Bolton Medical was founded in 1998 and is based in Sunrise, Florida, and Barcelona, Spain. The company was acquired in 2017 by Terumo (Tokyo, Japan), with Bolton Medical’s products merged into Terumo’s Vascutek line of vascular grafts. Bolton Medical manufactures Treovance and TREO, its EVAR endografts, with TREO being its newest. The company also manufactures an aorto-uni-iliac endograft and a customized endograft.
These endografts have been used for some time around the world, including Europe, China, South America, and Japan. In May 2020, the TREO endograft was approved by the FDA for use in the United States. This chapter will focus only on the TREO endograft.
TREO is currently indicated for treatment of infrarenal abdominal aortic aneurysms (AAAs). It is a three-piece modular device comprising nitinol stents sutured to a woven polyester fabric. The endograft should not be implanted in those with a nickel or polyester allergy. Permeability is low at 120 mL/min/cm 2 , theoretically mitigating plasma diffusion and development of Type V endoleak (aneurysm endotension). Sizes available are shown in Table 11.1 . The diameter of each leg of the main bifurcated stent-graft is always the same size (14 mm), regardless of proximal diameter or length. Leg extensions are always 15 mm in diameter proximally. Aortic cuffs can also be used to treat focal lesions in the aorta. If doing so, there must be proximal and distal aorta that fits the instructions for use (IFU) criteria for the proximal main body. Straight extension legs are also available, although sizes are more limited. Table 11.2 shows the IFU.
|Proximal main body diameter||20, 22, 24, 26, 28, 30, 33, and 36 mm|
|Lengths of main body (proximal end; ipsilateral end)||100, 120, and 140 mm|
|Leg extension diameter||All are 15 mm proximallyDistally: 9, 11, 13, 15, 17, 20, and 24 mm|
|Leg extension lengths||80, 100, 120, 140, and 160 mm|
|Aortic cuff diameters||Same as main body|
|Aortic cuff lengths||40, 55, and 70 mm|
|Straight leg extension diameters||9, 11, and 13 mm|
|Straight leg extension lengths||80 mm only|
|Pathology||Infrarenal abdominal aortic aneurysms|
|Aortic neck diameters||Infrarenal neck angle 0–60 degrees: 17–32 mm|
|Infrarenal neck angle 61–75 degrees: 17–30 mm|
|Suprarenal neck factors||Suprarenal neck angulation less than 45 degrees|
|Proximal landing zone||Infrarenal neck angle 0–60 degrees: 10 mm|
|Infrarenal neck angle 61–75 degrees: 15 mm|
|Distal landing zone||Iliac vessel diameter less than 13 mm: 10 mm|
|Iliac vessel diameter greater than 13 mm: 15 mm|
|Other||Ability for iliofemoral system to accept 18–19 French sheaths|
TREO has several unique features. There is dual proximal fixation with an open suprarenal fixation stent that extends 17 mm above the main body and infrarenal fixation barbs where the fabric begins proximally. This offers the theoretical advantage of mitigating Type I endoleaks and distal migration. Also unique to TREO are five rounded barbs within the main body legs to lock leg extensions in place (referred to as lock stent), theoretically mitigating the risk of Type III endoleaks and leg migration. Preliminary bench testing has demonstrated that it requires potentially 5× the force to dislodge legs with lock stent versus a comparable system with no system to lock the legs in place. Testing with physiologic fatigue stresses remains unavailable. Longer term testing that examines impact of renal function with suprarenal fixation is also unavailable. The endograft is also unique in that it allows for variability in leg extension placement. Variability of 1 cm on the contralateral side and 3 cm on the ipsilateral side is possible.
The deployment mechanism is of the “pin and pull” variety, allowing the operator to unsheathe the endograft via a turn knob mechanism. The suprarenal fixation stent is constrained in a clasping mechanism, which simultaneously folds the polyester fabric to constrain the infrarenal barbs. The main body is unsheathed before this clasp is disengaged, allowing the operator to make cranial and caudal adjustments before final deployment, allowing for a more controlled deployment.
TREO is “MRI conditional”, allowing patients to undergo MRI if the MRI is in normal or first level controlled operating modes with a 1.5 or 3 T magnetic field, a 720 G/cm or less magnetic field spatial gradient, and a maximum whole-body averaged specific absorption rate of 4 W/kg for 15 minutes of scanning. These recommendations are based on non-clinical trials.
Outcome data remain limited to short-term results. Most studies available are out of Europe and investigate the Treovance endograft. Few published studies are available for TREO. The ADVANCE trial was the first major study, which prospectively recruited 30 patients across five European centers. All deployments were successful, although one required an aortic cuff. No intraoperative Type I and Type III endoleaks were reported. There were no access site and endograft complications. No severe device complications occurred within 30 days.
The ADVANCE trial was designed more to validate 30-day safety. Other investigators evaluated 1-year outcomes in smaller series. In a single center study of eight patients, one patient required an aortic cuff for Type Ia endoleak, which did not recur at 1 month. One patient required bilateral common femoral reconstructions after the device was removed because of access complications. Five patients had 6-month follow-up and two had 1-year follow-up, with no device or aneurysmal sac complications. In another cohort of eight patients, all had technical successes with no 30-day device-related complications. At 3 months, one required surgical intervention for leg extension occlusion. At 1 year, six followed up and none had other device-related complications or Type I or III endoleaks.
One of the larger studies recruited 46 poor open surgical candidates in two European centers. Intraoperatively, eight adjunctive procedures were performed in seven patients (four for Type 1a endoleaks, two for Type 1b endoleak, and two for leg-extension kinking). At 30 days, one required a leg extension for a Type Ib endoleak. Seven Type II endoleaks and an asymptomatic common iliac artery stenosis were found, which did not require intervention. At 1 year, no deaths or aneurysmal sac ruptures occurred. Eight were defined to have “hostile” necks, defined to be either a <15 mm neck, (n=2) or >60 degrees angulation (n=5). One patient had both. The number of adjunctive procedures, Type I and II endoleaks, graft stenoses, organ injuries, and reinterventions were not significantly different.
Another five patient cohort was evaluated with implantation off of proximal neck IFU (which is not recommended by the authors and Bolton Medical). All five procedures were technical successes without need for adjuncts. At 12 and 18 months, no Type I or III endoleak, stent graft complication, or aneurysmal sac complication was noted.
All patients who are candidates for TREO implantation should have an arterial phase computer tomographic angiogram of the abdomen and pelvis, recommended to be done with at most 2 mm slices for more accurate measurements. When sizing for TREO, vessel diameter is measured from outer wall to outer wall. Whether this is done from manual measurements from axial images or through centerline 3D reconstructions is up to the discretion of the operator. Iliac and femoral arteries must be of an appropriate size to accept an 18 or 19 French main body system and a 13 or 14 French leg extension system. The main body side may be predicated on iliofemoral vessel size, tortuosity, and calcification. Leg extension length is an additional consideration. If leg extension length determination is more difficult on one side, consider placing the main body on that side; greater length variability will be available. Calcification of the intended proximal and distal landing zones will also be a consideration.
Be cognizant if internal iliac artery coverage is anticipated. Consider embolization to prevent Type II endoleaks if needed. Iliac branch devices are not available yet. Accessory renal arteries can usually be covered without complication. Consider an alternative procedure if proximal fixation will not be adequate or the renal arteries will need to be covered. If preoperative imaging shows a prominent meandering mesenteric artery, consider an alternate surgical strategy to avoid intestinal ischemia.