Coil/guidewire diameter/thickness (inches)
Microcatheter
0.010–0.012
Excelsior SL-10®; Prowler 10®
0.014
Prowler 14®
0.018
Excelsior 1018®; Prowler Plus®
Ensure the microcatheter has two radiopaque markers: one indicating the distal tip of the catheter and the second (proximal) marker indicative of the coil being out of the catheter and in the vessel/aneurysm lumen, when the proximal marker is just crossed by the radiopaque marker on the coil pusher forming a perfect ‘T’.
‘Unlock’ the coil. This maneuver involves counter clockwise twisting of the distal sheath at crimped site in case of GDC coils. In case of hydrocoils, slip the tubular black plastic piece off the sheath.
Using the pusher, advance the coil out of sheath to soften it in warm Ringers lactate (in case of GDC), or sterile steam (for hydrocoils). Then retract it back into the sheath.
Loosen the RHV of microcatheter and introduce the sheath until it touches and is in continuity with the hub of microcatheter. The RHV should be just tight enough that the coil can be easily advanced and retracted, without causing blackflow.
Prevention of backflow is particularly important in case of hydrocoils. To prevent it, a small tubing and one way stopcock are interposed between the RHV and microcatheter hub.
Prior to opening the RHV, the stopcock is turned so that the microcatheter is closed to the RHV, preventing backflow. Once the coil sheath is advanced through the RHV, tighten the RHV around the sheath (just enough to still enable smooth movement of sheath) and then open the one way stopcock to access the microcatheter. Advance the sheath all the way to microcatheter hub and then tighten the RHV more. However, one should still be able to move coil within the sheath without any difficulty.
Deploy the coil using fluoroscopy and roadmapping.
Once satisfied with the coil placement, detach the coil from the pusher by using the device provided for purpose, which passes an electrolytic current through the soldered joint between the coil and the pusher.
We preferentially use GDC coils. However, if hydrocoils are used, bear in mind that they expand on exposure to blood. Therefore, the time available for manipulation/deposition is limited (approx. 5 min). Taking too much time will cause the coil to expand causing inability to withdraw, or properly place them. Conversely, they may expand within the microcatheter causing occlusion and requiring the microcatheter to be replaced. For the same reason, ensure the microcatheter remains free of blood.
Deposit as many coils as necessary to affect obliteration of the lesion.
Sometimes a ‘combined’ strategy may be used, in which case coils are initially deposited to slow the rapid blood flow through the AVM, followed by occlusion using liquid embolic agent. If this strategy is used, ensure that the microcatheter is exchanged for one compatible with the liquid embolic agent.
Onyx
Additional Equipment/Devices
Onyx® 18, or Onyx® 34 (consider 34 for cases with brisk blood flow across fistula).
A DMSO-compatible microcatheter, e.g.,:
Marathon™ (ev3 Neurovascular, Irvine CA).
Echelon™ (ev3 Neurovascular, Irvine CA).
Rebar™ (ev3 Neurovascular, Irvine CA).
Ultraflow™ (ev3 Neurovascular, Irvine CA).
Procedure
Select a DMSO-compatible microcatheter and connect it to a continuously running flush of heparinized saline. We use Marathon™ microcatheter most frequently for the purpose.
Advance the microcatheter over a microwire, e.g., (Transend 0.010) using fluoroscopy and roadmapping as indicated. Other microwire options available for a marathon catheter include Mirage™ (ev3, 0.008) or X-Pedion™ (ev3, 0.010).
If a non-DMSO-compatible microcatheter is already in position (e.g., coiling was performed) and the vasculature had proven challenging to navigate, exchange the microcatheters over an exchange length wire (300 cm, see Chap. 5 for details on microwires).
When withdrawing the microcatheter to be discarded, or advancing the new microcatheter, keep an eye on the tip of microwire to ensure it does not advance inadvertently, or fall back.
For Satisfactory Onyx administration, ‘wedge’ the tip of microcatheter. This means placing or ‘wedging’ the catheter tip against the vessel wall where it branches.
Angiographically, confirm the correct position of the microcatheter tip and then clean the contrast out of the catheter by flushing with saline. This can be easily done with the pediatric transducer (depending upon its mechanism, press the wings of the transducer together, or pull the provided tab, to increase the flush rate and when done, ‘release’ the mechanism).
When ready to perform embolization, perform a blank roadmap, i.e., step upon the pedal as if performing a roadmap, but do not actually inject contrast.
Ensure the entire microcatheter system is free of blood.
Draw up the DMSO into the provided yellow colored syringe.
Disconnect the RHV from the microcatheter and attach the syringe with DMSO to the microcatheter. Make a meniscus to meniscus connection, ensuring there are no air bubbles or blood in the microcatheter. If needed, fill the hub of microcatheter with saline to ensure a proper connection.
Forewarn the patient that s/he may experience a ‘garlic like taste’ in the back of the throat with DMSO injection. Additionally, during injection and for a day or two thereafter, the patient’s breath and skin may carry the peculiar odor of DMSO.
Very slowly, inject 0.3–0.8 ml of DMSO depending on the deadspace of the microcatheter, such that the entire catheter is primed with it.
While undertaking the placement of the microcatheter and its priming, Onyx 18 or 34 is prepared concurrently, bearing in mind the following:
Onyx 18 (the numbers 18 or 34 are indicative of viscosity at 40 °C) penetrates deeper into the nidus because of its lower viscosity.
Onyx 34 should be used in high flow malformations, as it is less likely than Onyx 18 to flow into the venous sinus when injected from the arterial side.
Onyx solidifies in 5 min after exposure to blood or saline. To prevent this solidification within the microcatheter itself, ensure that it is free of contrast, saline and blood during Onyx injection.
The temperature of Onyx should be between 19 and 24 °C when used. If it is frozen because it was stored at a cooler temperature, take the bottles out at the outset of procedure and allow them to thaw at room temperature.
Place the bottle of Onyx on the Onyx mixer and set the mixer at 8. The mixer can concurrently shake 4 bottles at a time. Shake the Onyx bottle using the mixer for at least 20 min. The mixing should continue until you are just ready to inject Onyx. This will cause a thorough mixing of Onyx and tantalum powder, which assists in satisfactory visualization of the deposited Onyx.
Immediately prior to injection, draw up Onyx in the provided white 1-ml syringes. To do so, hold the bottle upright (in contrast to when drawing up other low viscosity fluids into a syringe, e.g., 1% Lidocaine) and aspirate using an 18G or 20G needle. If any air is noted in the syringe, turn the bottle over such that the bottle is superior and the syringe is below it. Inject the air into the bottle. Turn the bottle upright again, such that the syringe is again on top and continue to draw up Onyx. Draw a total of 1 ml of air-free Onyx into the syringe.
Detach the yellow DMSO syringe from the hub of the microcatheter.
Hold the catheter hub vertically and overfill the hub with DMSO.
Holding the Onyx syringe upright, make a meniscus to meniscus connection, ensuring that no air is introduced into the system.
Maintain the syringe containing Onyx in a vertical position. Maintain this position until the Onyx passes beyond the hub of the microcatheter. After that, the syringe can be held in a more comfortable position.
Inject Onyx slowly at a rate of 0.16 ml/min and not to exceed 0.3 ml/min. The injection should be slow and deliberate, using gentle thumb pressure.
After injecting approximately 0.3 ml (the volume of the microcatheter), track the Onyx under live fluoroscopy.
Visually ensure that none is going into a venous sinus, or the non-feeding arteries.
If there is reflux of Onyx over the microcatheter, wait for a couple of minutes to allow the Onyx to solidify. The solid Onyx plug may prevent further reflux. However, the reflux over the microcatheter should be no greater than 1 cm. Otherwise, it may become difficult to extract the catheter and lead to complications.
Once the contents of the syringe are completely injected, disconnect the syringe and replace with the next Onyx syringe making a ‘meniscus to meniscus’ connection. Again, ensure that no air or other substances such as, blood and contrast gain entrance into the microcatheter.
After the treatment is complete, wait a few seconds, slightly aspirate the syringe and gently pull the microcatheter to separate it from the cast.
If a resistance is encountered because the tip of microcatheter is strongly adherent to the Onyx plug, maintain a constant, gentle but firm pull upon it, until a sensation of ‘giveaway’ is felt when the tip of microcatheter breaks free from Onyx.
Double-Injection Technique
The technique first described by Dr. Robert Mericle enables better image interpretation during embolization, resulting in safer, more confident and usually a much greater volume of Onyx deposition. The operator can confidently determine that the Onyx deposition is entirely within the nidus perimeter and is not entering the draining vein prematurely, or refluxing excessively on to the catheter. This information is crucial as the angioarchitecture of the AVM may not be completely clear during embolization, leading to difficulties in determining whether to stop or continue, or alter the force or speed of injection.
Selectively catheterize an arterial branch directly supplying the AVM nidus as described above.
Use the best angiographic projections in two orthogonal planes to demonstrate the feeding arteries and draining veins distinctly from the nidus (Fig. 14.1a–o). If needed, use 3D angiography to select the appropriate working views.
Fig. 14.1
A right internal carotid artery injection demonstrating temporal AVM in AP (a) and lateral (d) views. The main feeding trunk of the MCA has hypertrophied (arrow) and is of the same caliber as the proximal M1 segment. (b and e) Due to the brisk flow, the venous drainage can be seen (arrows) in arterial phase. (c and f) The venous drainage (arrows) from the AVM is via cortical veins to the SSS and via vein of Labbé to right transverse sinus (f, thick arrow). (g) Angiography performed by injecting contrast through the microcatheter (thin arrow) rather than the guide catheter (thicker arrow). Therefore, only the AVM nidus (*) supplied by the catheterized branch is seen. The embolic agent, e.g., Onyx injected through the microcatheter will deposit largely in this part of the AVM. The microangiographic run has been ‘remasked’ and hence the appearance of the contrast as white rather than the characteristic black. Using double injection technique, the contrast from microangiography is allowed to wash out and then additional contrast is injected through the Guide catheter in the same run (Don’t step off the pedal in between the two runs). In the microangiography run, where the nidus is most obvious, it is remasked, and will appear as it does in (h), superimposed on the Guide catheter (h) run. The asterisk (*) demonstrates the part of the nidus supplied by the catheterized branch compared to the rest. We demarcate on the monitor, the outline of the catheterized nidus, the perimeter of the entire AVM, the draining veins and the course of microcatheter, using different colored erasable markers. As long as the table or patient are not moved, these demarcations remain reliable. If the embolization is undertaken visualizing these perimeters, it is safer. (i) The Onyx cast (arrow) consequent to embolization via microcatheter is well visualized. Arterial phases in AP (j) and lateral (k) views from post-embolization angiography. There appears to be a complete embolization of the AVM with only the Onyx cast (arrow) demonstrating the AVM. Due to the redistribution of blood flow, the normal vasculature including the lenticulostriate arteries (arrowhead) are much better visualized when compared to pre-embolization images (see b and e). Venous phase of angiography in AP (l) and lateral (m) views better demonstrate the normal cortical veins and sinuses. There is attenuation in the size of the vein of Labbé. The arrow in the lateral view (m) overlies the vein of Labbé and point to the Onyx casted MCA branch that was the largest feeder to the AVM. Angiography in AP (n) and lateral (o) views following craniotomy and resection of embolized AVM. The Onyx cast is gone and normal vasculature persists
Ensure that only the AVM is being supplied through the selected branch and not the normal cortical vasculature.
Gently perform microangiography through the microcatheter and allow the contrast to washout.
Then during the same run, repeat angiography through the guide catheter. Both injections are done as a single run. (Do not step off the pedal in between the injections.)
Scroll through the completed run to select the frame where the microcatheter DSA run is at its peak opacification.
‘Remask’ the selected frame.
The inverted ‘remasked’ microangiography run will appear white when played through the (black) Guide catheter run, i.e., the two runs are superimposed.
Using erasable markers or surgical marking pens, draw the following on the biplane DSA monitors.
- (i)
The perimeter around the nidus.
- (ii)
Perimeter of the nidus component visualized via the microcatheter injection.
- (iii)
Location of draining veins.
- (iv)
Position of microcatheter tip and course of the microcatheter.
- (v)
Possibly, other adjacent feeding pedicles.
- (i)
Draw each of the above in a different color, e.g., nidus visualized through microcatheter: red; veins: blue; microcatheter: green; perimeter of nidus through guide catheter: black.
As long as the patient, table and biplanar image intensifiers remain unchanged in position, these landmarks remain reliable, throughout prolonged injections.
As described above, treat the microcatheter with DMSO prior to embolization.
Perform blank roadmaps and commence onyx embolization.
When the amount of Onyx equal to the volume of the catheter has been injected (approx. 0.3 ml), commence checking the progress of Onyx deposition into the nidus in both planes, by transiently stepping on the pedal frequently to obtain fluoroscopic images.
Perform new roadmaps when the previously deposited Onyx needs to be subtracted to better visualize new deposition.
As long as the Onyx deposition is within the perimeter of AVM (obtained through the Guide catheter), it is safe to continue even if the deposition is in area not delineated by the microangiography run.
Once the treatment is complete, wait a few seconds, slightly aspirate the syringe and gently pull the microcatheter to separate it from the cast.
In case resistance is encountered because the tip of microcatheter is adherent in the Onyx plug, maintain a constant, gentle but firm pull upon it, until a sensation of ‘give way’ happens when the tip of microcatheter breaks free from Onyx. Occasionally, a quick ‘wrist flick’ is required to achieve separation of the microcatheter tip from the Onyx cast.
NBCA
Additional Equipment/Devices
Trufill kit comprising of NBCA/ethiodol/tantalum (Trufill, Cordis Endovascular).
Procedure
Advance the microcatheter attached to a continuously running flush of heparinized saline, over a microwire, placing its tip in the distal aspect of the feeding artery, using standard techniques. Depending on operator preference and nidal anatomy, the catheter tip may be wedged or positioned free.
Prepare the NBCA mixture on a separate table using clean gloves. This is to prevent any contamination with ionic catalysts.
Add the vial of tantalum powder to above mixture to enhance its radiopacity.
For a wedged injection: a comparatively dilute (25–33%) concentration is prepared by mixing 1 cc of NBCA with 2–3 cc of ethiodol in a shot glass.
Table 14.2 shows various concentrations recommended by manufacturer.
Table 14.2
NBCA Manufacturer Recommended Concentrations
Condition
Ethiodol: NBCA ratio
Ethiodol volume (cc)
NBCA volume (cc)
For deep penetration of the nidus, in the absence of AV fistula or high flow rates
3:1
75% Ethiodol:25% NBCA
0.75
0.25
2:1
67% Ethiodol:33% NBCA
0.67
0.33
Feeding pedicle injections close to the nidus at high flow rates where venous opacification occurs within 0.5 sec on contrast injection
1:1
50% Ethiodol:50% NBCA
0.50
0.50
1:2
33% Ethiodol:67% NBCA
0.33
0.67
Induce relative hypotension (20–30% decrease in MAP).
Perform test injections using subtracted fluoroscopic observation (blank road map) to assess catheter position and optimal rate of injection.
Ensure catheter lumen is devoid of ionic catalysts by irrigating with 5% dextrose.
Obtain a blank road map, then commence injecting NBCA slowly, under continuous visualization, over 15–60 sec.
Adjust the injection rate in order to obtain a solid nidal caste without reflux.
Stop immediately, if the NBCA enters a draining vein or sinus.
Resume after a few seconds and continue if satisfactory nidal filling is visualized. If the NBCA enters the vein again or there is proximal reflux, terminate the injection.
For a non-wedged injection: the NBCA should be more concentrated because of the more rapid flow and shorter arterial-venous transit time through the nidus.
At higher concentrations (NBCA ≥ 50%) up to 0.5 g of tantalum should be added to the mixture.
The injection rate is faster and injection time is shorter (1–3 s).
If there is a large direct fistula, or rapid flow, induce maximal hypotension and a very high concentration of NBCA. Alternatively, coils may be used first to slow down the rate of blood flow, followed by NBCA.
After completion of procedure, aspirate the microcatheter briskly and remove it quickly.
Aspirate the guide catheter and examine it fluoroscopically.
PVA
Polyvinyl alcohol (PVA) is available in sizes ranging from 50 to 1000 µm.
In the presence of agents like coils, Onyx and NBCA, it is primarily used in devascularization of AVM or tumor prior to surgery. However, Onyx appears to be usurping this role as well.
A far better indication for PVA is the devascularization of the ECA branches, e.g., in epistaxis or dural supply of meningioma. The explanation below is pertinent to lesions such as AVM, as well as, lesions of ECA, e.g., epistaxis.
Additional Equipment/Devices
Microcatheter selection should depend upon the size of the PVA particles used, to prevent catheter occlusion by the particles. Preferably use a larger caliber catheter (e.g., 2.3 Fr). If possible, avoid using tapered tip microcatheter, as it is more likely to occlude. We commonly use Marathon (ev3) while treating fistulae in the ECA branches.
Other microcatheter considerations include Prowler Plus (Codman) and Rapidtransit (Codman).
Procedure
Advance the microcatheter to its planned location, positioning it as close as possible to the malformation.
Inspect angiograms carefully for potentially dangerous collaterals that must not be embolized.
Measure the feeding vessels and lesion to select the appropriate size particles.
Bear in mind, the smaller the particles, the greater the likelihood of deep penetration into smaller vessels, e.g., precapillaries, resulting in cranial nerve deficits, etc.
Proceed to prepare the PVA mixture on a separate table/space, taking care that other equipment used during procedure does not get contaminated with the particles. Once the mixture is prepared, change gloves. Take extreme precautions that the PVA particles do not inadvertently contaminate drapes, catheters etc. leading to possibility of embolic complications.
Inspect the PVA particles for uniformity of size.
Inject 10 ml of non-ionic contrast into the bottle containing PVA. Conversely, it may be safer to remove the top of the bottle and empty the contents into a shot glass and then add the non-ionic contrast to it.
Shake to suspend the particles in the contrast.
Attach a 3-way stopcock to a 20-ml syringe.
Draw up the suspension into the syringe.
Attach a 3-ml syringe to the 3 way stopcock. The 3-ml syringe should be attached to the port in line with that which will be attached to the catheter. The larger 20-ml syringe is attached to the port perpendicular to these two.
Ensure the syringes and stopcock system are free of air bubbles.
Use the plungers of the small and large syringes to push the suspension back and forth between the syringes, while the stopcock is turned to close off the third (free) port, intended for the microcatheter. The movement will assist in keeping the PVA particles in suspension.
Draw suspension into the 3-ml syringe from the larger syringe and turn the stopcock, so that the port with the 20-ml syringe is blocked.
Change gloves and discard any towels etc. contaminated by PVA particles.
Detach the RHV from the microcatheter and make a meniscus to meniscus connection between the microcatheter and the free portal of the 3 way stopcock. Ensure the system is free of air bubbles.
Place a towel on the drape under the microcatheter to ensure it catches any PVA particles and the operating field is not inadvertently contaminated by potential emboli.
Confirm that the microcatheter tip has maintained its position. Perform angiography, if necessary.
Obtain a blank roadmap.Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
