Many physicians have never received adequate instruction on diseases of the aorta. This area was certainly ignored during my training, but with the advent of echocardiography and CT scanning, we’ve since learned a great deal.
Thoracic aortic disease is usually asymptomatic until a life-threatening event occurs. Aortic aneurysms are potentially a time bomb waiting to happen. There’s much individual variation, and the question of how to adjust for body size is still open to some debate, but typically, the thoracic aorta has a maximum dimension of 3.7 cm at the root. By the time we reach the ascending aorta, the maximum diameter should be less than 3.5 cm, and 3 cm at the arch. At the descending aorta, the maximum normal diameter is less than 2.5 cm.
Of ruptured aorta, 60% will originate from the ascending aorta, 10% from the arch, and 40% in the descending aorta (a few occupy more than one zone).
When to operate
One key thing we’ve learned is that in Marfan syndrome, which is a congenital abnormality, ruptures can occur at a much lower diameter than in other patients. Current recommendations are to operate if the ascending aorta is greater than 4.5 cm in patients with Marfan’s. You should also consider surgery with a diameter above 5.0 cm in patients with a bicuspid valve, who may also experience rupture at a lower diameter. All patients should consider surgery when the aortic diameter is greater than 6 cm. Elective surgery of asymptomatic patients can be far safer than reacting to acute complications.
Following the discovery of an aneurysm, one can use ultrasonic echocardiography, CT scanning or MR images to follow these patients. The simplest method, if possible, is to use echocardiography, which should be repeated after 6 to 12 months to look for expansion in an asymptomatic patient, and thereafter one test yearly. Familiar forms of thoracic aneurysm have now been identified. First-degree relatives of patients should be imaged, and repeat screening is recommended every two years. Risk is elevated during pregnancy. There are certainly other medical conditions that need to be looked for and these include: coarctation of the aorta and vasculopathies including syphilis, a condition which is extremely rare in this day and age, but which was once the most common cause of aortic aneurysms.
The cornerstone of medical management is blood pressure reduction. Beta-blockers may be combined with ARBs or ACE inhibitors, aiming for the lowest BP the patient can tolerate. Other atherosclerosis risk-reduction methods are appropriate, such as smoking cessation and lipid control.
In summary, we’ve taken the aorta for granted in most patients. But aortic dissection and rupture can often be preventable. If an echo turns up aortic enlargement in an asymptomatic patient, there’s plenty we can and should do.