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Endovascular stent grafting of aortic aneurysms
VASCULAR I
Endovascular stent grafting of aortic aneurysms
Treatment The majority of aortic aneurysms are situated in the infrarenal aorta, and so they can be repaired without major compromise to the renal and mesenteric circulation. The principle of aneurysm treatment in both open and endovascular repair is to produce a sealed conduit for blood to pass through the affected segment of aorta without leaking into (and pressurizing) the aneurysm sac. In the case of aortic stenting the graft is usually bifurcated (‘trouser graft’) in configuration, passing from the infrarenal aorta to the iliac vessels. In certain situations aorto-uni-iliac stent-grafts can be placed in combination with a femoral to femoral crossover graft to maintain contralateral leg perfusion. The following characteristics are demanded of the stent-graft in order to achieve satisfactory exclusion of the aneurysm by endovascular means: the introduction system should be of sufficiently small calibre and flexibility to allow insertion via the common femoral artery and passage up the iliac arteries the fixation mechanism should cause the proximal margin of the device to adhere firmly to the aortic wall at the desired point of implantation there should be adequate proximal and distal seals preventing leakage around the outside of the device into the sac (‘endoleak’) the device should be durable and should not fail during the lifetime of the patient. The first three prerequisites are largely fulfilled by current devices; the fourth is the subject of several long-term studies.
Jonathan Smout John D Rose Michael G Wyatt
Abstract This contribution reviews the current status of stent grafting for abdominal aortic aneurysms.
Keywords aortic; endoleak; endovascular; stent
Since 1991, treatment of aortic aneurysms with endovascular stents (endovascular aneurysm repair, EVAR) has become widely accepted as a viable alternative to open repair in selected patients. In many centres stenting has developed into the preferred first-line therapy in anatomically suitable patients owing to its superior 30-day mortality compared with open surgery.
Abdominal aortic aneurysms Aneurysmal dilatation of a vessel is defined as a 50% increase over the normal vessel diameter. For an abdominal aorta this approximates to a diameter of 3 cm in a male and 2.5 cm in a female. It is important to detect aortic aneurysms before they are at risk of rupture because the outcome following surgery for rupture is poor compared with elective surgery. Although many centres have survival rates from operated ruptured aortic aneurysms in excess of 50%, most patients with ruptured aneurysms die in the community before reaching hospital. Abdominal aortic aneurysms are five to nine times more common in men (present in 6% of those aged >80 years), and are strongly associated with increasing age, cigarette smoking, hypertension, hypercholesterolaemia and family history. The annual incidence of rupture increases with sac diameter, and reaches 50% for aneurysms of 8 cm in diameter. Studies have demonstrated survival benefits for the elective repair of aneurysms of 5.5 cm or greater in diameter.
Indications and contraindications for the endovascular repair of aneurysms With the development of aortic stent technology, the number of aneurysms suitable for EVAR is increasing. Over 70% of abdominal aortic aneurysms are morphologically suitable for endovascular repair with standard aortic stents. The morphology of the aneurysm neck is the main determining factor with regard to EVAR suitability. Although we discuss the newer developments of EVAR later in this article, traditional contraindications include: young age (<60 years) because of the lack of data on longterm durability short (<1.0 cm), conical or severely angulated proximal neck (the segment between the lowest renal artery and the sac) because of potential problems with graft fixation significant mural thrombus within the proximal neck severe iliac disease with extensive strictures or severe tortuosity.
Preoperative assessment
Jonathan Smout MD FRCS is a Specialist Registrar in Vascular Surgery at the Freeman Hospital, Newcastle upon Tyne, UK. Conflicts of interest: none declared.
Precise imaging of the aorta and iliac vessels is vital for EVAR planning. Spiral CT scanning with three-dimensional reconstruction allows an accurate assessment regarding EVAR suitability and device sizing (Figure 1). Most stents are modular in design, with each component (main body or iliac limb) available in a range of sizes that, in combination, allows a precise fit for each anatomical situation. It is often valuable to arrange a preoperative renal perfusion scan to provide details of the function of both kidneys, so care can be taken to protect a dominant kidney when there is functional disparity.
John D Rose FRCP FRCR is a Consultant Interventional Radiologist at the Freeman Hospital, Newcastle upon Tyne, UK. Conflicts of interest: none declared. Michael G Wyatt MSc MD FRCS is a Consultant Vascular Surgeon and Honorary Reader at the Freeman Hospital, Newcastle upon Tyne, UK. Conflicts of interest: none declared.
SURGERY 27:8
346
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Figure 2 A modern modular bifurcated aortic stent-graft.
a vascular surgeon with expertise in such repair. The procedure may be performed under local, regional or general anaesthesia depending on patient fitness and operator preference. Both common femoral arteries may be exposed surgically (although EVAR is carried out percutaneously in some centres in the UK). The renal arteries are located by angiography. The main body of the stent is inserted and deployed so that the top of the covered portion of the stent lies immediately below the renal ostia (Figure 4). Once the main body is in position, the positions of the internal iliac arteries are defined and the iliac limbs inserted just above the internal iliac ostia. Angiography is undertaken to check the patency of the renal and internal iliac arteries, and to Figure 1 Three-dimensional CT reconstruction of an abdominal aortic aneurysm, showing the proximal neck.
Aortic stent-grafts Devices consist of a stainless steel or nitinol (nickeletitanium alloy) framework covered with an impermeable fabric (Figure 2). Many modern grafts have a proximal uncovered segment to allow suprarenal fixation without causing obstruction to the renal artery ostia (Figure 3). Most devices have proximal external barbs or hooks to aid fixation to the aortic wall. As mentioned previously, most stents are modular in design and are bifurcated (bi-iliac) in configuration.
Insertion and deployment of aortic stent-grafts Endovascular repair of aortic aneurysms is ideally carried out in a dedicated operating theatre with high-quality digital radiographic equipment by an interventional radiologist and
SURGERY 27:8
Figure 3 Bare metal suprarenal fixation for stent-graft; the barbs allow improved wall anchorage.
347
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Angiography of an endovascular aneurysm graft. a Intraoperative image, during deployment of left limb, showing aneurysm sac (blue arrow) and lumbar arteries (white arrows). b Postoperative image showing suprarenal bare stent (green arrow), renal arteries (red arrows), branches of the superior mesenteric artery (blue bracket) and stent-graft in aorta and common iliac arteries (white arrow). Figure 4
confirm exclusion of the aneurysm sac. If persistent filling of the sac is seen, balloon moulding of the proximal or distal portions of the stent-graft may be needed to mould it against the aortic wall to achieve an adequate seal.
kinking of the graft body or limbs, or poor outflow owing to iliac or femoral artery stenosis. Graft thrombectomy and additional stenting may be undertaken if there are associated symptoms. Occasionally, a femorofemoral crossover procedure is needed.
Complications Stent-graft infection is rare. If graft infection is detected (e.g. on CT or labelled leucocyte scanning), the appropriate antibiotic therapy is given and subsequent management is similar to that for an infected conventional surgical graft.
Renal failure: elevation of serum creatinine concentrations is often seen after endovascular repair of aortic aneurysms, but usually reverts to normal in the recovery period. Renal damage may result from: coverage of the renal artery by the stent-graft nephrotoxic effects of iodinated contrast media cholesterol emboli a combination of these factors.
Classification of endovascular aneurysm repair-related endoleaks
An endoleak is a communication between the aneurysm sac and the circulation after endovascular repair of aortic aneurysms; endoleaks are classified into five types (Table 1). The commonest endoleak is the type 2, and this tends to be a relatively benign entity. Early type 2 endoleaks seal spontaneously in more than 80% of cases and are managed with CT surveillance. Type 1 and type 3 endoleaks are less common, but generally lead to sac enlargement and require early reintervention (most often with further co-axial stent placement). Open procedures (e.g. conversion to conventional repair) are occasionally required within the first few years to correct a problem with an EVAR.
4 5
Occlusion of the stent-graft is usually due to thrombosis secondary to poor blood flow. Contributory factors include
Table 1
SURGERY 27:8
Type Feature 1
2 3
348
Failure of proximal or distal attachment sites to seal, allowing blood to leak around the device into the redundant aortic sac Filling of the sac via collateral vessels (inferior mesenteric artery or lumbar arteries) Graft defect e break in the graft material or dislocation of a modular component of the stent-graft Graft wall porosity ‘Endotension’ or increasing aneurysm size without a visible leak
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Stent-graft migration: the most commonly used devices employ suprarenal fixation and barbs, so migration of the stent-graft distally is rare. Treatment is usually with an additional endovascular stent-graft (or ‘cuff’) to extend the covered section above the potential area of leakage. If a modular limb dislocates and results in a type 3 endoleak, it can be treated by endovascular limb extension.
that patients unfit for open repair have a poor prognosis independent of aneurysm repair. Durability Long-term problems with the durability of EVAR relate to graft failure, migration and endoleak. With EVAR being a relatively new entity, most long-term data relate to outdated devices. Data from the EVAR-1 trial demonstrated that 15% of the patients who were stented required secondary interventions, with approximately half being for type 2 endoleaks. With newer technologies, growing experience and a less aggressive approach to type 2 endoleaks, we would expect the secondary intervention rate to be smaller if the trial were to be repeated.
Wound-site complications: serious local complications are rare but occasionally re-exploration of the groin is required for repair of false aneurysms or evacuation of haematomas. Post-implantation syndrome: characterized by fever, leucocytosis and raised concentrations of inflammatory markers. Postimplantation syndrome is a common self-limiting illness that occurs within a few days of the procedure. Inspection of patients’ observation charts frequently demonstrates this phenomenon with a period of postoperative pyrexia.
Newer developments Fenestrated stents and branched grafts Placement of conventional aortic stents has always been limited by the confines of the origins of the major mesenteric and renal vessels. Where the ostia of these vessels are in close proximity to the proximal ‘landing zone’ of the stent, specialized grafts have been created with fenestrations (windows) to allow side-vessel perfusion to be maintained. Smaller stents may be placed through these fenestrations to maintain perfusion. The logical progression from fenestration has been the development of aortic stents with custom-made branches for the visceral vessels. This has widened the potential applications for these grafts; however, their use remains confined to specialist centres. Branched and fenestrated grafts are custom made and hence considerably more expensive than conventional infrarenal grafts.
Distal embolization: very rarely, patients who have undergone endovascular repair of aortic aneurysms may suffer small- or large-vessel embolization of the lower limb by atheromatous debris dislodged during insertion of the stent-graft. Conservative, radiological or surgical therapy is indicated depending on the degree of ischaemia.
Follow-up The imaging protocol should allow the early detection and treatment of complications. CT with administration of intravenous contrast shows endoleaks, occlusions and aneurysm sac size. Plain radiographs show mechanical complications, such as fractures of the stent struts, migration or distortion of the stentgraft. A typical protocol is CT at 1 and 12 months, followed by annual CT and plain radiographs. The latest follow-up protocols under consideration replace CT scans with Doppler ultrasound examination in order to reduce costs, nephrotoxicity and radiation exposure.
Hybrid endovascular repairs An alternative to creating a complex branched graft has been the development of ‘hybrid’ techniques in the management of thoracoabdominal aneurysms. These techniques combine an open approach to visceral artery revascularization with endovascular stenting of the aortic aneurysm. The open extra-anatomical bypass to the visceral vessels is often from the iliac arteries using prosthetic grafts. The stenting procedure can be carried out either at the same time as the original operation or in a staged fashion. Similar techniques are employed in the thoracic aorta where the origins of the carotid and subclavian vessels may be compromised.
Outcomes Safety Two large randomized controlled trials have examined open repair versus EVAR for the management of elective abdominal aortic aneurysms. The UK-based EVAR-1 trial and Dutch Randomized Endovascular Aneurysm Management (DREAM) trial produced broadly similar results, the 30-day mortality rate for EVAR being less than 2% compared with approximately 5% for open repair. Although both trials have demonstrated a reduction in long-term aneurysm-related death, they have not been able to show an improvement in all-cause mortality. It has therefore been argued that the extra costs associated with EVAR may not be justified by long-term all-cause mortality alone. The UK based EVAR-2 trial also looked at patients unfit for open surgery. Patients were randomized to either EVAR or medical therapy alone. Owing to difficulties in conducting such a trial and the relatively small number of patients enrolled, there have been criticisms of the validity of the results. The key points to draw from this study are the lower than expected rate of rupture for untreated aneurysms (9% per annum), and the fact
SURGERY 27:8
Endovascular repair of ruptured abdominal aortic aneurysms Although endovascular repair of acute aortic ruptures is not a new concept, it is still a specialist treatment option offered by only a few dedicated endovascular teams. Endovascular repair of ruptured abdominal aortic aneurysms is an attractive option, with published 30-day mortality rates of 6e17% in comparison to pooled mortality data of about 40% for emergency open repair. Important physiological advantages are conferred by the avoidance of laparotomy, aortic cross-clamping and general anaesthesia. To assess the benefits of EVAR in the treatment of aortic ruptures, methodically, the Immediate Management of Patients with Ruptured aneurysm: Open Versus Endovascular repair (IMPROVE) trial is planned to commence shortly. This trial will hopefully provide us with the necessary information to decide whether facilities should be made available at a national level for EVAR in aortic rupture.
349
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Endovascular repair of the thoracic aorta
First, stroke may result from manipulation of devices in the aortic arch, causing embolization to the intracerebral vessels, or from hypoperfusion owing to occlusion of the vertebral or carotid arteries. Second, coverage of the intercostal arteries by the graft may result in spinal ischaemia and paraplegia, although this is less common than with open repair owing to the avoidance of aortic cross-clamping and maintenance of visceral perfusion. A
Over the past decade, stent-grafts in the thoracic aorta have become an established technique for the exclusion of thoracic aortic aneurysms and for type B aortic dissection (i.e. dissection distal to the arch vessels). As with open repair, the aim is to provide durable exclusion of the aneurysm sac or dissection with minimal procedural morbidity and mortality. For thoracic aneurysms, the indications for stent-graft placement are similar to those for surgery (e.g. sac diameter >6 cm, symptomatic or rapidly enlarging aneurysms). There should be 15e20 mm of normal aorta distal to the left subclavian origin and proximal to the coeliac axis to provide proximal and distal seals. However, coverage of the left subclavian artery by graft material is often inevitable. Adjunctive surgical bypass procedures may be required to maintain adequate cerebral circulation when the aortic arch is involved in the disease process. These interventions follow similar principles to the ‘hybrid’ aortic surgery discussed previously. Placement of a stent-graft in the thoracic aorta is vulnerable to broadly the same complications as placement of stent-grafts in the abdominal aorta, with two further specific considerations.
SURGERY 27:8
FURTHER READING Beard JD, Gaines PA, eds. Vascular and endovascular surgery: a companion to specialist surgical practice. 3rd edn. Philadelphia, USA: Saunders; 2005. Earnshaw JJ, Murie JM, eds. The evidence for vascular surgery. 2nd edn. Shrewsbury: tfm Publishing; 2007. Hinchliffe RJ, Ivancev K. Endovascular aneurysm repair: current and future status. Cardiovasc Intervent Radiol 2008; 31: 451e9. Wyatt MG, Watkinson AF. Endovascular therapies: current evidence. Shrewsbury: tfm Publishing; 2006.
350
Ó 2009 Elsevier Ltd. All rights reserved.
Endovascular stent grafting of aortic aneurysms
Treatment The majority of aortic aneurysms are situated in the infrarenal aorta, and so they can be repaired without major compromise to the renal and mesenteric circulation. The principle of aneurysm treatment in both open and endovascular repair is to produce a sealed conduit for blood to pass through the affected segment of aorta without leaking into (and pressurizing) the aneurysm sac. In the case of aortic stenting the graft is usually bifurcated (‘trouser graft’) in configuration, passing from the infrarenal aorta to the iliac vessels. In certain situations aorto-uni-iliac stent-grafts can be placed in combination with a femoral to femoral crossover graft to maintain contralateral leg perfusion. The following characteristics are demanded of the stent-graft in order to achieve satisfactory exclusion of the aneurysm by endovascular means: the introduction system should be of sufficiently small calibre and flexibility to allow insertion via the common femoral artery and passage up the iliac arteries the fixation mechanism should cause the proximal margin of the device to adhere firmly to the aortic wall at the desired point of implantation there should be adequate proximal and distal seals preventing leakage around the outside of the device into the sac (‘endoleak’) the device should be durable and should not fail during the lifetime of the patient. The first three prerequisites are largely fulfilled by current devices; the fourth is the subject of several long-term studies.
Jonathan Smout John D Rose Michael G Wyatt
Abstract This contribution reviews the current status of stent grafting for abdominal aortic aneurysms.
Keywords aortic; endoleak; endovascular; stent
Since 1991, treatment of aortic aneurysms with endovascular stents (endovascular aneurysm repair, EVAR) has become widely accepted as a viable alternative to open repair in selected patients. In many centres stenting has developed into the preferred first-line therapy in anatomically suitable patients owing to its superior 30-day mortality compared with open surgery.
Abdominal aortic aneurysms Aneurysmal dilatation of a vessel is defined as a 50% increase over the normal vessel diameter. For an abdominal aorta this approximates to a diameter of 3 cm in a male and 2.5 cm in a female. It is important to detect aortic aneurysms before they are at risk of rupture because the outcome following surgery for rupture is poor compared with elective surgery. Although many centres have survival rates from operated ruptured aortic aneurysms in excess of 50%, most patients with ruptured aneurysms die in the community before reaching hospital. Abdominal aortic aneurysms are five to nine times more common in men (present in 6% of those aged >80 years), and are strongly associated with increasing age, cigarette smoking, hypertension, hypercholesterolaemia and family history. The annual incidence of rupture increases with sac diameter, and reaches 50% for aneurysms of 8 cm in diameter. Studies have demonstrated survival benefits for the elective repair of aneurysms of 5.5 cm or greater in diameter.
Indications and contraindications for the endovascular repair of aneurysms With the development of aortic stent technology, the number of aneurysms suitable for EVAR is increasing. Over 70% of abdominal aortic aneurysms are morphologically suitable for endovascular repair with standard aortic stents. The morphology of the aneurysm neck is the main determining factor with regard to EVAR suitability. Although we discuss the newer developments of EVAR later in this article, traditional contraindications include: young age (<60 years) because of the lack of data on longterm durability short (<1.0 cm), conical or severely angulated proximal neck (the segment between the lowest renal artery and the sac) because of potential problems with graft fixation significant mural thrombus within the proximal neck severe iliac disease with extensive strictures or severe tortuosity.
Preoperative assessment
Jonathan Smout MD FRCS is a Specialist Registrar in Vascular Surgery at the Freeman Hospital, Newcastle upon Tyne, UK. Conflicts of interest: none declared.
Precise imaging of the aorta and iliac vessels is vital for EVAR planning. Spiral CT scanning with three-dimensional reconstruction allows an accurate assessment regarding EVAR suitability and device sizing (Figure 1). Most stents are modular in design, with each component (main body or iliac limb) available in a range of sizes that, in combination, allows a precise fit for each anatomical situation. It is often valuable to arrange a preoperative renal perfusion scan to provide details of the function of both kidneys, so care can be taken to protect a dominant kidney when there is functional disparity.
John D Rose FRCP FRCR is a Consultant Interventional Radiologist at the Freeman Hospital, Newcastle upon Tyne, UK. Conflicts of interest: none declared. Michael G Wyatt MSc MD FRCS is a Consultant Vascular Surgeon and Honorary Reader at the Freeman Hospital, Newcastle upon Tyne, UK. Conflicts of interest: none declared.
SURGERY 27:8
346
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Figure 2 A modern modular bifurcated aortic stent-graft.
a vascular surgeon with expertise in such repair. The procedure may be performed under local, regional or general anaesthesia depending on patient fitness and operator preference. Both common femoral arteries may be exposed surgically (although EVAR is carried out percutaneously in some centres in the UK). The renal arteries are located by angiography. The main body of the stent is inserted and deployed so that the top of the covered portion of the stent lies immediately below the renal ostia (Figure 4). Once the main body is in position, the positions of the internal iliac arteries are defined and the iliac limbs inserted just above the internal iliac ostia. Angiography is undertaken to check the patency of the renal and internal iliac arteries, and to Figure 1 Three-dimensional CT reconstruction of an abdominal aortic aneurysm, showing the proximal neck.
Aortic stent-grafts Devices consist of a stainless steel or nitinol (nickeletitanium alloy) framework covered with an impermeable fabric (Figure 2). Many modern grafts have a proximal uncovered segment to allow suprarenal fixation without causing obstruction to the renal artery ostia (Figure 3). Most devices have proximal external barbs or hooks to aid fixation to the aortic wall. As mentioned previously, most stents are modular in design and are bifurcated (bi-iliac) in configuration.
Insertion and deployment of aortic stent-grafts Endovascular repair of aortic aneurysms is ideally carried out in a dedicated operating theatre with high-quality digital radiographic equipment by an interventional radiologist and
SURGERY 27:8
Figure 3 Bare metal suprarenal fixation for stent-graft; the barbs allow improved wall anchorage.
347
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Angiography of an endovascular aneurysm graft. a Intraoperative image, during deployment of left limb, showing aneurysm sac (blue arrow) and lumbar arteries (white arrows). b Postoperative image showing suprarenal bare stent (green arrow), renal arteries (red arrows), branches of the superior mesenteric artery (blue bracket) and stent-graft in aorta and common iliac arteries (white arrow). Figure 4
confirm exclusion of the aneurysm sac. If persistent filling of the sac is seen, balloon moulding of the proximal or distal portions of the stent-graft may be needed to mould it against the aortic wall to achieve an adequate seal.
kinking of the graft body or limbs, or poor outflow owing to iliac or femoral artery stenosis. Graft thrombectomy and additional stenting may be undertaken if there are associated symptoms. Occasionally, a femorofemoral crossover procedure is needed.
Complications Stent-graft infection is rare. If graft infection is detected (e.g. on CT or labelled leucocyte scanning), the appropriate antibiotic therapy is given and subsequent management is similar to that for an infected conventional surgical graft.
Renal failure: elevation of serum creatinine concentrations is often seen after endovascular repair of aortic aneurysms, but usually reverts to normal in the recovery period. Renal damage may result from: coverage of the renal artery by the stent-graft nephrotoxic effects of iodinated contrast media cholesterol emboli a combination of these factors.
Classification of endovascular aneurysm repair-related endoleaks
An endoleak is a communication between the aneurysm sac and the circulation after endovascular repair of aortic aneurysms; endoleaks are classified into five types (Table 1). The commonest endoleak is the type 2, and this tends to be a relatively benign entity. Early type 2 endoleaks seal spontaneously in more than 80% of cases and are managed with CT surveillance. Type 1 and type 3 endoleaks are less common, but generally lead to sac enlargement and require early reintervention (most often with further co-axial stent placement). Open procedures (e.g. conversion to conventional repair) are occasionally required within the first few years to correct a problem with an EVAR.
4 5
Occlusion of the stent-graft is usually due to thrombosis secondary to poor blood flow. Contributory factors include
Table 1
SURGERY 27:8
Type Feature 1
2 3
348
Failure of proximal or distal attachment sites to seal, allowing blood to leak around the device into the redundant aortic sac Filling of the sac via collateral vessels (inferior mesenteric artery or lumbar arteries) Graft defect e break in the graft material or dislocation of a modular component of the stent-graft Graft wall porosity ‘Endotension’ or increasing aneurysm size without a visible leak
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Stent-graft migration: the most commonly used devices employ suprarenal fixation and barbs, so migration of the stent-graft distally is rare. Treatment is usually with an additional endovascular stent-graft (or ‘cuff’) to extend the covered section above the potential area of leakage. If a modular limb dislocates and results in a type 3 endoleak, it can be treated by endovascular limb extension.
that patients unfit for open repair have a poor prognosis independent of aneurysm repair. Durability Long-term problems with the durability of EVAR relate to graft failure, migration and endoleak. With EVAR being a relatively new entity, most long-term data relate to outdated devices. Data from the EVAR-1 trial demonstrated that 15% of the patients who were stented required secondary interventions, with approximately half being for type 2 endoleaks. With newer technologies, growing experience and a less aggressive approach to type 2 endoleaks, we would expect the secondary intervention rate to be smaller if the trial were to be repeated.
Wound-site complications: serious local complications are rare but occasionally re-exploration of the groin is required for repair of false aneurysms or evacuation of haematomas. Post-implantation syndrome: characterized by fever, leucocytosis and raised concentrations of inflammatory markers. Postimplantation syndrome is a common self-limiting illness that occurs within a few days of the procedure. Inspection of patients’ observation charts frequently demonstrates this phenomenon with a period of postoperative pyrexia.
Newer developments Fenestrated stents and branched grafts Placement of conventional aortic stents has always been limited by the confines of the origins of the major mesenteric and renal vessels. Where the ostia of these vessels are in close proximity to the proximal ‘landing zone’ of the stent, specialized grafts have been created with fenestrations (windows) to allow side-vessel perfusion to be maintained. Smaller stents may be placed through these fenestrations to maintain perfusion. The logical progression from fenestration has been the development of aortic stents with custom-made branches for the visceral vessels. This has widened the potential applications for these grafts; however, their use remains confined to specialist centres. Branched and fenestrated grafts are custom made and hence considerably more expensive than conventional infrarenal grafts.
Distal embolization: very rarely, patients who have undergone endovascular repair of aortic aneurysms may suffer small- or large-vessel embolization of the lower limb by atheromatous debris dislodged during insertion of the stent-graft. Conservative, radiological or surgical therapy is indicated depending on the degree of ischaemia.
Follow-up The imaging protocol should allow the early detection and treatment of complications. CT with administration of intravenous contrast shows endoleaks, occlusions and aneurysm sac size. Plain radiographs show mechanical complications, such as fractures of the stent struts, migration or distortion of the stentgraft. A typical protocol is CT at 1 and 12 months, followed by annual CT and plain radiographs. The latest follow-up protocols under consideration replace CT scans with Doppler ultrasound examination in order to reduce costs, nephrotoxicity and radiation exposure.
Hybrid endovascular repairs An alternative to creating a complex branched graft has been the development of ‘hybrid’ techniques in the management of thoracoabdominal aneurysms. These techniques combine an open approach to visceral artery revascularization with endovascular stenting of the aortic aneurysm. The open extra-anatomical bypass to the visceral vessels is often from the iliac arteries using prosthetic grafts. The stenting procedure can be carried out either at the same time as the original operation or in a staged fashion. Similar techniques are employed in the thoracic aorta where the origins of the carotid and subclavian vessels may be compromised.
Outcomes Safety Two large randomized controlled trials have examined open repair versus EVAR for the management of elective abdominal aortic aneurysms. The UK-based EVAR-1 trial and Dutch Randomized Endovascular Aneurysm Management (DREAM) trial produced broadly similar results, the 30-day mortality rate for EVAR being less than 2% compared with approximately 5% for open repair. Although both trials have demonstrated a reduction in long-term aneurysm-related death, they have not been able to show an improvement in all-cause mortality. It has therefore been argued that the extra costs associated with EVAR may not be justified by long-term all-cause mortality alone. The UK based EVAR-2 trial also looked at patients unfit for open surgery. Patients were randomized to either EVAR or medical therapy alone. Owing to difficulties in conducting such a trial and the relatively small number of patients enrolled, there have been criticisms of the validity of the results. The key points to draw from this study are the lower than expected rate of rupture for untreated aneurysms (9% per annum), and the fact
SURGERY 27:8
Endovascular repair of ruptured abdominal aortic aneurysms Although endovascular repair of acute aortic ruptures is not a new concept, it is still a specialist treatment option offered by only a few dedicated endovascular teams. Endovascular repair of ruptured abdominal aortic aneurysms is an attractive option, with published 30-day mortality rates of 6e17% in comparison to pooled mortality data of about 40% for emergency open repair. Important physiological advantages are conferred by the avoidance of laparotomy, aortic cross-clamping and general anaesthesia. To assess the benefits of EVAR in the treatment of aortic ruptures, methodically, the Immediate Management of Patients with Ruptured aneurysm: Open Versus Endovascular repair (IMPROVE) trial is planned to commence shortly. This trial will hopefully provide us with the necessary information to decide whether facilities should be made available at a national level for EVAR in aortic rupture.
349
Ó 2009 Elsevier Ltd. All rights reserved.
VASCULAR I
Endovascular repair of the thoracic aorta
First, stroke may result from manipulation of devices in the aortic arch, causing embolization to the intracerebral vessels, or from hypoperfusion owing to occlusion of the vertebral or carotid arteries. Second, coverage of the intercostal arteries by the graft may result in spinal ischaemia and paraplegia, although this is less common than with open repair owing to the avoidance of aortic cross-clamping and maintenance of visceral perfusion. A
Over the past decade, stent-grafts in the thoracic aorta have become an established technique for the exclusion of thoracic aortic aneurysms and for type B aortic dissection (i.e. dissection distal to the arch vessels). As with open repair, the aim is to provide durable exclusion of the aneurysm sac or dissection with minimal procedural morbidity and mortality. For thoracic aneurysms, the indications for stent-graft placement are similar to those for surgery (e.g. sac diameter >6 cm, symptomatic or rapidly enlarging aneurysms). There should be 15e20 mm of normal aorta distal to the left subclavian origin and proximal to the coeliac axis to provide proximal and distal seals. However, coverage of the left subclavian artery by graft material is often inevitable. Adjunctive surgical bypass procedures may be required to maintain adequate cerebral circulation when the aortic arch is involved in the disease process. These interventions follow similar principles to the ‘hybrid’ aortic surgery discussed previously. Placement of a stent-graft in the thoracic aorta is vulnerable to broadly the same complications as placement of stent-grafts in the abdominal aorta, with two further specific considerations.
SURGERY 27:8
FURTHER READING Beard JD, Gaines PA, eds. Vascular and endovascular surgery: a companion to specialist surgical practice. 3rd edn. Philadelphia, USA: Saunders; 2005. Earnshaw JJ, Murie JM, eds. The evidence for vascular surgery. 2nd edn. Shrewsbury: tfm Publishing; 2007. Hinchliffe RJ, Ivancev K. Endovascular aneurysm repair: current and future status. Cardiovasc Intervent Radiol 2008; 31: 451e9. Wyatt MG, Watkinson AF. Endovascular therapies: current evidence. Shrewsbury: tfm Publishing; 2006.
350
Ó 2009 Elsevier Ltd. All rights reserved.