Makindo Medical Notes

Related Subjects: |Hypertension |Mechanical Thrombectomy |Stroke Penumbra |Cardiac Thrombolysis |Stroke Thrombolysis |Alteplase |Tenecteplase |Streptokinase |Reteplase

Mechanical thrombectomy is a critical endovascular procedure used to remove large clots from cerebral arteries in patients experiencing acute ischemic stroke. This intervention has revolutionized stroke management, significantly improving outcomes in eligible patients when performed promptly and effectively.

About

• Definition: Mechanical thrombectomy is an advanced endovascular procedure aimed at physically removing blood clots from large vessels in the brain to restore blood flow during an acute ischemic stroke.
• History: The technique has evolved with the development of specialized devices such as stent retrievers and aspiration catheters, becoming a standard of care in stroke centers worldwide.
• Purpose: To achieve rapid and complete recanalization of occluded arteries, thereby minimizing brain tissue damage and improving functional outcomes.

Evidence Base and Number Needed to Treat (NNT)

• Randomized Controlled Trials:
  • MR CLEAN: Demonstrated significant improvement in functional outcomes at 90 days in patients undergoing mechanical thrombectomy.
  • ESCAPE: Showed that mechanical thrombectomy within 12 hours of symptom onset significantly increased the likelihood of good functional outcomes.
  • REVASCAT: Confirmed the benefits of thrombectomy in reducing disability in acute ischemic stroke patients with large vessel occlusions.
  • SWIFT PRIME: Highlighted the effectiveness of thrombectomy with Solitaire FR device in improving outcomes.
  • EXTEND-IA: Demonstrated high recanalization rates and improved clinical outcomes with mechanical thrombectomy.
• Meta-Analyses: Comprehensive analyses of multiple trials have confirmed the superiority of mechanical thrombectomy over standard medical therapy alone in improving functional outcomes and reducing mortality.
• Number Needed to Treat (NNT):
  • Studies have reported NNT values ranging from 2 to 3 to achieve functional independence at 90 days, indicating high efficacy.
  • For mortality reduction, NNT is approximately 6-10, meaning 6-10 patients need to undergo thrombectomy to prevent one death.
• Guidelines: Clinical guidelines now recommend mechanical thrombectomy as standard care for eligible acute ischemic stroke patients with large vessel occlusions, based on robust evidence supporting its efficacy.

Pre-Thrombectomy Assessment

• Clinical Assessment:
  • National Institutes of Health Stroke Scale (NIHSS): A standardized tool used to quantify the impairment caused by a stroke. It assesses various neurological functions including consciousness, vision, motor skills, sensation, and language. A higher NIHSS score indicates a more severe stroke and helps determine eligibility for thrombectomy.
• Imaging:
  • Non-Contrast CT (NCCT) Scan: Primary imaging modality to rule out haemorrhage and identify early signs of ischemia.
  • CT Angiography (CTA): Evaluates the vasculature for large vessel occlusions, which are targets for mechanical thrombectomy.
  • CT Perfusion (CTP) or MRI Perfusion: Assesses the extent of the ischemic penumbra (salvageable brain tissue) versus the infarct core (irreversibly damaged tissue).
• Laboratory Tests:
  • Complete Blood Count (CBC): Evaluates hemoglobin levels, white cell count, and platelet count.
  • Coagulation Profile: Includes Prothrombin Time (PT), Activated Partial Thromboplastin Time (aPTT), and INR to assess bleeding risk.
  • Renal Function Tests:
    • Serum Creatinine: Critical for determining kidney function, especially important due to the use of contrast agents in imaging studies. Elevated creatinine levels may necessitate alternative imaging strategies or precautionary measures to prevent contrast-induced nephropathy.
    • Estimated Glomerular Filtration Rate (eGFR): Assesses the filtering capacity of the kidneys and helps in dosing medications.
  • Blood Glucose: Hyperglycemia can worsen stroke outcomes and needs to be managed appropriately.
• Patient Eligibility:
  • Time Window: Generally within 6 hours of symptom onset, though some guidelines allow up to 24 hours based on imaging criteria.
  • Vascular Eligibility: Presence of a large vessel occlusion in the anterior circulation (e.g., internal carotid artery, middle cerebral artery) or posterior circulation (e.g., basilar artery).
  • Clinical Eligibility: Significant neurological deficit as evidenced by a higher NIHSS score.
  • Imaging Eligibility: Sufficient salvageable brain tissue with a favorable penumbra-to-core ratio.
  • Contraindications: Extensive established infarct, uncontrolled hypertension, coagulopathy, or contraindications to endovascular therapy.

Indications

• Acute Ischaemic Stroke: Particularly due to large vessel occlusions (e.g., internal carotid artery, middle cerebral artery).
• Time Window: Typically within 6 hours of symptom onset, though some guidelines extend this to 24 hours based on advanced imaging criteria.
• Imaging Criteria: Presence of salvageable brain tissue (ischemic penumbra) as determined by CT perfusion or MRI.
• Patient Selection: Patients with a favorable functional outcome prediction, no contraindications for endovascular therapy, and sufficient vascular anatomy for device navigation.

Types of Mechanical Thrombectomy Devices

• Stent Retrievers: Devices like Solitaire and Trevo are deployed to ensnare and extract the clot mechanically.
• Aspiration Catheters: Systems such as ADAPT utilize continuous aspiration to remove clots.
• Combination Approaches: Utilizing both stent retrievers and aspiration to enhance clot retrieval efficiency.

Procedure

• Pre-Procedure Preparation:
  • Confirm diagnosis and eligibility through clinical assessment and imaging.
  • Obtain informed consent, considering the emergency nature of the procedure.
  • Prepare the patient in the angiography suite with appropriate monitoring.
• Access:
  • Femoral artery access is most common, though radial or direct carotid access may be used in specific cases.
  • Guidewire navigation to the site of occlusion under fluoroscopic guidance.
• Clot Retrieval:
  • Deploy the thrombectomy device (stent retriever or aspiration catheter) at the clot site.
  • Engage and extract the clot, ensuring complete removal and vessel patency.
  • Multiple passes may be necessary for complete recanalization.
• Post-Retrieval Assessment:
  • Confirm vessel patency and absence of residual clot through angiography.
  • Monitor for immediate complications such as vessel dissection or haemorrhage.
• Closure:
  • Remove the access sheath and achieve hemostasis, typically with manual compression or vascular closure devices.

Complications

• Vascular Injury: Including dissection, perforation, or rupture of the artery.
• Hemorrhage: Intracranial haemorrhage can occur, especially after reperfusion.
• Embolization: Clots may dislodge and cause distal vessel occlusions.
• Access Site Complications: Such as hematoma, pseudoaneurysm, or arteriovenous fistula.
• Contrast-Induced Nephropathy: Especially in patients with pre-existing kidney dysfunction.
• Reperfusion Injury: Resulting from the restoration of blood flow to ischemic tissues.

Outcomes

• Recanalization Rates: High rates of successful vessel reopening, particularly with modern devices.
• Functional Outcomes: Significant improvement in disability scales (e.g., modified Rankin Scale) compared to medical therapy alone.
• Mortality: Reduced mortality rates in patients undergoing mechanical thrombectomy.
• Time to Treatment: Critical factor; delays can diminish the benefits of the procedure.

Post-Procedure Care

• Monitoring: Intensive care unit (ICU) monitoring for neurological status and hemodynamic stability.
• Imaging: Follow-up imaging to assess reperfusion and detect any complications.
• Rehabilitation: Early initiation of physical, occupational, and speech therapy as needed.
• Antithrombotic Therapy: Management of antiplatelet or anticoagulant therapy based on individual patient factors.

Recent Advances

• Enhanced Imaging Techniques: Improved selection of candidates through advanced perfusion imaging.
• Newer Devices: Development of more efficient and easier-to-use thrombectomy devices.
• Extended Time Windows: Trials supporting mechanical thrombectomy beyond the traditional time frames in selected patients.
• Combined Therapies: Integration of pharmacological thrombolysis with mechanical retrieval for better outcomes.

Conclusion

Mechanical thrombectomy is a life-saving procedure for patients suffering from acute ischemic strokes due to large vessel occlusions. The success of the procedure hinges on rapid identification, appropriate patient selection through comprehensive pre-thrombectomy assessment, and the expertise of the endovascular team. Continuous advancements in imaging, device technology, and procedural techniques are enhancing the efficacy and safety of mechanical thrombectomy, offering hope for improved neurological outcomes and reduced mortality in stroke patients.

References

• Goyal, M., Menon, B.K., van Zwam, W.H., et al. (2016). Endovascular thrombectomy after large-vessel ischaemic stroke: A meta-analysis of individual patient data from five randomised trials. The Lancet, 387(10029), 1723-1731.
• Albers, G.W., Marks, M.P., Kemp, S., et al. (2018). Thrombectomy for Stroke at 6 to 16 Hours with Selection by Perfusion Imaging. The New England Journal of Medicine, 378, 708-718.
• National Institute of Neurological Disorders and Stroke (NINDS). Mechanical Thrombectomy for Acute Ischemic Stroke. Available at: NINDS - Mechanical Thrombectomy
• Smith, E.E., Sung, G., Saver, J.L., et al. (2018). A Trial of Endovascular Therapy After IV t-PA versus IV t-PA Alone for Stroke. The New England Journal of Medicine, 378, 2137-2147.
• World Stroke Organization. Guidelines for the Early Management of Patients with Acute Ischemic Stroke. Available at: World Stroke Organization - Guidelines
• Roux, F., Guiot, J., Sabri, A., et al. (2020). Mechanical thrombectomy for acute ischemic stroke: Evidence and future directions. Therapeutic Advances in Chronic Disease, 11, 2040622320965382.