Safeguards and Pitfalls in the Management of Retrograde Dissection Complicating Thoracic Endovascular Aortic Repair

Abstract

The aim of this chapter is to give hint on some special situations related to aortic dissection. Although they are not frequently encountered, these situations need a clear management strategy in mind of every aortic surgeon. The first one is retrograde proximal dissection complicating endovascular stenting of descending aortic pathologies: when to expect and how to manage. The second one is the different anatomical variations of aortic arch branches that may coexist with aortic dissection, such as aberrant subclavian artery and isolated vertebral artery. These variations, when present, add to the complexity of dissection repair and affect the management plan, either open surgical or endovascular.

1. Introduction

There is no doubt about the advantages of thoracic endovascular aortic repair (TEVAR) in the treatment of different descending thoracic aortic pathologies. However, endovascular intervention is not entirely devoid of risks. With the widespread use of endovascular stent grafts, some specific complications have been reported, such as different types of endoleak and the stent-induced retrograde type A aortic dissection (RAAD) [1].

2. Risk factors

Many risk factors have been identified for the development of RAAD following TEVAR [2, 3, 4, 5, 6, 7].

2.1 Stent oversizing and ballooning

Stent oversizing by 10–20% larger than the aortic diameter of the proximal landing zone is a common practice in TEVAR deployment to ensure device stability and avoid type I endoleak or late stent migration. However, more than 20% oversizing may increase the incidence of RAAD. So, there should be a balance between stent oversizing and tension exerted on the aortic wall by the radial force of the TEVAR stent.

Stent ballooning is generally contraindicated in aortic dissection patients but may be used in aneurysm cases to minimize the risk of endoleak. However, this may favor the occurrence of retrograde dissection following stent deployment [2, 3].

2.2 Proximal bare springs of TEVAR

One of the possible causes of injury to the aortic wall is the proximal bare springs which are intended to afford proximal fixation of the TEVAR stent graft. These bare metal springs in the proximal end of stents have been frequently related to the entry tear found in the arch of operated cases of RAAD. The common site for this tear is the lesser curve of the aortic arch, probably due to the high radial force of stent graft exerted on the aortic wall at this location [4, 5, 6].

2.3 Location of the primary entry tear of initial pathology

The location of the primary entry tear in acute type B aortic dissections (ATBAD) is important. RAAD has been found to happen more when the primary entry tear was located at the concavity of the distal aortic arch, in contrast to the site of convexity, as the site of concavity is devoid of anatomical barriers such as supra-aortic vessels [6, 7].

2.4 Diameter of the ascending aorta

The shape and diameter of the ascending aorta must be considered during the treatment of complicated type B dissections. Ascending aortic diameter exceeding 40 mm in patients of ATBAD was found to be more prone to RAAD, mostly due to the generalized weakness of fragile aortic wall of dissection patients [4, 5, 6].

2.5 Timing of TEVAR and type of initial pathology

Some studies linked the occurrence of RAAD to the original indication for TEVAR being more likely to happen with the initial pathology of type B intramural hematoma (IMH) rather than descending aortic aneurysm or type B aortic dissection. Cases of acute TBAD and clinical or CT signs of rupture or immediate malperfusion are class I indicated for immediate endovascular treatment. But in the absence of the prementioned signs, careful monitoring and initial medical management are justified among other ATBAD patients that may benefit from initial medical therapy together with endovascular stent graft placement within 3 months, in the subacute phase. Recent data on a larger cohort of patients with TBAD undergoing TEVAR in the subacute phase revealed lower 30-day mortality and less TEVAR-related complications [5, 6, 7].

3. Presentation and management

Patients with RAAD usually present with new onset chest pain or pulse deficit with history of previous TEVAR. Time interval after TEVAR varies from shortly after the procedure to months, especially in patients with uncontrolled blood pressure. A detailed assessment may reveal new pericardial collection or aortic regurgitation on transthoracic or transesophageal echocardiography, new flap, or mural hematoma in ascending aorta on multi-slice computed tomography (MSCT) scan. Figure 1 shows a MSCT reconstruction of one of our patients with a previously deployed TEVAR with subsequent occurrence of retrograde type A aortic dissection.

Figure 1.

CT aortography showing retrograde stanford type A aortic dissection following a previously deployed endovascular stent. (A). Protrusion of bare springs of proximal end of stent graft causing intimal tear at lesser curve of the aortic arch. (B). Axial cut revealing well-seated stent in descending aorta with complete thrombosis of false lumen but with dissection flap in ascending aorta, dividing it into true and false lumens.

3.1 Surgical management

Retrograde type A aortic dissection (RAAD) following TEVAR is a potentially life-threatening complication that mandates emergency surgical replacement of the dissected ascending aorta with the high risk of rupture as well as the segment of aortic arch showing the entry tear, usually located in the lesser curvature, through median sternotomy under hypothermic circulatory arrest [4].

Arterial inflow of cardiopulmonary bypass (CPB) is established through cannulation of the axillary artery, or both the axillary and the femoral arteries connected by “y” connector, and a cannula in the right atrium is used for venous drainage. Cerebral protection was achieved by unilateral antegrade cerebral perfusion through axillary artery combined with moderate hypothermia (25°C). We prefer dual arterial cannulation through axillary and femoral arteries with balloon catheter temporary inflated within the stent lumen to allow for lower body perfusion during the period of open distal anastomosis of arch reconstruction.

3.2 Proximal aortic root reconstruction

This depends on the degree of extension of aortic dissection into the aortic root components. Usually, RAAD stops at the level of the sinotubular junction with mild affection of sinuses and aortic valve. In this situation, the ascending aorta is excised down to the level of valve commissures, followed by a supracommisural replacement of ascending aorta using Dacron tube graft anastomosed to the reconstructed sinus segment of the root using continuous 3/0 prolene suture augmented from the outer aspect with Teflon felt to support the proximal suture line. Less commonly, the aortic valve may need resuspension or valve-sparing root replacement in case of extensive affection of the aortic root.

3.3 Distal arch reconstruction

The main goal of treatment of RAAD is to completely excise the stent-induced entry tear typically located in the lesser curve of aortic arch. Total hypothermic circulatory arrest and cerebral perfusion are used for open distal anastomosis. With continuous cerebral oxygen saturation monitoring, a hemiarch replacement is usually sufficient but careful removal of some of the proximal metal springs of the endovascular stent is prudent. This allows for the inclusion of the stent as well as the native aortic wall in the distal aortic suture line all in one layer. This achieves a hemostatic repair and prevent future endoleak. Interrupted 4/0 prolene pledgeted mattress sutures and Teflon felt are used to reinforce the suture line. The proximal end of the deployed TEVAR in one of our patients with RAAD is seen in Figure 2 with removal of the protruding metal using sternal wire cutter.

Figure 2.

Operative steps: (A) Opening the pericardium reveals extensive mural hematoma of the ascending aorta. (B) Snaring the carotid arteries and removing the cross-clamp for open distal anastomosis with trimming of metal springs of the stent using wire cutter. (C) Realignment of proximal end of endovascular stent with the native aortic wall after resection of the lesser curve and entry tear to perform Hemiarch replacement. (D) Dacron graft replacement of ascending aorta.

4. Discussion and follow-up

Our patient cohort includes 100 patients that received TEVAR as treatment for different descending aortic pathologies, during the period between January 2011 and January 2023. Fifty patients of our series received prosthesis with proximal bare springs. Eight patients (8%) developed RAAD with time interval ranged from 2 weeks to 6 months post TEVAR. All eight patients undergo emergency surgical replacement of ascending aorta with Hemi arch and trimming of metal springs. One patient died on the second postoperative day due to massive uncontrollable hematemesis with hemodynamic collapse 6 hours after extubation that failed to be resuscitated. One patient developed postoperative paraparesis of lower limbs that improved on insertion of spinal drain and discharged home with no residual weakness. The rest of patients had smooth uneventful postoperative course.

Gorlitzer and colleagues [6] reported in their patient cohort from August 2005 to February 2011 that retrograde aortic dissection occurred in 4 of 29 patients (13.8%) undergoing thoracic endovascular aortic repair (TEVAR) for acute complicated aortic type B dissection. In their series, a prosthesis with a proximal bare spring was used in 25 patients. The tip of the proximal bare springs induced a retrograde type A dissection in four patients. The primary entry tear was located at the concavity of the distal aortic arch. The mean duration of circulatory arrest was 56 ± 7 min. All patients survived surgery with no stroke, paraplegia, or renal failure. Postoperative CT scans revealed perigraft thrombus formation and stable aortic dimensions in all patients after 6 months.

A multicenter study of the European Registry on Endovascular Aortic Repair Complications conducted on 2009 reported on an incidence of rAAD post-TEVAR for either acute or chronic type B dissection of 1.33% (95% CI 0.75–2.4) [8].

Czerny and colleagues reported an overall RAAD incidence of 8% in a multicenter study of 66 patients with total arch de-branching and TEVAR (Zone 0), with an early (<7 days postoperatively) and delayed (>7 days postoperatively) incidence of 3 and 5%, respectively [9].

Luehr and Colleagues reported in a series of ten patients of type B aortic dissection that two patients (20%) developed retrograde type A aortic dissection on days 10 and 12 post-TEVAR. Both patients had a dilated ascending aorta and received a stent graft containing bare metal springs at the proximal end. Emergency ascending aortic replacement was performed under moderate hypothermia. In-hospital mortality was zero, and no patient developed paraplegia/paraparesis due to spinal cord ischemia. Luehr and colleagues recommended performing CT aortography 1 week after TEVAR, for the early detection of complications such as retrograde dissection as well as to assess the success of the endovascular intervention [10].

5. Impact of arch branches variations on surgical strategy of aortic dissection

5.1 Introduction

Traditionally, anatomical variations of the aortic arch and great vessels have been considered as an incidental finding of little clinical significance during routine computed tomography (CT) scanning; therefore, they were often overlooked and mostly unreported.

But from aortic surgery standpoint, the clinical significance of arch branching variations is triple-fold. First, some of these anatomical variations as aberrant subclavian artery may result in abnormal vascular ring formation around trachea and esophagus with compression symptoms as dyspnea and dysphagia. Second, these branching variations were found to occur more frequently in patients with thoracic aortic disease (TAD) than others, and therefore, these variations should be regarded as an anatomical marker for the risk of developing aortic aneurysm and dissection. Third, these variations have significant impact on the management plan whether open, endovascular, or hybrid, as well as the choice of arterial axis and cerebral protection methods in patients with aortic arch diseases and abnormal arch branching [11].

The key point for anatomical variations of arch branches is preoperative detection on multislice computed tomographic angiography (MSCTA) done to diagnose aortic aneurysm or dissection. This is a critical step in planning surgical and endovascular procedures involving the aortic arch because missing this may lead to serious problems such as branch occlusion or endoleak during endovascular treatment of type B aortic dissection, or cerebral ischemia during surgical repair of type A aortic dissection with postoperative neurological complications.

5.2 Types

The common anatomical variations related to aortic aneurysm and dissection include:

1. BOVINE ARCH (BA) or common origin of the innominate and left carotid artery (CILCA)

2. ABERRANT RIGHT SUBCLAVIAN ARTERY With left-sided aortic arch (ARSA)

3. ABERRANT LEFT SUBCLAVIAN ARTERY With right-sided aortic arch (ALSA)

4. ISOLATED LEFT VERTEBRAL ARTERY origin from aortic arch (ILVA).

5.2.1 Bovine arch (BA)

The bovine arch is defined as an aortic arch with common origin of the innominate and left carotid artery (CILCA arch). It is also called truncus bicaroticus or type I bovine arch. It represents the second most common arch configuration following the standard arch pattern of innominate trunk, left common carotid, and a left subclavian artery. Less commonly, “type 2 bovine arch” occurs when the left common carotid artery originates directly from the innominate artery rather than as a common trunk. The prevalence of the CILCA arch in the general population is around 15% [11].

• type I bovine arch [T1BA] means common origin of innominate and left common carotid artery

• type II bovine arch [T2BA], left common carotid originating from innominate artery.

The clinical relevance of the CILCA arch has become apparent in planning surgical and endovascular procedures involving the aortic arch. Also, a lot of research work has identified the CILCA arch as a potential anatomical marker for thoracic aortic disease (TAD).

Many patients who are candidate for thoracic endovascular aortic repair (TEVAR) present with this special anatomical configuration of bovine arch. Different studies reported a trend toward an increased risk of post-TEVAR complications in such patients with bovine arch, as retrograde dissection. So, further specific studies on the impact of the bovine arch configuration on TEVAR planning are needed [12].

It was proposed by certain hypothesis that in CILCA bovine arch, the peculiar anatomical configuration may entail a local biomechanical environment that adversely affects the aortic wall properties and its integrity. The relatively greater diameter of the arch vessels may alter local flow hemodynamics, leading to an increased wall shear stress, that may weaken the aortic wall [13].

During surgery for type A aortic dissection, bovine arch configuration allows for bilateral carotid perfusion when using axillary artery inflow. Also, in type B aortic dissection, the bovine configuration allows for more space in the arch for proximal landing of TEVAR.

5.2.2 Aberrant right subclavian artery (ARSA) with normal left-sided aortic arch (LSAA)

Aberrant right subclavian artery (ARSA) is a rare anatomical variant of the origin of the right subclavian artery from distal aortic arch or proximal descending aorta instead of the common origin with right carotid artery from the innominate trunk. A prevalence of 0.16–2% of ARSA has been reported. Of notice, aberrant right subclavian artery may coexist with common bicarotid trunk in some patients [14, 15, 16, 17].

During acute type A aortic dissection surgery and arch replacement procedures, the presence of ARSA should be checked carefully in the MSCT aortography. If so, axillary cannulation will be of no value in terms of antegrade cerebral perfusion, and another axis should be selected as direct bilateral osteal carotid cannulation.

During frozen elephant trunk (FET) procedure for arch replacement, intrathoracic control of ARSA is gained by meticulous dissection of the inferolateral aspect of right carotid artery above the innominate vein, followed by division of the ARSA and end-to-end anastomosis to 8-mm Dacron graft that can be connected to separate perfusion head then to the elephant trunk graft by the end.

In case of TEVAR for type B aortic dissection with ARSA, a more detailed study of carotids and vertebral arteries by cranial CT cerebral angiography is needed to evaluate the dominance of vertebral arteries, and the integrity of the circle of Willis then to decide to go for carotid subclavian bypass on left or right side or even bilateral in case of symmetric vertebral arteries because both subclavian arteries will be covered by the stent graft affecting the perfusion of both vertebral arteries. The MSCT of some of our patients with aberrant right and left subclavian arteries is shown in Figures 3–5.

Figure 3.

A. Left-sided aortic arch with aberrant right subclavian artery retrotracheal. B. Right-sided aortic arch with aberrant left subclavian artery origin retrotracheal.

Figure 4.

A. Aortography showing type B aortic dissection with collapsed true lumen, big false lumen, aberrant right subclavian artery, and common carotid trunk. The patient had bilateral carotid subclavian bypasses followed by TEVAR. B. Follow-up MSCT showing complete thrombosis of false lumen around the stent with no endoleak.

Figure 5.

MSCT aortography of one of our patients with right-sided aortic arch and aberrant left subclavian arising from Kommerell’s diverticulum.

5.2.3 Aberrant left subclavian artery (ALSA) with right-sided aortic arch (RSAA)

Right-sided aortic arch is a rare anatomical variation resulting from persistence of the embryologic right fourth aortic arch and involution of the left, which is the reverse of what happens in most of the population. Fifty percent of the cases (0.05%) are associated with an aberrant left subclavian artery arising from an outpouching called Kommerell’s diverticulum. Right-sided aortic arch is rare with prevalence of about 0.1% of the adult population. Of notice, right-sided aortic arch with aberrant left subclavian artery is much less common than left-sided aortic arch with aberrant right subclavian artery (0.5–2.0%) [18, 19, 20, 21].

Management of aberrant left subclavian artery depends on the presentation:

1. If the main presentation is compression symptoms of vascular ring with no aneurysm formation, so the treatment is to divide the ring around the esophagus through left thoracotomy followed by interposition graft reconstruction of ALSA or left carotid subclavian bypass.

2. If the problem is Kommerell’s diverticulum complicated by aneurysm formation or type B dissection, so the treatment is either open surgical repair through right thoracotomy to resect diverticulum aneurysm and replace descending thoracic aorta, or hybrid repair through median sternotomy to debranch the great vessels followed by TEVAR or to go for one-stage frozen elephant trunk procedure.

5.2.4 Kommerell’s diverticulum aneurysm (KDA)

Burckhard Friedrich Kommerell (1900—1990) described his diverticulum/aneurysm of the proximal lusorian artery in 1936 [22].

Kommerell’s diverticulum (KD) is defined as aneurysmal aortic dilatation at the origin of an aberrant subclavian artery (ASCA), either left or right. KD is a rare anomaly, occurring in 0.05–2.0% of the population. About 5% of patients with KD develop symptoms.While most patients with KD are asymptomatic, dysphagia is one of the common manifestations due to compression of the esophagus. KD is associated with risk of aortic rupture and/or dissection, as the tissue strength in the KD is very limited due to histological weakness, and this often leads to adverse aortic events [23].

5.2.4.1 Indication for surgery

According to the European Association of Cardiothoracic Surgery/Society of Thoracic Surgery EACTS/STS 2024 Guidelines for diagnosing and treating acute and chronic syndromes of the aortic organ, surgery for symptomatic KD is a well-established indication. However, indications for prophylactic intervention in asymptomatic patients remain based on limited reports. Observation of asymptomatic KD is generally appropriate. Current American College of Cardiology/American Heart Association guidelines recommend treatment when the orifice connecting the diverticulum to the arch is larger than 30 mm and/or the diverticulum diameter is larger than 50 mm (Figure 6) [7].

Figure 6.

Kommerell’s diverticulum aneurysm with right-sided arch aneurysm and aberrant left subclavian artery.

5.2.4.2 Operative strategy

A variety of treatment options have been reported to treat KD, including open, endovascular, or hybrid methods. The most common open approach is ligation/resection and subclavian transposition/bypass to release compression and to reestablish arterial circulation through a left thoracotomy. Open replacement of the aorta may be considered using partial heart bypass cannulating superior vena cava and distal aorta or femoral artery through a right thoracotomy. In symptomatic patients, surgery should include full decompression of the surrounding structures and fibrous bands surrounding the esophagus. Total arch replacement (TAR) through the frozen elephant trunk FET procedure may be considered if the condition is associated with aortic arch dilatation [7].

Endovascular option may be considered in patients with increased operative risk and who are anatomically convenient for stenting. This includes staged carotid-subclavian artery bypass followed by subsequent thoracic endovascular aortic repair (TEVAR). In young patients with low incidence of comorbidities, open repair through a thoracotomy is preferred due to its durability and efficacy in symptom relief. Endovascular therapy is less invasive and would be a good strategy for asymptomatic Kommerell’s aneurysm. However, in patients with symptomatic KDA, the open technique is the preferred option because relieving the compression on the esophagus would be key step. The basic concept to treat dysphagia is to remove the ASCA and all fibrous bands surrounding the esophagus through left thoracotomy [7].

During frozen elephant trunk procedure for KDA with arch aneurysm, because of the anatomical features of patients with right aortic arch + ALSA, in whom the aortic arch is sharply angulated or curved, available ready-made devices are prone to massive kinking and, therefore, modified intraoperatively assembled frozen elephant trunk works better according to the individual anatomy of arch angulation.

5.2.5 Isolated left vertebral artery origin from the arch (ILVA)

An isolated left vertebral artery (ILVA) is defined as vertebral artery which arises directly from the aortic arch. This anatomical variation has a prevalence of 0.79 to 6.1%. From surgical point of view, the preoperative diagnosis of an ILVA on CT aortography is important because missing this variation may lead to serious complications, such as occlusion or endoleak during endovascular treatment of TBAD or difficulties during the surgical approach to the aortic arch branches in type A aortic dissection with possible ischemia or infarction of the brain if the circle of Willis is incomplete. Many options, such as total arch replacement and frozen elephant trunk technique, have been reported to treat patients with aortic dissection and an ILVA. Whether an ILVA should be reconstructed or not in all cases is controversial. Most studies state that the ILVA should be reconstructed because sacrificing the ILVA may increase the risk of neurologic deficit owing to poor perfusion to the brainstem or cerebellum if arterial communication at the circle of Willis is inadequate [24].

In case of type B aortic dissection (TBAD) with an ILVA requiring endovascular therapy TEVAR, the proximal landing zone, dominance of the vertebral artery, and integrity of the circle of Willis are all studied in MSCT. Preoperative aortic CTA imaging characteristics may reveal right vertebral artery dominance, symmetric vertebral artery, or left vertebral artery dominance. The management entails ILVA reconstruction, such as ILVA-LCCA transposition of vertebral artery to left carotid artery, if the ILVA is dominant or symmetric with an incomplete circle of Willis, followed by TEVAR placement. Cerebral oximetry is used to monitor cerebral oxygen saturation during left carotid clamping period for the anastomosis.

During the treatment of Stanford type A aortic dissection (TAAD) with an ILVA, prior reconstruction of ILVA is recommended with ILVA-left common carotid artery (LCCA) transposition or bypass using saphenous vein graft segment under normothermic off-pump conditions. Median sternotomy incision is extended about 4 cm cranially to the left side of the neck for sufficient dissection of the LCCA and ILVA with enough length, and then, the ILVA is cut off. The LCCA is open with a hole puncher. The ILVA is end-side sutured to the LCCA with 6–0 Prolene line [25].

6. Conclusion

Retrograde type A aortic dissection (RAAD) following TEVAR is a life-threatening complication with potential risk of aortic rupture that needs high index of suspicion for early detection and emergency surgical intervention. Supra-commissural replacement of the dissected ascending aorta with Hemi arch procedure is usually sufficient and carries good outcome.

Congenital aortic arch variations are gaining more clinical importance with the introduction of advanced aortic therapies such as endovascular stents and the frozen elephant trunk. These anatomical variations are more common in patients with thoracic aortic disease. The key to success for case planning, whether open surgical or endovascular, is the detection of such variations on preoperative CT aortography to allow for optimum management.