Distal, medium-vessel occlusion thrombectomy – technical concerns
Distal, medium-vessel occlusions (DMVOs) are occlusions of the M2/3 middle cerebral artery, A2/3 anterior cerebral artery, and P2/3 posterior cerebral artery segments, and account for 25%–40% of all acute ischemic stroke cases. Their clinical outcomes with intravenous thrombolysis, which is the current standard of care, are moderate at best. With improving imaging technologies and a growing literature, DMVOs are increasingly recognized as a target for endovascular treatment (EVT)1,2.
What are the difficulties of a distal thrombectomy?
Distal, medium vessels were not an initial target for endovascular mechanical thrombectomy procedures. Their longer, more tortuous access route and thinner arterial walls potentially increase risk of dissection, perforation, and vasospasm; and the smaller at-risk tissue volumes constrain potential reperfusion benefit1.
Medium-sized vessels can be too small to navigate with regular-sized aspiration or distal access catheters (DACs) and they often get stuck at the ledge of a bifurcation points.
Furthermore, using a primary combined approach (ie, the combination of stent retriever, aspiration catheter or DAC and balloon guide catheter), and advancing the system in a tri-axial manner, as it is commonly done for large vessel occlusions (LVOs), may not be possible because of insufficient catheter length and diameter discrepancies.
To overcome this problem, comes a technique called “blind exchange mini-pinning technique” which consists in introduction of the microwire and microcatheter without aspiration catheter/DAC. Once the microcatheter is in place, the stent can be deployed and the microcatheter removed before the aspiration catheter/DAC (appropriate to the size of the vessel) is navigated to the site of occlusion2.
As catheter technology has improved, endovascular devices, sufficiently small and navigable to be applied to DMVOs, have iteratively advanced. While initial stent retrievers had radial diameters of 6 and 4 mm, smaller devices have recently been released, including 3 mm (e.g., the Catch Mini, pREset LITE, Mindframe Capture LP, Trevo XP ProVue) and 2.5 mm (e.g., the Tigertriever 13). They can be deployed through a 0.017 inch and 0.013 inch microcatheter respectively. Some devices (e.g., Tigertriver) afford the operator to control the amount of radial opening using an adjustable slider1,2. Similarly, technical advances in thromboaspiration devices have increased suitability for the distal vasculature, including increased flexibility, less traumatic tips, and appropriate suction force (e.g., MIVI Q3, Q4, Q5, Penumbra 3MAX, 4MAX, JET D, Microvention Sofia 5F). Alternatively it is possible to use 0.027 inch microcatheter as an aspiration catheter.
What type of anesthesia is recommended?
General anesthesia may have greater relative advantage compared with procedural sedation for EVT for DMVOs, as reduced patient movement facilitates catheter navigation to the more distal and fragile target arteries. However, concerns remain regarding the potential for general anesthesia to delay procedure start and lower blood pressure, impairing collaterals1.
Technique itself :
Initial DVO: M2 M3 P2 P3
1. Assess the patient clinically and split between pertinent and non-pertinent neurological deficit:
a. If non-pertinent deficit (f.ex. hypoesthesia) : STOP MT, go for best medical therapy
b. If pertinent deficit (f.ex. hemianopsia, speech disturbance): CONSIDER MT if there is salvageable tissue (evaluation based on perfusion study or clinical-radiological mismatch) – but take into account:
i. Experience of operator
iii. Consent of the patient
àif benefit>risk: PERFORM MT
Secondary DVO (post LVO during thrombectomy due to clot fragmentation or clot remnants)
1. Evaluate the neurological importance of the occlusion for the patient based on functional anatomy understanding and vascular collateral circulation
à If the branch is functional and benefit>risk: PERFORM MT*
à If the branch is non-functional and benefit
*consider that if DVO is caused by the clot migration due to IVT, the final outcome may be better compare to other DVOs
How to do it?
1. Put the patient under general anesthesia
2. Take as much low profile materials as you can:
- 0.17 inch microcatheter
- Soft microwire
- Small aspiration catheter: 3 MAX or microcatheter 0.027 inch alone
- Small stent-retrievers: 3 mm stent-retrivers (pRESET Lite, Tiger, Trevo, Eric, Catch Mini)
- Triaxial/quadriaxial systems
3. Consider crossing the clot without microwire
4. Consider adding Milrinone/Nipodypine i.a
Some location based concerns:
- while using SAFE technique (the stent-retriever + aspiration catheter removed en-bloc with a thrombus trapped in between) control the position of your aspiration catheter when removing the system, so the aspiration catheter do not jump over the stent-retriever causing clot shearing
- above sylvian point of MCA: MT become much more risky, consider aspiration only
and i.a thrombolytics