Not all grafts are created equal:
Improving valve-sparing aortic root surgery
By Amanda Chase, PhD
October 6, 2020
Aneurysm. A word with big implications for the patient, but what is it? An aneurysm is an outward bulging of an abnormal, weak spot on a blood vessel wall. Similar to a balloon, as the vessel wall expands, or bulges, the walls become thinner and tighter. As the size increases, so does the risk of rupture, akin to a balloon becoming too large and popping. Aneurysms can occur in any blood vessel, including the aorta, the largest artery in the body that carries blood from the heart to the rest of the body. Aortic aneurysms occur in about 5-10 cases per 100,000 in the US, and an aortic aneurysm rupture causes about 15,000 deaths annually. Aneurysms are usually asymptomatic, found during routine testing for other medical conditions or when the aneurysm has ruptured and resulted in more severe complications. Despite the implications of an aortic aneurysm, there are no non-surgical treatments, and aneurysms can only be treated with surgery after they have reached a certain size.
A highly specialized surgery for treating an aneurysm in the aorta near the heart (aortic root) is called a valve-sparing aortic root repair. This surgery was pioneered 28 years ago, and it revolutionized the management of aortic root aneurysms. Previously, a patient’s aortic root, including the aortic valve, was replaced with mechanical or bioprosthetic aortic valve sewn inside of a polyester tube. In a valve-sparing aortic root repair, only the diseased part of the aorta that is bulging and enlarged is replaced with an artificial Dacron tube, or graft. Importantly, the patient’s native aortic valve is spared (hence the name of the operation) and reconnected to the graft. Keeping the patient’s own aortic valve avoids the need for blood thinners, which would be required if a mechanical valve were to be used, and a patient’s native valve has far superior durability compared to bioprosthetic valves.
In the 28 years since the pioneering of this type of surgery, there have been modifications to the procedure, especially in the choice of graft used. Some surgeons have hypothesized that choosing grafts that mimic the pockets above the aortic valve (sinuses of Valsalva) and shape of the aortic root found in nature would be preferred, whereas others have demonstrated superior clinical outcomes using standard straight cylindrical grafts No consensus exists and the ideal graft choice is unknown. In their recently published manuscript in Circulation, a team of Stanford clinician-scientists, led by first author Michael Paulsen, MD, and senior author Y. Joseph Woo, MD, compared several graft options and technique modifications that can be used for the operation. The Stanford team used a novel and innovative 3D-printed heart simulator that can mimic flow (i.e., of blood), pressures, and other important factors of normal heart function. Porcine aortic roots were attached to the simulator, allowing the team to test the different graft configurations. This 3D left heart simulator is important for this research because it allows the researchers to control and reproduce the tests of the different grafts and techniques in a way that would not be possible in clinical studies. Use of the simulator allowed the team to do a complete test of the differences between each available graft. Surprisingly, they found that the original cylindrical graft without modifications or special shapes to mimic nature, termed a Straight Graft, appeared to act most like a patient’s own aortic root in terms of valve leaflet velocities and forces. This could mean less wear and result in better durability than other grafts. Importantly, the results were similar to what was seen in long-term clinical data. Overall, the researchers showed that the valve-sparing aortic root replacement operation is highly effective, regardless of conduit choice. Given the observed benefits of the Straight Graft, both the information from the simulated heart and clinical data, combined with a relatively lower cost and wide availability world-wide, makes that particular option preferred for this research team.