Title: Evaluation of aneurysmal dilatation in the chronically dissected aorta
Acute aortic dissection is a life-threatening process with an incidence of between 3.5 and 6 per 100,000 person-years. In this process, blood enters the wall of the aorta through a tear in the innermost layer and propagates longitudinally. This weakens the aortic wall with the potential for rupture, and when branch vessels are involved blood flow into end-organs may be compromised. Aortic dissections are pragmatically categorized into Type A, involving the ascending aorta, and Type B, not involving the ascending aorta. Patients with Acute Type A Aortic Dissection require an emergency operation to replace the ascending aorta whereas Acute Type B Aortic Dissection is typically managed with medications. In both situations, the descending aorta does not undergo intervention leaving it at risk for late aneurysmal dilatation, which occurs in between 25 and 60% of patients at 6-years.
Previous attempts to predict aneurysmal dilatation have had only marginal success. These studies relied primarily on clinical and morphological predictors, e.g. existing aneurysm, number of tears, age, and connective tissue disease. Our group has previously demonstrated that anatomic correlates of false lumen flow predict aneurysmal dilatation suggesting that hemodynamic forces likely influence the natural history of these patients. Until recently, measurement of pressure and flow required invasive procedures to directly measure these figures. Computational Fluid Dynamics (CFD) has been used in an effort to model these processes without invasive measurements. However, these techniques have never been validated and many assumptions are made that may influence the model output.
We are prospectively enrolling patients in a correlational study in which patients undergo computed tomographic angiography for construction of a CFD model and 4-d flow magnetic resonance angiography to measure flow non-invasively. This will allow us to test the influence of the most common assumptions (zero-pressure boundary conditions, zero-resistance boundary conditions, and rigid tube) on the modeled flow, wall-shear stress, and relative pressure. Additionally, we have partnered with the Chaudhuri lab in order to evaluate the mechanical properties of the normal and dissected aorta in order to improve upon an innovative deformable wall simulation. Our goal is to develop a validated model that will be able to predict aneurysmal dilatation. Doing so would improve not only operative planning by predicting the efficacy of operative techniques but also enhance surveillance by identifying patients who are at high risk for progression and may benefit from early elective intervention.