From Leonardo to the Valsalva graft: the physics behind valve-sparing aortic root replacement

They say nature is the greatest artist, capable of the most perfect engineering and design. This saying is particularly fitting when describing the aortic root, whose complex structure has fascinated scientists since the times of Leonardo da Vinci and has proven to be fundamental for the correct function of the aortic valve. Since their introduction in the 1990s, valve-sparing aortic root replacement techniques have become increasingly popular, especially in young patients, since they eliminate the need for valve replacement requiring anticoagulant therapy. They proved to be safe and durable, with a reported freedom from reoperation of 89.6% at 10 years [1]. The introduction of the Valsalva graft (Terumo Aortic Renfrewshire, UK) in 2000 was another innovation. Its pre-fashioned sinuses allow a closer imitation of the aortic root’s natural structure and it proved to offer satisfying results [2]. The study by Di Leonardo et al. [3] focuses on analysing the hydrodynamic performance of different valve-sparing techniques in an ex vivo model. The group used a Medtronic Freestyle graft as a simulation of a native aortic root and then proceeded to alter it to simulate a Yacoub remodelling procedure, a David reimplantation on a straight graft and a David reimplantation performed using a Valsalva graft—which they referred to as De Paulis reimplantation. The models were then tested in a pulse simulator. The systolic performance was evaluated through parameters such as the transvalvular pressure difference and the effective orifice area, while the diastolic performance was evaluated through the closing regurgitant volume. The efficiency of the systo-diastolic cycle was evaluated through the left ventricular energy loss. Lastly, the orifice area and the morphology of the cusps’ movement were also studied by high frame rate videos. All the parameters analysed showed that the De Paulis reimplantation had the closest performance and valve dynamics to the native valve. The role of the sinuses of Valsalva proved to be crucial in allowing a wide expansion of the aortic cusps during systole, which maximizes the effective orifice area, minimizes the transvalvular pressure difference and energy loss. Consequently, the De Paulis showed the highest efficiency, with an energy loss of 38 mJ, close to the 26 mJ of the healthy native valve, compared to about 70 mJ of the David and Yacoub models. This concept had been introduced before the birth of the Valsalva Graft, with Grande-Allen et al. [4] demonstrating the superiority of techniques that allow the potential for sinus space formation. The study in question invites the reader to think about how complex and fascinating the functioning of the aortic root and aortic valve is. Much like for the mitral valve, one should not talk about aortic valve, but the aortic valvar complex. Advanced aortic root surgery such as valve-sparing techniques requires a deep understanding of the hydrodynamic laws that determine how the valve will function both in the short and long terms. However, it is impossible to accurately recreate the complex conditions under which the valve operates in nature in a lab setting. Unfortunately, the study by Di Leonardo et al. had to settle for a close approximation. They performed the valve-sparing techniques one after the other on the same Freestyle conduits in the same order (with a total of 9 procedures on 3 test valves). They first performed a David reimplantation, then they altered it to create a Yacoub remodelling and, lastly, they created the De Paulis. Since the process was repeated 3 times on 3 different conduits, this poses the problem of a possible bias, since one cannot guarantee that the valve was properly spared all 3 times. Though this kind of studies can help us better understand how to get the best possible result, what counts the most in surgery is the clinical outcomes. With this in mind, the ex vivo results seem to agree with the long-term follow-up published by De Paulis et al. [5], in which a 91% 10-year freedom from reoperation was reported. This goes to show once more how nature really is the best architect. Time and time again, the conformation that most closely resembles the native aortic root proves to be the best option. A very interesting future development would be to closely examine the in vivo hydrodynamics of the aortic root through 4D flow magnetic resonance imaging on large cohorts of patients, to fill the gap between the numbers and equations and the real-world surgical results.