New insights into modelling of pre-dissection aortic diameter

Sometimes new ideas crop up in quite unspectacular moments. For example, while preparing the mammary artery. One uncontrolled movement may lead to a local dissection thereof. Those of us who have experienced it, and all the others who do not admit they have ever seen it in practice but have only heard about it, have also probably noticed that the dissected segment’s diameter is larger than the adjacent non-dissected mammary artery’s. In other words, an acute artery dissection obviously triggers an immediate artery-diameter increase—an observation that leads us to question whether the same process happens in large vessels such as the human aorta. We collected data on 63 patients with acute type A aortic dissection who for whatever reason had undergone CT before their dissection onset [1]. After comparing these CTs obtained before and shortly after dissection onset, we observed that the mean ascending aortic diameter increased by +32% due to dissection. In a similar study on aortic dissection type B, the mean descending aortic diameter increase measured +23% [2]. This information is undoubtably worth knowing whenever thoracic endovascular aortic repair or frozen elephant trunk operations are being considered in the context of acute aortic dissection. In almost all aortic dissection patients, the distal landing zone is a dissected aorta. The dissected flap is a non-elastic media layer. To reduce the risk of a dissection-flap rupture in the distal landing zone, it is important to avoid oversizing the stent graft—instead, a stent graft diameter resembling the pre-dissection aortic diameter’s should be chosen.

Little research has been done on the change in aortic geometry caused by acute aortic dissection since nearly all acute aortic dissection patients have undergone CT after, not before their dissection. The idea about how to solve this dilemma came from Jung and Park [3]. They decided to verify the +23% descending aortic diameter increase through its acute dissection, and true lumen maximum diameter as tools with which to predict pre-dissection aortic diameter. Jung and Park included in their study patients with acute type A aortic dissection and complete thoracic descending aortic remodelling after surgical repair. They assumed that the completely remodelled aorta would recover its pre-dissection size. Frozen elephant trunk patients were excluded from their study. Jung and Park discovered that maximum true lumen diameter and the effect of the +23% diameter increase the dissection causes frequently reveal a minimum 2 mm discrepancy from the post-remodelling aortic diameter (in 37% and 48% patients, respectively). What is interesting is that in patients whose circumferential dissection is extensive, it was more accurate to calculate the pre-dissection aortic diameter according to a +23% increase than by relying on the maximum true lumen diameter to model the pre-dissection aortic diameter. They made exactly the opposite observation in patients with less circumferential dissection. Jung and Park concluded that most reliable means of predict the pre-dissection aortic diameter is an evaluation relying on the extent of circumferential dissection together with the two aforementioned parameters.

If you cannot play the piano but want to throw a party with piano music, it is better to hire a pianist than to start learning to play the piano and play the music yourself. I am very much impressed reading this paper! The authors have clearly found an alternative way to analyse and model the pre-dissection aortic diameter according to the data that are actually available and without having to seek those patients who happened to have undergone CT before their dissection onset. Their method allows them to critically evaluate the methods now in use. However, I hear one questionable note, namely their assumption that a dissected aorta’s complete remodelling leads to the total restoration of aortic diameter. Perhaps Jung and Park are not out of tune, and their assumption is correct. Does the aorta return to its initial diameter after complete remodelling? There is not much evidence on this. That might be the title of the next outstanding report coming from South Korea.

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