What duplex findings would suggest a patent bypass graft with flow limitation?

• A. Complete occlusion of flow.
• B. Low flow with dampened distal signals.
• C. Normal or high-velocity flow with no occlusion; focal velocity elevations indicating stenosis.
• D. Normal or high-velocity flow with no complete occlusion; focal velocity elevations or dampened distal flow may indicate developing stenosis requiring surveillance.

Answer: (D)

The idea being tested is how a bypass graft can be patent yet still have flow-limiting problems detectable on duplex ultrasound. In a graft that remains open, the overall flow through the graft is normal or high, so you don’t see a complete lack of flow. The telltale sign of a problematic, flow-limiting lesion is a focal area where velocity spikes at a specific segment of the graft or at the anastomosis. That focal velocity elevation points to stenosis in that spot. If the stenosis is significant, it can also dampen the flow distal to the lesion, so you may see dampened distal signals as the downstream consequence of the narrowed segment. Putting those findings together—normal or high flow through a patent graft, with focal velocity elevations indicating a stenosis and possibly dampened distal flow—signals a graft that is currently open but has flow limitation that needs surveillance and possible intervention.

Patterns like complete occlusion would show no flow at all in the graft, and low flow with broad dampening without a focal acceleration would be less specific for a focal stenosis and more indicative of poor inflow or diffuse disease.