How can the direction of blood flow within a gastric varix be determined during endoscopic injection of Histoacryl (cyanoacrylate)?

Determining Blood Flow Direction in Gastric Varices During Histoacryl Injection

Primary Recommendation

Use Doppler ultrasound interrogation under EUS guidance to directly visualize and map blood flow direction within the gastric varix before and during cyanoacrylate injection. 1

Technical Approach to Flow Assessment

EUS-Doppler Interrogation (Gold Standard)

• Perform baseline Doppler flow assessment of the gastric varix before needle insertion to identify the direction and velocity of blood flow within the vessel 1
• Trace extramural vessels (feeding vessels) across the muscularis propria into the intramural varix to identify perforator veins, which reveal the direction of blood inflow 1
• Use color Doppler to map the entire variceal network, including connections to the left gastric vein, short gastric veins, and gastro-renal shunt, which defines flow patterns 1

Endosonographic Varicealography (Advanced Technique)

• Inject contrast under EUS guidance (endosonographic varicealography) to directly visualize the feeding vessel and flow direction in real-time, achieving technical success in approximately 87% of cases 2
• This technique allows identification of the dominant feeder vessel that should be targeted for injection to ensure glue flows in the direction of blood flow and achieves complete obliteration 2

Water Instillation for Enhanced Visualization

• Instill 100-200 mL of water through the echoendoscope into the gastric fundus to enhance delineation of intramural vessels from extramural collaterals 1
• This acoustic window improves Doppler signal quality and allows better visualization of flow patterns 1

Clinical Rationale for Flow Direction Assessment

Why Flow Direction Matters

• Injection site must be selected according to blood flow direction to ensure optimal glue distribution and polymerization within the varix 3
• Injecting against flow direction increases risk of premature glue extrusion, needle impaction, and systemic embolization 3
• The most protruding portion of the varix (highest intravariceal pressure point) must be avoided as an injection site, regardless of flow direction 3

Anatomic Considerations for Fundal Varices

• Fundal gastric varices (GOV2 and IGV1) exhibit high blood flow in their feeding channels, typically from the short gastric veins or posterior gastric vein 3
• These varices are isolated to the fundus and require direct assessment of their unique flow patterns, which differ from GOV1 varices that extend from esophageal varices 3

Practical Algorithm Without EUS

For Direct Endoscopic Injection (When EUS Unavailable)

• Identify the varix location and morphology endoscopically in retroflexion 1
• Infer flow direction from anatomic landmarks: fundal varices typically receive flow from short gastric veins (flowing toward the spleen) or gastro-renal shunt (flowing toward the left renal vein) 1
• Inject at the base of the varix rather than the apex to work with presumed inflow direction 3
• Use fluoroscopy with varicealography if available to visualize contrast flow direction before glue injection 1

Real-Time Feedback During Injection

• Monitor Doppler flow during and immediately after injection to confirm reduction or cessation of flow, indicating successful obliteration 1
• Significant reduction or near-absent Doppler flow is the endpoint that signals adequate treatment before withdrawing the needle 1
• Immediate disappearance of the varix on EUS occurs in approximately 80% of successful treatments when flow direction is properly targeted 2

Critical Safety Considerations

• Avoid injecting at the point of maximal protrusion where pressure is highest, as this dramatically increases embolization risk regardless of flow assessment 3
• Ensure intravariceal (not paravariceal) needle placement using EUS guidance, as superficial injection fails to address flow and risks perforation 3
• Flush the injection catheter with 1 mL distilled water or saline immediately after glue injection to prevent catheter occlusion and allow safe needle withdrawal 3

Evidence Quality Note

The 2023 AGA Clinical Practice Update 1 represents the most current guideline-level evidence and explicitly states that "Doppler interrogation during coil placement can be used to guide the number of coils required" and provides "real-time feedback of hemostasis." This same principle applies to cyanoacrylate injection, where Doppler assessment of flow direction and velocity is the standard of care for EUS-guided therapy. The Praxis Medical Insights guideline 3 confirms that "injection site should be chosen according to the direction of blood flow" but does not specify the technical method—EUS-Doppler fills this gap as the only practical real-time modality available.