Endovascular aneurysm repair
| Endovascular aneurysm repair | |
|---|---|
 Endovascular aneurysm repair | |
| ICD-9-CM | 39.51, 39.52, 39.7 |
Endovascular aneurysm repair (or endovascular aortic repair) (EVAR) is a type of endovascular surgery used to treat an abdominal aortic aneurysm (AAA) or thoracic aortic aneurysm, the procedure then specifically termed TEVAR (thoracic endovascular aortic/aneurysm repair). Aortic aneurysms are bulges in the aorta, the main blood vessel that brings blood from the heart to the rest of the body. In certain occasions, a specially designed custom-made graft device ("endograft"), which has holes (fenestrations) on the graft body to maintain the patency of certain important blood vessels, is used for the procedure, which is called FEVAR (fenestrated endovascular aortic/aneurysm repair). Standard EVAR is appropriate for aneurysms that begin below the renal arteries, where there exists an adequate length of normal aorta (the "proximal aortic neck") for reliable attachment of the endograft without leakage of blood around the device ("endoleak").
Patients with aneurysms require elective repair of their aneurysm when it reaches a diameter large enough where the risk of rupture is great. Repair is also warranted for aneurysms that rapidly enlarge or those that have been the source of emboli (debris from the aneurysm that dislodge and travel into other arteries). Lastly, repair is also indicated for aneurysms that are the source of pain and tenderness, which may indicate impending rupture. The options for repair include traditional open surgery or endovascular repair.
History
Noting the morbidity of open surgical repair of aortic aneurysms, particularly in the elderly and medically fragile patient, Dr. Juan Parodi began work on a less invasive procedure in 1976 at the Cleveland Clinic.[1] A few years later, Nicholas Volodos began similar work in Kharkov, Soviet Union and introduced in an article written in 1988.[2] Volodos performed the first endovascular repair of a thoracic aneurysm in 1987: a false aneurysm that likely developed from a motor vehicle accident three decades before. This patient did well, with successful endovascular thoracic aneurysm repair and died of unrelated causes 18 years later.
Parodi performed the first successful endovascular repair of an abdominal aortic aneurysm in 1990, although Volodos had attempted EVAR one year before in an unsuccessful procedure that was complicated by twisting an occlusion of the graft, requiring immediate conversion to traditional open surgical aneurysm repair.
Options for Treatment
When the aneurysm begins at close to the renal arteries, standard EVAR may not be contraindicated since there will be an inadequate length of suitable aorta for the endograft attachment. In these cases a fenestrated endograft may be useful, where the attachment of the endograft to the aorta may be placed above the renal arteries with each fenestration opposite a renal artery so that blood flow to the kidneys is maintained.
As another option in patients with short neck lengths below the renal arteries, EndoAnchors can be used to provide a more secure attachment. EndoAnchors are small, helically-shaped devices that are screwed through the endograft and into the aortic wall. After placement of multiple EndoAnchors, the configuration resembles, in principle, a traditional hand-sewn connection ("surgical anastomosis"). EndoAnchors not only increase the strength of the endograft-to-aortic connection, but they also improve sealing so that the risk of blood flow around the endograft (type Ia endoleak) is decreased.
When the aneurysm begins above the renal arteries, neither fenestrated endografts nor EndoAnchoring of an infrarenal endograft are useful (an open surgical repair may be necessary). Alternatively, a "branched" endograft may be used. A branched endograft has graft limbs that branch off of the main portion of the device to directly provide blood flow to the kidneys or the visceral arteries.
Patient Screening
Before patients are deemed to be a suitable candidate for this treatment, they have to go through a rigorous set of tests. These include a CT scan of the complete thorax/abdomen/pelvis, and blood tests. The CT scan gives precise measurements of the aneurysm and the surrounding anatomy. In particular the calibre/tortuosity of the iliac arteries and the relationship of the neck of the aneurysm to the renal arteries are important determinants of whether the aneurysm is amenable to endoluminal repair. In certain occasions that the renal arteries are too close to the aneurysm, the custom-made fenestrated graft stent is now an accepted alternative to doing open surgery.
The Procedure
The procedure is carried out in a sterile environment under x-ray fluoroscopic guidance. It is usually carried out by an interventional radiologist or vascular surgeon. The procedure can be performed under general, regional (spinal or epidural) or even local anesthesia.
Access to the patient's femoral arteries can be through small incisions at the top of each leg ("the groins"), or percutaneously through a needle and sheath. In either case, vascular sheaths are introduced into the patient's femoral arteries, through which the guidewires, catheters and eventually the endograft is passed.
Diagnostic angiography images or 'runs' are captured of the aorta to determine the location ofthe patient's renal arteries, so the stent graft can be deployed without blocking these. Failure to achieve this will cause renal failure. Precision and control of endograft deployment is extremely important. The "main" body of the endograft is placed first, follow by the "limbs" which join the main body and extend to the iliac arteries, effectively bypassing the aneurysm sac from blood flow
The abdominal aneurysm extends down to the common iliac arteries in about 25%-30% of patients. In such cases, the iliac limbs can be extended into the external iliac artery to bypass a common iliac aneurysm. Alternatively, a specially designed endograft, (iliac branch device) can be used. The preservation of the hypogastric (internal iliac) arteries is important to prevent buttock claudication and impotence, and every effort should be made to preserve flow to at least one hypogastric artery.
The endograft, once in place, acts as an artificial lumen for blood to flow through, and not into the surrounding aneurysm sac. This reduces the pressure in the aneurysm, which itself will usually thrombose and shrink in size over time.[3]
A newer adaption of EVAR is the Hybrid Procedure. A hybrid procedure occurs in the angiography room and aims to combine endovascular procedures with limited open surgery. In this procedure the stent graft deployment is planned to combine with an open operation to revascularise selected arteries that will be "covered" by the stent graft i.e. deprived of arterial inflow. In this method more extensive EVAR devices can be deployed to treat the primary lesion while preserving arterial flow to critical arteries.
Thoraco-abdominal aortic aneurysms (TAAA) typically involves such vessels and deployment of the EVAR device will cover important arteries e.g. visceral or renal arteries, resulting in end organ ischaemia which may not be survivable. The open operation component aims to bring a bypass graft from an artery outside the stent graft coverage to vital arteries within the coverage region. This component adds to the EVAR procedure in time and risk but is usually judged to be lesser that the risk of the major totally open operation.
Staging such procedures is common. A common example is revascularisation of the left common carotid artery and/or the left subclavian artery from the innominate artery or the right common carotid artery to allow treatment of a thoracic aortic aneurysm that encroachs proximally into the aortic arch to be treated without thoracotomy. Continued design improvement in stent graft including branched endografts will reduce but not eliminate this category of surgery. 'Chimney stents into the innominate artery with TEVAR into the proximal aortic arch have recently been described. Other surgeons favor limited thoracotomy with carotid-carotid bypass i.e. hybrid procedures.
All such procedures aim to reduce the morbidity and mortality of treating arterial disease in a patient population that is increasingly older and less fit than when major open repairs were developed and popularised. Even in those days, significant risks were accepted in the understanding than the large open operation was the only option. That is not the case in most patients today.
Complications
Durability and problems such as 'endoleaks' may require careful surveillance and adjuvant procedures to ensure success of the EVAR or EVAR/hybrid procedure. CT Angiography (CTA) imaging has in particular made a key contribution to planning, success, durability in this complex area of vascular surgery.
Arterial dissection,contrast-induced renal failure, thromboembolizaton, ischemic colitis, groin hematoma, wound infection, type II endoleaks, myocardial infarction, congestive heart failure, cardiac arrhythmias, respiratory failure
Endograft migration, aneurysm rupture, graft limb stenosis/kinking, type I/III/IV endoleaks
Endoleaks
An endoleak is a leak into the aneurysm sac after endovascular repair. Five types of endoleaks exist:[3]
- Type I - Perigraft leakage at proximal or distal graft attachment sites (near the renal and iliac arteries)
- Type II - Retrograde flow from collateral branches such as the lumbar and inferior mesenteric arteries
- Type III - Leakage between overlapping parts of the stent (i.e. connection between overlapping components) or rupture through graft material.
- Type IV - Leakage through the graft wall due to the quality (porosity) of the graft material
- Type V - Expansion of the aneurysm sac without an identifiable leak. Also called "endotension".
Use in aortic dissection
In uncomplicated type B aortic dissection, TEVAR does not seem either improve or compromise 2-year survival and adverse event rates.[4] Its use in complicated aortic dissection is under investigation.
References
- ^ Aho PS (2006). Expectations pf Endovascular Repair of Abdominal Aortic Aneurysm Academic dissertation.
- ^ Volodos' NL, Karpovich IP, Shekhanin VE, et al. A case of distant transfemoral endoprosthesis of the thoracic artery using a self-fixing synthetic prosthesis in traumatic aneurysm]. [Article in Russian] Grudn Khir. 1988 Nov-Dec;(6):84-6. PMID 3220297 [PubMed - indexed for MEDLINE]
- ^ a b Greenhalgh RM, Powell JT (2008). "Endovascular repair of abdominal aortic aneurysm". N. Engl. J. Med. 358 (5): 494–501. doi:10.1056/NEJMct0707524. PMID 18234753.
- ^ Nienaber CA, Rousseau H, Eggebrecht H; et al. (2009). "Randomized comparison of strategies for type B aortic dissection: the INvestigation of STEnt Grafts in Aortic Dissection (INSTEAD) trial". Circulation. 120 (25): 2519–28. doi:10.1161/CIRCULATIONAHA.109.886408. PMID 19996018.
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