Purpose: This is the first prospective evaluation of the relationship between shear stress and atherosclerotic plaque formation in a pulsatile, in vivo model.
Methods: A 50% aortic stenosis was created in six Yucatan micropigs by placing a suture line across the left half of the aorta. A specially modified 20 MHz Doppler ultrasound probe mounted at a 45 degree angle on a micromanipulator was used to measure blood flow velocity along the lateral aspects of the aorta. Shear stress at these locations was calculated with linear regression. The pigs were then fed a specially formulated hyperlipidemic diet for 7 months, after which their aortas were harvested. Plaque thickness was measured and correlated with mean, maximum, and minimum shear stress at each site and side on or away from the aortic plication and distance from the level of the aortic plication with general linear modeling.
Results: Plaque thickness was negatively correlated with the mean shear stress during the cardiac cycle (correlation coefficient -0.3972 p = 0.0164) and with the maximum shear stress during the cardiac cycle (correlation coefficient -0.4581 p = 0.0050). Plaque thickness was correlated with a multivariate model of mean shear stress, maximum shear stress, and their interactive effects with other parameters in the model with a correlation coefficient of 0.6733, (p = 0.0048).
Conclusions: This is the first prospective, in vivo study with a pulsatile, hyperlipidemic model, which clearly demonstrates that low shear stress is associated with plaque formation.