Xiaoying Lou Receives Georgia CTSA TL-1 Award to Study Aortic Dissection Flap Tissue Biomechanics

June 2018

Xiaoying Lou, MD, current PGY-3 resident in Emory's integrated cardiothoracic surgery training program, has received a Georgia Clinical and Translational Science Alliance (CTSA) TL-1 Award, which will provide stipend support for her 2018-2019 research sabbatical under the mentorship of thoracic aortic disease co-investigators Bradley Leshnower, MD, assistant professor of surgery, Emory Division of Cardiothoracic Surgery, and Wei Sun, PhD, associate professor, Wallace H. Coulter Department of Biomedical Engineering at Georgia Institute of Technology and Emory University.

The award will also fund the tuition for Dr. Lou's enrollment in the one-year Masters of Science in Clinical Research (MCSR) program at Laney Graduate School of Emory University. She will concurrently receive clinical training as the structural heart/transcatheter aortic valve replacement (TAVR) fellow within the Division of Cardiothoracic Surgery.

Dr. Lou's research project will strive to begin determining the optimal timing of surgical intervention for uncomplicated, or chronic, type B aortic dissection (TBAD) by examining differences between acute and chronic aortic dissection flaps.

Thoracic endovascular aortic repair (TEVAR) has come to be considered the treatment of choice for acute TBAD—a tear in the inner lining of the descending aorta—when it presents with such complications as malperfusion or rupture. TEVAR is a minimally invasive procedure that covers the primary aortic tear with a stent, enabling re-expansion of the true lumen (the normal passageway for the blood) while obliterating the false lumen (the passageway that forms after dissection that diverts normal blood flow) and preventing further aneurysmal degeneration.

Although excellent short and long-term outcomes have been observed for TEVAR in acute complicated TBAD, the optimal management of uncomplicated TBAD remains controversial. The standard approach for the latter has been medical treatment until complications arise, at which point open surgery or TEVAR is performed, though there is a high incidence of failure with this strategy.

Dr. Lou and her mentors suspect that the the key to understanding the divergent results between surgical interventions for complicated and uncomplicated TBAD, as well as to defining when surgery would be best for both conditions, can be found by studying the histology and biomechanics of aortic dissection flaps of patients undergoing operative intervention for TBAD. This proposal builds upon the team's prior work demonstrating that patients presenting with complicated TBAD that received TEVAR had more favorable aortic remodeling and improved long-term survival compared to patients with chronic TBAD that did not undergo intervention until complications arose.

The team's principal supposition is that dissection flaps gradually lose elasticity and mobility due to increasing fibrosis and vessel wall stiffness and that these changes occur over time, explaining why acute dissection flaps may be more amenable to remodeling after TEVAR than chronic flaps. However, the mechanics of this remodelling process have not been well-characterized or defined.

To better evaluate whether there are intrinsic differences between the histological and biomechanical properties of acute and chronic dissection flaps, the team has created an aortic tissue bank with samples collected intra-operatively—primarily from Emory University Hospital and Emory Saint Joseph's Hospital. Human aortic tissue samples will be collected and classified on the basis of duration from time of dissection, and then be subjected to histological analysis and biomechanical strength testing in Dr. Sun's tissue biomechanics laboratory at the Georgia Institute of Technology.

"Our goal is to characterize the interplay of factors underlying aortic remodeling in acute versus chronic aortic dissection and determine a timeline for these changes," says Dr. Lou. "Ultimately, the insights gained from this project will serve as a basis for understanding the mechanisms and pathobiology of aortic enlargement and remodeling, which may optimize timing, intervention, and follow-up for patients presenting with TBAD."

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