Prosthetic heart valve

Dr Daniel J Bell ◉ and Dr Ian Bickle ◉ et al.

Prosthetic heart valves are common. The four valves of the heart may all be surgically replaced. However, the aortic and mitral valves are the most commonly replaced.

Replacements may be tissue or metallic valves, only the latter being visualized on imaging investigations. Sometimes the annulus alone is replaced as seen in annuloplasty rings.

In recent times, aortic valves in select circumstances are being replaced via a transcatheter approach, called a transcatheter aortic valve implantation (TAVI) from a femoral artery approach.

Radiographic features

Evaluation of prosthetic valves often relies on multimodality imaging, including transesophageal echocardiography, transthoracic echocardiography, fluoroscopy, and computed tomography (CT) ³.

Echocardiography

Valve appearance on echocardiography is dependent on the type of valve, which are generally subdivided into two categories (mechanical and bioprosthetic) with examples as follows ⁵:

mechanical valves
- ball cage valves
  - Starr-Edwards caged ball valve
- tilting disk valves
  - Bjork-Shiley tilting disk valve
bioprosthetic valves
- homografts
- heterografts
- stented
  - Carpentier-Edwards stented aortic valve
- stentless
  - Biocor stentless aortic valve

Transesophageal echocardiography is the modality of choice to assess the status of a prosthetic heart valve; a baseline study is typically performed after placement, and subsequent studies rely on comparison with this baseline to assess for pathology.

Complications of prosthetic valves ⁵:

obstruction
- may be due to thrombus or pannus ⁴
  - may require MDCT to discriminate based on attenuation differences
    - pannus typically has a significantly higher attenuation, as measured by Hounsfield units (HU)
  - thrombogenic obstruction typically occurs with a subtherapeutic INR early after mechanical prosthesis implantation ⁶
    - typically occult to transthoracic studies
    - the posterior acoustic shadowing from the valve obscures the typical atrial location of thrombi
    - obstruction due to pannus tends to be a more chronic process, with a slow symptom onset and older valvular prosthesis
infective endocarditis
- with or without paravalvular abscess
paravalvular regurgitation
valve failure (see below)
- mechanical failure in mechanical valves
- degeneration of a biological valve
hemolytic anemia: rare, both biological and mechanical valves ⁷

Severe dysfunction of a prosthetic valve should be suspected when the following parameters are measured ⁵:

mitral valve
- severe regurgitation
  - vena contracta (VC) >0.6 cm
  - dense, triangular continuous wave Doppler envelope with early peak
  - systolic flow reversal on pulmonary venous Doppler
- severe stenosis
  - mitral inflow velocity peak >2.5 m/s
  - pressure half time >200 ms
aortic valve
- severe stenosis
  - peak outflow velocity >4 m/s
  - a ratio of the aortic velocity time integral (VTI) to the left ventricular outflow tract (LVOT) VTI less than 0.25
- severe regurgitation
  - doppler studies of the descending aorta show holodiastolic flow reversal
  - regurgitant jet fills more than 65% of the LVOT