“More or less”: management of type A aortic dissections in the endovascular era

Abstract

The management of type A aortic dissection presents a major therapeutic challenge in modern surgical practice. Whilst the traditional dictum, to provide timely surgical intervention with the minimum treatment needed to repair the ascending aorta as well as the primary tear, may be a reasonable strategy in older patients, a tailored approach is desired for younger patients to manage the immediate life-threatening condition, as well as for the management of lifelong complications of the residual dissected aorta. Endovascular technology continues to advance, providing an adjunctive role to open cardiac repair presently to manage downstream aortic pathology, with the aim of striving towards a complete endovascular solution for type A aortic dissections.

Introduction

Type A aortic dissection (TAAD) continues to be a major therapeutic challenge in modern surgery. Despite significant advances in preventative medicine, it continues to be a significant cause of morbidity and mortality, with a mortality rate of greater than 50% in untreated TAAD within the first 48 h [1]. Globally, the incidence of aortic dissection varies between 2.9 and 4.3 cases per 100,000 persons per year [2], and often not established until autopsy [3]. Though advanced age is a significant aetiological factor, younger patients present more challenges in terms of immediate and longer-term management [4]. Genetics also contribute to disease presentation, with 8% of patients with aortic dissection reporting a family history of aortic dissection and a further 20% having a first degree relative with a dilated thoracic aorta in the Nordic Consortium for Acute Type A Aortic Dissection (NORCAAD) registry [4].

Classification

The DeBakey classification, first described in 1965, organised aortic dissection presentations into three subgroups: type 1 showing a diffuse dissection arising within the ascending aorta and extending beyond, with type 2 localised to the ascending aorta and type 3 arising distal to the left subclavian artery [4]. In 1970, the Stanford classification was developed to simplify the categorisation of aortic dissection presentations, into type A denoting aortic dissections involving the ascending aorta and type B for aortic dissections arising distal to the left subclavian artery [5]. In the era of hybrid operative intervention for aortic dissection, a further sub-categorisation has evolved from the initial Stanford classification, with the derivation of the “non-Type A, non-Type B” aortic dissection involving the aortic arch alone or arising as a result of retrograde propagation of a dissection originating distal to the left subclavian artery [6].

More recently, the Penn and DISSECT classification systems have been introduced to account for the complexity of aortic dissection presentations, as well as to assist with clinical decision making in the short and long term and determine operative mortality risk [7, 8]. The Penn classification was developed as a means of classifying clinical presentations on the basis of the presence or absence of branch vessel malperfusion or circulatory collapse [8, 9]. The DISSECT classification system, on the other hand, takes into account duration of dissection, site of primary intimal tear, maximum trans-aortic diameter of dissected aorta, segmental extent of aortic involvement, clinical complications related to dissection and thrombosis of the false lumen [7].

Epidemiology

Studies have shown that TAAD involving only the ascending aorta occurs in roughly 30% of all TAAD presentations. As such, a majority of TAADs are much more complex involving significant real estate of the aorta distal to the left subclavian artery requiring long-term follow-up and treatment [10].

Age is a significant factor in the aetiology and incidence of aortic dissections, with mean age at presentation being 63 years [10]. Several other risk factors are also known to be related to aortic dissection presentations, including hypertension, atherosclerosis, aortic aneurysms, cardiac surgery, Marfan syndrome and cocaine consumption [10].

In several ethnic groups, the mean age is lower, and this has implications in the initial modality of treatment and long-term follow-up and compounded by poor blood pressure control. In New Zealand, the incidence of aortic dissections is significantly higher in the Maori population and occurs at a much younger age [11–13]. This also appears to be the case in Asian countries like China [14] and India [15], where the mean age of aortic dissections is closer to 50 years. Following operative intervention, these ethnic groups unfortunately do not have good long-term follow-up, with poor blood pressure control and limited access to best medical therapy, leading to aortic dilatation and complex aneurysm formation of the arch and descending aorta in the long term [15].

Spectrum of treatment

The treatment paradigm for TAADs is to provide timely surgical repair with the minimum treatment needed to repair the ascending aorta as well as the primary tear [16]. Whilst this seems to have significant logic to it, this dictum needs to be tailored to the continual evolution of endovascular technology and of the availability of local technical expertise. Whilst the minimalist approach may be optimal for a TAAD dissection in an elderly patient, this would be considered grossly inadequate for a younger patient with a more complex dissection [16]. Nearly 70% of patients have diffuse involvement of most of the aorta and this leads to significant angulation and tortuosity, when the residual dissected aorta weakens and undergoes aneurysmal degeneration [17]. As such a sequential strategy should be considered for the surgical management of TAAD, initially addressing life-threatening conditions followed by the management of lifelong complications of residual dissection of the aorta [16].

Modern treatment options

Modern operative techniques for the management of TAAD extend from ascending aortic replacement, together with aortic valve re-suspension or replacement, to aortic arch replacement and reconstruction of arch branch vessels, as well as classical or frozen elephant trunk [16].

The introduction of the branch-first technique allowed for sequential reconstruction and reperfusion of arch branches, minimising total cerebral circulatory arrest, as well as shortening distal organ and cardiac ischaemic time, besides reducing air and particulate embolisation during proximal aortic repair [18]. Matalanis et al. reported favourable perioperative outcomes utilising the branch-first technique, with a 3.1% mortality rate and a low incidence of neurological, renal, cardiac and respiratory complications, thereby demonstrating the quality of vital organ perfusion and protection [19]. From a future proofing perspective, total debranching together with a classic or frozen elephant trunk offers an easier solution to treat downstream aortic dilatation with endovascular solutions in collaboration with vascular surgeons [19].

Whilst endovascular treatment of sequelae following TAAD repair for complex dissection is well described (Fig. 1), primary management of TAAD via a total endovascular approach utilising an endograft poses challenges with patient selection, vascular access, stent graft design and aortic valve involvement [20]. Case reports of highly selected patients have demonstrated modest success with endovascular management of acute, subacute and chronic TAAD confined to the ascending aorta [21, 22]. Endovascular management for TAAD has typically been reserved for patients considered high risk or frail, as an alternative for open surgical intervention, but with appropriate morphologic characteristics [20, 23–25].

Fig. 1.

Completion of fenestrated aortic arch endograft with supra-aortic stenting following ascending aorta repair and innominate artery bypass for complex type A aortic dissection

Whilst trans-femoral, trans-apical, trans-carotid and trans-axillary approaches have made endovascular TAAD management feasible, it is limited by anatomical, technical and stent graft–related considerations [26]. From an anatomical perspective, considerations include the proximal and distal landing zones, the extent of the dissection distal to the sinotubular junction and proximal to the innominate artery and the absence of aortic regurgitation, as well as access vessel considerations [24, 27]. Whilst the absence of a proximal landing zone is the most common exclusion criterion for endovascular TAAD management, retrospective reviews of imaging of acute TAAD patients have demonstrated between a third to half of patients have suitable anatomy [24, 28]. Severe aortic regurgitation and dissection involving the aortic root are contraindications to endovascular management, whilst patients with connective tissue disorders could be considered for aortic endografting as a temporising measure until definitive open surgery [24, 28].

Advances in stent graft technology in the future will hopefully account for the distinct challenges of the ascending aorta, including the length of stent grafts and avoidance of multiple overlapping stents, as well as accounting for the haemodynamic force including significant changes in diameter and area throughout the cardiac cycle, to achieve an adequate landing length [20, 24]. Furthermore, an incorporated aortic valve and coronary artery solution, together with the ability to achieve a proximal seal to withstand displacement forces and prevent stent migration, adds extra complexity [20].

Whilst endovascular TAAD management avoids the need for median sternotomy, cardiopulmonary bypass and deep hypothermic circulatory arrest, it is not without risk of significant complications [29]. In particular, the fragility of the ascending aorta following TAAD can cause retrograde TAAD or aortic rupture during stent graft deployment [24]. Furthermore, the proximity of the coronary artery ostia and aortic valve to the proximal landing zone may cause inadvertent coronary artery coverage or aortic valve dysfunction [30]. The traversal of guidewires and sheaths across the aortic arch increases the risk of neuro-embolisation of thrombus [24], though the limited clinical evidence thus far has not demonstrated a higher incidence of stroke following endovascular treatment, when compared to open TAAD repair [20]. Finally, other potential complications include endoleaks leading to potential TAAD extension [26] and device migration, as well as supra-aortic vessel coverage [25].

Regarding the management of the sequalae following TAAD repair, a range of modern endovascular techniques and particularly the use of fenestrated or branched technology have been utilised to deal with downstream post-dissection aortic aneurysm (PDAA) presentations [31]. Whilst for fenestrated endografts, the connecting stents to the branch vessels can often be accomplished by groin access, it is different with branched endografts [32]. Branches to the visceral vessels are often downward facing and need access from the subclavian arteries to connect the branches, presenting a challenge with the branch-first technique of debranching all supra-aortic vessels [19, 31]. Advancement in endovascular armament has helped provide an innovative solution with the initial description of pre-curving available guide sheaths to development of steerable sheaths to allow for successful cannulation of these branched endografts from the groin rather than from proximal access [33, 34]. Complex endovascular repair of the PDAAs has been shown to be safe and durable, with the particularly vexed issue of stroke and spinal cord ischaemia reduced to under 5% with more contemporary results [31].

Understandably, the expertise to perform complex aortic endovascular interventions tends to be concentrated in larger centres with higher volumes [35]. However, lower volume centres also can set up an endovascular platform for management of future downstream thoracoabdominal aortic pathology following TAAD repair [36].

Our experience in hybrid open and endovascular intervention in a tertiary-level hospital in New Zealand (NZ) for a cohort of patients with complex TAADs was presented at the 2015 Charing Cross International Symposium [37]. Utilising a modified ascending repair with a single side branch, the ascending graft is planned to have at least 3 cm of landing zone distal to the side branch (Fig. 2). Once the ascending repair is completed, this side branch can be anastomosed to the innominate artery end to side, while the patient is being rewarmed. If the innominate artery is involved with the dissection, this graft is tunnelled to the base of the neck to be anastomosed to the common carotid artery on the right. This allows future proofing of the repair to endovascular solutions, but with the following limitations:

1. Endografts need at least 3 cm of proximal landing zone proximally within the prosthetic graft.

2. Native aortic valves and bioprosthetic valves can allow the nose cone of the endografts to be traversed to land the graft in the ascending aorta.

3. Debranching of the innominate or both the carotids then provides a simpler procedure of endovascular repair of the arch and proximal descending aorta.

Fig. 2.

Intra-operative image of a type A aortic dissection repair with side branch anastomosed to the innominate artery

In our small cohort experience in NZ, nearly 60% of patients needed complex repair of the arch and descending aorta within 18 months [37].

Conclusions

The contemporary management of TAADs continues to evolve with the advancement of cardiac surgical operative techniques and endovascular technology. A collaborative approach with cardiac and vascular surgeons as well as interventional radiologists allows for a comprehensive manner of managing long-term sequelae of a diseased aorta.

The modern endovascular armamentarium has a range of tools to support this change in philosophy to manage complex dissections. While this loosely supports specific centres to take up the bulk of the treatment, smaller centres can make appropriate amendments to their treatment paradigm to optimise outcomes in the short term and provide a better platform for endovascular management in the future. A dedicated aortic team meeting pre-operatively for every patient presenting with a complex aortic dissection can lead to durable operative solution allowing for improved short-term outcomes with the ability to provide long-term care for the residual downstream pathology.

A useful point to conclude would be that in regard to TAADs, in younger patients, doing more upfront is less as opposed to the older patient, where doing less is more.

Funding

None.

Declarations

Informed consent

Obtained for the figures used in this review paper in line with the local health district’s consent process.

Human and animal rights statement

No research involving human participants and/or animals were undertaken for this review paper.

Ethics approval

Not applicable, being a review article.

Conflict of interest

The authors of this review paper have no conflicts of interest to declare.