Acute aortic syndromes (AAS) are potentially life-threatening conditions that require urgent and meticulously planned attention. The emergency management of these cases, particularly when involving the aortic arch, encompasses the entire spectrum of cardiovascular surgery, from traditional open surgery procedures to hybrid and endovascular interventions. To determine the most effective therapeutic strategy, surgeons must rely on a uniform nomenclature supported by radiological and anatomical parameters. This review article examines in detail the different anatomopathological types of AAS with aortic arch involvement, offers guidance on key preoperative studies, and provides essential guidance for addressing each case, considering the new classifications and available procedures.

Common nomenclature

It is absolutely essential before addressing each case to use uniform terminology to describe the extent of the disease and the clinical conditions. For this, several classifications are mentioned that we should be familiar with:

• Ishimaru Zones: Used to describe the extent of the disease. They are divided into a range from 0 to 11, where Zone 0 corresponds to the ascending aorta, including the brachiocephalic trunk. Zones 1 and 2 encompass the aortic arch, with Zone 1 covering the involvement of the left carotid, and Zone 2 including the left subclavian.
• Azizzadeh Classification: Used in cases of traumatic thoracic aortic lesions, it describes four levels of severity ranging from grade I with simple intimal tear to grade IV which equates to rupture.
• TEM Classification (Type, Entry, Malperfusion): Used to summarize the extent of the disease in any acute aortic dissection and commented on in a previous blog entry. It consists of three key concepts: T (type), according to the modified Stanford classification (A for ascending aorta, B for descending aorta, non-A non-B for involvement of the arch with/without descending aorta not affecting the ascending aorta). E (entry) according to the location of the entry door (0: undetermined, intramural hematoma; 1: ascending aorta, zone 0; 2: aortic arch, zones 1 and 2; 3: descending aorta, zones 3-11). Finally, M (malperfusion) (0: absent, 1: coronary, 2: cerebral, 3: spinal, iliac and/or limbs; +: with presence of clinical signs, -: without presence of clinical signs).
• GERAADA Score: A new scoring system to estimate the 30-day mortality in cases of acute type A aortic dissection. anatomopathological types of AAS

In addition to these classifications, the pathophysiology of the different types of AAS is addressed and explained, defining each one with its particularities and explaining the frequent transition from one to another, as occurs in the case of intramural hematomas (IMH) that can evolve towards dissections:

• Aortic Dissections
  It defines aortic dissection as a rupture of the intimal layer that forms a false lumen. A crucial detail is the retrograde component that every dissection has to a greater or lesser extent, which is decisive for the treatment strategy.
• Aortic Aneurysm
  Isolated aortic arch aneurysms are rare, but are common in the descending thoracic aorta. The focus is on this latter group, especially if a chronic aortic syndrome turns acute. Thoracic endovascular aortic repair (TEVAR) is the first treatment option in practically all cases of AAS of the descending aorta with arch involvement, but with the peculiarity that the proximal and distal anchoring zones necessary for the implantation of the endoprosthesis are almost never ideal in cases of aneurysms.
• Blunt Traumatic Aortic Injuries
  These are generally due to a sudden deceleration and usually occur in the transition from the aortic arch to the descending aorta. This group of patients tends to be younger and therefore the vessel dimensions are smaller, which has implications in the treatment strategy, many times it is necessary to resort to endoprostheses used in iliac extensions.
• IMH
  Currently, evidence indicates that the predominant underlying mechanism is a tear of the arterial intima layer, as opposed to the previously accepted theory of a rupture of the vasa vasorum. Identifying the precise location of this initial tear can be a challenging task and delay diagnosis by imaging tests. It is generally located in the proximal part of the descending aorta or in the distal aortic arch. It is important to note that when the IMH is located in the lesser curvature, it increases the risk of developing a retrograde type A dissection, since, unlike its location in the greater curvature, there are no supra-aortic trunks that serve as a physical barrier to progression. In any case, TEVAR proves to be effective and sufficient in most cases to close the primary intimal flap in these cases with retrograde involvement.
• Penetrating Aortic Ulcer (PAU)
  Unlike other syndromes, PAUs are usually associated with coronary artery disease and peripheral occlusive arteriopathy. The lesions may span several segments and often present an IMH component. All these features can pose challenges when considering the use of TEVAR. Moreover, the decision to intervene should be based more on morphology and progression than on diameter, unlike the case of aortic aneurysms.

Preoperative study and intraoperative considerations

The key to planning an adequate operation or intervention is imaging techniques. Therefore, an electrocardiographically synchronized computed tomography angiography (angioCT) of the entire aortic lumen, including the circle of Willis, with fine cuts is recommended. A preoperative echocardiogram and a carotid ultrasound complement the basic diagnostics.

Interventions on the distal aortic arch and/or proximal descending aorta can reduce blood flow to the spinal cord by compromising the network of collateral branches or occluding segmental arteries, leading to spinal ischemia. Continuous monitoring of cerebrospinal fluid (CSF) pressure and pressure-dependent CSF drainage can counteract this. If the short version of the frozen elephant trunk (frozen-elephant-trunk [FET]) of 100 mm is used, the resulting risk of symptomatic spinal cord injury is very low, therefore the authors do not recommend CSF drainage in this case. In the case of metachronous TEVAR extension or single TEVAR procedure, CSF drainage is used as standard, with excellent results. Contraindications for CSF drainage include blood coagulation disorders. In the event of ischemic spinal cord injury occurring postoperatively without the placement of CSF drainage, for the reasons mentioned, immediate placement of CSF drainage is recommended after optimizing coagulation. It is attempted to maintain cerebrospinal perfusion pressure high enough, and if CSF pressure is high (>20 mmHg) or is increasing, intermittent drainages of several milliliters of CSF should be performed. The goal would be to maintain the recommended CSF pressure between 8 and 10 mm Hg.

In open surgery, monitoring and protection of the organs are fundamental for a successful operation or intervention. Blood pressure should be measured at three sites, including bilateral radial arteries and unilateral femoral artery. These measurements are essential to anticipate poor perfusion and its resolution through individual treatment approaches, such as the FET technique. The brain and spinal cord are the most vulnerable organs, and stroke is one of the most disabling complications in surgery or interventions on the aortic arch, making the perfusion strategy a cornerstone for neuronal protection. The standard protocol recommended is unilateral anterograde cerebral perfusion (ACP) through the right axillary or subclavian artery and the carotid artery with the brachiocephalic trunk occluded during lower body hypothermic circulatory arrest (HCA). Bilateral perfusion, by additional cannulation of the left carotid artery, would be necessary in case of irregular collateralization through the Willis circle. If a dominant left vertebral artery is detected in the preoperative ATC, even trilateral ACP perfusion should be established through the left subclavian artery. Lower body HCA is usually set at 26 °C, which leaves a sufficient margin for arch replacement. Temperature should be measured centrally (usually by intravesical thermometer) and at the surface (usually by nasopharyngeal or tympanic thermometer). Infrared spectroscopy should be used in all cases, whether surgery is open, hybrid, or endovascular. In the case of a single TEVAR procedure or a simultaneous FET and stent-graft extension, spinal cord monitoring should be extended, when possible, by checking motor evoked potentials and somatosensory evoked potentials. Current research has reported that neurophysiological monitoring of motor and somatosensory evoked potentials is a useful tool for detecting early perioperative paraplegia in an anesthetized patient.

As for the type of arterial cannulation to establish extracorporeal circulation, we speak of central cannulation (ascending aorta and/or axillary/subclavian artery) and peripheral (femoral artery) cannulation. Evidence seems to indicate that the best results are obtained if possible with axillary cannulation as the first option, as recommended in the 2019 clinical guidelines of the European Society of Vascular Surgery.

Another problem during the FET procedure is placing the stent-graft in the true lumen. In most cases the stent-graft should be placed under visualization in the true lumen. In cases where the true lumen cannot be clearly defined or when the dissection begins distally from the aortic arch, it is advisable to use a guide under fluoroscopy to ensure that the stent-graft is implanted in the true lumen. Having a hybrid operating room is extremely valuable when performing arch surgery and for this group is almost indispensable in endovascular procedures, although, in our environment, the use of a radioscopic arch may be sufficient.

Treatment options

1. Treatment of pathologies involving Zones 0 to 1.
   The standard approach for any proximal thoracic aortic pathology involving zones 0 to 2 is open replacement, usually in HCA of the lower body and selective ACP for brain protection. The extent of the disease determines the extent of treatment. The FET technique is very frequently used in case of lack of a sufficient proximal anchoring zone and in case of previous replacement of the ascending aorta when the progression of the disease has led to the formation of aneurysms in zones 0 to 3 with various distal extensions. Endovascular techniques are feasible, but due to the limited number of devices available on the market (for example, Nexus® prostheses), endovascular repair of the aortic arch with branching in the acute setting remains exceptional.
2. Treatment of pathologies involving Zones 2 to 4.
   In the absence of an adequate proximal anchoring zone, bypass or transposition of the left subclavian artery to the left common carotid artery is the first choice option to create a sufficient proximal anchoring zone and to be able to perform a TEVAR with guarantees. New endovascular revascularization techniques of the left subclavian artery have emerged showing promising prospects for the future, although they are still in the research phase. If extensive proximalization is required, double transposition, whether autologous or alloplastic, is an elegant method to obtain an adequate anchoring zone, especially for atherosclerotic aneurysms. In type B and non-A non-B aortic dissections, more extensive proximalization of the anchoring zones beyond zone 2 should be avoided. This is due to the exponentially increased risk of type A retrograde aortic dissection, which coexists with an inherently diseased proximal thoracic aorta, regardless of diameter. Precisely, if carotid-subclavian bypass or transposition does not create a sufficient proximal anchoring zone, the FET technique is generally applied through open surgery to avoid this increased risk of retrograde aortic dissection associated with TEVAR.
3. Treatment of more distal pathologies.
   In the vast majority of acute aortic syndromes, TEVAR is the method of choice. In acute aortic dissection it is vitally important to avoid oversizing the distal component of the endoprosthesis, and it is recommended that these have a conical shape to prevent the formation of a new entry induced by the endoprosthesis at the distal level. In addition, the importance of CSF drainage is emphasized, a standard tool that the article’s authors recommend in all cases of TEVAR.

COMMENTARY:

In summary, this review is presented as essential reading for cardiac surgeons, especially those of us facing the challenges of AAS, with a particular focus on those involving the aortic arch. Understanding the pathophysiology and origin of AAS, as well as their classification based on clinical and radiological criteria, is essential for effectively addressing them and ensuring optimal treatment in each case. In this article, all therapeutic options are addressed in a comprehensive and practical way, ranging from classic open surgery procedures to hybrid and endovascular interventions. Lastly, it is important to highlight the valuable contribution of a table that simplifies the process of choosing between hybrid/endovascular treatment and conventional surgery. This table is based on the presence of clinical and morphological factors, which facilitates decision-making in this complex pathology.

REFERENCE:

Walter T, Berger T, Kondov S, Gottardi R, Benk J, et al. Thoracic aortic emergencies involving the aortic arch: An integrated cardiovascular surgical treatment approach. Semin Vasc Surg. 2023 Jun;36(2):150-156. doi: 10.1053/j.semvascsurg.2023.04.016.