What is the optimal timing for CT (Computed Tomography) and MRI (Magnetic Resonance Imaging) scans, and when to consider TNK (tenecteplase) or tPA (tissue plasminogen activator) in acute stroke management?

Optimal Timing for CT, MRI, and Thrombolytic Therapy in Acute Stroke

For patients with suspected acute stroke, CT scan should be completed within 25 minutes of hospital arrival and interpreted within 45 minutes to facilitate timely administration of thrombolytic therapy. 1

Initial Imaging Assessment

• The primary goal of imaging in acute stroke is to distinguish between hemorrhagic and ischemic stroke, which is crucial for treatment decisions 2
• For patients within the thrombolytic treatment window (0-4.5 hours), either non-contrast CT (NCCT) or MRI is recommended to exclude intracranial hemorrhage (ICH) before thrombolytic administration 1
• CT scan should ideally be completed within 25 minutes of the patient's arrival in the Emergency Department and interpreted within 45 minutes of arrival 1
• Advanced imaging should not delay the administration of IV thrombolytic therapy in eligible patients 1

Imaging Selection Based on Treatment Window

For Patients Within 3-Hour Window:

• Either NCCT or MRI is recommended to exclude ICH (absolute contraindication) 1
• NCCT has traditionally been used due to wider accessibility, but MRI with diffusion-weighted imaging (DWI) offers superior sensitivity for detecting early ischemia 1
• Although MRI scan duration is slightly longer than CT (median 13 vs 9 minutes), MRI-based selection can be accomplished without delaying treatment 3
• Vascular imaging (CTA/MRA) should be performed during initial evaluation if it doesn't delay thrombolytic therapy and if an endovascular team is available 1

For Patients Beyond 3-Hour Window:

• Either MR-DWI or CTA-SI should be performed along with vascular imaging and perfusion studies, particularly if mechanical thrombectomy or intra-arterial therapy is contemplated 1
• For patients beyond 6 hours, multimodal imaging with perfusion assessment becomes essential for treatment selection 2

Thrombolytic Therapy Timing

• IV thrombolytic therapy (tPA/TNK) should be administered within 4.5 hours of symptom onset 4
• For patients within 0-3 hours of symptom onset, IV thrombolytic therapy is strongly recommended if no contraindications exist 4
• Before administering thrombolytic therapy, blood pressure must be <185/110 mmHg to limit bleeding complications 1
• Most patients with sustained hypertension above these levels will not be eligible for IV thrombolytic therapy unless blood pressure can be safely reduced 1

Tenecteplase (TNK) vs Alteplase (tPA)

• Tenecteplase has gained attention as an attractive alternative to alteplase due to its practical workflow advantages and possible superior efficacy in large vessel recanalization 5
• Recent evidence suggests tenecteplase appears to be at least equally, if not more safe and potentially more effective than alteplase in acute ischemic stroke treatment 5

Streamlining the Acute Stroke Protocol

• A systematic "code stroke" approach can reduce door-to-treatment times 6
• Implementing a CTA-for-All protocol for patients presenting within 24 hours of symptom onset has been shown to improve large vessel occlusion detection, increase mechanical thrombectomy rates, and hasten intervention 7
• Standardized stroke examinations and protocols for blood pressure management should be established to reduce time to complete each task 6

Common Pitfalls to Avoid

• Delaying thrombolytic therapy for advanced imaging beyond what is necessary to exclude hemorrhage 1
• Focusing solely on NCCT without vascular imaging may miss large vessel occlusions requiring endovascular therapy 2
• Administering thrombolytic therapy when blood pressure is >185/110 mmHg, which increases bleeding risk 1
• Failing to recognize early signs of large infarct on CT, particularly if it involves more than one third of an MCA territory, which is a strong contraindication to thrombolytic treatment 1