64. Aortic Root Aneurysms- Indications and Guidelines

Davut Cekmecelioglu MD MSc, Rohun Bhagat MD, Lars Svensson MD PhD
Cleveland Clinic Foundation
November 30, 2024

Abbreviations & Definitions

AATS – American Association for Thoracic Surgery
ACC – American College of Cardiology
AHA – American Heart Association
ASI – Aortic size index
BAV – Bicuspid aortic valve
BSA – Body surface area
CSAH – Cross-sectional area-to-height ratio
CTA – Computed tomography angiography
EACTS – European Association for Cardiothoracic Surgery
HTAD – Heritable thoracic aortic disease
IRAD – International Registry of Acute Aortic Dissection
LDS – Loeys-Dietz syndrome
MAT – Multidisciplinary aortic team
STS – The Society of Thoracic Surgeons
TGFBR – Transforming growth factor-beta receptor
TITAN SvS trial – Treatment in Thoracic Aortic Aneurysm: Surgery Versus Surveillance

Indications & Guidelines for Management by Grade/Stage of Disease

Traditional indications for managing thoracic aortic aneurysms have focused on absolute aortic diameter thresholds, grounded in biomechanical principles that correlate vessel diameter with wall stress as these factors relate to the risk of rupture or dissection. In the most current 2022 ACC/AHA (endorsed by AATS)1 and 2024 EACTS/STS2 guidelines on aortic pathologies, aortic root as well as ascending aortic aneurysms have been discussed together. Both guidelines emphasize that surgical indications must be determined based on several factors, including the patient’s age, the relative size of the aorta and aortic root, the structure and function of the aortic valve, and the experience of the surgical team. Key recommendations from both guidelines and their differences with surgical thresholds on emerging metrics are presented in Table 1. It is noteworthy that the EACTS/STS guidelines note “Root Phenotype” and “Ascending Phenotype” which refer to dilation primarily in the aortic root or ascending aorta, respectively.

The 2022 ACC/AHA guidelines suggest that elective repair of the aortic root or replacement of the ascending aorta should be considered for aneurysms with a maximum aortic diameter of ≥5.5 cm. For patients with an aneurysm of the aortic root or ascending aorta that has a diameter <5.5 cm, surgery is indicated in confirmed cases of rapid growth of the aortic root or ascending aorta (≥0.5 cm in 1 year, ≥0.3 cm per year for 2 consecutive years in patients with sporadic aneurysms, or ≥0.3 cm in 1 year in patients with HTAD or BAV (Class I)), under surgeons and multidisciplinary teams who have expertise in managing such patients.

Notably, patients with asymptomatic aneurysms of the aortic root or ascending aorta that have a maximum diameter ≥5.0 cm may be considered for surgical intervention by experienced surgeons on a multidisciplinary aortic team (Class IIa). Similarly, surgery performed by experienced surgeons may be reasonable for patients with asymptomatic aneurysms of the aortic root or ascending aorta and a maximal cross-sectional aortic area/height ratio ≥10 cm2/m (Class IIa).

Patients with BAV are recommended to undergo elective repair of the aortic root or replacement of the ascending aorta if the diameter of these structures exceeds 5.0 cm (Class I). When patients with BAV and associated aortic root enlargement have indications for aortic valve surgery because of severe aortic stenosis or regurgitation, repairing the aortic root or replacing the ascending aorta is recommended if the diameter exceeds 4.5 cm (Class I).

The guidelines for thoracic aortic disease also include recommendations for surgical intervention in patients with other conditions associated with aortic root disease. Surgery is appropriate at lower size thresholds in patients with certain genetic syndromes (Class IIa), such as Marfan syndrome (4.5-5.0 cm) with a family history of aortic dissection, Loeys-Dietz syndrome (4.5 cm), or a confirmed TGFBR1 or TGFBR2 mutation (see Table 1). Specific Class IIa recommendations are also made for women with Marfan syndrome who are considering pregnancy. In such cases, elective aortic surgery is suggested when the diameter of the aorta exceeds 4.0 cm. Furthermore, patients with Marfan syndrome who have a maximum cross-sectional area of the ascending aorta or root to height ratio that exceeds 10 cm2/m are also appropriate for surgical intervention (Class IIa).

In patients with an aneurysm isolated to the ascending aorta who meet the criteria for surgery, aneurysm resection and replacement with an interposition graft should be performed (Class I). In patients undergoing aortic root replacement with an aortic valve that is not suitable for sparing or repair, a mechanical or biological valved conduit aortic root replacement is indicated (Class I). In patients undergoing aortic root replacement, valve-sparing aortic root replacement is reasonable if the aortic valve is suitable for sparing or repair and when performed by experienced surgeons (Class IIa). Lastly, in patients undergoing cardiac surgery for indications unrelated to the aortic valve who also have an aortic root or ascending aortic diameter ≥5.0 cm, ascending aortic replacement may be reasonable (Class IIb).

Summary Table 1

ACC/AHA Guidelines (2022) EACTS/STS Guidelines (2024)
Class I
Symptomatic aneurysms Surgery is indicated for symptomatic aneurysms of the ascending aorta
Maximum diameter Surgery is indicated for asymptomatic aneurysms with a maximum diameter ≥ 5.5 cm
Growth rate Surgery is indicated for aneurysms with a growth rate ≥ 0.3 cm/year over 2 consecutive years or ≥ 0.5 cm in 1 year Surgery is indicated for aneurysms with a growth rate > 0.3 cm/year
Class IIa
Symptomatic aneurysms Surgery should be considered for symptomatic aneurysms of the thoracic aorta
Maximum diameter Surgery is reasonable for asymptomatic aneurysms with a maximum diameter ≥5.0 cm by experienced surgeons Surgery is reasonable for ascending phenotype with a maximum diameter ≥ 5.2 cm
Concomitant cardiac surgery Concomitant replacement of the ascending aorta is reasonable during aortic valve surgery for ascending aortic diameter ≥ 4.5 cm Concomitant replacement of the ascending aorta is indicated in patients undergoing non-aortic valve cardiac surgery with an ascending aortic diameter ≥ 5.0 cm
Concomitant cardiac surgery Concomitant replacement of the aortic root is reasonable in patients undergoing aortic valve surgery with an aortic root diameter ≥ 4.5 cm
BAV Aortopathy
Class I
Maximum diameter Surgery is indicated for patients with BAV and a maximum aortic diameter ≥ 5.5 cm Surgery is indicated for BAV-related ‘root phenotype’ aortopathy with maximum diameter ≥ 5.0 cm
Class IIa
Maximum diameter Surgery is reasonable for patients with BAV and a maximum aortic diameter ≥ 5.0 cm and an additional risk factor (family history of dissection, rapid growth rate, aortic coarctation, ‘root phenotype’ aortopathy) Surgery is reasonable for patients with BAV-related ‘ascending phenotype’ aortopathy with maximum diameter ≥ 5.0 cm if certain risk factors are present (age <50, ascending length >11cm, rapid growth rate, aortic coarctation)
Concomitant cardiac surgery Concomitant replacement of the aortic root or ascending aorta is reasonable during aortic valve surgery by experienced surgeons if maximum aortic diameter ≥ 4.5 cm
Hereditary Connective Tissue Disorders
Class I
Marfan Syndrome Surgery is indicated for a maximum aortic diameter ≥ 5.0 cm or cross-sectional aortic area to height ratio >10 cm2/m Surgery is indicated for a maximum aortic diameter ≥ 5.0 cm
Loeys-Dietz Syndrome Surgery is indicated for a maximum aortic diameter ≥ 4.5 cm in patients with TGFBR1 genetic variant Surgery is indicated for a maximum aortic diameter ≥ 4.5 cm in patients with TGFBR1 or TGFBR2 genetic variants
Class IIa
Marfan Syndrome with high-risk features (family history of dissection, >0.3 cm/yr aortic growth, diffuse aortic root dilatation, vertebral artery tortuosity) Surgery is reasonable for a maximum aortic diameter ≥ 4.5 cm
Loeys-Dietz Syndrome with high-risk features (family history of dissection, >0.3 cm/yr aortic growth, severe extra-aortic syndromic features) Surgery is reasonable for a maximum aortic diameter ≥ 4.5 cm in patients with TGFBR2 genetic variant* *Class IIb: ≥ 4.0 cm in patients with TGFBR1 genetic variant) Surgery should be considered for a maximum aortic diameter ≥ 4.0 cm in patients with TGFBR2 genetic variant
Imaging and Measurement Techniques
Diameter measurement in ECG-gated CTA Inner to inner measurement technique*; ensures precision in following ACC/AHA threshold criteria *Previously measured from the outer wall of the aorta in 2010 ACC/AHA/AATS guidelines Outer to outer measurement technique; recommended for consistency with prior European practices
Aortic size index (aortic diameter [cm] / BSA [m²]) ASI ≥3.08 cm/m2 is a Class IIb indication for intervention on an asymptomatic aneurysm of the aortic root or ascending aorta by experienced surgeons
Aortic height index (aortic diameter [cm] / patient height [m]) AHI ≥3.21 cm/m is a Class IIb indication for intervention on an asymptomatic aneurysm of the aortic root or ascending aorta by experienced surgeons
Cross-sectional aortic area to height ratio (cm2/m) A threshold ratio of ≥10 cm²/m is used as an indicator of increased risk and is a Class IIa indication for intervention on an asymptomatic aneurysm of the aortic root or ascending aorta A threshold ratio of ≥13 cm²/m is used as an indicator of increased risk and intervention is suggested
Aortic length measurement – Measured with the centerline method from the aortic annular plane to the brachiocephalic trunk Aortic length >11 cm should be considered for surgical intervention (Class IIa)

Supporting Evidence for Current Indications & Guidelines

The STS database revealed that the observed-to-expected mortality ratio for proximal thoracic aortic procedures remained above 1 until centers achieved an annual volume exceeding 24 cases. Despite this, only 116 centers performed at least 20 cases per year. Out of 1,045 total centers, just 24 performed 50 cases annually, reporting an operative mortality rate of 2.1%.3

International Registry of Acute Aortic Dissection (IRAD)4 analysis showed that >50% of dissections occur before the size criterion of 5.5 cm – which is the main argument for earlier intervention. According to the database of the general population5 compared to a baseline aortic diameter ≤3.4 cm, a diameter of 4.0-4.4 cm was associated with an 89-fold increased risk of aortic dissection, while a diameter ≥4.5 cm corresponded to a staggering 6300-fold increase in risk. Additionally, many experienced surgeons opt to selectively operate on patients with aneurysms measuring 5.0-5.4 cm, provided the surgical risk is low and outcomes are excellent.6-9 In the absence of prospective randomized data, these successful outcomes have served as the foundation for the recommendations in the current ACC/AHA guidelines.

A meta-analysis,10 along with several observational studies,6,11,12 suggests that ascending aortic aneurysms in patients with a tri-leaflet aortic valve and no underlying genetic aortic disorders typically grow slower than previously estimated, often at rates below 0.5 mm per year. The same meta-analysis also identified a correlation between accelerated aneurysm growth and a higher risk of rupture.10

For patients undergoing aortic valve surgery with an accompanying ascending aortic aneurysm ≥4.5 cm, guidelines recommended simultaneous aortic replacement in those with BAV. Evidence supports the safety of performing concomitant aneurysm repair when undertaken by experienced surgeons.9,13-16

Proposed parameters for enhancing risk prediction include the ratio of aortic diameter to patient height or BSA17 as well as the ratio of aortic area to height.7,8 While these measures have shown promise in retrospective analyses, none have been validated through prospective studies. Notably, a cross-sectional aortic area-to-height ratio of ≥10 cm²/m has been associated with higher mortality in unoperated patients with root or ascending aortic aneurysms, regardless of whether they had a tricuspid or bicuspid aortic valve. 7,8

Recent evidence has indicated that aortic elongation is a significant risk factor for type A aortic dissection.18-20 The Yale group recently expanded on this by adding longitudinal survival data, which enhances risk stratification.21 In their cohort, the aortic diameter followed a normal distribution, averaging 4.8 ± 0.7 cm, with approximately 16% of patients presenting with diameters of 5.5 cm or more. A key finding was the 5-fold increase in aortic events in patients with an aortic length of 13 cm or greater compared to those with lengths under 9 cm, with Kaplan–Meier analysis indicating improved event-free survival in patients whose ascending aorta was less than 12 cm in length. They also informed an increasing risk of aortic dissection beyond a size of 5.0 cm.

Ongoing Trials & Recent Publications

In the most recent and largest natural history analysis, which was published after the ACC/AHA guidelines were introduced,22 the risk of dissection for ascending thoracic aortic aneurysms with diameters of 5.0-5.4 cm was only 0.4/100 person-years. As such, lower thresholds for aneurysm repair should perhaps only apply to experienced centers.

TITAN: SvS Trial: Treatment in Thoracic Aortic Aneurysm: Surgery versus Surveillance is the first prospective multicenter RCT23 of patients with ascending thoracic aortic aneurysms with diameters of 5.0-5.4 cm that will compare outcomes of early elective surgery versus medical surveillance, the results of which could provide further guidance.

Expert Commentary

A good starting point for understanding when to operate on patients with thoracic aortic aneurysms is the 2010 ACC/AHA/STS guideline first authored by Hiratzka and colleagues. Confusion was created by another ACC/AHA valve guideline first authored by Nishimura and colleagues, but subsequently, an ACC/AHA guideline modification was issued regarding the aortic size between 5.0-5.5 cm, namely that in the hands of expert surgeons, it was reasonable to operate on aortic aneurysms between 5.0-5.5 cm in asymptomatic patients. As indicated above, in patients with connective tissue disorders, the size threshold differs by syndrome, patient family history, and risk factors. Note also the value of using the cross-sectional area to height ratio as an indication for surgery, particularly in short or tall patients, since shorter patients are at greater risk for rupture or dissection for an equivalent age and diameter of 5.0 cm. The recent studies from Yale highlight the increasing risk for patients with an aortic diameter greater than 5.0 cm. Age, co-morbidities, and surgeon/team experience must also factor into the timing and recommendation of surgery.

Sources

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