65. Distal Thoracic Aortic Aneurysms – Indications

Davut Cekmecelioglu MD MSc, Rohun Bhagat MD, Eric Roselli MD
Cleveland Clinic
December 30, 2024

Abbreviations & Definitions

AATS – American Association for Thoracic Surgery
ACC – American College of Cardiology
AHA – American Heart Association
B-SAFER – Branched stented anastomosis frozen elephant trunk repair
DTA – Descending thoracic aorta
EACTS – European Association for Cardiothoracic Surgery
FET – Frozen elephant trunk
HAR – Hybrid arch repair
HTAD – Heritable thoracic aortic disease
LSA – Left subclavian artery
PAU – Penetrating atherosclerotic ulcer
STS – Society of Thoracic Surgeons
TAAA – Thoracoabdominal aortic aneurysm
TAA – Thoracic aortic aneurysm
TEVAR – Thoracic endovascular aortic repair

Indications & Guidelines for Management

In this chapter, we describe indications and guidelines regarding the management of distal thoracic aortic aneurysms (TAA) (for management of more proximal aortic root and ascending aorta aneurysms, please review Chapter 63). Isolated aortic arch diseases in adults are rare and comprise less than 10% of aneurysms. Isolated surgical replacement of the aortic arch is also rare. The ascending and varying extent of the descending/thoracoabdominal aorta are usually involved in patients with aortic arch lesions. Therefore, surgical decisions when the arch is involved must address the proximal and distal aorta and cerebral protection strategies. Because of the proximity of the aortic arch to other thoracic structures, dilation may result in symptoms (such as dysphagia or hoarseness from recurrent laryngeal nerve palsy) before the diameter reaches a threshold typically considered for intervention.

According to the 2022 American College of Cardiology/American Heart Association (ACC/AHA) guidelines,1 elective repair is recommended for asymptomatic patients when the descending thoracic aorta (DTA) reaches or exceeds 5.5 cm, due to the increased risk of aortic-related events beyond 6 cm.3 In patients with an intact descending TAA and additional risk factors for rupture, intervention may be considered at diameters below 5.5 cm. Recognized risk factors for rupture include heritable thoracic aortic disease (HTAD), vascular Ehlers-Danlos syndrome, Loeys-Dietz syndrome, Marfan syndrome, aneurysm growth of at least 0.5 cm per year (more common in chronic dissection or with giant cell aortitis), symptomatic or saccular aneurysms, female sex, and infectious (mycotic) aneurysms.

Because it usually involves multiple segments of the aorta, approaches to the arch are often staged. Also, endovascular technology has been incorporated into the surgical armamentarium for arch repair in a variety of ways, including frozen elephant trunk (FET), hybrid arch repair (HAR – including elephant trunk with endovascular extension), and total endovascular repair. The 2022 ACC/AHA guidelines are more guarded with FET due to limited US data, and state that in patients undergoing open surgical repair of an aortic arch aneurysm, if the aneurysmal disease extends into the proximal DTA, an elephant trunk or FET procedure may be considered (Class IIB).1 The 2024 European Association for Cardiothoracic Surgery/Society of Thoracic Surgeons (EACTS/STS) guidelines,2 however, suggested that in patients with an intended one-stage aortic arch treatment, the FET technique should be considered (Class IIA).2

In elective thoracic endovascular aortic repair (TEVAR) involving zone 2 (distal arch), left subclavian artery (LSA) revascularization is recommended in both guidelines to reduce the risk of neurologic complications (Class I).1-2 The 2022 ACC/AHA (endorsed by the American Association for Thoracic Surgery [AATS])1 guidelines state that complete endovascular approaches may be considered by those with endovascular experience who have access to the appropriate devices (most of which are still investigational or require off-label use) without a specific level of recommendation.1

Despite no randomized controlled trials comparing TEVAR with open repair of descending TAA, the pivotal device trials⁴⁻⁶ have demonstrated reduced perioperative morbidity, increased clinical applicability, and lower follow-up aneurysm-related mortality in TEVAR compared with open surgical repair, so it has become the preferred treatment option for most patients who meet the anatomic criteria for the devices. Open repair of descending TAA follows a volume-outcomes relationship, where large institutional series have reported favorable outcomes,⁷⁻⁹ but these results have not been consistently reproducible in lower-volume centers.¹⁰ The decision between endovascular and open repair necessitates balancing anatomic suitability and vascular access considerations against the higher reintervention rates associated with TEVAR and the increased perioperative morbidity of open repair, which provides a more durable long-term solution. In some younger patients and those with HTAD, open repair may be preferred.

For patients with an intact degenerative thoracoabdominal aortic aneurysm (TAAA), repair is recommended at 6 cm or greater (Class I) per ACC/AHA;1 intervention may be reasonable at diameters below 5.5 cm when associated with higher rupture risk. Key high-risk features include rapid aneurysm growth of at least 0.5 cm per year, symptomatic aneurysm, significant morphological changes, saccular aneurysm, and penetrating atherosclerotic ulcer (PAU). It is noteworthy that the recommended threshold for TAAA is lower in the EACTS/STS guidelines (≥5.5 cm is Class I).2

Although significant advances have been made in endovascular therapies, open surgery remains the standard of care for patients with connective tissue disorders, providing excellent short- and long-term outcomes.¹¹,¹² The guidelines recognize the role of endovascular therapies in managing acutely life-threatening complications or as part of a multi-staged reconstruction in these patients, but it is primarily used as a bridge to definitive surgical repair. For TAAA patients in whom open repair is contraindicated, endovascular repair should be considered unless anatomical constraints preclude its feasibility, but there are very few commercially available devices. Many of these procedures are done either with a physical modified endograft or within a physical-sponsored investigational device exemption study. Other options for high-risk patients who do not meet endovascular inclusion criteria are a hybrid approach, but there is very little data available on these approaches. Both guidelines emphasize that patients with HTAD are suboptimal candidates for definitive endovascular repair. In symptomatic TAAA patients, diameter-based guidelines do not apply, and urgent evaluation for timely intervention is required.

Table 1. Summary Table

  ACC/AHA Guidelines (2022) EACTS/STS Guidelines (2024)
Aortic Arch
Class I
Symptomatic aneurysms Surgery is indicated for symptomatic aneurysms of the aortic arch irrespective of diameter Surgery is recommended for symptomatic aortic arch aneurysms, especially if presenting with pain or compression symptoms
Class IIA
Maximum diameter Surgery is reasonable for isolated aortic arch aneurysms with a diameter ≥5.5 cm in patients with low operative risk Surgery is reasonable for asymptomatic aneurysms with a diameter ≥5.5 cm, especially in patients with connective tissue disorders
Elephant Trunk Procedure If disease extends into descending aorta, an elephant trunk procedure may be considered (Class IIB) If disease extends distal to zone 2, elephant/frozen elephant trunk should be considered (Class IIA)
Descending Thoracic Aorta
Class I
Maximum diameter Repair is indicated for asymptomatic aneurysms with a maximum diameter ≥5.5 cm Surgery is recommended for asymptomatic aneurysms with a maximum diameter ≥5.5 cm
Endovascular vs open repair In patients without connective tissue disorders, endovascular repair is recommended over open surgery In patients eligible for TEVAR with planned left subclavian artery (LSA) coverage, LSA revascularization is recommended Endovascular repair is recommended as the first-choice therapy for acute complicated descending aortic syndromes In any TEVAR involving zone 2, LSA revascularization is recommended
Class IIA
Maximum diameter   Asymptomatic descending aortic aneurysms with high-risk features*, repair should be considered in diameters <5.5 cm** *Growth rate of ≥0.5 cm/yr, connective tissue disorders, saccular aneurysm, female sex, mycotic aneurysm

**This is Class IIB in 2022 ACC/AHA
Endovascular vs open repair Surgery is reasonable for patients who have anatomy unsuitable for endovascular repair, and who have a life expectancy of at least 10 years  
Thoracoabdominal Aorta (TAAA)
Class I
Maximum diameter Surgery is indicated for degenerative TAAA with a maximum diameter ≥6 cm Surgery is recommended for asymptomatic TAAA with a maximum diameter ≥5.5 cm
Endovascular vs open repair In patients with ruptured TAAA, or patients who have connective tissue disorders requiring intervention, open surgical repair is recommended  
Spinal cord, renal, and visceral organ protection -Cerebrospinal fluid drainage is recommended to reduce spinal cord ischemia during open or endovascular repair -Cold blood or crystalloid renal perfusion is recommended to protect against renal injury during open repair -In patients undergoing open or endovascular repair with end-organ ischemia or significant visceral/renal artery stenoses, additional revascularization is recommended  
Class IIA
Maximum diameter Surgery is reasonable for TAAA with a diameter: ≥5.5 cm by experienced surgeons <5.5 cm who have increased risk of rupture (symptomatic, rapid growth, saccular aneurysm, penetrating ulcers) Aortic repair should be considered for asymptomatic TAAA with high-risk features and diameter <5.5 cm
Penetrating Aortic Ulcer (PAU)
Class I
  In patients with PAUs with rupture, symptoms, or association with an ascending aorta intramural hematoma (IMH), urgent repair is recommended In patients with PAUs in the ascending aorta and the presence of IMH or rupture, urgent aortic repair is recommended
  PAU in the ascending aorta or proximal aortic arch (zones 0-1), open surgical repair is recommended.  
Class IIA
  In patients with PAUs of the aortic arch or descending thoracic aorta with associated IMH, urgent repair is reasonable In patients with high-risk* PAUs located in the distal arch or descending aorta, TEVAR should be considered if anatomically suitable *Pleural effusion, presence of IMH, large initial PAU depth (>1 cm) and diameter (>2 cm) or high growth size
  In patients with PAUs in the distal aortic arch (zones 2-3) or descending thoracic aorta, either open repair or endovascular repair is reasonable In patients with high-risk PAUs located in the distal arch or descending aorta unsuitable for TEVAR, open surgical repair should be considered after careful evaluation of operative risk
Imaging and Measurement Techniques
Measurement method Inner to inner vessel wall measurement technique; ensures precision in following ACC/AHA threshold criteria Outer to outer vessel wall measurement technique; recommended for consistency with prior European practices
Centerline method Recommended for accurate assessment, especially in complex anatomies Recommended for accurate assessment, particularly for tortuous vessels

Supporting Evidence for Current Indications & Guidelines

Open replacement of the aortic arch requires the use of cardiopulmonary bypass, hypothermia, and other adjuncts for neurologic and systemic protection. Various randomized and nonrandomized trials have compared different cannulation strategies (i.e., axillary, femoral, innominate),19-21 levels of hypothermia, and variations in cerebral perfusion (antegrade, select antegrade, retrograde),22-24 with no one technique dominating or being shown conclusively to be superior to another; nevertheless, there is overall mortality and stroke benefit of using any form of cerebral perfusion compared to isolated deep hypothermic circulatory arrest.23

The technique of placing an antegrade stent graft during circulatory arrest, now often referred to as a modified FET, has been shown to have low rates of in-hospital mortality or complications, suggesting a trend towards improved survival and facilitating future endovascular second-stage repair of the DTA.17

The 1-year results of the multicenter trial of patients who received the Vascutek Thoraflex Hybrid, FDA-approved in 2022, showed an 81% freedom from adverse events, with an 11% mortality and 5% stroke rate.18

Various hybrid and endovascular techniques have been developed to manage aneurysmal arch disease in high-risk patients. The Next-gen Fenestrated TEVAR trial demonstrated the feasibility of proximal landing zone coverage, with most endografts deployed in zones 0 or 1; however, a landing zone of <15 mm was associated with an increased risk of type I endoleak.¹³ Midterm follow-up data revealed a 5-year survival rate of 71% and an aneurysm-related event-free survival of 77%. The most common indication for reoperation was type Ia endoleak (5%).¹⁴ Nonrandomized comparisons between open and hybrid endovascular approaches have not demonstrated significant differences in outcomes.¹⁵⁻¹⁶

A meta-analysis of off-label branched endografts showed an overall early mortality rate of 6.1%, retrograde aortic dissection rate of 3.3%, and disabling stroke rate of 9.6%.25 Stroke remains the most frequent complication in the realm of endovascular arch repair using branched arch devices. Multiple industry-sponsored device trials are ongoing.

In a multicenter retrospective study using the MEDPAR (Medicare Provider Analysis and Review) data,26 the overall mortality rate after open surgical repair of descending TAA decreased in high-volume versus low-volume centers (11% versus 15%; p<0.01). Another report of Medicare data27 from patients with DTA-associated open repair (vs TEVAR) showed a greater risk of early postoperative mortality but a lower risk of late death. Despite the late advantage of open repair, the mean survival was superior for TEVAR.

The durability of open TAAA repair is well established.7 Direct comparisons between patients who undergo endovascular TAAA repair and open TAAA repair are challenging, given the current investigational status of endovascular techniques, the wide variety of approaches to endovascular repair, different patient populations, the variance of risk across the extents of TAAA repair, and the lack of prospective randomized studies of the two strategies. In a propensity-matched study of 278 pairs, Tong et al.28 found that open repair of DTA and TAAA had similar in-hospital mortality compared to endovascular repair (8.3% vs 7.6%, p=0.8), but resulted in significantly better 10-year survival (52% vs 33%, p<0.0001) and lower rates of aortic reintervention (4% vs 21%, p<0.0001). The 2018 meta-analysis by Rocha and colleagues29 examined 8 comparative studies of open and endovascular TAAA repair; endovascular repair outcomes were associated with lower rates of spinal cord deficit and renal failure necessitating hemodialysis. In the 2020 meta-analysis by the same group,30 the authors increased the number of studies analyzed (n=71, all with series of >10 patients); they found no difference in pooled rates of early mortality and permanent renal dialysis, a higher rate of overall spinal cord deficit after endovascular repair, and a trend toward a lower rate of stroke after endovascular repair.

Ongoing Trials/Recent Publications

B-SAFER: A prospective, single-center safety and feasibility study of the hybrid repair of thoracic aortic pathologies requiring repair of the aortic arch proximal to the origin of the innominate artery. Early analysis31 of 178 patients treated with the novel branched stented anastomosis frozen elephant trunk repair (B-SAFER) technique has been promising, with 5.6% operative mortality, 2.9% disabling stroke rate, and absence of paralysis.

In a prospective multicenter cohort study32 evaluating fenestrated-branched endovascular aortic repair for TAAAs (n=1109), early mortality was 2.7% and the incidence of early aortic rupture occurred in 0.4% of patients. Midterm follow-up showed a 5-year survival rate of 71% and an aneurysm-related event-free survival of 77%. The most common reason for reoperation was type Ia endoleak, occurring in 5% of patients.

A nonrandomized, prospective device feasibility trial evaluated the use of branched aortic endografts to address arch aneurysms involving the left subclavian artery.33 Thirty-one patients were enrolled, all of whom had successful implantation of the device in zone 2. Aneurysm type was fusiform in 12 patients and saccular in 19 patients (mean diameter of 5.48 cm). Mean follow-up was 25 months. At 1 month, there was 100% side branch patency, 97% freedom from endoleak (types I and III), and no death or permanent paraplegia. At 1 year, 5/31 patients expired with causes likely unrelated to the device. Additionally, at 1 year, 5/31 patients had an endoleak. One thoracic reintervention was required.

Expert Commentary

We are beginning to appreciate that most patients with thoracic aortic disease likely have a genetically triggered cause for their condition. As such, most patients with aneurysm, dissection, or both involving the more distal thoracic aorta will have multiple segments involved. A lifelong approach is paramount to achieving the best outcomes for these patients. This includes optimal medical management of hypertension, clinical genetics evaluation for most patients under the age of 70, and a plan for regularly scheduled maintenance imaging followed by staged repair when indicated based on the severity of degeneration as described above. Most patients with DTA disease are best taken care of by a multidisciplinary aortic team. When planning any single aortic procedure, it is often important to consider that another aortic operation may be required in that patient’s future. Fortunately, great advances have been made in the arenas of perfusion management during open repair and device development for endovascular repair, and the two approaches ought to be considered as complementary to one another as part of the comprehensive treatment strategy for patients with thoracic aortic disease.

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