Thoracic Aortic Aneurysm: Reading the Enemy’s Playbook

The vast database of the Yale Center for Thoracic Aortic Disease--which includes information on 3000 patients with thoracic aortic aneurysm or dissection, with 9000 catalogued images and 9000 patient-years of follow-up--has, over the last decade, permitted multiple glimpses into the "playbook" of this virulent disease. Understanding the precise behavioral features of thoracic aortic aneurysm and dissection permits us more effectively to combat this disease. In this monograph, we will first review certain fundamentals--in terms of anatomy, nomenclature, imaging, diagnosis, medical, surgical, and stent treatment. After reviewing these fundamentals, we will proceed with a detailed exploration of lessons learned by peering into the operational playbook of thoracic aortic aneurysm and dissection. Among the glimpses afforded in the behavioral playbook of this disease are the following: 1 Thoracic aortic aneurysm, while lethal, is indolent. Mortality usually does not occur until after years of growth. 2 The aneurysmal ascending thoracic aorta grows slowly: about 0.1 cm per year (the descending aorta grows somewhat faster). 3 Over a patient's lifetime, "hinge points" at which the likelihood of rupture or dissection skyrockets are seen at 5.5 cm for the ascending and 6.5 cm for the descending aorta. Intervening at 5 cm diameter for the ascending and 6 cm for the descending prevents most adverse events. 4 Symptomatic aneurysms require resection regardless of size. 5 The yearly rate of rupture, dissection, or death is 14.1% for a patient with a thoracic aorta of 6 cm diameter. 6 The mechanical properties of the aorta deteriorate markedly at 6 cm diameter (distensibility falls, and wall stress rises)--a finding that "dovetails" perfectly with observations of the clinical behavior of the thoracic aorta. 7 Thoracic aortic aneurysm and dissection are largely inherited diseases, with a predominantly autosomal-dominant pattern. The specific genetics are being elucidated at the molecular level. 8 Matrix metalloproteinase overactivity participates in the destructive processes that degrade an aorta in individuals genetically preprogrammed to develop aneurysms. 9 Most dissections are brought on via presumed momentary hypertensive crises by severe exercise or emotion. We look forward to a future in which the aneurysm diathesis can be determined by a genetic test (RNA or DNA based), in which matrix metalloproteinases can be specifically antagonized by medications, in which exercise and emotion can be modulated in susceptible patients, and in which mechanical properties of the aorta (in addition to simple dimension) can be assessed serially to guide the timing of operation more precisely. Genetic-based therapies (eg, development of drugs on the basis of discovered molecular proteomics) will likely become possible to prevent susceptible patients from forming aneurysms over the long term.