10 TECHNIQUES AND NUANCES OF PIPELINE DEPLOYMENT



10.1055/b-0037-146684

10 TECHNIQUES AND NUANCES OF PIPELINE DEPLOYMENT

EDISON P. VALLE-GILER, RYAN HEBERT, MICHAEL J. LANG, STAVRAPOLA I. TJOUMAKARIS, PASCAL JABBOUR, and ROBERT H. ROSENWASSER


Abstract


Flow diversion is an important tool for treatment of cerebral aneurysms, particularly with the Pipeline Embolization Device (PED). Complications are avoided by appropriate preoperative management, vessel imaging, and understanding of device deployment nuances. We recommend obtaining 3D rotational and high-magnification 2D angiography to accurately determine measurements of the aneurysm neck, as well as inflow and outflow parent vessel diameters. The PED is sized to the inflow vessel diameter. A triaxial setup is used with a long sheath, intermediate catheter and 0.027” delivery catheter. This improves support during loading and unloading of the PED system necessary for precise control of PED expansion and deployment. The “push-pull” technique maximizes metal coverage of the stent over the aneurysm neck and improves apposition to the parent vessel wall, though at the expense of foreshortening of up to 50% of nominal length. Procedural nuances can avoid the most common causes of device failure, such as incomplete expansion in highly tortuous vessels, incomplete device detachment from pusher wire, and endoleak. We recommend use of a single PED device, even if stasis is not immediately apparent, except in complex cases such as long fusiform dilatation, very wide-necked giant aneurysms, or significant inflow-outflow diameter mismatch. Second-generation Flex devices have a modified delivery platform. A second device can be deployed in a telescoping manner, but requires maintaining distal access following deployment of the initial stent. Giant aneurysms are treated with low coil mass embolization via a jailed microcatheter to prevent delayed rupture due thrombus remodeling and resulting inflammatory changes.




10.1 Introduction


Flow diversion has been a major breakthrough in the neurovascular field, allowing the treatment of very challenging aneurysms. 1 , 2 , 3 From all the flow diverters (FDs), the Pipeline Embolization Device (PED, Medtronic, Inc.) has been the most popular worldwide since its initial approval in 2011. 1


The popularity of the PED relies on its efficacy to treat aneurysms when compared to conventional coiling (> 80 vs. 66% aneurysm obliteration rates, respectively). It has also shown that it is an effective treatment, with minimal, if any, aneurysm recurrence rates. 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10


The PED is approved to use only for the endovascular treatment of adults (22 years of age or older) with large or giant, wide-neck intracranial aneurysms in the internal carotid artery, from the petrous to the superior hypophyseal segment.


In an attempt to widen the PED indications, the Prospective Study on Embolization of Intracranial Aneurysms with Pipeline Embolization Device (PREMIER) trial is evaluating the use of PED in all anterior or posterior aneurysms with a wide neck.


Although still off-label, the PED is used for the treatment of fusiform aneurysms and remnants of previously treated aneurysms. It is also a very good treatment option for very small and blister aneurysms located at curved vessels, where the use of intrasaccular treatments would increase the risk of aneurysm rupture. 4


Contraindications to PED are patients with active bacterial infection and those in whom dual-antiplatelet therapy is contraindicated or cannot be done.



10.2 Pipeline Properties


The Pipeline is a highly flexible, in stretch and compression, braided stent with high metal coverage (low porosity) that has flow diversion properties. 1 , 2 , 3 , 11 , 12 The device is composed of 48 braided strands of cobalt chromium (75%) and platinum tungsten (25%). The individual strands measure between 28 and 33 µm. 2 The PED is available with nominal diameters of 2.5 to 5 mm, with 0.25-mm increments in size. The length of the devices ranges from 10 to 35 mm, in 2-mm increments for the 10- to 20-mm lengths, and 5-mm increments for the 25- to 35-mm lengths. 4


When expanded to nominal diameter, the construct provides approximately 30 to 35% metal surface area coverage, with an average pore size of 0.02 to 0.05 mm 2 and a radial force of 2.0 mN/mm (3.0 mm vessel diameter). 2 , 4


The low porosity reduces the hemodynamic exchange between the aneurysm and parent artery, promoting thrombosis within the aneurysm. It also provides scaffolding for neointimal growth over the aneurysm neck, which creates a more durable treatment of aneurysms. 2 , 6 The stages of aneurysm transition have been described as follows 2 , 13 :




  • Mechanical-anatomical change, after flow diversion of the primary vector of blood flow once the device is deployed.



  • Physiological change, after several days to weeks, when the blood staggering within the aneurysm goes through thrombosis.



  • Biological, after months, when the device goes through endothelialization and thrombus resorption. There is a permanent biological seal across the diseased parent artery, while preserving physiological flow in the parent vessel and adjacent branches.



10.3 Preoperative Antiplatelet Therapy


In the following paragraphs, we describe our protocol for management of dual-antiplatelet therapy for patients undergoing flow diversion. Patients undergoing PED placement receive 75 mg/day of clopidogrel and 81 mg/day of aspirin 10 days prior to the intervention. Platelet function is tested using P2Y12 assay (VerifyNow; Accumetrics, San Diego, CA). A baseline test is obtained upon scheduling the case, and a “day-of-procedure” test is checked to calculate the percentage of platelet inhibition.


Patients who have platelet inhibition between 30 and 90% are cleared for the procedure. Patients with inhibition less than 30% are reloaded and the assay is rechecked. Patients who are poor responders to clopidogrel are then switched to prasugrel (40 mg loading dose, followed by a 5-mg daily maintenance dose). Patients with inhibition more than 90% are admitted to the hospital, their procedure is canceled, and clopidogrel is held until the platelet inhibition level falls to less than 90%. 9 Dual-antiplatelet therapy is continued for 6 months after the procedure, and then the patients stay on 81 mg/day of aspirin for life.



10.4 Intraoperative Measures


It is our preference to perform the procedures under general endotracheal anesthesia and continuous neurophysiological monitoring, including electroencephalography, somatosensoryevoked potentials, and brain stem auditory-evoked potentials. There are some centers that have shown that doing the procedure under conscious sedation may be equally safe. 14


As soon as fluoroscopic confirmation of good groin access is achieved, an intravenous bolus of 100 U/kg of heparin is given. Activated clotting time (ACT) is checked at baseline and every 30 minutes thereafter to aim for a goal of double to triple the baseline value. Heparin is discontinued, but not reversed, at the end of the procedure.


To select the correct PED size, we recommend having a three-dimensional rotational angiography as well as high-magnification fluoroscopic runs (anteroposterior and lateral views) for parent vessel and aneurysm measurements. Parent vessel inflow and outflow diameters as well as length of coverage are measured in all the views. To achieve best flow diversion and braid wall apposition, the rule is to match the size of the nominal PED diameter relative to the diameters of the proximal landing zone and parent vessel at the aneurysmal neck (inflow diameter). 4 , 12 A good wall apposition of the PED requires an equal or very close diameter of the target vessel.


Other factors to consider when choosing the correct size of the pipeline are as follows:




  • Foreshortening of approximately 50% and possible device shift during deployment must be kept in mind when choosing the length of the device.



  • During delivery, the device may expand to its maximum size, which is approximately 0.25 mm larger than the nominal diameter.



  • In case of giant aneurysms, where there could be a significant mismatch in the inflow and outflow parent vessel diameters, creating a multiple device construct may be necessary to achieve good wall apposition and maximize flow diversion.


Implantation of an undersized device may result in poor wall apposition, with the potential risk of an endoleak phenomenon and lack of vessel endothelialization in the future. It can also lead to migration of the device with potential aneurysm rupture. 15 Implantation of an oversized device increases the braid porosity due to an incomplete compaction of the strands, leading to lack of flow diversion and aneurysm obliteration failure. 4 , 12



10.5 Deployment Technique


We recommend using a triaxial system (long sheath, intermediate catheter, and a standard 0.027-inch internal diameter delivery catheter). Generally, an 8F femoral sheath, a 6F shuttle sheath (Cook Medical, Bloomington, IN), a 0.058-inch Navien catheter (Medtronic, Inc.), and a 0.027-inch Marksman microcatheter (Medtronic, Inc.) are used.


Once the appropriately sized PED has been selected, the introducer sheath is partially inserted into the rotating hemostatic valve at the catheter hub and sealed. Confirm back flush of saline at the proximal end of the introducer sheath and advance the introducer sheath until it is fully engaged in the hub. Push the PED until you see the fluoro-safe marker on the delivery wire, then start fluoroscopy.


The triaxial system is used to maximize support during forward loading of the system, thus facilitating the initial expansion of the PED and its conformation to the parent vessel while avoiding kickback. 16 The long sheath is generally brought up to the carotid bulb; the intermediate catheter is brought up to the petrous ICA; and under high-magnification fluoroscopic roadmap control, the delivery microcatheter and a Synchro II guidewire (Stryker Neurovascular, Fremont, CA) are manipulated to pass the neck of the aneurysm. Creating a generous “J” on the guidewire is generally enough to pass the aneurysm neck. The distal tip of the Marksman catheter needs to be a minimum of 20 mm past the aneurysm.


A straight vessel segment (generally M1 or M2) is chosen to bring the PED and push the distal part of the braid out of the delivery microcatheter. It is important, before deployment, to reduce the load in the system by slowly pulling back the Marksman microcatheter and the delivery wire together. Once completely unloaded, and in the desired deployment position within the parent vessel, a combination of a “push and pull” technique is used to deliver the PED (push the delivery wire while pulling the delivery catheter). 17


The “art” of the PED deployment comes to play by understanding that the metal coverage area of the device can be increased or decreased by loading or unsheathing the braid while deploying it. Forward wire pushing will increase the metal coverage area to a point, before starting to compress the device. Unsheathing the PED will decrease metal coverage area and eventually will stretch the braid. It is important to keep in mind that a higher metal coverage area is directly correlated with early obliteration of the aneurysm 18 ( Fig. 10.1).

Fig. 10.1 (a) Appropriate amount of forward push on the delivery wire. (b) Stretching of the braid due to too much unsheathing of the delivery catheter. (c) Too much forward push on the delivery wire and possible compression of the braid. (Reproduced with permission of Medtronic, Inc.)

Once the PED had been deployed, the distal coil needs to be pulled inside the Marksman (Medtronic, Inc.), so that it does not get caught in the braid when being removed. To complete this step, rail the microcatheter over the delivery wire. Care must be taken to minimize bumping of the proximal end of the device with the microcatheter, thus potentially pushing the device into the aneurysm. Once the Marksman (Medtronic, Inc.) tip had passed through the PED braid, retract the delivery coil into the microcatheter tip. If the delivery coil cannot be retracted into the microcatheter, advance the Marksman to a straight vessel segment (generally M1) and try to retract the wire again. If this maneuver does not work, pull the delivery wire until the distal coil gets snugged together with the delivery catheter, and remove them simultaneously, paying attention not to move the PED braid from its original position.


It is important to recognize possible deployment failures.




  • When bringing the PED up to the distal tip of the delivery catheter, if the delivery forces start to increase too much , stop pushing the wire before causing damage to the microcatheter (sometimes the Marksman can accordion). At this point, try to straighten the system by pulling the microcatheter and delivery wire together to create a different vector of deployment. This concept, called “unloading” is especially important when trying to deploy the PED in vessel curvatures.



  • When working in tortuous anatomy and the PED does not expand after unloading the system and pushing and torquing the delivery wire, bring the Navien catheter (Medtronic, Inc.) intracranially for more support. The Navien is advanced over the Marksman (Medtronic, Inc.) to the unopened part of the PED. The PED is then fully unsheathed within the Navien catheter. At this point, the PED deployment is a combination of unsheathing from the Navien and pushing on the Marksman (Navien functions as the Marksman, and Marksman functions as pusher/delivery wire). 19



  • If, while deploying the PED against the convexity of a curve, the PED does not expand, get a new vector of deployment. It is important to “unload” the system until the system achieves a new vector of deployment, along the concavity of the curve. At this point, push more wire to continue the deployment; this is the so-called center-and-push technique 16 ( Fig. 10.2).



  • If, after deployment, there is inadequate vessel wall apposition (endoleak), create a generous “J” on the Synchro II guidewire (Stryker Neurovascular, Fremont, CA) and pass it through the PED several times to push the device against the vessel wall. Another option, although not very frequently used in our practice, is to use a hyperglide balloon (Medtronic, Inc) to assure device-wall apposition. Ballooning may be associated with mechanical vessel injury that predisposes to intimal hyperplasia and in-stent stenosis. 4 , 20

Fig. 10.2 Center-and-push technique. When the braid does not expand because it is leaning against the convexity of the curvature (a), unload the system by pulling both microcatheter and delivery wire together (b). In that way, a new vector of deployment is created (c). This is the so-called center-and-push technique. (Reproduced with permission of Medtronic, Inc.)

The number of devices that are optimal to achieve flow diversion is still a matter of discussion. Complete intra-aneurysmal stasis during initial embolization is not required for ultimate aneurysm thrombosis and should not be the end point of the procedure. 4 , 11 , 20 We prefer to use a single PED, reserving multiple device placement only for those aneurysms that remain unchanged or do not sufficiently decrease in size at the 6-month follow-up. 15 , 21 Less than 24% of patients in our series required more than one PED. 9 Placement of multiple devices in a single setting increases the length of the procedure and the number of complications. 20


Multiple device constructs during the first treatment setting are reserved for complex cases with suboptimal aneurysm neck coverage, long fusiform aneurysms, very wide neck aneurysms, reconstruction of a dilated long vessel, and ruptured aneurysms in which immediate occlusion is needed. We also consider multiple PED placements when there is a dramatic mismatch between the inflow and outflow parent vessel diameter, choosing the first device based on the outflow parent vessel diameter, and the second device based on the inflow parent vessel diameter. Using multiple PEDs may increase the device stability, increase the metal coverage area, and prevent PED migration into the aneurysm. 4 , 15 , 20


When creating a multiple device construct, it is very important not to lose distal access past the aneurysm. Once the first device is deployed, the Marksman (Medtronic, Inc.) is railed over the delivery wire to a straight vessel segment to capture the distal coil and remove the pusher wire. The goal would be to deliver and “telescope” the second PED within the already deployed PED. The distal coil is pushed out of the delivery catheter at a straight vessel segment, so the second device is at the tip of the microcatheter, ready to be delivered. At this point, the entire system is unloaded and pulled to the desired landing zone within the already deployed PED. An initial “push” is necessary to deliver the second device, then a combination of pushing the delivery wire and pulling (unsheathing) the Marksman (Medtronic, Inc) is necessary for deployment. When telescoping devices, it is very important to avoid “dragging” the second device because it can create damage to the strands of the already deployed PED.


In case of giant aneurysms, it is our approach to do low coil mass embolization and use steroids to prevent delayed aneurysm rupture and attenuate the effects of intra-aneurysmal thrombosis, worsening mass effect, and neurological deficits. 21 , 22 After positioning the Marksman microcatheter (Medtronic, Inc) distal to the aneurysm neck, we navigate a second microcatheter, parallel to the Navien, into the aneurysm sac to deploy coils via the “jailing” technique. After deployment of the PED, the aneurysm is coiled, without achieving high coil packing density and without occluding the aneurysm neck covered by the PED. 22 Subtotal aneurysm packing reduces the need to coil across the aneurysm neck, thus reducing the risk of coils protruding into the parent vessel subjacent to the PED. 22


Finding the parent vessel outflow in giant aneurysms can be challenging. Sometimes, it requires creating a Marksman “loop” within the aneurysm before the outflow is found. These circumstances would require straightening the delivery catheter before PED deployment, which most of the times can be achieved by unloading the system. Seldom, the Marksman cannot be straightened without losing outflow access. In these cases, after positioning the Marksman catheter in a straight M1 segment, a second Marksman catheter is brought up parallel to the Navien catheter (Medtronic, Inc.). A Solitaire stent (Medtronic, Inc.) is partially deployed to “jail” the Marksman (Medtronic, Inc.) carrying the PED and create a distal anchor point. At this point, the looped Marksman can be reduced safely, without losing outflow access. 23

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May 23, 2020 | Posted by in NEUROSURGERY | Comments Off on 10 TECHNIQUES AND NUANCES OF PIPELINE DEPLOYMENT

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