Can regurgitant flow damage the left atrial endothelium in patients with prosthetic mechanical heart valves
2005
Background and aim of the study: Previous in-vitro
studies of mechanical heart valves (MHVs) in the
closed position demonstrated the formation of regurgitant
flows, with bubbles and jets forming vortices
during each systole. The study aim was to determine
whether the regurgitant flow observed in patients
with MHVs can damage the left atrial endothelium,
due to shear stresses exerted on the endothelial layers.
This objective has been accomplished by appropriate
in-vitro simulation experiments.
Methods: In these experiments, leakage flow through
several commercial MHVs was investigated. The
geometry of the set-up closely resembled that of the
left atrial anatomy. Water was forced through the slit
of a closed MHV and directed toward the hemispherical
cup coated with fluorescent paint. The flow
field between the valve and the cup was photographed
using high-speed videography, from
which local velocities were measured, using digital
particle imaging velocimetry. Qualitative damage to
the surface of the cup was assessed from the amount
of fluorescent paint removed from the cup.
Results: The experimental results and calculations
indicated that flows through the gaps of the closed
valves were sufficient to generate strong vortices,
with velocities near the atrial wall in the range of 0.5
to 4.0 m/s, depending on the valve. This led to high
shear stresses on the left atrial wall, which far
exceeded physiologically acceptable levels.
Conclusion: The calculated shear stresses exceeded
by orders of magnitude the maximum physiologically
tolerated stresses. This suggests that shear stresses
associated with regurgitant jets in MHVs may damage
the endothelial cells, leading to the activation of
the inflammatory reaction, enhanced procoagulation,
platelet activation and aggregation, and mechanical
cell denudation.
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