🩸 Aspiration Thrombectomy Catheter Technique Simulator

Navigating the Large-Bore Aspiration Catheter to the Clot Face

The ADAPT (A Direct Aspiration first-Pass Technique) approach begins the same as any endovascular thrombectomy — femoral or radial access, a guide catheter into the cervical vasculature — but diverges at the intracranial segment: instead of threading a stent retriever through and past the occlusion, a large-bore reperfusion catheter is advanced over a microwire/microcatheter combination until its distal tip sits directly against the proximal thrombus face. The clot is never crossed.

• 0.054–0.072″: Typical catheter ID (0.068–0.088″ outer diameter class)
• ~20–30 min: Time: puncture to first pass (ADAPT median, comprehensive centers)
• 6–7F: Distal access catheters (DAC) (navigated through 8–9F guide sheath)
• High: Vessel tortuosity tolerance (flexible braided/coil-reinforced shafts)

Catheter construction and trackability

Modern aspiration catheters used in ADAPT (Penumbra ACE/JET, Sofia, React, Millipede) share a common engineering challenge: maximizing internal lumen diameter for suction flow while retaining enough flexibility and pushability to navigate the tortuous path from femoral artery to a distal intracranial vessel.

Shaft construction, tip to hub: • Distal segment: soft, highly flexible braided/coiled polymer for atraumatic navigation through cerebral curves (carotid siphon, MCA bifurcation) • Mid shaft: increasing stiffness gradient (dual or triple durometer) for pushability without kinking • Proximal shaft: stiffer reinforced tubing bonded to a hub compatible with vacuum tubing or a locking aspiration syringe • Lumen: maximized inner diameter (up to 0.072″ in largest platforms) — suction force scales with the fourth power of radius, so even small ID gains meaningfully increase flow

A microcatheter/microwire pair is typically advanced first, coaxially inside the aspiration catheter, to provide a supportive rail and to gently probe past tortuous segments — the aspiration catheter then tracks over this assembly rather than being pushed blind.

Positioning at the clot face — why crossing is avoided

The defining principle of direct aspiration is that the catheter tip is parked flush against — not through — the proximal thrombus surface. This is a deliberate departure from stent-retriever technique, where a device must be deployed distal to and within the clot.

Rationale for stopping at the face: • Avoids mechanical disruption of the clot before suction is applied, which can shower fragments distally before any retrieval device is in place • Reduces risk of vessel perforation from advancing a relatively large-bore catheter past a tight occlusion into fragile distal arterioles • Preserves the thrombus as a single, intact mass that the vacuum can act upon as a plug rather than as loose debris

Road-mapping with digital subtraction angiography confirms tip position under fluoroscopy; a gentle contrast puff at the catheter tip verifies apposition against the clot without antegrade flow past it before aspiration begins.

ADAPT was first described by Turk et al. (2014) as a simplified first-line strategy: catheter to the clot, aspirate, done — reserving stent retrievers for cases where aspiration alone is insufficient, rather than as the default first maneuver.

Vacuum Pump Activation — Generating Continuous Aspiration Force

Once the catheter tip is confirmed against the thrombus face, aspiration is initiated: either a dedicated mechanical/electric pump maintaining constant negative pressure, or a 60 mL locking syringe manually drawn back and locked. The vacuum propagates down the full catheter lumen, converting a static tube into an active suction channel pulling blood and clot material proximally.

• 20–29 in Hg: Typical vacuum level (≈ 68–98 kPa negative pressure)
• ~1–2 L/min: Pump flow rate class (dedicated aspiration pump systems)
• 60 mL: Manual syringe volume (locking syringe, continuous draw)
• Optional: Separator wire use (clears catheter if flow stalls)

Pump-driven versus syringe-driven aspiration

Two practical methods generate the negative pressure that powers the technique:

Dedicated aspiration pump: • An electric or vacuum-canister pump maintains constant, operator-set negative pressure (commonly 20–29 in Hg) throughout the withdrawal, without the fatigue or pressure fluctuation of manual technique • Tubing connects the pump canister to the catheter hub; a foot pedal or inline valve allows on/off control while both of the operator's hands remain on the catheter and guide system • Flow is continuous and steady, which matters because clot engagement depends on sustained (not pulsatile) suction to hold the thrombus against the tip

Manual syringe aspiration: • A 60 mL syringe is attached to the catheter hub, drawn back fully, and locked with a stopcock or thumb-lock mechanism to sustain negative pressure • Simpler and equipment-light, but pressure can decay over the course of a prolonged pull and requires re-locking if a fresh syringe is swapped in

Both approaches rely on the same physical principle: pressure differential between the catheter lumen and the vessel drives flow of blood, and eventually clot, from the occlusion site back through the catheter toward the collection reservoir.

Fluid dynamics of the suction column

The suction generated at the catheter tip is not an instantaneous point force — it forms a flow field extending a short distance upstream of the tip, drawing in blood and the outer surface of the thrombus.

Key physical relationships: • Flow rate through the catheter scales approximately with the fourth power of internal radius (Hagen–Poiseuille-like behavior for the tubing itself) — this is why maximizing catheter ID is a central design goal • Effective suction force at the clot interface depends on the pressure differential, the catheter ID, and how completely the tip contacts (seals against) the clot surface • A poor seal — catheter diameter much smaller than the vessel or clot cross-section — lets blood bypass around the tip, diluting suction force applied directly to the thrombus and slowing effective engagement • A close size match between catheter tip and clot/vessel diameter improves the seal, concentrates negative pressure onto the clot face, and shortens time to full engagement

This is the physical basis for the catheter-to-clot size match parameter in the simulator above: a snugger fit means more of the vacuum acts directly on the thrombus rather than leaking around it as bypass flow.

Clot Engagement & Ingestion — Aspiration, Corking, and Thrombus Consistency

What happens next depends heavily on clot composition. Softer, red blood cell-rich thrombus tends to deform and be drawn fully into the catheter lumen, disappearing from view on fluoroscopy as it is aspirated proximally. Firmer, fibrin/platelet-rich thrombus instead adheres to the tip opening as an intact plug — a phenomenon interventionalists call "corking" — without ever fully entering the lumen.

• Ingested: Soft (RBC-rich) clot (passes through catheter lumen)
• Corked: Firm (fibrin-rich) clot (adheres at tip, removed en bloc)
• ~25–35%: First-pass full ingestion (of ADAPT first-pass attempts)
• ~30–40%: First-pass corking removal (of ADAPT first-pass attempts)

Thrombus histology and its effect on aspiration behavior

Retrieved thrombi analyzed histologically fall on a spectrum from red (erythrocyte-rich, fibrin-poor) to white (fibrin- and platelet-rich, erythrocyte-poor), with most clinical clots showing mixed composition.

Red, erythrocyte-rich thrombus: • Softer, more deformable, lower friction coefficient against the catheter lumen wall • Tends to be aspirated fully into and through the catheter — visibly "disappears" from the occlusion site on live fluoroscopy as it is drawn proximally into the collection canister • Generally associated with faster engagement and higher first-pass full ingestion rates

White, fibrin/platelet-rich thrombus: • Firmer, more cohesive, more resistant to deformation under suction • Rather than passing through the lumen, the leading edge adheres to and occludes the catheter tip opening — the vacuum holds it in place as a single plug rather than pulling it inside • This corked plug is removed by withdrawing the whole catheter (not by continued in-lumen suction), described in the next stage

The corking phenomenon — mechanism and clinical significance

Corking occurs when thrombus consistency and cross-sectional area exceed what the catheter lumen can accept as a continuous ingested column, so the clot instead forms a cohesive plug sealing the tip.

Why corking is clinically favorable, not a failure mode: • A corked plug held by continuous negative pressure is mechanically a single retrieved unit — the entire thrombus burden, or the vast majority of it, is captured against the tip rather than fragmented into pieces travelling through the lumen • Because the clot never fully enters (and therefore never impacts) the catheter's internal lumen walls along its length, there is less shear exposure that could shed embolic fragments • Angiographically, corking is often recognized by an abrupt cessation of any residual contrast passage at the tip combined with a sudden increase in resistance felt by the operator advancing the syringe plunger or observing pump flow

Why poor size match increases fragmentation risk: • If the catheter tip is markedly smaller than the thrombus cross-section, only the outer rim of the clot is engaged; the vacuum can shear off that rim while the bulk of the clot remains in the vessel, or dislodged fragments can embolize to previously unaffected distal branches • A closer size match promotes complete circumferential engagement of the clot face, favoring either full ingestion or clean corking rather than partial shearing

Interventional literature (e.g. Kabbasch et al., Delgado Almandoz et al.) reports first-pass complete or near-complete recanalization (mTICI 2b–3) with ADAPT in roughly 50–90% of cases across published series, largely driven by whether the clot is efficiently ingested or corked rather than fragmented.

Catheter Withdrawal Under Continuous Aspiration

Whether the clot has been ingested or corked, the single most important technical rule of ADAPT applies now: negative pressure must never be released mid-withdrawal. The catheter — with the thrombus adherent to or contained within its tip — is pulled back as one continuous unit, through the guide catheter or sheath, and out of the body, all while suction remains active.

• Never mid-pull: Suction release timing (core rule of the technique)
• Slow, steady: Withdrawal speed (under fluoroscopic visualization)
• Flow arrest: Guide catheter role (balloon guide adds proximal control)
• Reduced: Distal emboli w/ balloon guide (vs. non-balloon guide catheters)

Why continuous suction during withdrawal matters

A corked or partially ingested clot is held at the catheter tip purely by the pressure differential and by mechanical adherence to the lumen opening. If suction is interrupted — even briefly — while the catheter is still inside the vessel, the pressure holding the clot in place is lost and the thrombus can detach, re-embolizing to the same or a different distal territory.

Operators therefore maintain the aspiration source (pump running, or syringe plunger held fully locked back) for the entire withdrawal sequence: 1. Confirm resistance/plug sensation at the tip (corking) or visualize clot disappearing into the lumen (ingestion) 2. Withdraw the aspiration catheter as a unit, slowly and steadily, under continuous fluoroscopic visualization 3. Continue suction through the guide catheter/sheath and out through the hemostatic valve 4. Only release the vacuum once the catheter tip — and any adherent clot — is confirmed outside the patient, typically expelled into a basin or collection trap for inspection

Balloon guide catheters and flow arrest

Many ADAPT protocols pair the aspiration catheter with a balloon guide catheter (BGC) positioned in the cervical internal carotid or vertebral artery. Inflating the BGC balloon during withdrawal arrests or reverses antegrade flow in the parent vessel, which meaningfully reduces the risk of new distal emboli during the pull:

• With antegrade flow arrested, any small fragment that does shear off the main thrombus during withdrawal is far less likely to be carried further downstream into a previously unaffected branch • Some protocols additionally aspirate through the guide catheter itself during BGC inflation, creating a proximal-to-distal suction gradient that further discourages fragment migration • Comparative registry data (e.g. the multicenter ASSIST/COMPASS analyses) associate BGC use with modestly higher first-pass effect and lower rates of new-territory emboli versus conventional (non-balloon) guide catheters

The combination of tip-level continuous aspiration plus proximal flow arrest is often referred to as achieving control at both ends of the retrieval pathway.

Because the entire clot-plus-catheter unit is withdrawn together under sustained vacuum, ADAPT procedure times are frequently shorter than stent-retriever-based passes, which require device deployment, a dwell period for clot integration, and then a separate retrieval maneuver.

Flow Restoration — and the Combined-Technique Rescue Pathway

A completion angiographic run through the guide catheter confirms the result: full antegrade flow restoration (mTICI 2b–3) ends the procedure. When aspiration alone — even after repeat passes — leaves a significant residual filling defect, operators do not simply repeat the same maneuver indefinitely; instead, a combined approach deploys a stent retriever through the aspiration catheter for a solumbra-style rescue pass.

• Near-complete/complete: mTICI 2b–3 target (reperfusion grading scale)
• ~2–3 attempts: Repeat-pass ceiling (before switching strategy)
• Higher: Combined technique success (aspiration + stent retriever vs. either alone)
• Stent + aspiration: Solumbra approach (concurrent use through same access)

Confirming reperfusion and defining first-pass effect

After catheter withdrawal, a digital subtraction angiography run through the guide catheter grades reperfusion using the modified Thrombolysis in Cerebral Infarction (mTICI) scale:

• mTICI 0–1: no or minimal antegrade flow past the original occlusion — aspiration has failed to remove the clot • mTICI 2a: partial filling of less than half the affected vascular territory • mTICI 2b: substantial filling of half or more of the territory • mTICI 2c/3: near-complete to complete reperfusion — the target endpoint

"First-pass effect" (FPE) — achieving mTICI 2b–3 on the very first device pass — is a key quality metric across all mechanical thrombectomy techniques, strongly associated with better long-term functional outcomes, because each additional pass adds procedure time, radiation, and cumulative vessel-wall trauma risk.

When aspiration alone is insufficient — the combined/rescue pathway

If the first aspiration pass leaves significant residual occlusion, operators typically attempt one or two additional aspiration passes, sometimes with an upsized catheter or improved positioning. If repeat direct aspiration still fails to achieve adequate reperfusion, the strategy shifts to a combined technique rather than persisting indefinitely with aspiration alone:

Solumbra-style combined approach: • A stent retriever is deployed through the same large-bore aspiration catheter, directly across the residual thrombus • The stent is allowed a short dwell time to integrate with the clot matrix • The stent retriever and the aspiration catheter are then withdrawn together, with continuous suction applied through the aspiration catheter exactly as in the pure-aspiration technique — combining the stent's clot-capture geometry with the vacuum's embolic-fragment control

Why combine rather than choose one technique upfront: • Aspiration alone is fast and effective for softer, well-matched clots but can struggle with organized, fibrin-rich, or oversized thrombus • Stent retrievers alone can extract firm clot effectively but risk shedding fragments during the pull unless flow is otherwise controlled • The combined approach uses each mechanism's strength: the stent physically engages a stubborn clot, while continuous aspiration through the same catheter suppresses embolization during retrieval

Randomized and registry comparisons (including the ASTER and COMPASS trials for first-line strategy, and multiple combined-technique registries) show no clear superiority of aspiration-first versus stent-retriever-first as an initial strategy — but consistently support switching to a combined technique after failed passes rather than repeating the same single-device approach indefinitely.