Acute type A aortic dissection intimal tears by 64-slice computed tomography: a role for endovascular stent-grafting?

AIM: The goal of this study was to identify physical characteristics of primary intimal tears in patients arriving to the hospital alive with acute type A aortic dissection using 64-multislice computerized tomography (MSCT) in order to determine anatomic feasibility of endovascular stent-grafting (ESG) for future treatment. METHODS: Radiology database was screened for acute type A aortic dissection since the time of acquisition of the 64-slice CT scanner and cross-referenced with surgical database. Seventeen patients met inclusion criteria. Images were reviewed for number, location, and size of intimal tears and aortic dimensions. Potential obstacles for ESG were determined. RESULTS: Ascending aorta (29%) and sinotubular junction (29%) were the most frequent regions where intimal tears originated. Location of intimal tears in nearly 75% of patients was inappropriate for ESG, and 94% of patients did not have sufficient proximal or distal landing zone required for secure fixation. Only 71% of patients underwent surgical aortic dissection repair after imaging and 86% of entry tears detected on MSCT were confirmed on intraoperative documentation. Only one patient would have met all technical criteria for ESG using currently available devices. CONCLUSION: Location of intimal tear, aortic valve insufficiency, aortic diameter>38 mm are major factors limiting use of ESG for acute type A dissection. Available stents used to treat type B aortic dissection do not address anatomic constraints present in type A aortic dissection in the majority of cases, such that development of new devices would be required.

Hemodynamic determinants of aortic dissection propagation by 2D computational modeling: implications for endovascular stent-grafting.

AIM: Aortic dissection is a life-threatening aortic catastrophe where layers of the aortic wall are separated allowing blood flow within the layers. Propagation of aortic dissection is strongly linked to the rate of rise of pressure (dp/dt) experienced by the aortic wall but the hemodynamics is poorly understood. The purpose of this study was to perform computational fluid dynamics (CFD) simulations to determine the relationship between dissection propagation in the distal longitudinal direction (the tearing force) and dp/dt. METHODS: Five computational models of aortic dissection in a 2D pipe were constructed. Initiation of dissection and propagation were represented in 4 single entry tear models, 3 of which investigated the role of length of dissection and antegrade propagation, 1 of which investigated retrograde propagation. The 5th model included a distal re-entry tear. Impact of pressure field distribution on tearing force was determined. RESULTS: Tearing force in the longitudinal direction for dissections with a single entry tear was approximately proportional to dp/dt and L2 where L is the length of dissection. Tearing force was much lower under steady flow than pulsatile flow conditions. Introduction of a second tear distally along the dissection away from the primary entry tear significantly reduced tearing force. CONCLUSION: The hemodynamic mechanism for dissection propagation demonstrated in these models support the use of ß-blockers in medical management. Endovascular stent-graft treatment of dissection should ideally cover both entry and re-entry tears to reduce risk of retrograde propagation of aortic dissection.

Coupling between protein-laden films and a shearing bulk flow.

Two-dimensional protein crystallization on lipid monolayers at a quiescent air/water interface is now a well-established process, but it only operates under a very restricted set of conditions and on a very slow time scale. We have recently been able to significantly extend the conditions under which the proteins will crystallize as well as speed up the process by subjecting the interface to a shearing flow. Here, we investigate the two-way coupling between a protein-laden film and the bulk flow that provides the interfacial shear. This flow in a stationary open cylinder is driven by the constant rotation of the floor. Using the Boussinesq-Scriven surface model for a Newtonian interface coupled to the Navier-Stokes equations for the bulk flow, we find that the surface shear viscosity of protein-laden films under most conditions is small or negligible. This is the case for films subjected to constant shearing flow, regardless of the duration of the flow. However, when the film is intermittently sheared, significant surface shear viscosity is evident. In these cases, the surface shear viscosity is not uniform across the film.