Prosthetic heart valve

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 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 is generally subdivided into two categories (mechanical and bioprosthetic) with examples as follows ^4,5:

• 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
  • maybe due to thrombus or pannus ⁴
    • differentiation on MDCT:
      • pannus appears as a circular or semicircular mass extending from the prosthesis ring, can demonstrate enhancement and typically shows a significantly higher attenuation as measured by Hounsfield units (HU) with a recommended cut-off point of >145 HU (sensitivity 88%, specificity 96%)
      • thrombus appears as an irregular lobulated non-enhancing mass
    • thrombogenic obstruction typically occurs with a subtherapeutic INR early after mechanical prosthesis implantation ⁶
      • ​typically occult to transthoracic echo 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 slow symptom onset and in older valvular prosthesis
• infective endocarditis
  • with or without valvular vegetation or 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 an 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

See also

• transcatheter aortic valve implantation (TAVI)