Selection of specific management protocols for patients with aortic aneurysms depends on the disease morphology as well as patient’s age, overall health status, and comorbidities involved. In cases involving smaller and relatively stable abdominal or thoracic aortic aneurysm (AAA or TAA), watchful waiting represents a commonly preferred approach. Radical surgical or endovascular interventions are generally reserved for cases when the diameter of the aneurismal sac is larger than 5cm to 5.5cm, or the annual expansion rate exceeds 1.0 cm, or when the aneurysm becomes symptomatic.
Surgical Repair of Aortic Aneurysms
Prior to the advent of AAA/TAA endovascular repair tools and techniques, a highly invasive and risky surgical repair procedure constituted the only curative option for patients with advanced and rupture prone aortic aneurysm. Conducted under the general anesthesia the procedure takes a few hours and entails a major and highly traumatic operation with a 10-15 inch cut in abdominal wall, clamping and isolation of aneurysmic segment of aorta, incision into the aneurysm, evacuation of the clot contained within, placement of a synthetic graft, and wrapping of the graft with remnants of the aortic wall.
The typical surgical aneurysm repair is associated with a substantial (5% to 8%) mortality rate and serious complications, such as stroke, myocardial infarction, renal failure etc.
Due to the close proximity to the heart, the risk and complication rates of surgical intervention for aneurysm repair on the thoracic aorta increase multifold resulting in an average procedural mortality rate of up to 30 percent.
The high cost of the procedure is largely the result of extended ICU and hospital stays, which can last upwards of a week (but average roughly 10-12 days). Further, postoperative recovery may require up to six additional weeks subsequent to discharge, making temporary disability a major consideration for many patients.
Notwithstanding these drawbacks, open surgical aortic aneurysm repair is still commonly regarded as highly effective treatment modality that virtually eliminates the risk of aneurismal sac rupture and does not require extensive postoperative follow-up exams or revisions.
However, because of high prevalence of elderly and health-impaired persons in diagnosed aortic aneurysm caseloads and traumatic nature of AAA/TAA surgery, only a fraction of the patients who could benefit from surgical aneurysm repair is deemed eligible for such a procedure.
Abdominal Aortic Aneurysm Repair with Endovascular Stent-Grafts
During the past two decades, advances in interventional technologies paved the way for the advent of a considerably less invasive and risky endovascular AAA repair procedure. The procedure involves a transcatheter deployment of the specially designed endovascular prosthesis (typically combining sealing functions of the vascular graft and full or partial stenting support structure) into a defective segment of aorta with the goal of excluding the aneurysmal sac from blood circulation.
The endovascular stent-grafts (SGs) – which come both in self-expanding or balloon-expandable versions – are typically anchored to an undamaged part of the aorta both above and below the aneurysm via a compression fit or/and with a special fixation mechanism like hooks, barbs, etc.
To accommodate a great morphological diversity of aortic aneurysms the vast majority of endovascular SGs is employing a modular design concept providing the aorto iliac, bifurcated and straight tubular device configurations to cover a variety of AAA indications. Several SG systems also feature an open stenting structure at proximal end to enable suprarenal device deployment required in about 30% to 35% of all AAA cases warranting intervention.
In its idea, the endovascular repair of abdominal aortic aneurysm was intended to produce clinical outcomes comparable to these yielded by the open surgery, while reducing the associated trauma, recovery time, morbidity and the overall treatment cost. It was also generally expected that availability of less-invasive endovascular treatment option would allow to extend caseloads coverage to sizable rupture-prone AAA patient subsets who are poor surgical candidates.
Limitations of Endovascular AAA Repair
Findings from numerous clinical studies and real-life experience in the field seem to indicate that endovascular aortic aneurysm repair via stent-graft placement tends to provide immediate procedural outcomes comparable to these obtainable with open surgery. Furthermore, the typical ICU and hospital stay for endovascular AAA repair averages 2 days (though it may last twice longer for patients with significant comorbidities). All of these translates into reduced inpatient costs of AAA repair relative to open surgery, although the high price of stent-grafting devices largely offsets these cost savings. Post-discharge recovery is also shortened from weeks or months to an average 7-10-day period.
Unfortunately, comparative long-term clinical efficacy and cost-effectiveness of the endovascular approach to aortic aneurysm repair appears to be problematic due to unavoidable shortcomings of available aortic stent-graft designs and complications associated with their less than perfect performance in situ.
The major problems associated with the endovascular AAA repair approach include relatively high incidence of endoleaks (up to 15%), endotension, and device failure, which multiply the risk of catastrophic aneurysm rupture and necessitate costly revisions (in up to 35% of the cases) as well as long-term (or life-long) patient surveillance (with mandatory imaging exams). Due to that, the actual overall cost of endovascular repair in many considerably exceeds expenses incurred in traditional open surgery.
Another limitation of endovascular stent-grafting relates to its ability to accommodate complex aortic aneurysm morphology and branch involvement. Based on some end-user and industry reporting, only about 50% of patients that develop intervention-warranting AAAs are considered good candidates for endovascular repair with currently available product configurations.
According to some recent reporting, endovascular aneurysm repair (EVAR) treatment with certain stent grafts also appears to be associated with higher late mortality rates (due to aneurysm rupture) compared to surgical AAA repair. Based on available long-term follow-up data, mortality in AAA patients retrofitted with the market-leading SG averages 1.3% and 1.5% at four and five years compared to 0.7% and 0.9% for AAA surgery.
Endovascular Repair of TAA
Introduced in Europe and the U.S. in 1998 and 2005, accordingly, endovascular techniques for aneurysm (and aortic dissection) repair on thoracic aorta represented a logical extension of the very same basic concept and technology platforms that enabled the development of AAA stent-grafts.
Because of extremely high mortality and morbidity rates associated with TAA surgery, the need for minimally invasive endovascular treatment option was even more compelling than that in AAA case.
Similar to AAA endovascular repair devices, TAA stent-grafts are intended to minimize the risk of catastrophic thoracic aortic aneurysm rupture via effective exclusion (isolation) of the aneurismal sac from blood circulation.
Unlike AAA implants, commercially available TAA stent-grafting devices feature relatively simple tubular unibody architecture with sealing cuffs (or flanges) at proximal and distal end.
Insertion of TAA SGs is done under fluoroscopic guidance via a singular femoral puncture with the use of standard transcatheter techniques. Depending on the aneurysm morphology, one or two overlapping devices might be used to ensure proper aneurismal sac isolation.
The average ICU and hospital stays and post-discharge recovery period for endovascular TAA repair procedure are generally similar to these for AAA stent-grafting intervention.
Although practical clinical experience with endovascular repair of thoracic aortic aneurysm remains somewhat limited, findings from European and U.S. clinical studies with TAA stent-grafting tend to be very encouraging. Based on these findings, stent-grafting of rupture-prone aneurysm on ascending thoracic aorta can be performed with close to perfect technical success rate yielding radical reduction in intraoperative mortality and complications compared to TAA surgery as well as impressive improvement in long-term patient survival.
Similar to AAA endografting, the main problems associated with the use of TAA SG systems include significant incidence of endoleaks and occasional device migration which require reintervention.
Aortic Aneurysm Repair Procedure Volumes
Based on the industry reporting, national and international healthcare authority data, and MedMarket Diligence estimates, in 2015, approximately 915 thousand patients worldwide were diagnosed with rupture-prone abdominal or thoracic aortic aneurysms and aortic dissections warranting radical intervention, of which roughly 359.5 thousand (or about 39.3%) were actually referred for surgical or transcatheter treatment. Covered APAC market geography (with combined population of about 2,63 billion) accounted for the largest 37.6% share of all aortic aneurysm repairs performed, followed by the U.S. with 25.6%, largest Western European states with 21.3% and the rest-of-the-world with the remaining 15.5%.
Endovascular stent-grafting techniques were utilized in approximately 162.5 thousand aortic aneurysm repair procedures in 2015, which included an estimated 133 thousand AAA-related and about 29.5 thousand TAA-related interventions (including these targeting selected thoracic aortic dissections).
The cited figures reflected a disparity both in the relative volumes of treated AAA and TAA patients and, especially, in the share of these managed with the less invasive EVAR techniques. The latter indicator was the highest for the U.S. (~75%), compared to 52% for Western Europe, 39% for APAC and only 36.6% for the ROW market geography.
During the forecast period covered in the report, the total global volume of endovascular aortic aneurysm repairs is projected to grow 5.7% per annum to approximately 243 thousand procedures, combining a 5.5% annual expansion in AAA-related interventions with a 6.6% average annual increase in TAA (aortic dissection)-related interventions.
Projected healthy gains in endovascular aortic aneurysm repair procedures should reflect continuous penetration of non-surgical (no option) AAA and TAA patient caseloads, coupled with significant incursion into surgery-eligible patient subsets both in AAA, TAA, and aortic dissection indications. Increasing reliance on utilization of less traumatic AAA and TAA stent-grafting techniques will be expedited by ongoing qualitative improvements in the endograft and delivery tools design that keep yielding more reliable, durable, versatile, and end-user friendly systems with reduced propensity to mechanical and functional failure (device kinking, fracture, endoleaks, migration, etc.) and associated clinical complications.
The largest relative gains in AAA and TAA EVAR procedures (10.9% and 11.8%, accordingly) can be expected in covered APAC territories (mostly China and India) and grossly underserved ROW zone (6.5% and 7.5%). Largely mature U.S., Western European (and Japanese) markets are likely to register a low single digit advances in utilization of endovascular AAA/TAA repair techniques.
The global procedure volume forecast for aortic aneurysm repair is presented below.
Projected Dynamics of Aortic Aneurysm Repair Procedures,
World Total, 2015-2022 (#000)
Indications / Procedures 2015 2016 2017 2018 2019 2020 2021 2022 CAGR 2016-2022 Total EVAR AAA/TAA Procedures 15 16.3 17.6 18.9 20.2 21.5 22.8 24.1 6.70% Diagnosed AAA & TAA Caseloads 165 170 175 180 185 190 195 200 2.80% Treated AAA & TAA Patients 56 58.5 61 63.5 66 68.5 71 73.5 3.90% Abdominal Aortic Aneurysm (AAA) Repair Treated AAA Patient Caseloads 45 47 49 51 53 55 57 59 3.90% Surgical Repair Procedures 33 34 35 36 37 38 39 40 2.80% Endovascular Repair Procedures 12 13 14 15 16 17 18 19 6.50% Thoracic Aortic Aneurysm (TAA) Repair Treated TAA Patient Caseloads 11 11.5 12 12.5 13 13.5 14 14.5 3.90% Surgical Repair Procedures 8 8.2 8.4 8.6 8.8 9 9.2 9.4 2.30% Endovascular Repair Procedures 3 3.3 3.6 3.9 4.2 4.5 4.8 5.1 7.50% Total Surgical AAA/TAA Repairs 41 42.2 43.4 44.6 45.8 47 48.2 49.4 2.70%
Notes: AAA = abdominal; aortic aneurysm. EVAR = endovascular aneurysm repair. TAA = thoracic aortic aneurysm.