or thrombus also can be identified using CCT.

The opening, closing, and range of occluder motion vary for different tilting disc models of mechanical valve replacements ( Table 17-1 ).

TABLE 17-1

The Opening, Closing, and Range of Occluder Motion for Different Tilting Disc Models of Mechanical Valve Replacements

Bileaflet Hemidisc Occluder
Carbomedics (Sorin Group, Milan, Italy) 78 35 43
St. Jude Medical (St. Paul, MN) 85 35 50
Single Tilting Disc Occluder
Bjork-Shiley (Irvine, CA) 60 0 60
Medtronic-Hall (Minneapolis, MN) 60 0 60
Omniscience (Medical CV, Ivea Grove Heights, MN) 60 0 60

Current bileaflet occluder mechanical valves (e.g., those manufactured by St. Jude Medical, Inc., St. Paul, MN, or Carbomedics) generate little artifact, and the sewing ring and occluders are clearly imaged with non–contrast-enhanced imaging. Single tilting disc valves also can be well imaged. The motion of the occluders can thus be assessed for obstruction due to thrombus or pannus on cine imaging. The opening angle is established with reference to the plane of the base of the sewing ring. Cardiac CT is able to accurately determine the opening angle.

Identification of thrombus or pannus requires contrast enhancement of the blood pool.

Assessment of occluder motion of bileaflet mechanical valves in the aortic position is difficult by TEE because the valve ring is oriented away from the probe, and fluoroscopy is variably able to convincingly depict occluder motion; hence, CCT may provide a novel contribution.

The wire struts of bioprostheses (e.g., Edwards Lifesciences, Irvine, CA) are easily seen, and the leaflets also may be seen. The heavy metal struts (stents) of some models may generate artifacts.

Complications of valve replacement surgery such as pseudoaneurysms of the left ventricular outflow tract and ascending aorta are well depicted by CCT.

For images of normal bileaflet occluder prosthetic mechanical heart valves, see Figures 17-1 through 17-4 ;

Figure 17-1

Aortic valve replacement (Carbomedics) in the closed ( A and C ) and open ( B and D ) positions. Normally, as in this example, the closed position of each occluder is 35 degrees, and the open is 78 degrees. The sewing ring is clearly seen, as are the two occluders.

Figure 17-2

A single-disc aortic valve replacement with elevated gradient. The valve opens normally, with lines showing the baseline of the valve annulus and the open disc; the opening angle is measured with these two lines ( A ). The valve closes normally to the plane of the annulus on CT ( B ). The valve geometric orifice area was measured from the short axis view of the valve, as marked by the black circle ( C ). Thick maximum intensity projection images are useful for qualitative assessment of disc motion and confirmation of appropriate orientation for measurement of disc excursion. Representative images are shown during systole ( D ) and diastole ( E ); the valve can be viewed from multiple orientations ( F ). Disc opening ( G ) and closure is confirmed with cinefluoroscopy. On echocardiography, the valve cannot be well visualized ( arrow ) and assessment of disc function is not possible ( H ); with Doppler scanning, an elevated gradient is observed ( I ). On the basis of the normal disc excursion on CT and the elevated gradient and low effective orifice area index on echocardiography, this patient meets criteria for patient–prosthesis mismatch. In addition, after correction for pressure recovery, the effective orifice area of 1.3 cm 2 increases to 1.6 cm 2 , suggesting pressure recovery may also be contributing to the gradient.

(Reprinted with permission from LaBounty TM, Agarwal PP, Chughtai A, et al. Hemodynamic and functional assessment of mechanical aortic valves using combined echocardiography and multidetector computed tomography . J Cardiovasc Comput Tomogr. 2009;3(3):161-167.)

Figure 17-3

Example of a bileaflet aortic valve replacement with elevated gradient. The short axis of the valve ( A ) is used to measure the geometric orifice area. The valve discs open normally on CT ( B ); the opening angles are measured with the lines with the valve annulus as a baseline. The valve discs close normally on CT ( C ). Thick maximum intensity projection images permit qualitative confirmation of disc opening ( D ) and closing ( E ). On the basis of the normal valve function on CT and elevated gradient and low effective orifice area index on echocardiography, this patient meets the criteria for patient–prosthesis mismatch.

(Reprinted with permission from LaBounty TM, Agarwal PP, Chughtai A, et al. Hemodynamic and functional assessment of mechanical aortic valves using combined echocardiography and multidetector computed tomography. J Cardiovasc Comput Tomogr. 2009;3(3):161-167.)

Figure 17-4

Multiple reconstructed images from a cardiac CT data set have been obtained demonstrating prosthetic aortic and mitral valve replacements with St. Jude valves (St. Jude Medical, St. Paul, MN). These images demonstrate normal movement of the prostheses at various angles. Extreme thresholding has been used to eliminate all soft tissues and cardiac chambers. See

For images of single tilting disc prosthetic mechanical heart valves, see Figures 17-5 and 17-6 ;

Figure 17-5

Multiple cardiac CT images through a Bjork-Shiley prosthetic aortic valve demonstrate a stuck aortic valve leaflet. Note: Window width level has been optimized to view the metallic components of the prosthetic aortic valve. See Figure 17-6 and

Figure 17-6

Because of the high-resolution data set acquired on the CT study, and the four-dimensional volumetric data set, double oblique reformations allow accurate evaluation of prosthetic valve function and accurate measurement of opening angles of the valve leaflets. See Figure 17-7 and

For images of obstructed bileaflet occluder prosthetic mechanical heart valves, see Figures 17-7 through 17-9 ;

Figure 17-7

A 47-year-old man with prior mechanical aortic valve replacement (AVR) who had not been taking his warfarin for 5 years. Echocardiographic and CT images depicting obstruction of the bileaflet mechanical AVR. A, Transesophageal echocardiography (TEE) of the left ventricular outflow tract (LVOT) view yields the LVOT diameter (2.1 cm), and demonstrates a large (2 cm) thrombus on the AVR. B, Spectral profiles of the LVOT (V1) and transvalvular (V2) flow, which yield an effective orifice area of 0.6 cm 2 (0.785 × 2.1 2 × 0.74 /4.45 = 0.6 cm 2 ). C, Color Doppler flow mapping reveals highly eccentric flow across the AVR, consistent with obstruction of the hemidisc occluders. D, Cardiac CT images reveal concentric left ventricular hypertrophy consistent with aortic valve obstruction. Diastole ( E ), systole ( F ): The occluders close to normal angles, but open less than normal. G, Spectral recording of flow across the AVR yielding diminished or absent opening clicks, but present closing clicks, consistent with obstruction. See Figure 17-8 and

Figure 17-8

Same patient as Figure 17-7 . A and B, Transesophageal echocardiographic views of a large thrombus on the ring of a bileaflet mechanical AVR. The thrombus is approximately 2 cm in size and sits into the valve orifice as well. C and D , Contrast-enhanced cardiac CT images of the thrombus. E and F, Surgical images of the same thrombus. See

Apr 10, 2019 | Posted by in COMPUTERIZED TOMOGRAPHY | Comments Off on Assessment of Prosthetic Heart Valves
Premium Wordpress Themes by UFO Themes