Stacey Chen and Deane E. Smith
This chapter is a revision and update of that included in the previous editions of the TSRA Review written by Joshua B. Goldberg (2nd edition) and Stephen H. McKellar (1st edition).
Background
Aneurysms of the aortic arch can occur anywhere along the aorta from the proximal origin of the innominate artery to the distal origin of the left subclavian artery. Isolated aortic arch aneurysms are rare; they are usually associated with either ascending or descending aortic pathology.
Pathophysiology
Aortic arch aneurysms occur as a result of medial degeneration, which weakens the aortic wall. Following the law of LaPlace: Tension = (Pressure x Radius) / (Wall Thickness), as wall thickness decreases, tension will subsequently increase. Likewise, the resultant enlarging radius further contributes to increasing tension, predisposing to aneurysmal formation with an increased risk of dissection or rupture. Medial degeneration occurs with normal aging; however, it is accelerated by long-standing hypertension and atherosclerosis, connective tissue disorders, inflammatory arteritis disorders, and infections. In patients with heritable connective tissue disorders and aortic arch aneurysms, the ascending aorta is usually also involved. These patients present at a younger age with accelerated aortic growth.
BAV is the most common congenital heart malformation and affects 1-2% of the population. No single gene has been identified in association with BAV; however, studies have demonstrated that there is a familial genetic component, and it is an independent risk factor for aortic aneurysm formation and dissection. BAV is associated with fibrillin-1 deficiency in the aortic media resulting in matrix metalloproteinase activation, disrupting the extracellular matrix and predisposing to aortic (ascending and arch) aneurysm formation.
Clinical presentation
Similar to ascending or descending aortic aneurysms, aortic arch aneurysms are usually asymptomatic and appear as incidental findings on imaging. However, due to their anatomic location, aortic arch aneurysms do have the potential to displace or compress mediastinal structures and patients can present with shortness of breath (i.e. lung), hoarseness (i.e. left recurrent laryngeal nerve), stridor (i.e. trachea), dysphagia (i.e. esophagus), or superior vena cava (SVC) syndrome. Patients with rupture of an aortic arch aneurysm can present with acute upper chest and shoulder pain, massive hemoptysis, or sudden death.
Diagnosis
Diagnosis of aortic arch aneurysms is based on imaging. Aortic arch aneurysms can be detected on chest radiographs, most commonly identified as widening of the superior mediastinum. Other findings on chest radiograph may include displacement or compression of the trachea or esophagus and/or calcifications in the aortic arch. The most common diagnostic modality is computed tomography angiography (CTA). CTA not only provides information regarding aortic wall thickness, calcifications, the presence of luminal thrombus, and extent of the aneurysm, but three-dimensional reformation also provides excellent visualization of the aorta and its branched vessels allowing for accurate measurement of the aneurysm size. Transthoracic echocardiogram (TTE) is a helpful adjunctive imaging modality that allows for evaluation of the aortic root and ascending aorta that are often involved in aortic arch aneurysms. TTE also allows for evaluation of associated aortic regurgitation or impaired left ventricular function. The combination of CTA and echocardiogram are useful in both diagnosis and preoperative surgical planning of aortic arch aneurysms.
Treatment
Symptomatic patients should be promptly evaluated and taken for urgent/emergent surgical intervention as aortic arch aneurysms are life-threatening conditions and symptoms should raise concern for aortic rupture or dissection. Treatment of asymptomatic aortic arch aneurysms is dictated by the size and etiology of the aneurysm. Because isolated aortic arch aneurysms are rare and natural history studies of the aortic arch are lacking, guidelines for surgical intervention of specifically the aortic arch have not been established. Rather, the guidelines for aortic arch aneurysms follow those for surgical intervention of ascending aortic aneurysms:
- Marfan syndrome or EDS, vascular type: ≥5.0 cm
- Special considerations: <5.0 cm if family history of aortic dissection or 4.1–4.5 cm in a female patient contemplating pregnancy
- LDS: ≥4.0 cm
- Sporadic: ≥5.5 cm
- Growth of aneurysm at a rate of ≥0.5 cm/year
- Maximum area (cm2) / patient’s height (m) ratio >10
It is important to note that while guidelines recommend replacement of the ascending aorta once the diameter reaches 5.0 cm in patients with BAV, there is no recommendation for aortic arch replacement in these patients. In addition, there is currently no consensus for the management of moderate aortic arch aneurysm with concomitant cardiac surgery. Management for these patients should be individualized.
Surgical Technique
Surgical management of aortic arch aneurysms is complex and challenging. With the introduction of newer technologies and techniques, operative options continue to evolve and are dependent on the location of the aneurysm within the arch (i.e., proximal, transverse, and distal) and extent of involvement of either the ascending or descending thoracic aorta. An important consideration to surgical repair is cerebral protection with: (1) deep hypothermic circulatory arrest (DHCA) typically at a goal of 18–22oC, (2) DHCA in conjunction with selective antegrade cerebral perfusion (SACP), or (3) DHCA in conjunction with retrograde cerebral perfusion. There is no consensus on the superiority of one strategy over another and which strategy is selected is often surgeon and institution specific.
Open/Hybrid Repair
- Total arch replacement: Total arch replacement involves replacement of all three supra-aortic branches (i.e., innominate, left common carotid, and left subclavian arteries). This can be performed with a branch graft and reimplantation of the three supra-aortic branches using either an “island” patch or “peninsula” technique or using a multi-branch graft with individual anastomoses to the three supra-aortic branches.
- Elephant Trunk (ET) technique. ET is a 2-stage technique that is used for extensive aortic pathology. The first stage involves replacing the ascending aorta and aortic arch. A tube graft is intussuscepted into itself and placed into the lumen of the proximal descending thoracic aorta. The distal anastomosis is performed and the arch portion of the graft is withdrawn and the supra-aortic vessels are re-anastomosed. The first stage leaves a segment of the distal end of the graft freely floating in the descending aorta. The second stage involves descending thoracic or thoracoabdominal repair via a left posterolateral thoracotomy with a new tube graft, which is anastomosed to the previous graft from the first stage.
- Frozen Elephant Trunk (FET) technique. FET is a single-stage technique that is used for complex aortic pathology. Similar to the ET technique, after resection of the aortic arch, a conventional graft is sewn to the descending aorta. The stented part of the graft is then deployed into the descending thoracic aorta under direct visualization. The aortic graft and the stent graft are anastomosed via a circumferential suture, eliminating the risk of a proximal endoleak. The arch can then be reconstructed. There are multiple variations of arch reconstruction; depending on the graft used, there may be individual branches for reconstruction of the supra-aortic branches or a debranching technique can be used. An important potential complication of this technique is paralysis.
- Hybrid repair. combination of open and endovascular procedures with the core principle of creating adequate proximal and distal landing zones, which require debranching via anatomical or extra-anatomical revascularization.
Endovascular Repair
Total endovascular aortic arch repair is an area of ongoing research using fenestrated and branched endograft stents. Important complications are stroke and the need for early re-intervention. Currently, this technique should be limited to carefully selected patients with suitable anatomy and who are considered unfit for open surgery.
When selecting the most appropriate surgical approach for the management of aortic arch replacement, it is important to consider patient anatomy and etiology of the aneurysm. According to the 2018 consensus document for the treatment of thoracic aortic pathologies involving the aortic arch from the European Association for Cardio-Thoracic Surgery (EACTS) and the European Society for Vascular Surgery (ESVS), stent-graft deployment should not be performed for patients with a proximal and/or distal landing zone <25mm or a maximum diameter >38mm and Zones 0–2 TEVAR should be avoided in patients with connective tissue disease if the proximal landing zone involves native aortic tissue.
Suggested Readings
- Czerny M, Schmidli J, Adler S, et al. Current options and recommendations for the treatment of thoracic aortic pathologies involving thoracic aortic pathologies involving the aortic arch: an expert consensus document of the European Association for Cardio-Thoracic surgery (EACTS) and the European Society for Vascular Surgery (ESVS). Eur J Cardiothorac Surg. 2019;55(1):133-162.
- Rommens KL and Estrera AL. Contemporary management of aortic arch aneurysm. Semin Thorac Cardiovasc Surg. 2019;31(4):697-702.
