What are the timing recommendations for digital subtraction angiography (DSA) in patients with acute ischemic stroke and suspected large vessel occlusion?

Timing of Digital Subtraction Angiography (DSA) in Acute Ischemic Stroke with Large Vessel Occlusion

Direct Answer

DSA should be performed immediately as part of endovascular thrombectomy (EVT) procedure when large vessel occlusion (LVO) is identified on initial CT angiography (CTA), not as a separate diagnostic step. DSA serves as the definitive imaging modality during the EVT procedure itself, not as a standalone diagnostic test in the acute stroke workflow 1, 2.

Optimal Imaging Workflow Without Standalone DSA

Initial Imaging Protocol (0-6 Hours)

All patients with suspected acute ischemic stroke and potential LVO should undergo immediate non-contrast CT (NCCT) followed immediately by CT angiography (CTA) from arch-to-vertex without delay 1, 3. This combined approach should be completed within 30-45 minutes of emergency department arrival 3, 4.

• NCCT excludes hemorrhage and provides rough estimate of ischemic core using ASPECTS 1
• Multiphase CTA detects and localizes the occlusion, estimates collateral flow, and allows procedural planning 1
• CTA has 91.1% positive predictive value and 95.1% negative predictive value compared to DSA for detecting LVO, making it sufficiently accurate for treatment decisions 5

Role of DSA in Acute Stroke Management

DSA is not performed as a separate diagnostic procedure but rather as the initial step of the EVT procedure itself 1, 2. The workflow proceeds as follows:

• CTA identifies LVO at primary or comprehensive stroke center 1, 6
• Patient proceeds directly to angiography suite for EVT if eligible 1
• DSA is performed at start of EVT procedure to confirm occlusion location and guide intervention 1, 2

Extended Window Patients (6-24 Hours)

For patients presenting beyond 6 hours from last known well, add CT perfusion (CTP) or MRI with diffusion-weighted imaging to the initial NCCT and CTA protocol to identify salvageable tissue 1, 3. This advanced imaging should not delay the procedure once LVO is confirmed and patient meets clinical criteria 1.

Critical Timing Considerations

Time-to-Treatment Priorities

The goal is door-to-groin puncture time minimization, not door-to-DSA time, as DSA occurs simultaneously with treatment initiation 1, 7. Key time benchmarks include:

• NCCT interpretation within 45 minutes of arrival 3, 2
• CTA performed immediately following NCCT without returning patient from scanner 1, 6
• Direct transfer to angiography suite once LVO confirmed on CTA 1, 6

When NOT to Delay for Additional Imaging

Do not perform standalone diagnostic DSA before deciding on EVT 1, 2. The decision pathway is:

• NCCT + CTA identifies LVO → proceed directly to EVT with DSA as first procedural step 1, 6
• Intravenous alteplase should be administered (if eligible) without waiting for DSA or EVT preparation 1, 4

Common Pitfalls to Avoid

The most critical error is treating DSA as a separate diagnostic step rather than as the initial component of the EVT procedure 1, 2. This outdated approach causes unnecessary delays:

• CTA provides sufficient diagnostic accuracy (>90% PPV/NPV) to make EVT decisions 5
• Performing diagnostic DSA separately adds 60-120+ minutes to treatment time 5
• Modern guidelines recommend CTA as the operational standard for rapid LVO identification 7

Another major pitfall is delaying CTA acquisition 1, 6. Primary stroke centers must perform CTA alongside NCCT for all suspected LVO patients, as missing LVO identification leads to lost EVT opportunities 6, 5.

Practical Algorithm

1. Suspected acute stroke with NIHSS ≥6 arrives at emergency department 1
2. Immediate NCCT (within 30-45 minutes) to exclude hemorrhage and assess ASPECTS 3, 4
3. Immediate multiphase CTA (same imaging session, no delay) from arch-to-vertex 1, 6
4. If LVO identified on CTA: Administer IV alteplase if eligible, then proceed directly to angiography suite 1
5. DSA performed as first step of EVT procedure to confirm occlusion and guide thrombectomy 1, 2
6. For late-window patients (>6 hours): Add CTP or MRI perfusion during initial imaging, but do not delay EVT once decision made 1, 3

The paradigm shift is clear: DSA timing is determined by EVT timing, not as a separate diagnostic decision point 1, 2, 7.