What is the significance of the mechanical click in a St Jude (St. Jude Medical) valve?

Understanding the Mechanical Click of a St. Jude Valve

The mechanical click of a St. Jude valve represents normal valve function and is an audible manifestation of the opening and closing of the valve's bileaflet mechanism. The clicks are critical diagnostic indicators that confirm proper mechanical valve function and are visible on imaging as brief, intense, high-velocity signals during echocardiographic assessment. 1

Anatomical and Functional Basis of the Click

St. Jude valves are bileaflet mechanical prosthetic heart valves with specific design characteristics:

• Two separate discs (leaflets) that open and close almost in synchrony
• Opening angle of approximately 85° relative to the valve annulus plane 1
• Closing angle of approximately 30° for smaller valves (19-25 mm) and 25° for larger valves (27-31 mm) 1
• Three orifices when open: a smaller central slit-like orifice between the leaflets and two larger semi-circular orifices laterally 1

The clicks occur due to:

• Impact of the metallic/pyrolytic carbon leaflets against the valve housing during opening and closing
• Both opening and closing movements produce audible clicks
• The sound is more pronounced during valve closure 1

Clinical Significance of the Click

1. Diagnostic Value

• Normal valve function: The presence of clear, consistent clicks indicates proper mechanical function
• Abnormal findings: Absence or muffling of clicks may suggest valve thrombosis, pannus formation, or other dysfunction 1
• Imaging correlation: Clicks appear as brief, intense signals on spectral Doppler recordings 1

2. Patient Experience

• Approximately 65-73% of patients are aware of their valve clicks 2, 3
• Sound pressure level at 1 meter distance for St. Jude Medical valves is approximately 24-25 dB(A), which is quieter than some other mechanical valve types 2, 4
• Patient complaints related to valve noise:
  • Sleep disturbances (9-20% of St. Jude valve recipients) 2, 3
  • Only 11-12% of St. Jude valve patients report wanting a less noisy valve 2, 4

3. Prognostic Significance

• St. Jude valves demonstrate excellent long-term durability with:
  • No reported mechanical failures in long-term studies 5, 6
  • 15-year freedom from valve-related death of 91% 5
  • Low thrombogenicity compared to other mechanical valves 5, 6

Assessment of Valve Clicks

Echocardiographic Evaluation

• Spectral Doppler recordings show opening and closing clicks as brief, intense signals 1
• Continuous wave Doppler (CWD) for aortic valves and pulsed wave Doppler (PWD) for mitral valves best demonstrate these clicks 1
• M-mode imaging can show normal opening and closure of the discs 1

Computed Tomography Assessment

• ECG-gated CT can evaluate leaflet motion in fully open and closed positions 1
• CT can measure leaflet angles relative to the valve ring 1
• Limitation of motion is likely when leaflet opening/closing angle deviates >4° from manufacturer specifications 1

Clinical Pearls and Pitfalls

Pearls:

• The presence of clicks is reassuring for normal valve function
• St. Jude valves generally produce less noise than other mechanical valves like Björk Shiley Monostrut or Duromedics Edwards 2, 3, 4
• Patients with better hearing, younger age, and sinus rhythm are more likely to be aware of valve clicks 3

Pitfalls:

• Absence of clicks should prompt further evaluation for potential valve dysfunction
• Patients should be counseled preoperatively about the expected clicking sound to reduce anxiety
• Valve noise can be conducted through both air and body tissues - approximately 51% of patients can hear their valve through body conduction 3

By understanding the significance of the mechanical click, clinicians can better educate patients and use this physical finding as part of ongoing valve assessment.