New Frontier in Minimally Invasive Treatment for Abdominal Aortic Aneurysms
Mr Lee (not his real name), a 68-year-old Chinese man, was referred to Tan Tock Seng Hospital (TTSH) after his general practitioner (GP) felt a pulsating mass in his abdomen. A Computerised Tomography (CT) scan revealed a large Abdominal Aortic Aneurysm (AAA).
He has severe ischaemic heart disease after a myocardial infarction which left him with impaired ejection fraction of 20%. He refused to undergo treatment for his AAA, as his neighbour had open surgical repair of AAA 8 years ago and stayed in the hospital for 12 days, spending a significant time in the intensive care unit. His daughter echoed the same thought, and felt that his ‘heart was too weak for him to undergo major surgery’.
I reassured him that advances in technology have resulted in widespread application of minimally invasive treatment for AAA and explained that his neighbour’s traditional surgery for AAA involved a laparotomy, cross-clamping of the aorta, and a prosthetic graft replacement of the aneurysmal portion, resulting in his prolonged stay at the hospital and significant morbidity and mortality.
The minimally invasive treatment of AAAs, using endovascular techniques grew in popularity during the 1990s. Today, a majority of AAAs are treated using the EndoVascular Aneurysm Repair (EVAR) method.
EVAR is carried out with two small incisions in the groin, where several stent grafts are passed into the aneurysmal aorta and deployed for reinforcement while under fluoroscopic x-ray guidance. This creates a new path for blood to flow through, thus excluding blood flow from the aneurysm. Randomised controlled trials have shown a reduction in operative mortality by more than half in patients undergoing EVAR, as compared to traditional open surgery.
How Do AAAS Present?
AAAs are primarily a condition of the elderly, affecting those above 55 years old, with a predilection for males. The main risk factors are hypertension and cigarette smoking.
Most patients have their AAAs discovered incidentally on imaging for an unrelated symptom, or because they feel a pulsatile mass in their abdomen. Unfortunately, some patients present with a ruptured AAA or symptomatic AAA (AAA in the presence of abdominal and back pain is a sign of impending rupture), and require emergent surgery. The mortality from ruptured AAAs are 80%, and the treatment for this is often open surgery via laparotomy, as the patient is usually too unstable for EVAR.
This highlights the importance of early detection and elective repair to reduce the mortality and morbidity associated with a ruptured AAA. Treatment is offered to patients when their AAAs grow to more than 5.5cm.
When Is Evar Suitable?
80% of AAAs are infra-renal (below the kidney blood vessels) and are suitable for conventional EVAR. However, 20% of AAAs may not be suitable for the standard off-theshelf EVAR devices and will require customisation and complex endovascular treatment.
A few complex EVAR options are illustrated below.
A) Fenestrated EVAR
Fenestrated EVARs are custom-made devices tailored to the patient’s anatomy, and manufactured to fit individual patients should they have complex aneurysms that cannot be treated with conventional EVAR. These patients usually have juxtarenal aneurysms or thoracoabdominal aneurysms which extend very closely to or involve the renal and visceral vessels. These EVAR devices have small fenestrations (holes) to accommodate the renal arteries, superior mesenteric arteries and coeliac arteries.
Traditionally, these patients require an open surgical repair of their aneurysm, which carries a higher risk. Unfortunately, in the past, some patients unfit for open surgical repair had to accept the risk of rupture and mortality as the aneurysm grew.
With fenestrated EVAR, we have been able to offer a treatment option for such patients previously deemed inoperable.
B) Branch Graft EVAR
Up to 30% of AAAs are associated with concomitant iliac aneurysms. The traditional approach to iliac aneurysms was to sacrifice the internal iliac arteries, in order to achieve total exclusion of the common iliac artery aneurysm. However, this can be associated with catastrophic bowel ischaemia, buttock necrosis, and pelvic ischaemia, causing buttock claudication.
As part of our armamentarium in TTSH to treat such complex aneurysms, we use the Iliac Bifurcation Device (IBD) to maintain patency of the internal iliac artery and pelvic circulation, while repairing the aneurysm effectively. This device comes with a side branch which is deployed in conjunction with a main EVAR stent graft. Another smaller stent graft is then placed into the side branch to channel blood into the internal iliac artery to preserve it.
C) Novel Devices
There are several EVAR devices available in the market and each has its own strengths and limitations. A device’s suitability for its patient depends on individual considerations.
Thus, a variety of EVAR devices is currently employed at TTSH. The latest innovative treatment for AAA is called Endovascular Aneurysm Sealing (EVAS). This technique involves the use of two stent grafts inserted into the aorta with specially attached endobags, which are then inflated with a liquid polymer that subsequently hardens to occupy the entire aneurysm cavity. This acts to anchor the stent graft and seals the entire aneurysm.
This new technique reduces the risk of treatment failure associated with traditional EVAR devices such as persistent blood flow in the aneurysm after EVAR, which is known as endoleak. Endoleaks can occur in a few ways. It can occur as a result of migration of the EVAR stent graft or because blood is able to squeeze past the EVAR stent graft to continue to fill the aneurysm. Endoleaks can also happen when blood enters the aneurysm directly through small vessels feeding into the aneurysm. The EVAS device addresses all these clinical challenges and provides another option for treatment of AAAs.
With the advent of new closure devices, EVAR can now be performed with two 1 to 2 cm stab incisions in the groin rather than conventional 6 to 8 cm surgical incisions.
This has allowed us to perform EVAR for patients under local anaesthesia, if their underlying co-morbidities deem them at too high a risk for general anaesthesia.
Up to 50% of EVAR performed by TTSH are now percutaneous. The advantages include shorter operative time, less post-operative pain, lower risk of infection, lesser blood loss and smaller scars.
The story continues …
Mr Lee subsequently underwent percutaneous EVAR. With minimal pain experienced after the surgery, he was able to ambulate independently on the first day after his surgery and was discharged from hospital on the second day. A month later, during his scheduled review, Mr Lee’s daughter remarked that she can hardly even see the scars from the operation.
Primary care physicians are indispensable partners in healthcare for our population and play an important role in managing the chronic conditions of patients. For patients above the age of 55 years old, especially males with a history of hypertension and/or cigarette smokers, an abdominal examination may be able to elicit a pulsatile mass characteristic of AAA.
Should you suspect that a patient has AAA or clinical examination proves inconclusive for AAA, we can arrange for a simple ultrasound scan for further investigation. If a patient’s AAA has reached the size criteria for treatment, a CT scan will be arranged in preparation for EVAR planning. Should a small AAA be detected, the patient will then be placed on an ultrasound surveillance programme with scanning intervals ranging from 6 months to 1 year, and intervention offered only when the size criteria for treatment is met.
Multidisciplinary Team In TTSH
All EVARs in TTSH are performed by vascular surgeons in collaboration with the interventional radiologists along with a team of anaesthetists, radiographers, nurses and operating theatre support staff. Patients undergo stringent pre-operative assessment and are referred to other specialties such as Cardiology, should they require further pre-operative optimisation.
This is especially important as most AAA patients have other cardiovascular co-morbidities, and a multidisciplinary approach towards aneurysm surgery ensures that every patient receives high quality, safe and individualised care.
By Adj. Assistant Prof. Glenn Tan
Head of the Vascular Diagnostic Laboratory and Consultant in the Department of General Surgery in Tan Tock Seng Hospital.