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Endovascular treatment of aortic dissections

Medical therapy is the current standard approach to patients presenting with Stanford type B or descending aortic dissections. This is because surgery has been associated with higher rates of morbidity and mortality, especially in the context of multiorgan failure. However, the early mortality rate in patients treated medically is still above 10% even in the 1990s. Moreover, up to 22% of patients fail medical therapy, such as this case with thoracoabdominal malperfusion state presented by Ito et al. [1,2]. Consequently, there is an increasing series of publications reporting the use of endovascular rescue for aortic dissections [3–6]. The complex high-risk nature of this case and the sophistication of this group of operators is easily overshadowed by the spectacular success of simple stenting. However, this case is not as straightforward as it may seem. Computed tomography scans, TEE, intravascular ultrasound (IVUS), and selective catheterization for relative luminal pressures were done to define the levels of aortic involvement, search for entry and reentry sites, and delineate the sources and adequacy of visceral blood supply as well as the extent of mural clots. The general goal of stenting is to seal the primary intimal tear and reduce blood flow into the false lumen. This is to achieve collapse (and eventual thrombosis) of the false lumen by eliminating pressurization and to prevent aneurysmal degeneration of the thinned outer aortic wall of the false lumen. Ironically, this can result in ischemia or infarction of end-organs supplied by the aortic branches: critical flow to aortic branch vessels may have originated from the false lumen that is now thrombosed or collapsed; or alteration of the relative pressures in the true versus false lumen can cause the septum or flap to abut against an arterial orifice. In the case described, a dissection plane, typically within the media of the aortic wall, splits the ostium of the right renal artery into an intimal segment attached to the dividing septum, or intimal flap, from its adventitial segment on the true aortic wall. This can conceptually be described as an unbuttoning of the ostia of arterial branches, with separation of its adventitial ostial button from its corresponding intimal ostial button. This opening on the intimal flap now constitutes a natural fenestration into the false lumen that can be both harmful and helpful. These can be a reentry site for continued pressurization of the false lumen. On the other hand, continued blood flow through these fenestrations might be critical to the perfusion of visceral organs and the spinal cord. Rarely, continued blood flow into the false lumen serves the function of preventing the propagation of clots that can occlude across the orifices of the arteries supplying visceral, spinal, or Adamkiewicz arteries. The patient was therefore wisely consented not only for aortic stenting, but also for an endovascular strategy that encompasses the possible need for fenestration or stenting of visceral arteries. Intraprocedurally, aortic diameter was measured using IVUS, which is acceptable in this circumstance since general anesthesia was not used. Otherwise, true aortic diameter could be underestimated. Furthermore, since aortic transseptal hemodynamics is altered with stent placement or fenestration, IVUS can monitor the behavior of the flap without contrast expenditure. The choice of an uncovered self-expanding stent turned out to be judicious, as well as avoiding the temptation to postdilate. Hemodynamic goals, primarily the restoration of visceral perfusion, were already attained. A consequence of failure of overambitious attempts at rebuttoning the intimal ostia to its corresponding adventitial segment (due to malalignment/malapposition/kinking) is end-organ ischemia. Also, tearing or additional trauma to the intimal flap or aortic wall by the rigid stent edges has been reported [7]. There is no question that we have a lot more to learn about patient selection and procedural strategy in these very sick and mostly elderly patient population. For instance, real-time monitoring to avoid paraplegia due to spinal cord ischemia might be accomplished with intraprocedural motor-evoked potentials combined with, say, test balloon occlusion of the false lumen [8]. A multidisciplinary approach to these difficult problems is mandatory [9]. As a former mentor of mine would say, for every case, we must plan for the worst, but expect the best.