The Missing Role Of Hydrodynamic Stresses On Ascending Aortic Dissection

Ascending aortic dissection is a lethal illness characterized mainly by a tear that develops in the aortic wall when the wall stress by the blood pressure exceeds the wall endurance limits. The estimation of the timing for a surgical treatment of a dilated ascending aorta is based, in practice, on the aortic size, and a recommended criterion for preventive surgical repair is an aortic diameter equal to 5 cm-5.5 cm. However, cardiothoracic surgeons refer to the dissection size paradox, which means that they often encounter unsuspected cases of ascending aortic dissection and/or rupture at aortic diameters less than the recommended criterion. The Laplace law, which is employed by the clinicians for the estimation of wall stress, is generally insufficient to predict ascending aorta dissection because it applies to a straight tube under uniform static blood pressure, whereas an ascending aorta is a curved tube under static and hydrodynamic stresses. Here, we take into account the dynamic stresses generated by the curvilinear motion of the blood and produce novel expressions, which explain the dissection size paradox and indicate the location at which a dissection may appear. Our results are in agreement with the increasing clinical evidence that the aortic length is an indispensable complement to the aortic diameter in the risk stratification and in the decision making for an in time surgical intervention. Employing the derived expressions, a preventive health care system tool can be developed, which will unveil "unsuspected" cases that previously were considered of lower risk for surgical intervention.