The Visceral Hybrid Repair of Thoraco-abdominal Aortic Aneurysms – A Collaborative Approach

Article Outline

• Abstract
• Introduction
• Patients and Methods
  • Data collection
  • Patient series
  • TAAA presentation
  • TAAA type, size and aetiology
  • Surgical approach and technique
  • Co-morbidities
• Results
  • Simultaneous and staging of the visceral hybrid
  • Visceral bypass graft patency
  • Endovascular stent-grafting and endoleak
  • Mortality
  • Morbidity
  • Neurological
  • Renal failure
• Discussion
  • Patient cohort
  • Traditional open repair a feasible alternative?
  • Simultaneous versus staged visceral hybrid repair
  • Endoleak
  • Paraplegia
  • Mortality
  • Fenestrated/branched stent-grafting
• Conclusion
• Financial Declaration
• Conflicts of Interest
• Acknowledgements
• References
• Copyright

Abstract 

Objective

To report the collaborative data of 3 major European Vascular Units using the ‘visceral hybrid’ procedure for thoraco-abdominal aortic aneurysms and dissections.

Methods

A consecutive series of 107 urgent and elective high-risk patients were included in a prospectively collected database.

Results

All stents involved the entire thoracic and abdominal aorta with left subclavian coverage in 19 and revascularisation in 12. The distal landing zone was in the infra-renal aorta in 75% and in the iliac artery in 25%. The 30-day mortality rate was 16/107 (14.95%). 13/107 (12.1%) of the patients suffered spinal cord ischaemia which was complete and permanent in 9/12 (8.4%). 4 patients (3.7%) required long term dialysis and a segment of gut infarction requiring resection occurred in 3 (2.8%). Most patients had visceral bypass grafting and aortic stent-grafting performed in one stage. In 18 patients the stenting was performed later. Three of these patients ruptured before the stenting procedure was undertaken.

Conclusion

These early results of visceral hybrid repair for high-risk patients with complex thoraco-abdominal aortic aneurysms are encouraging, in a group of patients in whom fenestrated/branched stent-grafting is not an option and open surgery hazardous.

Keywords: Visceral hybrid thoraco-abdominal, aortic aneurysm

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Introduction 

The repair of thoraco-abdominal aortic aneurysms (TAAAs) by traditional open techniques has a high morbidity and mortality. These risks have persisted despite advances in operative technique (including left heart bypass, spinal cord protection, hypothermic cardiopulmonary arrest and selective visceral perfusion) and higher standards of peri-operative care.

Parodi's use of the first endovascular stent-graft in 1991 for an infra-renal abdominal aortic aneurysm is well known.¹ By 1994, endovascular techniques had developed such that Dake was able to use them for descending thoracic aortic aneurysms (TAAs). This use for aneurysms limited to the thoracic segment showed significant early promise. However stent-grafting for more extensive TAAA was necessarily limited by the presence of the visceral and renal arteries, which could not be safely covered.

Hybrid repairs of TAAA refer to procedures combining both open surgical and endovascular techniques (either staged or combined as one operative procedure). By bypassing vital aortic side branches first, it is possible to cover their origins with a stent-graft and thus achieve total aneurysm exclusion. When the visceral and renal vessels are involved in the TAAA and require retrograde re-vascularisation, we refer to this operation as the visceral hybrid repair.

These visceral hybrid repairs of TAAA begin with an open abdominal procedure to first bypass the visceral and renal vessels followed by aortic endovascular stent-grafting to exclude the aneurysm (either as part of the same procedure or intentionally delayed). These repairs are particularly attractive as they avoid the need for a thoracotomy, supra-coeliac aortic cross clamp and left or full heart bypass, therefore potentially reducing the ischaemia reperfusion insult.

St Mary's described one of the earliest cases in 2002² and we subsequently reviewed our experience of our first 29 cases in 2006.³ Since then, a number of other centres have also described their experience of the visceral hybrid procedure but individual series in the published literature remain small. We report the results of collaboration between 3 major European vascular surgical centres using the visceral hybrid repair for TAAA for over 100 consecutive cases. Fig. 2 shows our increasing cumulative experience with the visceral hybrid repair for TAAAs.

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Patients and Methods 

Prospectively collected data for 118 consecutive patients who underwent attempted visceral hybrid procedures for TAAA and dissections between January 2002 and October 2007 was obtained from three major European vascular surgical centres:

This data was retrospectively reviewed, synthesised and analysed.

Data collection 

A database was designed by the authors and distributed between all 3 centres involved. The data to be collected was decided upon by the collaboration of authors although individual units were at liberty to collect their own additional data. Data was collected prospectively by the individual centres and stored on a Microsoft Excel spreadsheet on password-protected computers. This was collated at regular intervals into one database, upon which data analysis and interpretation took place.

Patient series 

All patients who underwent a visceral hybrid were entered into the database. The decision to perform a visceral hybrid rather than an open or fenestrated repair was made by each unit on an individual patient basis, and composed of around two-thirds of all TAAAs treated. All type IVs and fit type III patients were offered open repair. During the latter part of the study period, fenestrated repair was offered in less fit, asymptomatic patients where the anatomy was favourable. Eleven free ruptures were excluded from the data set. This left a consecutive series of 107 elective and urgent patients, of which 67 were male and 40 were female. The median age was 67 (Range 29–81). 18.7% (20/107) were over 75 years of age at the time of operation. 65 of these patients were from St Mary's, 24 from Heidelberg and a further 18 were treated at Munich.

TAAA presentation 

79.4% (85/107) were elective cases and 20.6% (22/107) were urgent. Of the elective cases, 22.4% (19/85) of patients described some symptoms associated with their aneurysms including chest, epigastric, back discomfort and weight loss. The urgent cases were truly symptomatic describing significant pain associated with their aneurysm although they had no radiographic evidence of leak.

TAAA type, size and aetiology 

45 Crawford Type II, 32 Type III and 11 Type I TAAAs were treated. 17 were classified as complex (9 dissections, 3 in an ‘hourglass’ configuration, 3 false aneurysms, 1 mycotic aneurysm and 1 intramural haematoma). The remainder of the patients had TAAA of the following types: 1 Type IV, 1 Type V (according to Safi's modification of the Crawford classification, see Table 1 and Fig. 1). The median aneurysm size was 7.31cm (Range 4–13cm). The aetiology of the majority of these TAAA was atherosclerotic degeneration – 64.8% (66/107). 26.2% (28/107) were due to dilation of chronic type B dissections. 7.5% (8/107) patients had a known diagnosis of Marfan's syndrome or similar connective tissue disorder and had dissections, secondary to their underlying disorder, associated with aneurysmal degeneration. 2.8% (3/107) developed false aneurysms following previous aortic surgery (1 previous type IV repair, 1 Carrell patch aneurysm, 1 previous aorto-bi-iliac repair) and 2.8% (3/107) had aneurysms that were mycotic in origin. One patient required a visceral hybrid for an extensive progressing intramural haematoma.

Table 1. Crawford's Classification of Thoraco-abdominal Aortic Aneurysms¹⁹

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• Figure 1 

  Safi's Classification System of Thoraco-abdominal Aortic. Aneurysms.^21.

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• Figure 2 

  Collaborative Number of Visceral Hybrids Performed for All Units.

Surgical approach and technique 

The technique of visceral hybrid repair has previously been well described.³ All cases were performed under general and epidural anaesthesia, with the patient in a supine position. A transperitoneal abdominal approach was used, which allowed exposure of the abdominal aorta and the origins of the renal arteries, the coeliac axis, and the superior mesenteric artery (SMA). The choice of inflow site for retrograde visceral artery bypass grafting was determined for each patient by previous abdominal aortic surgery and the extent of the aneurysmal disease. In the cases where an abdominal aortic aneurysm had already been repaired (n=21; 19.6%), the bypass grafts were anastomosed in an end-to-side fashion to the existing aortic graft, allowing room for stent deployment more proximally. Otherwise, the distal aorta or iliac arteries were selected. Either two inverted bifurcated Dacron grafts, or a single bifurcated graft with extra side branches for the renal arteries were used. The limb to the coeliac axis was tunnelled in front of the renal vein through the loose areolar tissue behind the pancreas, and the anastomosis was performed to the inferior aspect of the confluence between the hepatic and left gastric arteries. The graft to the SMA was placed in a “ lazy C” configuration. The renal artery bypasses were subsequently performed using an end-to-side renal anastomosis. Doppler signals were then confirmed in each recipient artery in turn, with the origins of the host vessel ligated to prevent endoleaks. The grafts were then excluded in the retroperitoneum by primary closure or, if that was not possible, by use of an omental flap to prevent bowel adhesion and consequent problems.

After debranching and revascularization of the visceral and renal arteries, endovascular exclusion of the thoraco-abdominal aneurysm was carried out. In the most extensive TAAAs, stent coverage extending into the aortic arch was required to achieve an adequate proximal landing zone. The left subclavian artery (LSCA) was covered in 19 patients with 12/19 (63.2%) patients undergoing LSCA re-vascularisation procedures.

Co-morbidities 

Table 2 demonstrates the co-morbidity prevalent in this patient group. The majority of patients (88.2%) were American Association of Anaesthesiologists (ASA) score >3, and a third (36.4%) had pre-operative renal impairment as defined by a serum creatinine >105μmol/l. A quarter of patients (26.2%) had undergone a previous coronary intervention, and 17.8% had symptoms of cardiac failure (New York Heart Association (NYHA) Functional Classification >1). Over a quarter (26.2%) of the patients had undergone previous thoracotomy with almost a fifth of patients (19.6%) having undergone previous abdominal aortic surgery, meaning many of these patients were high risk for open surgery.

Table 2. Patient co-morbidities and risk factors

Co-morbidity/factor	No of patients (n=107)	Percentage of patients (%)
Smoking (current or prior)	52	48.5
Hypertension	83	77.6
Previous MI, coronary stent or bypass	28	26.2
Symptomatic heart failure (NYHA >1)	19	17.8
Renal impairment (serum creatinine>105μmol/l)	39	36.4
ASA>3	88	82.2
Previous thoracotomy	28	26.2
Previous abdominal aortic surgery	21	19.6

(NYHA=New York Heart Association; ASA=American Association of Anaestheiologists).

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Results 

The visceral hybrid procedure (visceral bypass grafting+aortic stent-grafting) was successfully completed in 92.5% (99/107). Eight patients did not undergo a complete procedure (Table 3). In 4 patients, the procedure was abandoned due to peri-operative instability and 2 of these patients did not survive to discharge. One patient suffered an antegrade aortic arch dissection during the procedure; a formal aortic arch replacement was not performed and this patient died. The procedure was also abandoned in a patient who had an aneurysm secondary to a chronic type B dissection. Peri-operatively, a low flow rate in the true lumen was noticed and this was considered insufficient for safe revascularization of the renal and visceral arteries. This patient died from aneurysm rupture 10 days after the procedure was abandoned. In the two patients that survived to discharge, visceral bypasses were not completed as the first patient developed a pneumothorax peri-operatively and despite being supported with inotropes, became so cardiovascularly unstable that the procedure had to be abandoned. The other suffered a peri-operative arrest and subsequently required the insertion of a permanent pacemaker.

Table 3. Details of cases where a visceral hybrid procedure was not completed

The remaining 4 patients had successful visceral bypass grafting as part of a staged procedure but failed to proceed to aortic stent-grafting.

Simultaneous and staging of the visceral hybrid 

76.6% (82/107) of patients underwent visceral bypass grafting and aortic stent-grafting simultaneously within the context of the same procedure. The remaining 19.6% (21/107) underwent staged procedures. The median length of interval between first and second procedure was 20 days (Range 12–55). Unfortunately 3 patients ruptured whilst waiting for endovascular completion; 1 on day 4 post-bypass grafting, 1 on day 11 and the other 167 days later (this patient spent a significant amount of time on intensive care following the initial visceral/renal bypass grafting and never recovered to a point where aortic stent-grafting could be performed safely). One patient did not survive to undergo stenting and died after visceral bypass grafting from multi-organ failure 59 days after the visceral bypass grafting procedure.

Visceral bypass graft patency 

Visceral bypass graft patency was assessed intra-operatively with Doppler and thrombectomy performed as necessary. All patients had CT scanning prior to discharge, or sooner if branch graft occlusion was suspected from deterioration of renal function or signs of bowel ischaemia. Repeat CT scans were performed at 1 month, 6 months and 12 post procedure, with annual surveillance CT scans after the first year. Visceral/renal bypass graft patency at 30 days was 86.9% (93/107) of patients. Three patients developed bowel ischaemia and required resection (2.8%).

Endovascular stent-grafting and endoleak 

Talent and Valiant (Medtronic), Tag (Gore), Zenith (Cook) and combinations thereof were all used. The decision on which stent to use was made on a case-by-case basis. Each patient had a median of 4 stents placed (Range 1–9). The LSCA was covered in 19 patients and re-vascularised in 12 with a trend to move revascularisation towards the end of the series. The initial endoleak rate was 32.7% (33/101). See Table 4 for details.

Table 4. Details of endoleaks found on the 30-day CT scan

Endoleak Type		n
1	Either 1a or 1b	2
	1a	4
	1b	2
	1a+1b	1
1+2		4
2		11
3		5
Ambiguous	1 or 2	1
	2 or 3	2

Mortality 

Overall thirty-day mortality was 14.95% (16/107). The causes of death are shown in Table 5. Of the patients who died of rupture, one was after an abandoned procedure, and two occurred whilst waiting for the second stage of a planned staged procedure.

Table 5. 30-day mortality

Morbidity 

All patients went to an intensive care unit (ICU) post-procedure and there was a median ICU stay of 6 days (Range 0–66).

Neurological 

One patient who underwent a simultaneous aortic arch debranching procedure, developed a vocal cord palsy, and one patient suffered an embolic stroke post procedure. 12.1% (13/107) of patients suffered some degree of spinal cord ischaemia, of which there was at least a partial recovery in a third (4/13) patients, meaning 9/107 (8.4%) patients had full and permanent paraplegia. Two of the patients who died within 30 days of the visceral hybrid procedure also suffered from spinal cord ischaemia.

Renal failure 

A quarter (28/107, 26.2%) of patients required haemofiltration in the immediate post-operative period, and 4/107 (3.7%) patients required long term dialysis post-procedure.

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Discussion 

Patient cohort 

There are several striking characteristics of the patient population described. Almost a fifth of this cohort were over 75 years of age and as a whole, this patient group had significant co-morbidities rendering many unfit for an open repair.

Traditional open repair a feasible alternative? 

More than a quarter of the patients have had a previous thoracotomy for either cardiac or open thoracic aortic surgery. A redo thoracotomy in any patient is hazardous but in patients with concomitant co-morbidities, the risk is that much greater. We suggest that many of these patients would not have been offered a traditional open repair particularly one requiring a repeat thoracotomy. In addition, a fifth of our patients had some involvement of the distal aortic arch and over half of these patients required arch vessel re-vascularisation in addition to stenting. In open surgery, this proximal extension of the aneurysm would have made the traditional repair even more challenging. The success of a traditional approach is related to the extent of the aneurysm and in these very extensive aneurysms, the visceral hybrid may offer an advantage for these challenging patients.

Simultaneous versus staged visceral hybrid repair 

Although the visceral hybrid repair removes the need for a thoraco-laparotomy and aortic cross clamp, the bypass grafting via mid-line laparotomy still requires extensive intra-abdominal dissection. This procedure (excluding endovascular aneurysm exclusion) can take several hours and is still a significant physiological insult to an elderly patient with significant co-morbidities. As a result of this, some vascular surgeons choose to perform the visceral hybrid in two stages. This decision is made both pre- and peri-operatively.

Preoperatively, some of the authors elect to stage the visceral hybrid over a simultaneous procedure based on two hypotheses: (1) reduction of operation time associated with lower complication rates (hypothermia, blood loss, coagulation disorders) and (2) stabilization of spinal cord perfusion.⁴ The blood supply to the spinal cord is known to be from lumbar and intercostals vessels but is now thought to also have a supply derived from a collateral network of blood vessels.⁵ By allowing time for this network to ‘adjust’ to the presence of the visceral bypass grafts, it is felt that the staged aortic stenting might cause less disruption to this spinal cord blood supply network.

A similar argument pertains to peri-operative decisions to stage the visceral hybrid. In a haemodynamically unstable patient, extensive thoraco-abdominal aortic stenting would further compromise blood supply to the spinal cord when the blood pressure is already low, further increasing the risk of spinal cord ischaemia. By shortening the procedural time and staging the procedure, one can have the patient treated in an intensive care setting early, correct their parameters and stent-grafting can take place once the patient is haemodynamically stable again.

The most obvious disadvantage to a staged approach is the ongoing risk of rupture whilst waiting for endovascular completion of the procedure. Our series has 3 patients who ruptured whilst waiting for stenting and 1 that died before the second stage could be completed. Although some of the authors see a benefit in staging the visceral hybrid, it is difficult to accept the risk of rupture in the intervening period.

Another advantage of a simultaneous approach is that access for stent-grafting is facilitated with the abdomen already open for visceral bypass and a conduit may be easily included with the visceral grafts. Furthermore, the visceral grafts can be protected from embolisation during stent insertion and also checked thereafter for patency.

Overall, the majority of authors still advocate performing the visceral hybrid as a single stage procedure.

Endoleak 

The robustness and long-term durability of all endovascular aneurysm repairs has been the subject of much debate. Almost a third (32.7%, 33/101) of all patients undergoing a visceral hybrid demonstrated some type of endoleak, whilst the St Mary's initial report in 2006 demonstrated an even higher initial endoleak rate of 42% (11/29).³ The complex anatomies of the TAAAs we treat with this procedure have not changed and the reduction in endoleak is attributable to our ever-increasing experience as well as improvements in endovascular technology. Our general approach to endoleaks is summarised in Table 3. On completion angiography, if a type I endoleak is found, on-table intervention is normally undertaken. Type II endoleaks on the other hand are managed conservatively unless there is definite sac enlargement on surveillance post-operative CT scanning. We treat type III endoleaks by re-lining existing stent grafts.

Paraplegia 

Paraplegia remains one of the most feared complications of TAAA repair regardless of modality. In the open repair, despite excellent anaesthetic support, aortic cross-clamping necessitates cardiovascular instability. Changes in mean arterial blood pressure affect spinal cord perfusion and have been implicated in causing paraplegia both peri-⁶ and post-operatively.⁷ Also, despite investigation into the concomitant use of both motor⁸ and or sensory evoked potentials⁹ as operative adjuncts, or extensive pre-operative identification of the Artery of Adamkiewicz¹⁰ (or other major anterior segmental spinal cord artery) it remains unclear which intercostals/lumbar vessels require reattachment, the number of vessels that should be reattached and what relevance this has to the development of post-operative neurological deficit. The visceral hybrid does eliminate aortic cross-clamping and there is better cardiovascular stability during these procedures. However, the use of endovascular stent-grafts necessitates occlusion of aortic side branches. Despite the fact that our first report from St Mary's reported no paraplegia, we have always been aware of the potential risk of its development-particularly in those patients with type II TAAA requiring extensive aortic stent coverage. With this in mind, we have always routinely used cerebro-spinal fluid (CSF) drainage in all patients undergoing extensive thoracic stenting.

Confusingly, paraplegia rates across the three centres remained similar despite one unit not using routine CSF drainage. Although there have been reports of post-operative paraplegia being reversed with the insertion of a CSF drain in both open¹¹ and endovascular¹² TAA repairs, our results merely prove that the pathophysiology of the development of paraplegia in TAAA repair is still incompletely understood. Although CSF drainage may not be the complete solution, we would still advocate its routine use. Perhaps, biochemical markers of central nervous system damage may yield more answers to this complex question.

Mortality 

With exacting patient selection, in high-volume tertiary referral centres, some units have reported 30-day survival rate of 95% in a cohort of 2286 patients undergoing open TAAA repair.¹³ These results are in stark contrast to previous reports quoting 30-day mortality reports as high as 30%.¹⁴ Rigberg et al. recent report suggests that over a large state-wide population, overall elective patient mortality was 19% at 30 days.¹⁵ Clearly, any treatment modality that improves outcome in patients with TAAA is welcome and our current 30-day mortality rate of 14.95% demonstrates a comparable mortality to the traditional open repair in a group of patients with particularly extensive aneurysms. These results can be considered more impressive given that many of our patients would have been refused a traditional open repair in the first instance. A recent systematic review of hybrid open-endovascular repairs for TAAAs demonstrated a comparable overall early and long-term mortality rate for completed procedures of 15.5%.¹⁶ Although this was based on a series sampled from the literature and smaller than our own (58 patients from 13 small series from vascular units around the world), it suggests that the visceral hybrid technique may also be transferable if performed in centres with suitable expertise.

Fenestrated/branched stent-grafting 

The endovascular revolution has and continues to significantly impact on aneurysm repair. Just as endovascular stent-grafting was integral to the development of the visceral hybrid repair, there are now total endovascular TAAA repair options to a select group of patients in the form of fenestrated and branched grafts. The visceral hybrid repair removed the need for thoraco-laparotomy and aortic cross clamping. A wholly endovascular approach removes the need even for laparotomy, intra-abdominal dissection and visceral/renal arterial clamping seen in the hybrid. With the introduction of these newer endovascular therapies, some are now questioning whether there will be a role for debranching hybrid repairs. We argue that this thinking is premature. Fenestrated and branched endo-grafts remain a technology only suitable for select patients with specific aneurysmal anatomies and current endovascular technology for TAAA is limited by a number of anatomical factors including: ostial stenoses, tortuosity and angulation. Extensive pre-operative planning is vital to successful deployment. The bespoke manufacture of such grafts can take several weeks. These grafts are therefore inappropriate for urgent patients. In addition, the costs of these new stent-grafts are prohibitive to many centres around the world despite potential patient benefits.

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Conclusion 

Patients with TAAA are an elderly population with multiple significant co-morbidities. The patient cohort themselves may ultimately be the limiting factor in achieving even lower rates of morbidity and mortality. Therefore, regardless of the operative modality used, TAAA repair will remain a significant challenge to vascular surgeons around the world.

Despite being a relatively new technology, a wholly endovascular approach is clearly attractive and recent reports show a survival benefit over an open repair and potentially even that of the visceral hybrid.¹⁷, ¹⁸ For suitable patients, this may represent the future of TAAA repair. This collaborative report provides the largest consecutive series available for visceral hybrid repairs of TAAA. The early results are acceptable in a patient cohort with few other options. In high-risk patients in whom fenestrated or branched stent-grafting is not an option, and open surgery hazardous, the visceral hybrid represents a viable, robust and transferable treatment alternative. Therefore, in unfit patients with a type I, II or III TAAA, we offer the visceral hybrid procedure in preference to an open operation and for the time being will continue to do so.

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Financial Declaration 

AMTL. Choong research is funded by the Imperial College Healthcare Biomedical Research Centre as well as an educational grant from Medtronic, Inc, Minneapolis, MN, USA.

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Conflicts of Interest 

There are no known conflicts of interest.

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Acknowledgements 

The authors acknowledge the contribution of AMTL. Choong, P. Heider and M. Hanke.

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