Description of Condition
A thoracic aortic arch aneurysm (TAA) is an abnormal dilation or ballooning of a diffuse or localized portion of the artery with a diameter 50% greater than the normal diameter of healthy aorta. Approximately 25% of all aneurysms occur in the thoracic aorta. TAAs can occur anywhere along the aortic arch and are categorised based on zone classifications, established by Mitchell and Ishimaru (Mitchell 2002). The thoracic aorta is divided into five zones (zones 0 to 4) from the proximal ascending aorta to the mid descending thoracic aorta and this corresponds to the site of the aneurysm (Moulakakis 2013). The true incidence of TAAs is difficult to assess, as many remain undiagnosed. A population-based study estimated the incidence of thoracic aortic aneurysms at 5.9 cases per 100,000 person-years and this is predicted to further increase (Booher 2011). TAAs mainly affect elderly patients, and both genders are affected equally. The majority of TAAs are degenerative in nature and result from alterations in the biomechanics of the vascular wall that lead to loss of structural integrity and wall strength and this is related to the aging process. The underlying cause of TAAs is diverse in nature including congenital connective tissue disorders. Description of Intervention
· Open Repair
The routine approach for a TAA is via a median sternotomy. During thoracic repair cardiopulmonary bypass is required and the aneurysm is resected and replaced with a prosthetic Dacron tube graft (Takkenberg 2003). The brachiocephalic vessels are removed from the arch before resection and are then re-implanted into the Dacron tube graft. Surgeons are now using new multi-limbed prosthetic arch grafts where the arch vessels are anastomosed individually, thereby reducing the duration of hypothermic circulatory arrest and rate of embolic events. The introduction of retrograde and antegrade cerebral perfusion in combination with cerebral protection has resulted in reduced rates of neurological events during aortic arch repair.
· Hybrid repair
Hybrid arch repair is a combination of open surgical repair (OSR) and endovascular procedures to treat aortic arch diseases. The hybrid procedure aims to simplify OSR. This surgical procedure is a two-stage approach that involves, firstly a condensed portion of OSR without the necessity for circulatory arrest and cardiopulmonary bypass, and the second stage involves thoracic endovascular repair (EVAR). Both stages can be carried out in the same operation or separated over a short period of recovery. An open sternotomy is required for the debranching of the three main branching vessels (brachiocephalic artery, left common carotid artery and left subclavian artery) on to the ascending aorta before stent grafting. Hybrid repair has proven beneficial in cases with extensive diseases that also affect the distal aorta. The diseased section of the descending aorta is repaired using an endovascular stent graft that gives the appearance of an ‘elephant trunk’ (Harris 2013). Hybrids are classified into three types according to the extent of aortic arch lesion and the presence of the landing zones (Moulakakis 2013):
1. Type I: The debranching procedure involves brachiocephalic bypass and endovascular repair of the
aortic arch.
2. Type II: A type II repair entails an open ascending aorta reconstruction that creates an appropriate
proximal landing zone, great vessel revascularization, and endoluminal aneurysm exclusion.
3. Type III: Elephant trunk procedure with complete EVAR of the TAA.
How intervention may work
Intervention for TAAs via a hybrid approach reduces the incidence of invasive surgery, while cardiopulmonary bypass and antegrade cerebral perfusion can be avoided. The availability of off-the-shelf stent grafts that can be easily delivered and deployed in complex aortic arch anatomies has encouraged more surgeons to treat complicated cases using the hybrid approach. Although there are reported improvements in the results of mortality and morbidity, there is still diversity in opinion in surgical management of these aortic aneurysms, between international guidelines and within the surgical community
Why is it important to do this review
TAAs represent a genuine unmet clinical need, affecting an estimated 3-4% of patients over the age of 65 years diagnosed with this life-threatening condition. It is anticipated that the incidence and prevalence of TAAs will accelerate with an increasing and aging population (Elefteriades 2010). In the event of rupture, sudden death is almost certain, whereas the risk of mortality is reduced in surgical repair of the aneurysm. Management of patients with TAAs represent a continuing formidable challenge to cardiovascular interventionist and is an area of on-going research and development (Wong 2011). OSR, although traditionally challenging and risky, is the gold standard of therapy for many patients with TAAs (DeBakey 1957). The introduction of hybrid repair, a two-stage surgical procedure consisting of open debranching of the supra-aortic arch vessels, followed by endovascular repair of the distal aorta (Zone 4) has reduced the rates of mortality (5.7%) and morbidity (5%) (Slisatkorn 2014). Despite improved standards of perioperative care, operative techniques and use of protective adjuncts, OSR and hybrid repair are still associated with considerable morbidity and mortality rates. There is a need to evaluate the effectiveness and safety of these interventions for the treatment of TAAs with the aim of improving outcomes in all patient groups, particularly for the older patient, as this is the typical patient affected with TAAs. Our proposed systematic review will focus specifically on hybrid and OSR for TAAs.
Objectives
• To evaluate the effectiveness and safety of hybrid technique versus open arch repair in the management of thoracic aortic arch aneurysms.
• Criteria for considering studies for this review
Types of studies
Randomised controlled trials (RCTs) and non-randomised trials will be included in this review.
Types of Participants
Patients with TAAs that affect zones 0 to 4
Types of interventions
· Hybrid repair is a two-stage approach involving supra aortic debranching with or without thoracotomy and endovascular repair.
· OSR requires a median sternotomy with complete resection of the diseased portion of the diseased
thoracic aorta and reinsertion of the branching vessels of the arch.
Outcomes
The proposed outcomes are in accordance with the relevant Society of Vascular Surgery (SVS) Reporting Standards (Fillinger 2010).
Primary outcomes: · Prevention of rupture of aortic aneurysm
· Prevention of death from aneurysm rupture
· Prevention of death associated with primary or secondary treatment of the original aortic pathology
Secondary outcomes: · Neurologic events (stroke, transient ischemic attack, paraplegia, paraparesis) · On-going ischemia (e.g. Renal failure) · Hospital admission for medical treatment of the original pathology or its sequelae
Data collection and Analysis
Two review authors will independently review the eligibility of trials, extract data and evaluate the risk of bias of all included trials. Any discrepancies will be settled by discussion with a third author. If
necessary, we will contact authors of individual studies to obtain more information or for clarification. Data analysis will use methods informed by the Cochrane Handbook for Systematic Reviews of Interventions 5.1.0 (Higgins 2011)
