It’s a well-known fact that aortic aneurysms are ticking time bombs. Yet the ascending aorta, where 60% of ruptured aneurysms originate, has received appallingly little attention in medical education, resulting in inadequate training of many physicians. The area was certainly ignored during my studies.
Since the advent of echocardiography and CT scanning, however, we have learned a great deal. Coming out of the heart, the thoracic aorta has a maximum dimension of 4 cm at the root. By the time it becomes the ascending aorta, the diameter should be < 3.5-3.8 cm, and 3 cm at the arch. The descending aorta’s diameter shouldn’t exceed 2.5 cm.
There’s much individual variation, and the question of how to adjust for body size is still open to debate. The meeting of the American Society of Echocardiography in June this year had nothing new to offer in this respect, but there are multiple tables in the literature that can be helpful (e.g. Roman MJ et al. Am J Cardiol 1989;64:507-12). In my opinion, the numbers above are reasonable starting points, and you need to adjust based on the size of your patient.
Cause for concern
Current recommendations — with some minimal variations in the available literature — advise to consider surgery if the ascending aorta has a diameter > 5-6 cm. We know that in people with Marfan’s syndrome, the aorta has a tendency to rupture at a much lower diameter, though. If you have patients with this congenital abnormality, start thinking about surgery at around 5 cm. Individuals with a bicuspid valve may also experience rupture at a lower diameter. Again, use your clinical judgement and also consider surgical risks before making a call.
About 1-2% of the general population has a bicuspid heart valve, and it’s estimated that 50% of these people will develop either aortic stenosis or aortic insufficiency. They should be followed long-term. The simplest method — if the patient is asymptomatic — is to start with echocardiography, which should be repeated 6 months later to look for expansion of an aneurysm. Afterwards, one test yearly is reasonable in most cases. CT scan and MRI are often done initially to confirm your echocardiography findings. It’s certainly worthwhile to involve a surgical colleague when following these patients.
The major cause of aortic rupture is cystic medial necrosis. Familial forms of thoracic aneurysm have been identified, and there are a number of other medical conditions that need to be considered when someone presents with a dilated aorta. For instance, look for aortic coarctation as well as vasculopathies including syphilis. While the latter condition is rare in this day and age, it was, at one time, the most common cause of aneurysms of the aorta.
We tend to take the aorta’s ability to withstand the test of time for granted, but it’s worthwhile to keep an eye on it. Scrutiny and appropriate interventions can often prevent aortic dissection and rupture. If a patient is found to have an aortic enlargement, strict control of blood pressure (BP) and surveillance should be the norm. While we lack official data, getting the BP down to < 120/80 mm Hg is my personal target.
Gregory P. Curnew, MD, FRCPC is Associate Professor at McMaster University in Hamilton, ON, and Director of the Coronary Care Unit at Hamilton General Hospital.