Treatment of aortic syndromes with arch involvement

Acute and chronic thoracic aortic syndromes involving the arch are life-threatening conditions that require urgent and carefully planned treatment. Emergency care of acute thoracic aortic entities encompasses the entire spectrum of cardiovascular surgery, ranging from traditional open surgery to hybrid procedures and endovascular interventions. The decision as to which therapeutic procedure is optimal should be made by a specialized aortic team and performed promptly.

The treatment of acute and chronic aortic syndromes involving the aortic arch are a challenge for the entire aortic team of any hospital. Acute aortic syndromes are potentially life-threatening conditions with a significant mortality rate if left untreated [1]. Early diagnosis and targeted therapy are critical for successful treatment.

Preoperative considerations of perioperative planning, therapeutic goals, organ protection, and individualized treatment strategies with the entire portfolio of cardiovascular surgery are the basis of successful care. Preoperative diagnostics have improved significantly over the past decade. Several treatment options have been developed and improved. Therapeutic options are manifold, ranging from conventional open surgery with use of the heart-lung machine, hypothermic lower body circulatory arrest (HCA), and selective antegrade cerebral perfusion (SACP), to hybrid techniques combining open and endovascular approaches, to fully endovascular treatment options.

The purpose of this manuscript is to provide an overview of the current knowledge on the pathophysiology of acute aortic syndromes involving the aortic arch, to summarize the necessary preoperative diagnostic workup despite the urgency of the scenario, and to discuss the current range of treatment options and their outcomes for the management of acute aortic syndromes involving the aortic arch.

Pathologies of the aortic arch should be treated in a specialized aortic center by a specialized interdisciplinary aortic team.

Terminology

In order to speak a common language, harmonization of terminology is essential. In describing the extent of disease, we refer to the Ishimaru zones of the aorta according to current definitions (Fig. 1) [2]. In the case of traumatic aortic injury, we use the Azizzadeh classification, which describes four degrees of severity (grades I-IV), ranging from an intimal tear as grade 1, to an intramural hematoma (grade 2), to a pseudoaneurysm (grade 3), to grade 4, which represents a rupture [3]. In any acute aortic dissection, TEM classification is applied to summarize the extent of the disease, evaluate the clinical condition, and determine an initial treatment strategy [4,5]. This classification adds the term “non-A non-B aortic dissection” (involving the aortic arch and descending aorta but not the ascending aorta) to the established modified Stanford classification. T stands for the type of dissection (A, B or non-A non-B), E describes the localization of the primary entry. E0 describes a clinical scenario in which no primary entry is visible. When localized in the ascending aorta, it is classified as E1, in the aortic arch as E2, and in the descending aorta as E3. Accordingly, type B has only subgroups E0 and E3, and in non-A non-B dissections, subgroups E0, E2, and E3 are possible. M describes the presence or absence of malperfusion. M0 indicates no clinical or radiographic evidence of malperfusion; M1 represents coronary malperfusion; M2 represents supraaortic malperfusion; and M3 represents spinal, visceral, renal, and lower extremity malperfusion. Note that clinical symptoms are additionally described with a + ( Fig. 2) [4].

In the case of acute type A aortic dissection, the recently introduced GERAADA score is the first preoperative risk stratification score to provide an estimate of 30-day mortality [6]. The calculation can be accessed via the homepage of the German Society for Thoracic and Cardiovascular Surgery (DGTHG) at www.dgthg.de/de/GERAADA_Score. Further studies have already confirmed the validity of the score [7,8].

The basis of every treatment strategy is a common language for anatomical/radiological findings, as well as their clinic.

Pathologies

When describing the pathophysiology of acute aortic syndromes, it should be noted that there may be smooth transitions from one entity to another, such as intramural hematoma to dissection. The most common acute and chronic aortic pathologies – aortic dissection, aortic aneurysm, (traumatic) aortic rupture, intramural hematoma (IMH), and penetrating aortic ulcer (PAU) – will be briefly reviewed below.

Aortic dissection: the underlying definition of a dissection is intima-media rupture with the formation of a perfused false lumen. The retrograde dissection component, which is more or less pronounced in each dissection, should be emphasized. It is highly relevant for the right treatment strategy and should have a decisive influence on it [2,9]. Involvement of the aortic arch is common and the retrograde component very often determines the extent of the treatment strategy in terms of the presence, absence, or need to create a proximal landing zone. According to recent recommendations, this should be at least 2.5 cm long, preferably healthy tissue [2]. If a bypass, of the left subclavian artery (LSA) to the left common carotid artery (LCCA), or a transposition of it does not create an adequate proximal landing zone, the in Figure 3 shown total aortic arch replacement was performed using frozen elephant trunk technique (FET), since the extension of the proximal landing zone by a more extended supraaortic transposition is associated with an increased risk of retrograde type A aortic dissection and this should be avoided [10,11].

Aortic aneurysm: Isolated aortic arch aneurysms are rare, but thoracic descending aortic aneurysms involving the distal aortic arch are more common. Therefore, the latter group is usually the focus if a chronic aortic syndrome becomes acute. Thoracic endovascular aortic repair (TEVAR) is the first-line treatment strategy for almost all acute thoracic aortic sysndromas involving the distal arch. Again, the problem of healthy landing zone is of utmost importance, with monosegmental aneurysm with adequate proximal and distal landing zone being the exception and not the rule [12,13].

Traumatic aortic rupture: a very specific entity is traumatic aortic rupture, which is usually due to abrupt, usually horizontal, deceleration. This mechanism is often associated with a lesion at the junction of the distal aortic arch and the descending aorta. Exactly at the point where the connective tissue suspension of the arch ceases and the descending aorta is fixed only by the parietal pleura. Because this cohort of patients is typically much younger than other patients with acute thoracic aortic syndrome, the arch configuration is different, with a type III arch being observed much more frequently than a type I or type II arch. In addition, aortic and access vessel diameters are smaller, due to young age. This has significant implications for treatment strategy, as standard thoracic stent grafts typically do not fit and alternative approaches such as iliac extensions must be used, regardless of the need for transposition or bypass from LSA to LCCA [14].

Intramural hematoma: IMH is a subtype of aortic dissection usually presents clinically as acute aortic syndrome. While rupture of the vasa vasora has been considered an underlying pathophysiologic mechanism, the presence of a primary intima-media tear has become a commonly accepted mechanism. However, identifying this primary entry can be difficult and often requires several days and multiple CTAs to visualize [9,15,16]. The location of the primary entry is usually expected to be in the distal aortic arch or proximal descending aorta [9]. The location (internal or external curvature) makes the difference in terms of the risk of developing retrograde type A aortic dissection (higher in the case of internal curvature), when the site of primary entry is at the external curvature, the supraaortic branches, usually act as an anatomic barrier preventing further retrograde spread [17]. Consequently, closure of the primary entry can very often be achieved by TEVAR, even in cases where there is retrograde spread into the ascending aorta if there are no proximal connections between the lumina [9].

Penetrating aortic ulcer (PAU): PAUs, unlike all other acute and chronic thoracic aortic syndromes, have an obliterative pathophysiology that has tremendous implications for subsequent procedures. These are precisely the patients who have a very high probability of having coronary artery disease, obliterative supraaortic vascular disease, and peripheral obliterative arteriopathy. This often complicates access for stent-graft implantation, for example. These lesions may also have a multisegmental distribution pattern and often an IMH component is present concomitantly. Penetrating ulcers are most commonly located in the distal aortic arch. Progression of this underlying disease in the sense of a mass is often accompanied by paralysis of the left laryngeal nerve. In contrast to classic aneurysms, diameter thresholds cannot be used regularly to indicate treatment. Recommendations for lesion length and depth to indicate treatment are available, but morphology and progression (usually more pronounced than in classic aneurysm formation) provide better guidance than diameter alone [2,16,17].

Pre- and intraoperative considerations

Imaging certainly has the greatest significance here. ECG-triggered, thin-slice computed tomography angiography (CTA) of the entire aorta, including the circulus arteriosus Wilisii, is recommended. Furthermore, an echocardiogram and duplex sonography of the carotids form the basis of preoperative diagnostics. Ideally, it would be supplemented with a current coronary angiogram, but situational urgency may prevent this.

During classic open surgery, organ monitoring and protection are critical. Arterial blood pressure measurements should be taken at three sites if possible. Usually, these are the bilateral radial arteries, as well as unilateral monitoring of the common femoral artery to anticipate malperfusion and its resolution by the individual treatment approach – such as the FET technique [18]. The brain and spinal cord are the organs most susceptible to ischemia, bilaterally, or in the case of an incomplete dorsal circulus Wilisii, trilateral selective antegrade brain perfusion are of greatest importance [19]. Hypothermia of the lower half of the body is usually established at 26° C, which leaves adequate margin for replacement of the arch. Temperature should be measured centrally, usually in the bladder, and at the surface, usually nasopharyngeally, to obtain a four-dimensional picture [18,20]. If the short FET version (100 mm) is used, the residual risk of symptomatic spinal cord injury (SCI) is very low [21]. Therefore, in our setting, CSF drainage is the exception in this surgery. In metachronous TEVAR extension, a CSF drain is established as standard. If necessary, this can be drained milliliter by milliliter if the CSF pressure increases. Several studies prove the excellent results [22,23]. Bitemporal near-infrared spectroscopy (NIRS) is used in all cases, regardless of whether open, hybrid, or endovascular surgery is performed [19].

Treatment options

Determination of the optimal management of acute aortic syndromes involving the aortic arch must always be based on a synopsis of the patient’s clinical situation and the location of the pathology. Regarding the anatomical/radiological factors, as mentioned above, we rely on the Ishimura zones shown in Figure 1 for this purpose.

Treatment of pathologies involving zones 0-2: The standard approach for any proximal thoracic aortic pathology affecting zones 0-2 is open replacement, usually in lower body HCA and SCAP to protect the brain. The extent of the disease determines the extent of the treatment. A detailed elaboration of the aortic root and ascending aorta treatment options is beyond the scope of this manuscript. If stent-graft delivery in zone 2 is not possible, or if an even more proximal landing zone would be necessary, complete aortic arch replacement using the frozen elephant trunk technique may be considered for these patients even in the acute emergency situation. The FET technique is also used in previous aortic replacement where progression of the natural history of the disease has resulted in aneurysm formation from zones 0-3. To some extent, these patients may also be candidates for branded, or fenestrated prostheses, but this has less relevance in the acute emergency situation due to the prolonged manufacturing time of the prosthesis [24]. Complete debranching of the aortic arch followed by TEVAR remains an option but has become the exception due to the excellent results of the FET technique [25].

Treatment of pathologies involving zones 2-4: When an adequate proximal landing zone is not available, LSA-to-LCCA bypass or transposition is the first-line option to generate an adequate proximal landing zone. If further proximalization is required, double double transposition – autologous or alloplastic – is an elegant method to create an adequate landing zone [26,27]. More extensive proximalization of landing zones beyond zone 2 should be avoided because of the marked increase in risk of retrograde type A aortic dissection attributable to inherently diseased proximal thoracic aorta regardless of diameter [13,28].

Interventional approaches to treat zone 0-2 are technically feasible but carry an increased risk of retrograde type A aortic dissection/Ia endleak the more proximal the landing zone.

Treatment of distally located pathologies: Here, TEVAR is the method of choice in the vast majority of acute aortic syndromes. In acute aortic dissection, the correct choice of stent-graft diameter is of utmost importance, as oversizing of the distal stent-graft component may lead to “distal stent-graft new entry” (dSINE). This can be compensated by distal tapering, [24,29]. Furthermore, protection of the spinal cord is of utmost importance, therefore CSF drainage is a standard tool in all TEVAR cases at our clinic [21–23].

Postdissection aneurysms may require an additional treatment step by open or endovascular closure [24,30,31]. Fenestrated or fenestrated endovascular thoracoabdominal completion is feasible and initial results in selected scenarios are encouraging [32,33].

At this point, we should briefly mention native and prosthetic aortic infections, which require special attention. While the first group is rare, the second is increasing. In native infections, TEVAR can be used as a bridge to definitive therapy, and in selected cases, infection control can be achieved without further therapy [34]. However, as a rule, extensive surgery with total or subtotal removal of the infected alloplastic material with orthotropic aortic reconstruction using a neoaorta formed from bovine pericardium is an excellent method to achieve durable treatment success. This approach has the advantage that antibiotic therapy can be discontinued after a certain period of time, according to current guidelines. Recurrence rates are very low. Exceptions are fungal infections, for which antifungal therapy should be continued for life [35–40].

Postoperative care

A stringent follow-up protocol is mandatory for the further course of aortic patients and forms the basis for anticipating potential further aortic events – in treated and untreated, upstream and downstream aortic segments. Thin-layer CTA of the entire aorta is the gold standard here. In our clinic, CTAs are performed at discharge, six months, 12 months, and annually thereafter. Regardless of the CTA exam, each follow-up appointment includes a detailed interview, focused physical exam, strict adjustment of cardiovascular risk factors, and scheduling a new exam appointment. We are currently evaluating whether regular CTA at discharge is predictive of regular CTA even at six months to reduce radiation exposure to the minimum necessary.

Regular outpatient follow-up, regardless of the choice of treatment option, is mandatory. Ideally in a specialized aortic outpatient clinic.

Take-Home Messages

• Acute and chronic thoracic aortic syndromes involving the arch are life-threatening conditions that require urgent and carefully planned treatment.
• Emergency care of acute thoracic aortic entities encompasses the entire spectrum of cardiovascular surgery, ranging from traditional open surgery to hybrid procedures and endovascular interventions. In addition, practitioners must rely on a consistent nomenclature based on radiologic and anatomic parameters to select the most effective therapeutic strategy.
• The decision as to which therapeutic procedure is optimal should be made by a specialized aortic team and performed promptly.
• Regardless of whether the treatment is conservative or invasive, the patient should undergo consistent follow-up in a specialized aortic outpatient clinic. Such thorough and frequent monitoring ensures early detection of complications or progression of the affected person’s underlying disease for the future.

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