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Thoracic aortic aneurysm: How to counsel, when to refer

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Release date: June 1, 2018
Expiration date: May 31, 2019
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ABSTRACT

Thoracic aortic aneurysm (TAA) is usually clinically silent and progresses slowly until a tipping point is reached, after which the aortic diameter can expand more rapidly and the condition can potentially end in aortic dissection or rupture. Causes include bicuspid aortic valve and genetic syndromes (Marfan, Loeys-Dietz, and Ehlers-Danlos syndromes) and familial associations, but many cases are idiopathic. Clinicians should therefore be alert for clues on chest imaging, and consider screening in first-degree relatives of patients known to have aortic disease. Early referral to a cardiologist specializing in aortic disease is key.

KEY POINTS

  • Screening and referral depend on clinical context. A size-based model to determine screening, referral, follow-up, and management serves most cases but should be modified in the context of connective tissue disease or family history of aneurysm and dissection.
  • Medical management involves strict blood pressure and heart rate control with beta-blockers and angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers. Activity modifications should be tailored to the individual, although extreme isometric exercises and heavy lifting should be discouraged.
  • Patients with TAA should be followed up annually, unless the patient is presenting for initial evaluation or significant changes are seen with dedicated imaging.


 

References

Thoracic aortic aneurysm (TAA) needs to be detected, monitored, and managed in a timely manner to prevent a serious consequence such as acute dissection or rupture. But only about 5% of patients experience symptoms before an acute event occurs, and for the other 95% the first “symptom” is often death. 1 Most cases are detected either incidentally with echocardiography, computed tomography (CT), or magnetic resonance imaging (MRI) during workup for another condition. Patients may also be diagnosed during workup of a murmur or after a family member is found to have an aneurysm. Therefore, its true incidence is difficult to determine. 2

With these facts in mind, how would you manage the following 2 cases?

Case 1: Bicuspid aortic valve, ascending aortic aneurysm

A 45-year-old man with stage 1 hypertension presents for evaluation of a bicuspid aortic valve and ascending aortic aneurysm. He has several first-degree relatives with similar conditions, and his brother recently underwent elective aortic repair. At the urging of his primary care physician, he underwent screening echocardiography, which demonstrated a “dilated root and ascending aorta” 4.6 cm in diameter. He presents today to discuss management options and how the aneurysm could affect his everyday life.

Case 2: Marfan syndrome in a young woman

A 24-year-old woman with Marfan syndrome diagnosed in adolescence presents for annual follow-up. She has many family members with the same condition, and several have undergone prophylactic aortic root repair. Her aortic root has been monitored annually for progression of dilation, and today it is 4.6 cm in diameter, a 3-mm increase from the last measurement. She has grade 2+ aortic insufficiency (on a scale of 1+ to 4+) based on echocardiography, but she has no symptoms. She is curious about what size her aortic root will need to reach for surgery to be considered.

LIKELY UNDERDETECTED

TAA is being detected more often than in the past thanks to better detection methods and heightened awareness among physicians and patients. While an incidence rate of 10.4 per 100,000 patient-years is often cited, 3 this figure likely underestimates the true incidence of this clinically silent condition. The most robust data come from studies based on in-hospital diagnostic codes coupled with data from autopsies for out-of-hospital deaths.

Olsson et al, 4 in a 2016 study in Sweden, found the incidence of TAA and aortic dissection to be 16.3 per 100,000 per year for men and 9.1 per 100,000 per year for women.

Clouse et al 5 reported the incidence of thoracic aortic dissection as 3.5 per 100,000 patient-years, and the same figure for thoracic aortic rupture.

Aneurysmal disease accounts for 52,000 deaths per year in the United States, making it the 19th most common cause of death. 6 These figures are likely lower than the true mortality rate for this condition, given that aortic dissection is often mistaken for acute myocardial infarction or other acute event if an autopsy is not done to confirm the cause of death. 7

RISK FACTORS FOR THORACIC AORTIC ANEURYSM

Risk factors for TAA include genetic conditions that lead to aortic medial weakness or destruction such as Loeys-Dietz syndrome and Marfan syndrome. 2 In addition, family history is important even in the absence of known genetic mutations. Other risk factors include conditions that increase aortic wall stress, such as hypertension, cocaine abuse, extreme weightlifting, trauma, and aortic coarctation. 2

DIAMETER INCREASES WITH AGE, BODY SURFACE AREA

Figure 1.
Figure 1.
The thoracic aorta consists of the root and the ascending, arch, and descending segments ( Figure 1 ); the abdominal aorta consists of the suprarenal and infrarenal segments. 8,9 These divisions are useful, as aneurysmal disease can be confined to specific locations along the length of the vessel, and the location can affect the clinical presentation and management decisions and lend insight into the pathogenesis.

Normal dimensions for the aortic segments differ depending on age, sex, and body surface area. 8,44,45 The size of the aortic root may also vary depending on how it is measured, due to the root’s trefoil shape. Measured sinus to sinus, the root is larger than when measured sinus to commissure on CT angiography or cardiac MRI. It is also larger when measured leading edge to leading edge than inner edge to inner edge on echocardiography. 10

TAA is defined as an aortic diameter at least 50% greater than the upper limit of normal. 8

Aortic diameters: Upper limits of normal
The aorta increases in diameter by 0.7 to 1.9 mm per year if not dilated, and larger-diameter aortas grow faster. 11 In addition, men

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