The first pass effect is a term used in mechanical thrombectomy to describe a specific and desirable event: complete recanalization of an occluded intracranial artery achieved with a single pass of the retrieval device, without needing additional attempts or adjunct techniques. This concept has become an important framework for evaluating both procedural technique and device design in acute stroke care, because it reflects how efficiently a clot can be removed under real procedural conditions. This article explains what the first pass effect means, why it has drawn attention as a discussion point in the field, and how device design factors into it.
What Counts as a First Pass in Mechanical Thrombectomy?
A "pass" refers to one complete cycle of advancing a retrieval device, such as a stent retriever, to the level of the clot, deploying it, and withdrawing it from the body, typically alongside aspiration. A first pass is simply the initial attempt made during a given procedure. The first pass effect specifically refers to cases where this single attempt achieves complete or near-complete restoration of blood flow through the previously occluded vessel, meaning no second pass, additional device, or rescue technique is required to finish the recanalization.
Why Is Complete Recanalization on the First Attempt Considered a Meaningful Outcome Predictor?
Every additional pass required during a thrombectomy procedure adds time to the overall case, and time is a central concern in acute stroke treatment given how quickly brain tissue can be affected by prolonged interrupted blood flow. Additional passes can also carry incremental procedural considerations, such as vessel wall irritation or clot fragmentation, that are generally best avoided when possible. For these reasons, the number of passes required to achieve recanalization has been discussed in the field as a potential outcome predictor, with fewer passes generally viewed as a favorable procedural characteristic. This is distinct from claiming that any specific device guarantees a particular outcome for an individual patient, which is not something this article asserts.
How Does Device Efficiency Relate to Achieving the First-Pass Effect?
Device efficiency in this context refers to how well a retrieval device integrates with and captures a clot on its initial deployment, without the clot fragmenting, sliding off the device, or requiring repositioning. Design characteristics such as the retrieval device's cell structure, radial force, and length can all influence how effectively it engages with clot material of varying consistency on a single pass. INVAMED's KinG Intracranial Revascularization Device is a stent retriever designed for large vessel occlusion in acute stroke therapy, intended to capture and remove clots from intracranial arteries to restore perfusion, according to the manufacturer's stated intended use. No specific numeric first-pass success rate is available for the KinG device, and none is claimed in this article.
Does Clot Composition Affect Whether the First-Pass Effect Is Achieved?
Clot composition varies considerably between patients, with some clots being more fibrin-rich and firm while others contain a higher proportion of red blood cells and are comparatively softer. This variation is generally understood to influence how a clot interacts with a retrieval device, with certain compositions integrating more readily into the device structure on a single pass than others. Because clot composition cannot typically be determined with certainty before the procedure begins, achieving the first-pass effect involves an interplay between device design, technique, and the specific clot the operator encounters, rather than being solely a function of any one factor.
Adjunct Techniques and Their Relationship to First-Pass Outcomes
Many thrombectomy procedures combine a stent retriever with an aspiration catheter system in a combined technique, which some operators use with the goal of improving the likelihood of complete recanalization on the initial attempt. The specific combination of devices and technique used during a given procedure is determined by the treating physician based on the occlusion location, available equipment, and institutional practice patterns. Additional information on stent retriever devices used in these procedures is available through INVAMED's neurovascular interventions category page, and indications for the KinG device specifically are described on its product page.
Can a physician predict in advance whether the first-pass effect will occur?
Physicians cannot reliably predict before the procedure whether a single pass will achieve complete recanalization, since this depends on factors including clot composition, vessel anatomy, and how the device interacts with the clot in real time. Imaging can provide some clues about occlusion characteristics, but the outcome of any given pass is generally assessed during the procedure itself. This uncertainty is a routine part of acute stroke intervention.
Device availability and regulatory status vary by country. Please contact INVAMED or your authorized local distributor for current regulatory information applicable to your region.