Fluid mechanics of aortic stenosis

Area of Science:

• Cardiovascular Science
• Biomedical Engineering
• Medical Imaging

Background:

• Aortic stenosis (AS) is a significant cardiovascular condition.
• Accurate hemodynamic assessment is crucial for AS management.
• Bioprosthetic valves are commonly used, and their flow dynamics in AS require detailed study.

Purpose of the Study:

• To investigate the in vitro flow characteristics of bioprosthetic valves under varying degrees of simulated aortic stenosis.
• To evaluate the accuracy of Doppler techniques in assessing pressure gradients and flow patterns in AS.
• To understand the impact of stenosis severity on jet velocity, turbulence, and flow field characteristics.

Main Methods:

• In vitro flow mapping studies using an adult aortic flow chamber and a left heart stimulator.
• Employed techniques including flow visualization, laser Doppler anemometry (LDA), continuous-wave (CW) Doppler, and colour Doppler flow mapping (CDFM).
• Utilized bioprosthetic valves (0.5-5.0 cm2) to simulate different severities of aortic stenosis.

Main Results:

• CW Doppler accurately predicted pressure gradients (r=0.99) using the Bernoulli equation.
• All degrees of AS produced jet-type flow fields with varying degrees of skewness, necessitating multi-view Doppler measurements.
• Increasing AS severity led to narrowed jets, increased peak velocity (4-7 m/s), elevated turbulence (1.0-2.3 m/s), and increased jet instability and proximal acceleration.
• Quantitative interpretation of CDFM was challenging in moderately to severely stenotic valves due to high velocities and turbulence.

Conclusions:

• Doppler echocardiography, particularly CW Doppler, is effective for pressure gradient estimation in AS.
• Flow visualization and LDA provide detailed insights into the complex, non-symmetric jet dynamics in AS.
• High velocities and turbulence in moderate to severe AS may pose risks to blood components and aortic walls, and challenge quantitative CDFM accuracy.