Neurointervention · IR Playbook

Mechanical Thrombectomy for Acute Ischaemic Stroke (EVT)

Mechanical thrombectomy is catheter-based removal of an occlusive intracranial thrombus in acute ischaemic stroke, performed with a stent retriever, a large-bore aspiration catheter, or both in combination. It works because the ischaemic penumbra is tissue that is electrically silent but structurally intact, sustained by leptomeningeal collaterals at a perfusion pressure just above the infarction threshold; restoring antegrade flow before collateral failure converts penumbra back to functioning brain, which is why every complication of the procedure is either a failure to reperfuse in time or an injury inflicted on already fragile, autoregulation-impaired tissue. In the HERMES pooled analysis of five early-window trials, 90-day functional independence (mRS 0-2) was 46.0 percent with thrombectomy versus 26.5 percent with medical care, with a number needed to treat of 2.6 for reduction of disability by at least one mRS grade. The dominant serious risk is symptomatic intracranial haemorrhage, reported in 6 percent of thrombectomy patients versus 1 percent of controls in BAOCHE.

Learning objectives

Indications

Absolute contraindications

Relative contraindications

Equipment

Procedure steps

  1. Re-verify time of last known well, NIHSS, prestroke mRS, ASPECTS or PC-ASPECTS, and the site of occlusion on CTA against the guideline thresholds before the patient reaches the table. Confirm intravenous thrombolysis has been given if eligible, and that giving it has not delayed transfer to the angiography suite.Pearl: Have the anaesthetic and nursing teams prepare the table while imaging is being reviewed, so that consent, positioning and groin preparation happen in parallel rather than in series.
  2. Position supine with the head in the head holder and both groins exposed. Choose conscious sedation where the patient can protect the airway and cooperate, and general anaesthesia for agitation, obtundation, posterior circulation stroke or airway compromise. Maintain systolic blood pressure at or above 140 mmHg until reperfusion so that collateral flow to the penumbra is preserved.
  3. Puncture the right common femoral artery over the femoral head under fluoroscopic or ultrasound guidance and place an 8 Fr sheath. Puncture below the inguinal ligament and above the femoral bifurcation; a high puncture is the origin of retroperitoneal haemorrhage and a low puncture of pseudoaneurysm, both of which matter more than usual in a patient who has just received a thrombolytic.Pearl: Ultrasound-guided single-wall puncture reduces access-site complications in the thrombolysed patient and adds under a minute to the case.
  4. Advance the 0.035 inch hydrophilic wire and select catheter into the target common carotid or dominant vertebral artery, then exchange or telescope the 8 Fr balloon guide catheter into the distal cervical internal carotid artery, or a 6 Fr guide into the V2 segment for posterior circulation. Watch for wire buckling into the arch and for damping of the pressure waveform, which signals guide-induced spasm or dissection. The step is complete when the guide sits stably above the carotid bulb with a clean pressure trace.Pearl: Telescoping a 6 Fr intermediate catheter inside the balloon guide gives a stepped transition that tracks around a type III arch where the guide alone will prolapse.
  5. Acquire a biplane digital subtraction angiogram of the target circulation through the guide catheter. Define the exact proximal and distal extent of the clot, grade the leptomeningeal collateral filling on the venous phase, and confirm there is no unexpected dissection or tandem cervical lesion. Poor collaterals predict rapid core growth and argue for the fastest possible first pass rather than a technically elegant one.
  6. Track the 0.070-0.088 inch aspiration catheter over the microcatheter and microwire until its tip abuts the proximal clot face. Advance the assembly as a coaxial unit so no single component leads unsupported. The catheter is correctly positioned when its tip is in contact with, and not embedded within, the thrombus.Pearl: A gentle contrast puff through the aspiration catheter just short of the clot confirms tip position without needing to cross the occlusion.
  7. Steer the 0.014 inch microwire through the thrombus with the softest possible tip load, then advance the microcatheter over it into the patent vessel beyond. Confirm intraluminal position with a gentle low-volume contrast injection through the microcatheter before deploying anything. Extravasation or a persistent contrast blush at this point means perforation and mandates immediate abandonment of the pass.Pearl: Aim the microwire at the largest expected residual lumen rather than the geometric centre of the vessel; clot is usually eccentric and the wire follows the path of least resistance.
  8. Unsheath the stent retriever so that it spans the entire clot with a few millimetres of normal vessel at each end, sizing 6 x 40 mm for internal carotid terminus and M1 and 4 x 20 mm for M2. Allow 3-5 minutes of integration time for the struts to engage the thrombus. Avoid deploying across the anterior choroidal artery origin where this can be achieved without losing clot coverage.Pearl: A control run after deployment often shows partial flow restoration through the stent struts, which reperfuses the penumbra while the device integrates.
  9. Inflate the balloon guide catheter to arrest antegrade flow, start continuous aspiration through both the guide and the distal aspiration catheter, then withdraw the stent retriever and aspiration catheter together as a single unit into the guide. Aspirate the guide catheter until brisk back-bleeding of clean blood is obtained before deflating the balloon. The pass is complete when the device is out and the guide flushes clear.Pearl: Withdrawing the stent retriever into the aspiration catheter rather than past it, while both are pulled together, keeps the clot corked at the aspiration catheter tip and reduces fragment loss.
  10. Perform a full biplane run after each pass and grade reperfusion on the mTICI scale. Stop at mTICI 2b or better. If reperfusion remains mTICI 0-2a, change one variable for the next pass rather than repeating the same manoeuvre. Beyond roughly three unsuccessful passes the incremental chance of reperfusion falls while the risk of vessel injury, vasospasm and haemorrhage rises, so weigh continuing against stopping.Pearl: Recording which technique achieved the successful pass, and at which pass number, is the single most useful piece of case data for improving first-pass effect over time.
  11. If the intracranial result is satisfactory and a flow-limiting cervical internal carotid stenosis or occlusion remains, decide between angioplasty alone and angioplasty with stenting. Stenting commits the patient to dual antiplatelet therapy within an acutely infarcted, blood-brain-barrier-disrupted territory and increases symptomatic haemorrhage risk; angioplasty alone avoids this where residual flow is adequate.
  12. Remove the sheath and achieve haemostasis by manual compression or a closure device, documenting distal pulses. Hand over to the stroke unit with the final mTICI grade, number of passes, any perforation or new territory embolisation, the antithrombotic plan, and an explicit blood pressure target.Pearl: State the post-procedure blood pressure ceiling verbally and in writing at handover; it is the single instruction most often lost between the angiography suite and the ward.

Complications

Exam pearls

Viva questions

A patient presents at 14 hours from last known well with an M1 occlusion, NIHSS 14, prestroke mRS 0, age 74, ASPECTS 4. Your centre has no CT perfusion. Do you treat?
Yes. The 2026 AHA/ASA guideline gives a COR 1 recommendation for selected patients aged under 80 with internal carotid artery or M1 occlusion at 6-24 hours, NIHSS 6 or more, prestroke mRS 0-1 and ASPECTS 3-5, without significant mass effect. Selection is expressed in ASPECTS, so the absence of perfusion imaging does not exclude this patient; the requirement is that there is no significant mass effect on the non-contrast CT.
You have deployed a 6 mm stent retriever across an internal carotid terminus clot and achieve mTICI 3, but the patient wakes with a dense contralateral hemiplegia far worse than baseline. What has happened anatomically?
Most likely occlusion or avulsion of the anterior choroidal artery, which arises from the supraclinoid internal carotid artery just proximal to the terminus and supplies the posterior limb of the internal capsule. It has no meaningful collateral supply, so a small perforator infarct there produces a dense hemiplegia despite complete large-vessel reperfusion.
Why is direct contact aspiration suggested as the first-line strategy in basilar artery occlusion rather than a stent retriever?
The ESO-ESMINT basilar guideline suggests aspiration first-line based on limited evidence. Mechanistically, the basilar trunk gives off numerous small pontine perforators with no collateral supply, and dragging a stent retriever along that surface risks shearing or occluding them; aspiration at the clot face avoids traversing and abrading the perforator-bearing segment.
Mid-procedure, a test injection through the microcatheter shows contrast extravasating into the subarachnoid space. What is your first action, and what must you not do?
Inflate the balloon guide catheter to arrest inflow and reverse heparin with protamine, while leaving the microcatheter in place. The critical error is withdrawing the microcatheter, because it may be tamponading the perforation; if bleeding continues, the same microcatheter is used to coil or embolise the perforated branch.
After a successful thrombectomy with mTICI 3, the ward asks you for a blood pressure target and suggests keeping systolic below 140 mmHg. What is your answer and why?
Decline it. In anterior circulation large vessel occlusion successfully recanalised to mTICI 2b, 2c or 3, an intensive systolic target below 140 mmHg for the first 72 hours carries a COR 3 Harm designation. Reperfused brain has impaired autoregulation and lowering pressure aggressively risks extending infarction in marginally perfused tissue.
A patient has an M3 occlusion with NIHSS 4. The referring physician asks for thrombectomy. What do you say?
Decline routine thrombectomy. DISTAL and ESCAPE-MeVO, both published in 2025, were neutral for medium and distal vessel occlusion, with numerically higher symptomatic intracranial haemorrhage, stroke progression and recurrent stroke in the thrombectomy arms. There is no evidence base supporting a benefit that would justify the added procedural risk in a mild deficit.
What does an mTICI grade of 2b actually mean, and why is 2c or 3 preferred as an endpoint?
mTICI 2b denotes antegrade reperfusion of more than half the previously occluded target territory. It is the accepted minimum threshold for technical success, but 2c and 3 represent near-complete and complete reperfusion respectively, and greater extent of reperfusion correlates with better functional outcome, so 2b is the point at which further passes stop being clearly beneficial rather than the point of an optimal result.
You find a fetal posterior cerebral artery on the diagnostic run in a patient with an internal carotid terminus occlusion. How does this change your assessment of the final result?
The occipital lobe is supplied from the internal carotid artery rather than the basilar artery, so the target territory includes the posterior cerebral artery distribution. A final run showing restored middle and anterior cerebral artery flow but a persistently unfilled fetal posterior cerebral artery is not a complete result, and grading it as mTICI 3 would be wrong.

References