Importance of Aortic Morphology in Planning Aortic Interventions

Traditionally, preoperative assessment for open aortic interventions has focused on patient factors, such as cardiopulmonary status and the presence of comorbidities. These are the principal determinants of success because morbidity and mortality from such procedures is due to factors related to the incision, duration and location of the cross clamp, and the postoperative inflammatory response. These factors have been shown consistently to predict the outcome of open surgical repair of abdominal aortic aneurysms (AAA) and are incorporated in preoperative risk prediction systems, such as the Glasgow Aneurysm Score and the POSSUM predictor equation. Endovascular treatment of aortic pathology does not present such a physiological insult, as incisions are smaller and no cross-clamping is required. The postoperative inflammatory response is much less marked, and some patients can return directly to general wards after their procedure without the need for stabilization in a high-dependency environment. Perioperative and short-term mortality is reduced in endovascular repair, but increased emphasis is placed on mediumto long-term outcomes due to device failure of different types and subsequent re-intervention. The general consensus that anatomy of the diseased aorta and its branches is more important than physiological status in predicting the success of endovascular intervention has been illustrated by work showing that physiology-based risk prediction systems are not valid in endovascular aneurysm repair (EVAR) and probably not in thoracic endovascular aortic repair (TEVAR). Several classifications systems for the anatomy of the diseased aorta have been proposed. However, many existing methods are surprisingly nebulous. Dividing pathology into thoracic, thoracoabdominal, and abdominal is a useful start, as there are certain challenges unique to interventions in each area. Sub-classification into groups, particularly in relation to the visceral aortic branches, has proven difficult. For example, the meaning of ‘‘juxtarenal’’ in terms of an AAA simply means that a crossclamp cannot be applied below the renal arteries. This is not a particularly objective definition. The traditional Crawford type classificationofdescending thoracicaneurysms isnot necessarily applicable to endovascular repair, but the length of aortic coverage is important from the perspective of postoperative paraplegia. It is known that certain anatomical features predispose to the risk of adverse outcome. At present, there is no universally accepted classification system for the anatomyof the aorta with regards to location of interventions.