Indications for aortic aneurysmectomy: too many variables and not enough equations?

Endografting for treatment of thoracic aortic pathology continues to gain popularity; in some countries, endovascular aortic repair numbers now exceed open surgery cases. The skills and understanding of open surgical teams are not always translated into endovascular interventions, which may be led by a cardiologist or vascular surgeon with little knowledge of thoracic pathology. The indications for intervention on the dilated aorta continue to be debated despite volumes of literature and multisocietal guidelines. The challenge of making a binary decision in the face of competing continuous risks depends on a best guess as to when the risk of the natural history of the disease exceeds that of the operation. Unfortunately, we have more information about average risk than actual (patient-specific) risk, and only for some of the variables determining those risks. Individual patient-specific operative risk can be calculated for some procedures by means of the Society of Thoracic Surgeons database, although surgeon-specific risk models are really required. On the other side of the balance, aortic dissection and rupture represent material failure of the aortic wall when tensile stress exceeds tensile strength. When framed in this way, it is not surprising that diameter is imprecise, as this is only one of the variables in the law of Laplace. The circumferential (hoop) stress is the product of radius and intraluminal pressure, divided by wall thickness. We also have no good measures of the material properties of the wall that determine strength, although a great deal of attention has been paid to the genetic markers for aortic wall abnormalities. Other factors, such as smoking or poorly controlled hypertension, likely should enter into our clinical assessment because they impact wall strength as well. For now, discussions with patients should be framed with all these elements in mind.